BO GIAO DUC VA DAO TAO «< 1 r NHA XUAT BAN GIAO DUC VIET NAM

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1 BO GIAO DUC VA DAO TAO «< 1 r NHA XUAT BAN GIAO DUC VIET NAM

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3 BO GIAO DUC VA DAO TAO LUONG DUYEN BINH (Tdng Chu bien) VU QUANG (Chu bien) NGUYfiN XUAN CHI - DAM TRUNG DON BUI QUANG HAN - DOAN DUY HINH IX (Tdi bdn lan thit ha) NHA XUAT BAN GIAO DUC VIET NAM

4 CAUTRUCCAC TRANG SACH GIAO KHOA 1. Phan ndi dung bai hoc gom cac trang in thanh hai cdt : mot cdt la ndi dung chinh cija bai hoc, cdt cdn lai chq nhd, trinh bay cac hinh ve, tranh, anh, bieu bang, dd thi, cac ndi dung thii yeu, cac cau hdi (ki hieu ^i) de giao vien va hoc sinh cung tham gia xay dung bai hoc. Tuy nhien, vdi cac hinh, dd thi,... cd kich thudc Idn thi in tran trang. 2. Sau phan ndi dung bai hoc la phan tdm tit bai hoc, duoc in dam. Cudi mdi bai hoc la phsn cau hdi (ki hieu "? ) va bai tap (ki hieu ) de hoc sinh lam d nha. Phin dap an va dap so bai tap duoc in a cudi cudn saeh. 3. Sau mot sd bai hoc cd nhung bai doc them ghi la "Em cd biet?" Ch/u tracli nliiem xuat ban : Chu tich HDQT kiem Tong Giam doc NGO TRAN AI Pho Tong Giam doc kiem Tong bien tap NGUYIN QUY THAO Bien tap lan dau NGUY N TIEN BINH - PHAM TH! NGOC THANG Bien tap tai ban D6 THj Bl'CH LIEN Bien tap kj thuat: TA THANH TUNG Trinh bay bia va minh hoa TA THANH TUNG SCfa ban in Dd THI Bl'CH LIEN Che ban : CONG TY CO PHAN Ml THUAT VA TRUYEN THONG Ban quyen thuoc Nha xuat ban Giao due Viet Nam - Bo Giao due va Dao tao Trong saeh co silr dung mot so tu lieu anh eua Thong tan xa Viet Nam va cac tac gia khac. VAT LI 11 Ma so: CH105T0 In cuon (ST), khd 17 x 24 cm. In tai Cong ty c6 phan In Khoa hoc Ky thuat - HN. So in: 116. SoXB: /CXB/ /GD. In xong va nop IL/U chieu thang 2 nam 2010.

5 PHAN MOT DIENH. DIEN TCr HOC Nam cham dien eua mot xiclotron Nhung kien thuc ve Dien hoc va Dien tit hoc la co so eua nhieu ung dung quan trong trong ddi song va trong cac nganh ki thuat hien dai.

6 DIEN HOC. DIEN TU* HOC fe- ^^? Dien tich, Dien triidng Dong dien khong doi "J.; dien trong cac moi trudng *' Tu ti'u'dng ^^ C. dien tii

7 CHL/ONG I Dien tich. Dien tri/crng r whm! "wp^ May phat tinh dien Van-do-grap (Vandergraaf) Trong chuong nay, ta de cap den nhung dac trung quan trong nhat eua dien tich va dien trudng. 06 la nhung van de sau : Dien tich, Dien trudng Dinh luat Cu-I6ng. Thuyet electron Cuong do dien trudng. Dudng sue dien Dien the. Hieu dien the Tu dien. Dien dung eua tu dien

8 OlEN TICH DINH LUAT CU-LONG O Trung hoc ca sd (THCS), ta da biet cac vat mang dien hoae hut nhau, hoae day nhau. Luc tuong tac dd phu thuoc vao nhung yeu td nao va tuan theo quy luat nao? I - SU" NHIEM OlEN CUA CAC VAT. DIEN TICH. TUOfNG TAC DIEN 1. SU nhiem dien eua cac vat Ta da biet, khi co xat nhiing vat nhu thanh thuy tinh. thanh nhira. manh pohetilen,... vao da hoae lua... th) nhijng vat do se co the hiit duoc nhijng vat nhe nhu meiu giay, sgi bong,... Ta noi rsng nliitiig vat do dd hi iiliiem dien. Hinh 1.1 Sau khi CO xat vao da, chiec thuoc nhua hut dupe mau xop. Ngay nay, nguoi ta vsn dira vao hien tuong hiit cac vat nhe de kiem tra xem mot vat co nhi^m dien hav kh6n2. 2. Dien tich. Dien tich diem Vat bi nhilm dien con goi la vat mang dien, vat tfch dien hay la mot dien tfch. Dien la mot thuoc tfnh ciia vat va dien tfch la so do do Ion ciia thuoc tfnh do. Tuong tu nhu khoi luong la so do miic quan tinh eua mot vat. Hinh 1.2 Dien ticli diem la mot vat tfch dien co kfch thu6c rat nho so voi khoang each tai die'm ma ta xet. HI Tren Hinh 1.2, AB va MN la hai thanh da du'oc nhiem dien. Mui ten chi chieu quay cue dau 6 khi dua dau M den gan, Hdi dau B va dau M nhiem dien cung dau hay trai dau? 3. TUofng tac dien. Hai loai dien tich 0 THCS, ta da.lam nhieu thf nghiem dd thay cac dien tfch hoae daiy nhau, hoae hiit nhau (Hinh 1.2). Su day hay hiit nhau gioa cac dien tfch do la sif tuang tac dien. HI

9 Ngucfi ta thira nhan rang chi co hai loai dien tfch la dien tfch duong (kf hieu bang da'u +) va dien tfch am (kf hieu bang da'u -). Cdc dien tieh cdng loai (dau) thi day nhau. Cae dien tieh khde loai (dau) thi hut nhau. Chii y : Khai niem dien ticti am, dien tfch duong trong Vat If hoc khac vdi khai niem.so am, sd duong trong Toan hoc. ChSng han, sd am ludn ludn nhd hon sd dtrong, nhimg nguoc lai khdng the noi dien tich am ludn ludn nhd hon dien tfch duong duoc. II - DjNH LUAT CU-LONG. HANG SO DIEN MOI I.Djnh luat Cu-long Nam 1785, Cu-I6ng, nha bac hoc ngucd Phap, Mn dau tien thiet lap duoc dinh luat ve su phu thuoc ciia lue tuong tac giiia cac dien tfch diem (goi tat la luc dien hay licc Cu-ldng) vao khoang each giiia chiing. Ong dcing mot chiec can xoan de do lue day giiia hai qua cau nho tfch dien ciing dau (Hinh 1.3). Hai qua cau nho nay dugfc coi la nhiing dien tfch diem. Sac-lo Cu-I6ng (Charles Coulomb, ), nha bac hoc ngudi Phap CO nhieu edng trinh nghien euu ve tinh dien va tii. H;n/7 1.3 Can xo^n Cu-I6ng Can xodn Cu-ldng A la qua csu kim loai cd dinh gan d dau mot thanh thang dung. B la qua cau kim loai linh ddng gdn d dau mot thanh nam ngang. Dau kia ciia thanh cd mot qua ddi trong. ^ va B duoc tich dien ciing dau. Thanh nam ngang dugc treo bang mot sgi day manh cd tinh dan hoi chdng lai sir xoan. Khi hai qua cau d^y nhau, thanh ngang se quay cho den khi tac dung ciia lue day tfnh dien can bang vdi tac dung ciia lire dan hdi ciia day treo. Biei gdc quay va chifiu dai ciia thanh ngang, ta se tinh dugc lue day tinh dien giiia hai qua cau A va B.

10 ^' Neu tang khoang each giiia hai qua cau len ba lan thi \uc tuong tac giufa chung tang hay giam bao nhieu lan? Ket qua, 6ng tha'y lue nay ti le nghich vdi binh phuong khoang each giiia hai qua cau. I* Mat khac, c6 the chiing minh bang thuc nghiem la : lue tuong tac giiia hai dien tfch ti le thuan vdi tfch do Idn eua hai dien tfch do. Q2 Hinh 1 4 De nghien cihi sir phu thuoc ciia lue tuong tac gioa hai qua cau A va B trong can xoan Oi4dng (Hinh 1.3) vao do Idn ciia dien tich, ta cd th^ giii nguyen dien tich eua qua cau B va cho qua cau A tie'p xiic vdi mot qua cau kim loai C, gidng het no nhung trung hoa v6 dien. Vi If do ddi xirng, dien tich CLia qua cau A se bi chia lam ddi. Cii nhu vay, ta cd the tiep tue lam cho dien tich ciia qua cau,4 bang. -I TT'--- dien tfch ban dau. Ta se tha'y do Idn eua lue tac dung giiia hai qua csu A va B bang > -- ^>dd Idn ciia lue ban dau. Nhu vay, lue dien ti le vdi dien tfch eua qua cau A. Tuong tii, liic dien ciing ti 16 vdi dien tieh Ciia qua cau B. Do dd. lire dien ti le vdi tfch eua hai dien ti'ch. Phdi hop eae ket qua tren, ta ed dinh luat Cu-ldng duoc phat bieu nhu sau : Luc hut hay day gida hai dien tich diem ddt trong chdn khdng cd phuffng trung vdi dudng thdng ndi hai dien tieh diem dd, cd do Idn ti le thuan vdi tieh do Idn eua hai dien tieh vd ti le nghich vdi binh phuong khoang each giua chung (Hinh 1.4). F=km (i.i) trong dd, k la he sd ti le, phu thuoc vao he don vi ma ta dung. Trong he don vi SI, k ed gia tri : /: = N.m^ "c^ (1.2) Viec nghien ciiu lire tuong tac giiia cac dien tfch da eho phep ta do dugc cae dien tich, tiic la so sanh do Idn Ciia dien tfch edn do vdi dien tfch don vi. Mudn the, ta chi can so sanh lue tuong tac eua hai dien tfch nay vdi mdt dien tfch thu ba dat each chiing nhiing khoang bang nhau, trong ciing mot mdi trudng. Trong edng thiie (1.1), F duoc do bang don vi niutcfn (N); r duoe do bang don.vi met (m); cdn q. va <72 du<?c do bang don vi culdng (kf hieu la C). 8

11 2. Liic tifong tac giofa cac dien tich diem dat trong dien moi dong tinh. Hang so dien moi a) Dien mdi la mdi trudng each dien. b) Thf nghiem chiing td rang, khi dat cac dien tfch diem trong mot dien mdi ddng tfnh (chang han trong mot chat dau each dien) thi lire tuong tac gifia chiing se yeu di e lan so vdi khi dat chiing trong chan khdng. e duoc goi la hang so' dien mdi eua mdi trudng (e > 1). Cdng thiic eua dinh luat Cu-ldng trong trudng hop nay la : F = k mi (1.3) sr Ddi vdi chan khdng thi e = 1. c) Hang sd dien mdi la mdt dac trung quan trong cho tfnh chat dien ciia mot chat each dien. Nd cho biet, khi dat cdc dien tich trong chat do thi luc tde dung giiia chiing senhd di bao nhieu lan so vai khi ddt chiing trong chdn khdng. ^E Bang 1.1 HSng so dien moi ciia mot sd chat i Chat Khong khi (6 dieu kien chuan) Dau hoa Nude nguyen chat Parafin Giay Mica Ebonit Thuy tinh i Thach anh 1 e 1, (coi nhubangi) 2, ,7-^7 2, ,5»j Khong the ndi ve hang so' dien moi ciia chat nao dudi day? A. Khdng khi khd. B. Nude tinh khie't. C. Thuy tinh. D. Dong. J i Cac dien tich ciing dau thi day nhau, trai dau thi hut nhau. Life hut hay day giu'a hai dien tich diem dat trong chan khong co phuong trung vdi dudng thang noi hai dien tich diem do, co do Idn ti le thuan vdi tfch do Idn ccia hai dien tich va ti le nghjch vdi binh phuong khoang each giufa chung. Ocn vi dien tich la culong (C). F = k "^''1.^ = 9.10^^^' CAU HOI VA BAI TAP 1. Dien tich diem la gi? 2. Phat bieu dinh luat Cu-ldng. 3. Lye tuong tac giua cac dien tich khi dat trong mot dien moi se Idn hay nho hon khi dat trong chan khdng?

12 Hang so dien moi eua mot chat cho ta biet 6. Trong trudng hop nao sau day, ta cd the coi dieu gi? cac vat nhi^m dien la cac dien tich diem? A. Hai thanh nhua dat gan nhau. B. Mot thanh nhua va mot qua cau dat gan nhau. C. Hai qua cau nhd dat xa nhau. D. Hai qua cau Idn dat gan nhau. Chpn cau dung. Neu nhung diem giong nhau va khac nhau Khi tang dong thdi dd Idn ciia hai dien tich.. ^.,,.. ^,..,,.,-.....^,,,. u' - u- I- - ^-' giua dinh luat Cu4ong va dinh luat van vat diem va khoang each giua chung len gap doi Z- A' hap dan. thi lye tuong tac giua chiing A. tang len gap ddi. D.,..-., 8. Hai qua cau nho mang hai dien tich cd dd Idn B. giam di mot nua. u- u J-. - U U.;>. u- bang nhau, dat each nhau 10 cm trong chan C. giam di bdn lan. I^l^^^g ^^^ ^^^ ^^^^^ 1^^ ^^3^ ^^^ 1^^,3 g. Q-3 ^ D. khdng thay ddi. Xac dinh dien tich ciia hai qua cau dd. Em CO biet? SON TiNH OlEN Trong cdng nghe son phun, ngudi ta dung mot sung cd khi nen de phun nhung hat son nhd li ti den bam vao vat can son. Dong tac nay gidng nhu viec phun nude hoa hay phun thud'c mudi... Mot phan nhung hat son den bam vao vat can son. Mot phan kha Idn bay vao khdng khi vua gay lang phi, vua gay d nhidm. De khic phuc nhuac diem nay, ngudi ta da cai tien cdng nghe son phun thanh cdng nghe son tmh dien. Trong cdng nghe nay, mui eua sung phun lam bang kim loai va duac ndi vdi cue duong eua mot may phat tinh dien. Cue am eua may duoc ndi vdi vat can son. Cac hat son bay ra khdi sung phun se duoc nhidm dien duong va bi hut ve phia vat can son. So vai Idp son phun thi lop son tinh dien se bam chic hon vi cd them luc dien hut cac hat son vao vat can son. Trong cdng nghe nay, vat can son phai bang kim loai. 10

13 n 2 THUYET ELECTRON DINH LUAT BAO TOAN DIEN TICH Dua tren co so nao de giai thfeh cac hien tuong nhiem dien? I - THUYET ELECTRON Cau tao nguyen tii ve phuc'ng dien dien. Dien tich nguyen to a) Nguyen tir ed ca'u tao gdm mot hat nhan mang dien duong nam d trung tam va eae electron mang dien am chuyen ddng xung quanh. Hat nhan ed eau tao gdm hai loai hat la ncrtron khdng mang dien va prdtdn mang dien duong (Hinh 2.1). trinh 2.1 Mo hinh nguyen tci heli Electron cd dien tfch la -1,6.10"'^ C va khdi luong la 9,1.10-3' ]^g protdn ed dien tfch la +1,6.10"'^ C va khdi lugfng la 1,67.10"^^ kg. Khdi luong eua notron xap XI bang khdi luong eua prdtdn. Sd prdtdn trong hat nhan bang sd electron quay xung quanh hat nhan nen do Idn ciia dien tfch duong ciia hat nhan bang do Idn eua dien tfch am eua cac electron va nguyen tir d trang thai trung hoa vi dien. b) Trong cac hien tuong dien ma ta xet d chuong trinh Vat If Trung hoe pho thdng (THPT) thi dien tfch eua electron va dien tfch eiia prdtdn la dien tfch nhd nhat ma ta ed the ed duoe. Vi vay, ta goi chung la nhung dien tich nguyen to {km hoae duong). Ta higu sir trung hoa ve dien eua nguyen tir nhu sau : VI tdng di6n tich ciia cac electron cd do Idn bang dien tich ciia hat nhan va khoang each giiia cac electron va hat nhan rat nhd so vdi khoang each ttr nguyen tir nay den nguyen tir khac nen lire dien ma he dien tfch nay tac dung len cac dien tich khac coi nhu bang khdng. Do do nguyen tu nay khdng cd tuong tac dien vdi cac nguyen tir khac.

14 Ml Hay van dung thuyet electron de giai thich hien tuong nhilm dien eua thanh thuy tinh khi CO xat vao da. Cho rang, tron^g hien tuong nay, thuy tinh bj nhiem dien dudng va chi co cac electron co the di chuyen tu vat no sang vat kia. 2. Thuyet electron Su eu tru va di chuyen eua eae electron tao nen eae hien tugfng dien va tfnh chat dien mudn mau mudn ve eiia tu nhien. Thuyet difa vdo su cu tru vd di chuyen eua cdc electron de gidi thich cdc hien tuang dien vd cdc tinh chat dien eua cdc vat goi Id thuyet electron. HI Ndi dung eua thuyet electron vd viec giai thfeh su nhidm dien eiia cae vat nhu sau : a) Electron cd the rdi khdi nguyen tti de di chuyen ttr noi nay den noi khac. Nguyen t;i bi mat electron se trd thanh mot hat mang dien duong goi la ion duang. Vf du : Nguyen tu natri bi mat mot electron se trd thanh ion Na""". b) Mot nguyen tu trung hoa cd the nhan them electron de trd thanh mot hat mang dien am va duoe goi la ion dm. Vf du : Nguyen tii elo nhan them mot electron se trd thanh ion Cl~. e) Mot vat nhidm dien am khi sd electron ma nd ehiia Idn hon so dien tfch nguyen td ducmg (prdtdn). Neu sd electron ft hon sd prdtdn thi vat nhism dien duong. II-VAN DUNG ^ Hay neu mot dinh nghla khac ve vat dan dien va vat each dien. B: Chan khdng din dien hay each dien? Tai sao? 1. Vat (chat) dan dien va vat (chat) each dien Vat (chat) ddn dien Id vat (chat) co chua nhieu dien tich tudo. Dien tfch tu do la dien tfch cd the di chuydn tir diem nay den diem khac trong pham vi the tfch ctia vat dan. Kim loai ed ehiia nhieu electron tu do ; eae dung dich axit, bazo va mudi ed ehua nhieu ion tu do. Chung ddu la cac chat dan dien. Vat (chat) each dien la vat (clidt) khong chua hodc chua rat it dien dch tu do. Khdng khf khd, dau, thuy tinh, sii, cao su, mot sd nhua,... la eae chat each dien. ^ R] 12

15 2. Sii nhiem dien do tiep xuc Neu cho mot vat chua nhidm dien tiep xiic vdi mot vat nhidm dien thi nd se bi nhi6m dien ciing da'u vdi vat dd. Dd la su nhiim dien do tiep xuc. Neu cho hai qua ci\x kim loai da tfch dien tiep xiic vdi nhau va do chfnh xac cae dien tfch, ta se tha'y tong dien tfch ciia hai qua eau sau khi tiep xiic bang tong dai sd dien tfch eua hai qua eau trude khi tiep xtic (Hinh 2.2). Nhu vay, viec gan da'u cho hai loai dien tfch tuy la hinh thurc, nhung nd da giiip ta tfnh toan dugc cae dien tfch theo phuong phap dai sd. HI 3. Su nhiem dien do hucrng utng Dua mot qua eau A nhi6m dien duong lai gan dau M ciia mot thanh kim loai MN trung hoa ve dien (Hinh 2.3). Ta tha'y dau M nhism dien am, edn dau N nhidm dien duong. Su nhidm dien ciia thanh kim loai MN la su nliiem dien do hudng ung (hay hien tuong cam ling tinh dien). Ne'u dua qua eau A ra xa, thanh kim loai MA'' lai trd lai trang thai trung hoa vi dien. Di6u dd chiing td do Idn eua eae dien tfch am va duong d eae dau M va A^ la bang nhau. CE Hien tuong tuong tu cung xay ra khi qua cau A nhiem dien am. Hinh 2.2 PP! Hay giai thich su nhiem dien eua mot qua cau kim loai khi cho nd tiep xuc vdi mot vat nhiem dien dudng. t + /W N Hinh 2.3 B5 Hay van dung thuyet electron de giai thich hien tudng nhiem dien do hudng ung. Biet rang trong kim loai cd electron tu do. Ill - DjNH LUAT BAO TOAN DIEN TICH Trong mot he vat ed lap ve dien, tdng dai so eua cae dien tieh Id khdng ddi. He vat cd lap ve dien la he vat khdng ed trao doi dien tfch vdi cac vat khac ngoai he. 13

16 Thuyet electron la thuyet dua vao sucutru va di chuyen eua cac electron de giai thich cac hien tuong dien va cac tinh chat dien eua cac vat. Dien tich eua electron la dien tich nguyen to am (-e = -1,6.10"^^ C). Oien tich eua proton la dien tieh nguyen to duong (+e= 1,6.10"^'C). Cd the giai thich cac hien tuong nhiem dien do cp xat, do tiep xuc va do hudng lirng... bing thuyet electron. Djnh luat bao toan dien tich : Tong dai so eua cac dien tich eua mot he vat co lap ve dien la khong thay doi. CAU HOI VA BAI TAP 1. Trinh bay ndi dung eua thuyet electron. 6. Dua mdt qua cau Q tich dien duong lai 2. Giai thich hien tuong nhi m dien am cija mot 9^" dau M ciia mot khdi tru kim loai MN qua cau kim loai do tiep xuc bang thuyet electron. ('^"''^ 2-'^)- {^m + 3. Trinh bay hien tuong nhiem dien do hudng ling va giai thich hien tuong dd bang thuyet Q M i N electron. ^ u o ^ Hinh Phat bieu dinh luat bao toan dien tich va van dung de giai thich hien tuong xay ra khi cho mot qua cau tich dien duong tiep xuc vdi mot Tai iw va A/ se xuat hien cac dien tich trai dau. qua cau tich dien am. Hien tuong gi se xay ra neu cham tay vao diem /, trung diem ciia MN? Chon cau dung. Dua qua cau tich dien Q lai gan qua cau M nhd, nhe, bang bac, treo 6 dau mot soi chi thang dung. Qua cau bac M bj hiit dinh vao qua cau Q. Sau dd thi A. Dien tich d M va W khdng thay doi. B. Dien tich d M va A/ mat het. Q ^len tich d M cdn, d N mat. - ^'^" *'^^ ^ '^^'' ^ ^ "- A. M tiep tue bj hut dinh vao Q. 7. Hay giai thich hien tuong bui bam chat vao cac B. M rdi Q va vsn bi hut lech ve phia Q. '^^"^ ^^^* ^^.^"' "^^^ ^^ ^^^^ ^^^^ thuong xuyen quay rat nhanh. C. M rdi 0 ve vi tri thang diing. D. M bi day lech ve phia ben kia.

17 DiEN TRirCUNG VA CUdNG DO DIEN TRI/CING Dl/GfNG sac DIEN Tai sao hai dien tfch a each xa nhau trong chan khdng lai tac dung duoc luc len nhau I - DIEN TRUdNG 1. Moi tri/dng truyen tuorng tac dien Gia sir ta dat hai qua cau tfch dien trai da'u trong mot binh kfn rdi hiit het khdng khf ra (Hinh 3.1). Theo nhu bai 1, luc hut giiia hai qua eau khdng nhijng khdng yeu di ma lai manh len. Nhu vay, phai ed mot mdi trudng nao dd truyen tuong tac dien giqa hai qua eau. Mdi trudng dd la dien trudrjg. Bom chan khdng ehi cd the hiit duoc cac phan tu khdng khi ra khdi binh ma klidng hiit duoc dien trudng. Hinh Dien tri/dng Dien trudng Id mot dang vat chat (mdi trudng) bao quanh dien tieh vd gdn lien vdi dien tieh. Dien trading tac dung lue dien len edc dien tieh khde ddt trong nd. Mot dien tfch Q nam tai mot diem trong khdng gian se gay ra xung quanh nd mot dien trudng. Mot dien tfch q nam trong dien trudng dd se bi Q tae dung mot lue dien. Nguge lai, q ciing gay ra mot dien trudng tac dung len Q mot lue true ddi (Hinh 3.2). qo q M Hinh

18 II - CUdNG DO DIEN TRLTCfNG 1. Khai niem citarng do dien truofng Gia sir cd mot dien tfch diem Q nam tai diem O. Dien tfch nay tao ra mdt dien trudng xung quanh nd. De nghien eiiru dien trudng eua Q tai diem M, ta dat tai dd mot dien tfch diem q, goi la dien tich thii, va xet lue dien tae dung len q (Hinh 3.2). Theo dinh luat Cu-ldng, q eang nam xa O thi lire dien cang nhd. Ta ndi dien trudng tai cac diem cang xa Q eang yeu. Rd rang la can phai xay dung mot khai niem dac trung cho su manh, yeu ciia dien trudng tai mot diem. Khai niem dd la cudng do dien trudng. Neu dien trudng do nhi^u dien tich di6m gay ra thi dinh nghia nay vin dung. Thuc vay, lire dien do mdi dien tich diem tac dung len dien tfch thir q CO do Idn ti le thuan vdi q. Do dd, dp Idn eua tdng hop cac luc dien cung vin ti le vdi q, dii dd la tong vecta. Vi vay, trong trudng hgp dien f trucfng philc tap thi thuang sd vin la do Idn eua lire dien tac dung len dien tfch 1 C va vin cd the' laylam sd do cudng do dien trudng. 2. Djnh nghia Ta cd the lay do Idn eiia luc dien tac dung len dien tfch thir q = +\ C de dac tiamg eho eudng do dien trudng tai diem ma ta xet. Tuy nhien, theo cdng thiic (1.1), do Idn F eua luc dien ti le thuan vdi q, ntn thuong so ehfnh la dd Idn eua lue dien tae dung len q dien tfch 1 C. Do dd, ta se lay thuong sd nay lam so do eiia eudng do dien trudng. Ta ed dinh nghia sau : Cudng dp dien trudng tai mat diem la dqi luang dac trung cho tde dung luc eua dien trudng tai diem dd. Nd dupe xde dinh bdng thuang so eiia dp Idn lue dien F tde dung len mdt dien tich thu q (duong) ddt tai diem dd vd dp lan eua q. E = (3.1) trong dd E la cudng do dien trudng tai die'm ma ta xet. 3. Vector cudng do dien trudng Vi luc F la dai luong veeto, edn dien tfch q la dai lugng vd hudng, nen eudng do dien trudng E eung la dai lugng veeto. 16

19 Cucmg do dien tnrcmg dugfc bieu dian bang mot vecta goi la vecta cuong do dien trudng. ^^^'jf-'^^-^'i^^i'- ^BStESfUs^f^-K' q A^^^t^'-^^-'^^^ - Veeto eudng dd dien trudng E cd : (3.2) - phuong va chieu trung vdi phuong va chieu eua luc dien tac dung len dien tich thir q duong ; - chieu dai (mddun) bieu dien do Idn eua eudng do dien trudng theo mdt ti xfeh nao dd. ^ Hay chiing minh veeto cudng dp dien trudng tai diem /W eua mot dien tich diem 0 co phuong va chieu nhu tren Hinh D0n vj do cudng do dien trudng Ne'u trong edng thiic (3.1), do Idn ciia luc F dugc do bang don vi niuton, do Idn eua dien tieh q dugc do bang don vi culdng thi do Idn ciia cudng do dien trudng E phai dugc do bang don vi niuton tren culdng (N/C). Tuy nhien, ngudi ta dung don vi do cudng do dien trudng la vdn tren met (ki hieu la V/m), (xem mue 4, phan II, bai 5). 5. cudng dd dien trudng eua mot dien tich diem Tii cac cdng thiic (1.1) va (3.1), ta suy ra edng thiie tfnh eudng do dien trudng ciia mdt dien tfch diem Q trong chan khdng : F \Q\ E = ~ = k^^ q r^ (3.3) Cdng thiie nay eho tha'y : Do Idn eua eudng do dien trudng E khdng phu thude vao do Idn eua dien tfch thii q. 6. Nguyen li chong chat dien trudng Gia sir cd hai dien tfch diem Q, vaq^ gay ra tai diem M hai di n trudng ed eae veeto eudng do dien trudng, va E^iWmh 3.4). 2-VATLI 11.(C)-A

20 Neu dat mdt dien tfch thir q tai M thi nd se ehiu tac dung eua luc dien nhu the' nao? Nguyen If chdng chat dien trudng dugc phat bieu nhu sau : Cdc dien trudng,, E^ ddng thdi tac dung luc dien ten dien tich q mot cdch doc lap vdi nhau vd dien tich q chiu tde dung eua dien trudng tdng hap E : E = E^+E^ (3.4) Cdc vecta cudng dp dien trudng tai mot diem duac tdng hgp theo quy tac hinh binh hdnh. Ill-DUO^NG sure DIEN \...-js- Hinh ^ ^..Vfc > v-. i 1. Hinh anh cac dudng sure dien Dat hai qua cau kim loai trong mdt be nhd hinh hop chir nhat, cd thanh bang thuy tinh trong sud't, trong dung dau each dien. Cho mdt ft eae hat each dien (nhu mat eua chang han) nam lo liing trong dau. Khuay deu cac hat each dien rdi tich dien trai dau cho hai qua cau. Ta se thay cac hat each dien nam dgc theo nhiing dudng ndi hai qua eau (Hinh 3.5). Cd the ehup anh cac dudng nay mdt each de dang. Ngudi ta da chiing minh dugc rang, cac hat nhd dd da bi nhiem dien va nam dgc theo nhcrng dudng ma tiep tuyen tai mdi diem trung vdi phuong eua veeto cudng do dien trudng tai dd. Mdi dudng dd duge goi la mdt dudng sue dien. 2. Djnh nghia Dudng sde dien Id dudng md tiep tuyen tai mdi diem eua nd Id gid eua veeta cudng dp dien trudng tai diem dd. Ndi each khde, dudng sue dien Id dudng md luc dien tde dung dpe theo dd VATU 11.(C)-B

21 3. Hmh dang difcmg siifc eua mot so dien trudng a) Ta ehi ed the ve ngay duge nhiitig dudng siic dien trong nhiing trudng hgp don gian. Vi du : Dudng sire dien trong dien trudng ciia mdt dien tfch diem (Hinh 3.6 va 3.7). b) Trong nhirng trudng hgp khac thi phai dung phuong phap ehup anh va ve theo anh ehup (Hinh 3.8 va 3.9). 4. Cac dac diem eua dudng sure dien a) Qua mdi diem trong dien trudng cd mdt dudng su'c dien va ehi mdt ma thdi. b) Dudng siie dien la nhiing dudng ed hudng. Hudng ciia dudng siie dien tai mdt diem la hudng eua veeto cudng do dien trudng tai diem dd. e) Dudng siic dien eua dien trudng tinh dien la dudng khdng khep kfn. Nd di ra tir dien tfch duong va ket thiic d dien tieh am. Trong trudng hgp chi cd mdt dien tieh thi eae dudng sire di ttr dien tfch duong ra vd cue hoae di tir vd cue den dien tfch am. d) Tuy eae dudng siic dien la day dac, nhung ngudi ta ehi ve mdt sd ft dudng theo quy udc sau : Sd dudng siie di qua mdt dien tfch nhat dinh dat vudng gdc vdi dudng siic dien tai diem ma ta xet thi ti le vdi cudng do dien trudng tai diem dd. Nhu vay, d ehd cudng do dien trudng Idn thi cac dudng siic dien se mau, edn d ehd eudng do dien trudng nhd thi cac dudng siic dien se thua. BF? Hinh 3.9 O Hinh 3.8 va 3.9, cac dien tfch cd Cling do Idn. f^ Dua vao he thong dudng siic (Hinh 3.6 va 3.7), hav chutig minh rang, cudng do dien trudng eua mot dien tich diem cang gan dien tich diem do thi cang Idn. 19

22 5. Dien trudng deu Dien trudng deu Id dien trudng md vecta cudng dp dien trudng tai moi diem deu cd cdng phuang, chieu vd dp lan ; dudng sdc dien Id nhimg dudng thdng song song cdch deu. Hinh 3.10 Dien trudng trong mdt dien mdi ddng tfnh nsm giiia hai ban kim loai phang rong, dat song song vdi nhau va tfch dien ed do Idn bang nhau, trai dau la mdt dien trudng deu (Hinh 3.10). Dien trudng la mot dang vat chat bao quanh cac dien tich va truyen tudng tac dien. Cudng do dien trudng dac trung cho tac dung luc eua dien trudng : = hay F = qe. \Q\ CUdrng do dien trucrng eua mot dien tich diem trong chan khong : f = ^,. Vector cudng dp dien trudng eua dien truofng tong hop : f =., + fj. Tiep tuyen tai moi diem ciia dudng siitc dien la gia eua vector tai do. CAU HOI VA BAI TAP 1. Dien trudng la gi? 6. Phat bieu nguyen li chong chat dien trudng. 2. Cudng do dien trudng la gi? No duoc xac dinh 7. Neu dinh nghia va cac dac diem ciia dudng nhu the nao? Don vi cudng do dien trudng siic dien. lagi? 8. Dien trudng deu la gi? 3. Veeto cudng do dien trudng la gi? Neu nhung dac diem eua veeto cudng dp dien trudng tai mot diem. 4. Viet cong thiic tinh va neu nhung dac diem ciia 9, cudng do dien trudng eua mot dien tich diem. 5. Cudng dp dien.trudng eua mot he dien tich diem duoc xac dinh-nhu the nao? Dai luong nao dudi day khong lien quan den cudng do dien trudng ciia mot dien tich diem Q tai mot diem? A. Dien tich Q. 20

23 B. Dien tich thu q. 12. Hai dien tich diem Q, = +3.10"^ C va C. Khoang each rtu 0 den q. q^= ^ C dupe dat each nhau 10 cm D. Hang sd dien mdi ciia mdi trudng. trong chan khdng. Hay tim cac diem ma tai dd cudng do dien trudng bang khdng. Tai cac 10. Don vi nao sau day la don vi do cudng do diem dd cd dien trudng hay khdng? dien trudng? A- Niuton. B. Culdng. ^3^ Tai hai diem A va B each nhau 5 cm trong C. Vdn nhan met. D. Vdn tren met. chan khdng cd hai dien tich q^ =+16.1 Q-^Cva q2 = "^ C. Tinh cudng do dien trudng 11. Tinh cudng dd dien trudng va ve veeto cudng,.>,, -. j-j-- * * ^ ^, ^ tong hop va ve veeto cuong do dien truong tai do dien trudng do mpt dien tich diem +4.1 Q-s C ^,1^ ^ nam each A mdt khoang 4 cm va each gay ra tai mot diem each nd 5 cm trong g ^^^ khoana 3 cm chan khdng. Em CO btet? DIEN TRUONG GAN MAT OAT Thuc nghiem cho tha'y, tren be mat Trai Oat ludn ludn ton tai mot dien trudng hudng thsng dung tu tren xud'ng duai, cd cudng dp vao khoang tu 100 V/m den 200 V/m. Nhu vay, con ngudi ludn ludn sdng trong mot khong gian cd dien trudng, tu trudng va trong trudng. Khdng biei, khi di du hanh vu tru dai ngay, trong con tau khdng cdn cac trudng dd nua thi cupc sdng eua nha du hanh se bi anh hudng nhu the nao? 21

24 4 CONG CUA LI/C DIEN Tuong tac tinh dien cd nhieu diem tuong dong vdi tuong tac hap din. Ta se thay, cong cua luc dien cung cd nhung diem tuong tu nhu cdng cua trong luc. I - CONG CUA Ll/C OlEN d\ K c q T F M Hinh Dac diem cua life dien tac dung len mot dien tich dat trong dien trucrng deu Dat dien tfch q duong {q > 0) tai mdt diem M trong dien trudng deu (Hinh 4.1), nd se chiu tac dung eua mdt lue dien F = qe. Luc F Id luc khdng ddi, ed phuang song song vdi cae dudng sue dien, chieu hudng tii ban ducmg sang ban am, do Idn bang qe M va «i\x d F s> \s H Hinh Cong cua luc dien trong dien trudng deu a) Dien tieh q duong di ehuyen theo dudng thang MN, lam vdi cac dudng siic dien mdt gdc a, vdi MN - s (Hinh 4.2). Ta ed edng eua lue dien : voi "^MN ~ ^-^ ~ Fscosa F - qe va scosa = dthi : ^MN = qed (4.1) trong do d = MH la do dai dai sd, vdi M la hinh chieu eiia diem dau dudng di, H la hinh chieu ciia diem cudi dudng di tren mdt dudng sue. Ta chgn chieu duong cho MH cung chieu vdi ehi^u ciia dudng siie. Vi ^ > 0 nen F ciing chieu vdi E. Do dd, a vira la gdc gioa luc dien F va do ddi s, vira la gdc giua hudng cua dudng sije va hudng eua do ddi s. 22

25 - Neu a < 90 thi eosa > 0, do dd ^ > 0 (M// ciing chieu dudng sire) va Ay^^ > 0. - Neu a > 90 thi cosa < 0, do dd c? < 0 {MH nguge chieu dudng sijc) va Ay^^ < 0. Trong trudng hgp ^ < 0, ta cd the chiing minh cdng thiie (4.1) van diing va quy udc ve dau cua d van giii nhu tren. b) Dien tfch q di ehuyen theo dudng gap khiie MPN. Tuong tu nhu tren, ta cd : "^MPN ~ ^^icosaj+ F52Cosa2 Vdi ^jcosofi + 52eosa2 = d, ta lai cd : c) Ket qua tren cd the md rong eho eae trudng hgp dudng di tii M den N la mdt dudng gap khue hoae dudng cong. Nhu vay, edng eiia lue dien trong su di ehuyen cua dien tich trong dien trudng deu titm den N Id '^MN ~ Q^^ khdng phu thude vdo hinh dang eiia dudng di md chi phu thude vdo vi tri eiia diem dau M vd diem cudi N cua dudng di. HI 3. Cong cua iiic dien trong su di chuyen cua di^n tfch trong dien tritdng bat ki Ngudi ta cung da chung minh duge rang, edng eiia luc dien trong su di ehuyen cua mdt dien tfch q tir mdt diem M den mdt diem A^ trong mdt dien trudng bat ki cung khdng phu thude hinh dang dudng di tii M den N ma ehi phu thude vao vi tri cua M va N (Hinh 4.3). Day la mdt tfnh chat chung cua dien trudng tinh dien. Dae tfnh nay cho tha'y, trudng tinh dien la mdt trudng the. EH II - THE NANG CUA M6T OlEN TICH TRONG OlEN TRirdNG 1. Khai niem ve the nang cua mot dien tich trong dien tritdng HI Hay neu su tuong tu gioa cong ciia luc dien trong trudng hgp nay vdi cong cua trong luc. Hinh 4.3 Gi Cho mdt dien tieh diem Q nam tai tam cua mot vdng trdn. Khi di chuyen mot dien tich thcf q doc theo cung MN cua vdng trdn dd thi cong cua luc dien se bang bao nhieu? 23

26 Tuong tu nhu the' nang eua mdt vat trong trgng trudng, the ndng ciia mot dien tich q trong dien trudng dac trung cho khd ndng sinh cdng cua dien trudng khi ddt dien tich q tai diem md ta xet trong dien trudng. Ta se lay sd do the' nang eua dien tieh trong dien trudng la edng ma dien trudng cd the sinh ra khi cho dien tfch di chuyen tir diem ma ta xet den diem mdc de tfnh the' nang. Diem mdc thudng dugc coi la diem ma luc dien het kha nang sinh edng. Ddi vdi mdt dien tieh q (duong) dat tai diem M trong dien trudng deu thi edng nay la : A = qed = Wy^ trong dd d la khoang each tir diem M den ban am ; W^^ la the' nang cua dien tfch q tai M. Trong trudng hgp dien tfch q nam tai diem M trong mdt dien trudng bat ki do nhieu dien tfch gay ra thi cd the lay the' nang bang edng eua luc dien khi di ehuyen ^ ttr M ra vd cue {A^^}. Dd la vi d vd cue, tiic la d rat xa cae dien tfch gay ra dien trudng, thi dien trudng bang 0 va luc dien ciing bang 0. Do vay : Wu = AMOO (4.2) d day, ta hieu do 2. SU phu thuoc cua the nang W^^ vao dien tfch q giam the nang la hieu giua gia tri cua the Vi dd Idn ciia luc dien ludn ti le thuan vdi dien tich thir (7 nen cdng nang a diem dau va A^^^va do dd, the nang cua dien tfch tai M ciing ti le thuan vdi q : gia tri cua the nang d diem cudi. Dp giam ^MQO = '^M - ^M'J i^-^) the nang la mot dai y^ j^ ^Q^ j^g ^5- jj jg^ j^gng phu thude q ma chi phu thude vi trf luong dai so. j-»' ii,f» j-»... ^ ' ' ' ' - * diem M trong dien truong. 3. Cong cua die dien va do giam the nang cua dien tfch trong dien trudng Is] The nang cua dien tich thcr q ^^ ^i^h luat bao toan va chuyen hoa nang lugng, ta cd the suy trong dien trudng ra ket qua sau day : ^ - i, r-o - *u f^hi mdt dien tich q di chuyen tit diem M den diem N trone Q neu 0 02 se thay ^ -^ *» ddi the nao khi q di '"^^ -^ trudng thi cdng md luc dien tae dung len dien tich dd chuyen dpe theo sinh ra se bdng dp gidm the ndng cda dien tieh q trong dien cung han? trudng. B5 24

27 25 "^MN - ^M ^N HSaioc :^«c#ewb3s-i*ijfcxr/sw.'s*ww^sf!vj^/*!''ss»i^^ hr*fi--.ti.^v-i^r3w«sa3»x'fc;'ffij«e«->«i-3- (4.4) Cong cua luc dien trong su di chuyen ciia mot dien tich khong phu thuoc hinh dang dudng di ma chi phu thuoc vj tri diem dau va diem cuoi cua dircmg di trong dien trucmg. The nang cua mot dien tich diem q tai diem /M trong dien trirdmg : '^M ~ ^Moo - ^M^ The nang ti le thuan vdi q. Cong cua litc dien bang do giam the nang eua dien tich trong dien trudng. CAU HOI VA BAI TAP 1. Viet cdng thiic tinh cdng ciia luc dien trong sy di chuyen ciia mot dien tich trong mot dien trudng deu. 2. Neu dac diem ciia cdng ciia luc dien tac dung len dien tich thu q khi cho q di chuyen trong dien trudng. 3. The nang ciia dien tich q trong mot dien trudng phu thuoc vao q nhu the nao? Cho dien tich thii q di chuyen trong mdt dien trudng deu doc theo hai doan thing MN va NP. Biei rang luc dien sinh cdng duong va MN dai hon NP. Hdi ket qua nao sau day la dung, khi so sanh cac cdng A^^^ va A^^p ciia luc dien? A. /*MN * ^NP- B. A^f^ < Af^p. ^MN NP- D. Ca ba trudng hop A, B, C deu cd the xay ra. Mdt electron di chuyen dupe doan dudng 1 cm, doc theo mot dudng siic dien, dudi tac dung cua luc dien trong mot dien trudng deu cd cudng dp dien trudng V/m. Hoi cdng cua lye dien cd gia tri nao sau day? A.-1, J. C.-1, J. B.+1, J D.+1, J. 6. Cho mot dien tich di chuyen trong dien trudng doc theo mot dudng cong kin, xuat phat tii diem M roi trd lai diem M. Cdng ciia luc dien bang bao nhieu? 7. Mot electron dupe tha khdng van td'c ban dau 6 sat ban am, trong dien trudng deu giua hai ban kim loai phang, tich dien trai dau. Cudng dp dien trudng giua hai ban la V/m. Khoang each giiia hai ban la 1 cm. Tinh dong nang ciia electron khi nd den dap vao ban duong. 8. Cho mot dien tich duong Q dat tai diem 0. Dat mot dien tich am q tai diem M. Chiing minh rang the nang cua q 6 iw cd gia trj am.

28 EN THE Hliu DIEN THE The nang W^ cua dien tich q trong dien trudng dac trung cho kha nang sinh cdng cua luc dien tac dung len dien tich q. The nang 14/^ vua phu thuoc dien trudng tai tv\, vua phu thuoc q. Co dai luong nao dac trung rieng cho kha nang sinh cdng cua dien trudng, khdng phu thuoc vao dien tich q? I-OlEN THE 1. Khai niem dien the Trong edng thiic tinh the nang eua mdt dien tieh q tai mdt diem M trong dien trudng Wy^ = Ay^^ = Vyiq thi he sd V^. khdng phu thude q, ma chi phu thude dien trudng tai M. Nd dac trung cho dien trudng ve phuong dien tao ra the nang eua dien tieh q. Ta ggi nd la dien the tai M. 1/ - ^M _ ^Mc y\a 'M 2.0 nh nghia Dien the tai mdt diem M trong dien trudng Id dai luang dac trung rieng eho dien trudng ve phuong dien tao ra the ndng khi dot tai do mot dien tieh q. Nd duac xde dinh bdng thuang sdciia edng ciia luc dien tde dung len q khi q di ehuyen titm ravd cue vd dp lan cua q. A ^M q (5.1) B] ChCrng minh rang, dien the tai moi diem trong dien trudng eua mot dien tich diem am (Q < 0) deu cd gia tri am. 3. Oon vi dien the Don vi dien the la vdn (kf hieu la V). Trong edng thuc (5.1), neu ^ = 1 C ; Ay^^,= ljthiv^=lv 4. Oac diem cua dien the Dien the la dai lugng dai so. Trong edng thiie (5.1), vi ^ > 0 nen : neu A^, > 0 thi V^>0; neu A^^ < 0 thi V^ < 0. HI 'M M M» Dien the' cua dat va eua mdt diem d vd cue thudng duge chgn lam mdc (bang 0). 26

29 II-HIEU OlEN THE 1. Hieu dien the'^'^ giiia hai die'm M va A^ la hieu giira dien thei/^ va V^ (Hinh 5.1) : 2. Oinh nghia ^MN = ^M-^N (5.2) Tiir cdng thiic (5.2) ta suy ra : Hinh 5.1 Khi di chuye'n q tu M den N thi dien truong sinh cong A^^. Mat khac, ta cd the viet: d Ket qua. ta thu dugc : q ^Mco - ^MN + ^Noo t^mn A 9 Q (5.3) vay, hieu dien the giiia hai diem M, N trong dien trudng dqe trung eho khd ndng sinh cdng cua dien trudng trong sit di ehuyen cda mot dien tieh tit M den N. Nd duac xde dinh bdng thuang sd eua edng eua luc dien tde dung len dien tieh q trong sit di ehuyen tit M den N vd dp Idn eiia q. Don vi hieu dien the ciing la vdn. Vdn la hieu dien the giiia hai diem ma neu di chuyen dien tfch q=\c tii diem ng den diem kia thi luc dien sinh edng la 1 J. 3. Oo hieu dien the Ngudi ta do hieu dien the tinh dien bang tinh dien ke'. Ph&i chfnh eua tinh dien ke' gdm mdt cai kim bang kim loai (1) ed the quay xung quanh mdt true gan tren mdt cai cin ciing bang kim loai (2). He thdng duge dat trong mdt cai vd kim loai (3) va dugc each dien vdi vd (Hinh 5.2). 4. He thurc giuta hieu dien the va citdng do dien trudng Xet hai diem M va N tren mdt dudng siie dien eua mdt dien trudng deu (Hinh 5.3). (1) HiSu dien the con goi la dien ap. Hinfi 5.2 Mudn do fiieu difin the giira ban duong va ban am ciia mdt ta dien phing, ngudi ta ndi ban am vdi v6 va ban duong vdi csn cua tinh dien k6'. Kim tich dien ciing da'u vdi c&i va nam trong dien tnidng giira can va vd nen chiu tac dung cua lire dien, lam cho nd quay cho den khi tac dung cua luc dien bi can bang bdi tac dung ciia trong luc. Gdc quay ciia kim ti le vdi hieu dien the giiia can va vd. M N Hinh

30 Ne'u di ehuyen mdt dien tfch q tren dudng thang MN thi cdng eua luc dien se la : vd\d=mn. ^MN = qed Hieu dien the giira hai diem M, A'^ la : u MN - = Ed hay d d (5.4) Cdng thiie nay eho thay tai sao ta lai dung don vi eiia eudng do dien trudng la vdn tren met (V/m). Cdng thiic (5.4) cung diing cho trudng hgp dien trudng khdng deu, neu trong khoang d rat nhd dgc theo dudng siic dien, eudng do dien trudng thay ddi khdng dang ke. Dien the tai mot diem AI dac trung cho kha nang sinh edng eua dien trudng khi dat tai d6 mot dien tich q. ><.j,. M q q Hieu dien the giiira hai diem dac trung cho kha nang sinh cong ecia dien trudng trong su di chuyen eua dien tieh q tu diem no den diem kia. 'MN' AviN Oorn vi cua dien the va hieu dien the la von (V). He thurc gicra hieu dien the va cudng do dien trudng : U = Ed. CAU HOI VA BAI TAP 3 28 Oien the tai mdt diem trong dien trudng la gi? Nd dupe xac dinh nhu the nao? Hieu dien the giua hai diem trong dien trudng la gi? Viet he thiic lien he hieu dien the giua hai diem vdi cdng do lye dien sinh ra khi cd mdt dien tich q di chuyen giua hai diem dd. Viet he thiic giua hieu dien the va cudng do dien trudng, noi rd dieu kien ap dung he thuc dd.

31 Biet hieu dien the L/^^,^ = 3 V. Hdi ding thiic nao dudi day chac chan dung? A. V,, = 3 V, B. ^, = 3 V. Khi mdt dien tich Q = -2 C di chuyen tu diem M den diem N trong dien trudng thi luc dien sinh cdng - 6 J. Hdi hieu dien the U^^^ cd gia tri nao sau day? A.+12V. C. +3 V. Chpn cau dung. B. D. 12 V. 3V. Tha mot electron khong van toe ban dau trong mot dien trudng bat ki. Electron dd se A. chuyen dong doc theo mdt dudng siic dien. B. chuyen dong tti diem cd dien the cao xuong diem cd dien the thap. C. chuyen dong tii diem cd dien the thap len diem cd dien the cao. D. diing yen. Cd hai ban kim loai phang dat song song vdi nhau va each nhau 1 cm. Hieu dien the giua ban duong va ban am la 120 V. Hdi dien the tai diem M nam Irong khoang giua hai ban, each ban am 0,6 cm se la bao nhieu? Moc dien the d ban am. Tinh cdng ma luc dien tac dung len mot electron sinh ra khi nd chuyen ddng tii diem M den diem N. Biet hieu dien the L/^^^g = 50 V. Em CO biet? THIET B! LOC BUI TINH OIEN Oe tranh lam d nhidm khdng khi, trong cac d'ng khdi cua cac nha may dien, nha may xi mang, nha may gach, nha may hoa chat,... ngudi ta thudng lap cai loc bui ttnh dien. Thiei bi Ipc bui tfnh dien gom mot he thong cac thanh hoae ban kim loai bd tri doc theo true cua d'ng khdi. O hai 1^ 1^^^ I + /^ +^m' -fs'- I,yy -t-su 1.' y^.!?. i i>.-a.. Cac hat bui va khoi bay len theo luong khi thai Thanh trong ong khoi Cac thanh hoae ban kim loai tfch dien am Tam kim loai hinh mat tru tich dien duong Day noi dat Hmh 5.4 ben thanh trong d'ng khdi cd hai tam kim loai hinh mat try (Hinh 5.4). Cac thanh hoae ban kim loai duac ndi vdi cue am cua nguon dien cao the. Hai tam kim loai mat try dugc ndi vdi cue duang. Khi cac hat byi, khdi bay tu dudi len qua cac thanh hoae ban kim loai thi chung se bi nhiem dien am. Do dd, chung se bi hut dinh vao cac tam kim loai mat try va bi trung hoa ve dien. Mot bd phan ca hoc ISc nhe hai tam nay lam cho cac hat bui, khdi rai xudng va duac dua ra ngoai. Hieu dien the giua hai tam kim loai mat try vdi cac thanh hoae ban kim loai vao khoang vai chyc nghin vdn. Hinh 5.5 Trong anh (chijp ngay ) la hai ong khoi ciia Nha may nhiet dien Pha Lai. Ong khoi cija day chuyen san xuat cu (ben trai) phun khoi bui nhieu, con ong khoi cua day chuyen san xuat moi (ben phai) da duoc loc bui tot. 29

32 6 Tu OIEN Trong quat dien, tivi, tu lanh, stacte cua den d'ng,... ta thudng thay cd ty dien. Vay ty dien la gi La thiec I-TUDIEN Hmh 6.1 La thiec khac 1. Tu dien la gi? Tu dien la mdt he hai vat ddn dat gdn nhau vd ngdn cdch nhau bdng mot Idp cdch dien. Tu dien dung de chiia dien tich. Tu dien la dung cu duge dung pho bien trong cac maeh dien xoay chidu va cac maeh vd tuyen dien. Nd ed nhiem vu tich va phdng dien trong maeh dien. Hinh 6.2 Anh ehup mot so loai tu dien Hmh 6.3 Tu dien duge dung pho bien la tu dien phang. Ca'u tao eiia tu dien phang gdm hai ban kim loai phang dat song song vdi nhau va ngan each nhau bang mdt Idp dien mdi. Hai ban kim loai nay ggi la hai ban eua tu dien. Trong thue te, hai ban kim loai thudng la hai tam giay thiec, kem hoae nhdm ; Idp dien mdi la Idp giay tam mdt chat each dien nhu parafin. Hai ban va Idp each dien duge cudn lai va dat trong mdt vd bang kim loai (Hinh 6.1 va 6.2). Trong maeh dien, tu dien duge bieu diin bang ki hieu ve tren Hinh 6.3. Hmh 6.4 HI Sau khi tich dien cho tu dien, neu ndi hai ban bang mot day dan thi se xay ra hien tugng gi? 2. Cach tich dien cho tu dien Mudn tieh dien cho tu dien, ngudi ta ndi hai ban cua til dien vdi hai cue eua ngudn dien (Hinh 6.4). Ban ndi vdi cue ducmg se tich dien duong, ban ndi vdi cue am se tich dien am. HI 30

33 Vi hai ban tu dien rat gsn nhau, nfin do cd su nhiem dien do hudng ling, dien tieh cua hai ban bao gid cung cd do Idn bang nhau nhung trai dau. Ta ggi dien tieh cua ban duong la dien tieh ciia tu dien. II - DIEN DUNG CUA TU DIEN I.Djnh nghia Dung mdt ngudn cd hieu dien the' nhat dinh de tieh dien eho mdt sd tu dien khac nhau. Ta se thay do Idn ciia dien tieh ma chiing tieh duge eung khac nhau. Nhu vay kha nang tich dien eiia cac tu dien d mdt hieu dien the' nhat dinh la khac nhau. Mat khac, ngudi ta da chiing minh duge chat che bang li thuyet la : Dien tich Q md mot tu dien nhatfttnh tich duac ti le thuan vdi hieu dien theu ddt giua hai bdn cua nd. Q = CUhayC = ^ (6.1) Dai lugng C ggi la dien dung eiia tu dien. Nd dac trung cho kha nang tieh dien eua tu dien d mdt hieu dien the nhat dinh. That vay, dudi mdt hieu dien the' U nhat dinh, tu ed dien dung C Idn se tich dugc dien tich Q Idn. Vay : Dien dung ciia tu dien Id dqi luang dac trung cho khd ndng tieh dien eua tu dien a mot hieu dien the nhat dinh. Nd duac xde dinh bdng thuang so cua dien tich cua tu dien vd hieu dien the giua hai bdn cua nd. 2. Dtfn vi dien dung Trong edng thiic (6.1), ne'u Q do bang don vi culdng (C), U do bang don vi vdn (V) thi C do bang dcm vi fara (ki hieu la F). Fara Id dien dung eua mdt tu dien md neu ddtgiita hai bdn eiia nd hieu dien the 1 V thi nd tieh duac dien tich 1 C. Cae tu dien thudng dung ehi ed dien dung tir 10"'-^ F den 10~^ F. Vi vay, ta thudng dung cae udc eiia fara : 1 mierdfara (ki hieu la.if) = I.IQ-^ F 1 nandfara (ki hieu la nf) = 1.lO"*^ F 1 piedfara (ki hieu la pf) = I.IQ-^^ p 31

34 a) Md hinh cau tao b) Anh ehup mdt tu xoay Hinh 6.5 TiJ xoay +AQ Hinh Cac loai tu dien a) Ngudi ta thudng lay ten ciia Idp dien mdi de' dat ten cho tu dien : tu khdng khi, tu giay, tu mica, tu sii, tu gdm,... Tren vd eua mdi tu dien thudng ed ghi cap sd lieu, chang han nhu 10 )J.F V. Sd lieu thii nhat cho biet dien dung eiia tu. Sd lieu thii hai la gia tri gidi han eua hieu dien the' ed the dat vao hai cue ciia tu. Vugt qua gidi han dd, tu dien ed the bi hong. b) Ngudi ta edn che tao tu dien ed dien dung thay doi duge (edn ggi la tu xoay). Tu xoay ed mdt ban ed dinh (thue ra la mdt he thdng ban) hinh ban nguyet va mdt ban linh ddng ciing hinh ban nguyet. Ban linh ddng cd the quay quanh mdt true vudng gdc vdi ban ed dinh tai tam (Hinh 6.5). Khi xoay ban linh ddng, dien tich ciia phan ddi dien giiia hai ban se thay doi lam eho dien dung ciia tu dien thay doi. 4. Nang luong cua dien trudng trong tu dien Khi tu dien dugc tich dien thi giua hai ban eua tu dien se ed mdt dien trudng. Ne'u ta tudng tugng eho mdt lugng dien tieh nhd + AQ di chuyen theo mdt day dan tir ban duong sang ban am (Hinh 6.6) thi dien trudng se sinh cdng. Day dan se ndng len chiit it. Den ban am thi dien tieh + AQ se trung hoa bdt mdt lugng dien tieh am la -AQ. Dien tich eiia tu dien bi giam di mdt lugng AQ. Neu eii tiep tue lam nhu tren thi se den liie tu dien het dien. Dien trudng se triet tieu. Toan bd cdng ma dien trudng sinh ra da lam tang ndi nang ciia day dan. Nang lugng nay do dien trudng eung cap. Vay, khi tu dien tieh dien thi dien trudng trong tu dien se du trir mdt nang lugng. Dd la nang lugng dien trudng. Ngudi ta da ehiing minh duge cdng thiie tinh nang luong cua dien trudng trong tu dien w Q' 2C

35 Tu dien la dung cu thudng dung de tich va phong dien trong maeh dien. Cau tao cua tu dien phing gom hai ban kim loai phang dat song song vdi nhau va ngan each nhau bang Idp dien moi. Oien dung cua tu dien dac trung cho kha nang tich dien cua tu dien d mot hieu dien the nhat djnh. Don vi dien dung la fara (F). C=- U Khi tu dien tich dien thi dien trudng trong tu dien se du triir mot nang lucrng. Dd la nang luong dien trudng. CAU HOI VA BAI TAP 1. Tu dien la gi? Tu dien phang cd cau tao nhu A. mica. *^ ^^ '^ B. nhua polietilen. 2. Lam the nao de tich dien cho tu dien? Ngudi ^ gi^y ^^^ ^^ng dich mudi an. ta goi dien tich cua tu dien la dien tich ciia ban, ^ PI^Q9 ' D. giay tam parafin. 3. Dien dung ciia tu dien la gi? 7. Tren vd mdt tu dien cd ghi 20 pf V. Noi hai ban ciia tu dien vdi mdt hieu dien the 120 V. 4. Nang luong cua mdt tu dien tich dien la dang nana luonq ql? ^) "'"'"'^ ^'^'^ '"''^ ^^^ ^^ '^'^'^ b) Tinh dien tich tdi da ma tu dien tich dupe, 8*. Tich dien cho mot tu dien cd dien dung 20 af 5. Goi Q, C va U la dien tich, dien dung va hieu dudi hieu dien the 60 V. Sau dd thao tu dien ra dien the giua hai ban ciia mot tu dien. Phat khoi nguon. bieu nao dudi day la dung? ^^ ^.^^ ^.^^ ^^^ ^ ^.^,^ A. C ti le thuan voi Q. ^^ j^^^ ^^^^ ^^ ^^^^ ^^^^^^ ^^^^^ ^^ ^i^^ ^^^^ B. Cti le nghjch vdi U. ra khi phdng dien tich Aq = 0,001 q tii ban C. C phu thuoc vao Q va U. duong sang ban am. D. C khdng phu thuoc vao Q va U. c) Xet luc dien tich cua tu dien chi cdn bang ^ 6. Tronq trudng hop nao dudi day, ta khdng cd ^, o Tinh cong ma dien truong tronq tu dien sinh ra mot tu dien? ^ \,,.^ ^ khi phong dien tich Aq nhu tren tu ban duong Giua hai ban kim loai la mot lop sang ban am luc dd. 3-VATLI 11.(C)-A 33

36 T; DIEN TICH ong ket chirongl OlEN TRl/OfNG 1. Cd hai loai dien tich la dien tieh am va dien tich duong. Cae dien tieh eung dau thi day nhau, trai da'u thi hut nhau. Don vi dien tieh la culdng (C). 2. Dinh luat Cu-ldng vi lire tuong tae giiia eae dien tieh diem dat trong chan khdng : F = 9.10' 9l92 3. Thuyei electron la thuyet can cii vao su eu trti va di chuydn eiia eae electron de giai thich eae hien tugng dien va cae tinh chai dien eua cae vat. Dua vao thuyet electron cd the giai thfeh duge cae hien tugng nhiem dien do eg xat, do tie'p xiic va do hudng ling Xung quanh mdi dien tieh ed dien trudng eiia dien tieh dd. Nd tac dung luc len eae dien tfch khac dat trong dd. 5. Cudng do dien trudng eiia mdt dien tfch diem trong chan khdng : m dien tich diem r'- Don vi cudng do dien trudng la vdn tren met (V/m). f Dudng siic dien la dudng ma tie'p tuyen tai mdi diem eiia nd la gia cua veeto cudng do dien trudng. 7. Cdng eua lire dien khdng phu thude vao hinh dang dudng di ma ehi phu thude vao vi trf diem dau va diem cudi eua dudng di trong dien trudng. 8. The nang eua mdt dien tfch diem q tai diem M Uong dien trudng ti le thuan vdi q : W, V. 9. Dien the tai mdt diem dac trung eho dien trudng ve kha nang sinh edng khi tac dung luc len mdt dien tfch q. He thiic giiia dien the' va cdng A^^^ la : n,= 10. Hieu dien the: ^MN ~ ^M 'M» MS - 'MN Don vi dien the va hieu dien the' la vdn (V). 11. He thirc giua eudng do dien trudng deu va hieu dien the': U = Ed. 12. Dien dung cua tu dien : C = Q Don vi dien dung la fara (F). u 13. Dien trudng trong tu dien ed du tru nang lugng VATU 11.(C)-B

37 CHUONG II Dong dien khong do! Ca dien (Electrophorus) an nau trong cac song 6 Nam Ml, giet chet cac con ca ma no bst duoc bang cac xung dien co cudng dp toi 1 A. No thuc hien dieu do bang each tao ra mot hieu dien the vai tram von doc theo than ciia no va tao ra dong dien chay qua nuoc 6 xung quanh tu dau den duoi cua no. Chuong nay de cap den nhung van de sau day ve ddng dien khdng ddi. Oinh nghia cudng dp ddng dien. Nguyen tac hoat ddng ciia nguon dien. Suat dien ddng ciia nguon dien. Cau tao va hoat ddng cua pin va acquy G.S. Om (Georg Simon Ohm) ( ). Cong va cdng suat ciia nguon dien. Dinh luat Om doi vdi toan maeh. Ghep cac ngudn dien thanh bp 35

38 7 DONG DIEN KHONG DOI NGU6N DIEN O THCS, ta da biei ddng dien la gi, biet nguon dien tao ra ddng dien chay trong maeh dien kin va cd nhieu hieu biei khac ve ddng dien. Trong bai nay, ta se biet ddng dien khdng doi la gi va vi sao nguon dien cd the tao ra ddng dien chay kha lau trong maeh dien kin. I-DONG DIEN Nhd lai cac kie'n thiie da hge d THCS va tra Idi eae eau hdi dudi day : 1. Ddng dien la gi? 2. Ddng dien trong kim loai la ddng dich ehuyen cd hudng eiia eae hat dien tich nao? 3. Chieu eua ddng dien dugc quy udc nhu the nao? Chieu quy udc eua ddng dien chay qua day dsn kim loai ciing chieu hay nguge chieu vdi chieu dich ehuyen ed hudng ciia cac hat dien tieh? 4. Ddng dien chay qua cae vat dsn cd the gay ra nhiing tac dung nao? Ddi vdi mdi tac dung hay k^ ten mdt dung cu ma boat ddng cua nd dua chii yeu vao tae dung dd eua ddng dien. 5. Tri sd eua dai lugng nao eho biet miic do manh, yeu eua ddng dien? Dai lugng nay dugc do bang dung cu nao va bang don vi gi? Hinh 7.1 Cac dien tich dich chuyen qua tiet dien thang S cua vat dsn theo phuong vuong goc voi tiet dien nay. II - Cl/dNG Dp DONG DIEN. DONG DIEN KHONG DOI 1. Cudng do donq '*'^" Cac dien tfch duong hoae dien tieh am dich chuyen ed hudng deu tao thanh ddng dien. Hinh 7.1 md ta trudng hgp cac dien tich duong dich chuye'n theo phuong vudng gdc vdi tiet dien thing S eua vat dan. R6 rang la ddng dien eang manh, die la cd eudng do eang Idn, neu eang cd nhieu dien tieh dich ehuyen qua tiet dien thing eua day dan trong mdt don vi thdi gian. 36

39 Neu ed mdt lugng dien tieh (dien lugng) Aq dich chuye'n qua tiet dien thang S cua vat dsn trong khoang thdi gian At thi eudng do ddng dien / duge xac dinh la : >'": 1=^ At (7.1) vay, cudng dp ddng dien Id dqi luang dac trung cho tac dung manh, yeu cua ddng dien. Nd dupe xde dinh bdng thuang so eua dien lupng Aq dich chuyen qua tiet dien thdng cua vat ddn trong khoang thdi gian At vd khoang thdi gian dd. Cudng do ddng dien cd the' thay doi theo thdi gian. Vi vay, edng thiic (7.1) cho gia tri trung binh ciia cudng do ddng dien trong khoang thdi gian A?. Neu lay At cang nhd thi cdng thiic (7.1) cho gia tri cang ehfnh xac cua cudng do ddng dien tai mdt thdi diem (dugc ggi la cudng do ddng dien tlie thdi). 2. Dong dien khong doi Ddng dien khdng ddi Id ddng dien cd chieu vd cudng dp khdng thay ddi theo thdi gian. HJ Thay cho cdng thiie (7.1), eudng do ddng dien khdng doi duge tinh theo edng thiic : MJ Neu nnot vf du ve mot maeh dien trong dd cd ddng dien khdng doi chay qua. / = i (7.2) trong dd, q la dien lugng ehuyen qua tiet dien thing cua vat din trong khoang thdi gian t. R? Trong ngdn ngii thudng ngay, ed khi ngudi ta ggi ddng dien khdng doi la ddng dien mdt chieu. Can chii y ring, ddng dien khdng ddi la ddng dien mdt chieu, nhung ed nhung ddng dien mdt chieu lai ed eudng do thay ddi theo thdi gian (vf du : ddng dien chay qua day din ndi hai ban ciia mdt tu dien da duoe tfch dien trude dd). w5 Do cudng do ddng dien bang dung cu gi? Mac dung cu dd nhu the nao vao maeh? 37

40 3. Ddn vj cua cudng do dong dien va cua dien luqrng a) Don vi eua eudng do ddng dien trong he SI la ampe va dugc xac dinh la : i*j Trong thai gian 2 s c6 mot dien lugng 1,50 C dich ehuyen qua tiet dien thing cua day tde mot bdng den. Tfnh cudng dp ddng dien chay qua den. BE Ddng dien chay qua mdt day dan bang kim loai cd cudng do la 1 A. Tfnh sd electron djch chuyen qua tiet dien thing cua day dan nay trong khoang thdi gian 1 s. 1 C 1 A = = 1 C/s 1 s Ampe la mdt trong biy don vi ea ban cua he SI va dugc dinh nghia theo tuong tae tir eiia ddng dien (xem chuong IV). 8!?1 b) Don vi ciia dien lugng la culdng (C), dugc dinh nghia theo don vi ampe : 1 C= 1 A.s Culdng la dien lugng dich chuyen qua tiet dien thing ciia day din trong thdi gian 1 giay khi ed ddng dien khdng doi eudng do 1 ampe chay qua day din nay. H! Ill-NGU6N DIEN BS Cac vat cho ddng dien chay qua dugc goi la cac vat gi? Cac hat mang dien trong cac vat loai nay cd dac diem gi? ^K GiQa hai dau mot doan maeh hosc giofa hai dau bong den phai cd dieu kien gi de co ddng dien chay qua chung? 1. Dieu kien de co dong dien a) Nhd lai eae kien thiie da hoc d THCS di tri Idi C5 va C6. b) Ket luan : Dieu kien deed ddng dien Id phdi ed mdt hieu dien the ddt vdo hai dau vat ddn dien. Hieu dien the' nay tao ra trong vat din mdt dien trudng. Dudi tac dung ciia lue dien, cae hat mang dien vin chuyen ddng hdn loan nhung cd them ehuyen ddng ed hudng. Chuyen ddng cd hudng nay tao thanh ddng dien trong vat din. Hay ke ten mot sd nguon dien thudng dung. 38 cac 2. Nguon dien a) Nhd lai nhirng kie'n thiic v^ ngudn dien da hge d THCS de tri Idi C7, C8 va C9.

41 b) Su tdn tai hieu dien the giiia hai cue cua ngudn dien : Ngudn dien duy tri hieu dien the giiia hai cue cua ngudn dien. Hieu dien the giiia hai cue eua ngudn dien duge duy tri ngay ea khi cd ddng dien chay qua cac vat din ndi lien giira hai cue eiia nd, cd nghia la su tich dien khac nhau d eae cue cua ngudn dien tiep tue duge duy tri. Dieu nay duge thuc hien trong nhieu ngudn dien, bang each tich eae electron khdi nguyen tir va chuye'n cac electron hay ion duong ra khdi mdi cue ciia ngudn dien. Khi dd mdt cue thira electron dugc ggi la cue am (cd dien the thap hon), cue kia thiia ft hoae thieu electron duge ggi la cue duong (ed dien the cao hon). Viec tich cae electron ra khdi nguyen tir khdng the do cac lue dien (lue Cu-ldng, nhu da hge d chuong I) thuc hien, ma phai do cdc luc khde bdn chat vdi luc dien thuc hien vd dugc goi Id cdc luc la. K: Bd phan nao cua maeh dien Hinh 7.2 tao ra ddng dien chay trong maeh dien nay khi ddng cong tae K? Hmh 7.2 1*1 Neu mac maeh dien theo sd do Hinh 7.3 thi so ehi cua vdn ke va sd vdn ghi tren nguon dien cd mdi lien he gi? Dieu do cho biet cd gi ton tai giua hai cuc cua nguon dien? IV - SUAT DIEN DONG CUA NGUON DIEN 1. Cong cua nguon dien Trong maeh dien kin (Hinh 7.4), ngudn dien tao ra hieu dien the' (hay dien ap) giira hai diu maeh ngoai gdm cac vat din ndi lien hai cue cua ngudn dien va do dd tao ra mdt dien trudng d maeh ngoai. Dudi tic dung ciia luc dien, cac dien tfch duong d maeh ngoai dich chuyen tir cue duong (ed dien the' cao hon) tdi cue am eua ngudn dien (cd dien the' thap hon) tao thanh ddng dien. De duy tri su tich dien d hai cue va do dd duy tri hieu dien the' giiia hai cue nhu trude, ben trong ngudn dien (maeh trong) dudi tae dung eiia cac luc la, cae dien tich duong dich ehuyen nguge chilu dien trudng. Khi dd cac lue la thue hien mdt edng thing edng ein cua luc dien ben trong ngudn dien. Nguon dien Hmh 7.3 Hmh

42 Tuong tu nhu vay, trong trudng hgp d maeh ngoai la su ehuyen dich eua eae dien tich am (cae electron) tir cue am tdi cue duong dudi tac dung eua lue dien thi d maeh trong cac dien tieh am dich chuyen tir cue duong tdi cue am dudd tae dung cua cac lue la. Cdng cda edc luc la thue hien lam dich ehuyen edc dien tich qua ngudn dugc gpi la cdng eiia ngudn dien. Nhu vay, ngudn dien khdng ed tac dung tao them cac dien tich ma ed vai trd nhu mdt "may bom dien tich". Ngudn dien Id mot ngudn ndng lugng, vi nd cd khd ndng thuc hien cdng khi dich chuyen cdc dien tich duang ben trong ngudn dien nguge chieu dien trudng, hodc dich chuyen cdc dien tich dm ben trong ngudn dien ciing chieu dien trudng. 2. Suat dien dong cua nguon dien a) Dinh ngjiia Suat dien ddng '^eua mot ngudn dien Id dqi lugng dqe trung cho khd ndng thue hien edng eua ngudn dien vd duge do bdng thuang sd giiia cdng A eua lite la thue hien khi dich chuyen mot dien tich duong q nguge chieu dien trudng ben trong ngudn dien vd do lan cda dien tich q do. b) Cdng thuc e) Dan vi ^ A q (7.3) Tir dinh nghia va cdng thiic (7.3), ta thay suat dien ddng ed eung don vi vdi dien the' va hieu dien the' la vdn (V) : 1 V = 1 J/C (1 vdn = ^ '"" ) -" ' 1 culdng ( So vdn ghi tren mdi ngudn dien cho biet tri so ciia suat dien ddng ciia ngudn dien dd. Nhu da biet d THCS, sd vdn nay eung la gia tri cua hieu dien the'giua hai cue eiia ngudn dien khi maeh ngoai hd. Vi vay, suat dien ddng eiia ngudn dien co gid tri bang hieu dien the'gida hai cue ciia nd khi mqch ngodi lid. 40

43 Trong maeh dien kin, ddng dien chay qua maeh ngoai va ea maeh trong. Nhu vay, ngudn dien eung la mdt vat din va cung ed dien trd. Dien trd nay duge ggi la dien tra trong eua ngudn dien. Vi vay, mdi ngudn dien duge dac trung bing suit dien ddng f va dien trd trong r cua nd. V - PIN VA ACQUY WE Hay lam thf nghiem vdi pin dien hoa tu tao : cam hai manh kim loai khac loai (ching han mdt manh ddng va mot manh tdn) vao mot niia qua quat hay ncra qua chanh da dugc bdp nhun ca qua trudc dd va do hieu dien the giua hai manh kim loai nay (Hinh 7.5). 1. Pin dien hoa ca'u tao chung ciia cac pin dien hoa la gdm hai cue ed ban chat hoa hge khac nhau dugc ngam trong chat dien phan (dung dich axit, bazo hoae mudi...). HF Manh dong -si Manh ton 6rj a) Pin Vdn-ta (Volta) Pin Vdn-ta la ngudn dien hoa hge duge che' tao diu tien gdm mdt cue bing kem (Zn) va mdt cue bang ddng (Cu) duge ngam trong dung dich axit sunfuric (H2SO4) loang (Hinh 7.6). Do tae dung hoa hge, eae ion kem Zn^"*" tir thanh kem di vao dung dich axit sunfuric. Thanh kem thita electron nen tieh dien am. Mat khac, eae ion H"^ cd trong dung dich tdi bam vao cue ddng va thu lay cae electron cd trong thanh ddng. Do dd, thanh ddng mat electron nen tfch dien duong. Ket qua la giua hai cue ciia pin Vdn-ta ed mdt hieu dien the xac dinh va la gia tri eua suit dien ddng ciia pin Vdn-ta : ap _ = U.-U, = 1,1 V Zn 1 j i zrfi! : Dung dich H2SO4 Hinh 7.5 Hmh

44 K ' ' ^ 1 ; Zn Cu + ip'^'f'l^ JjjL _ - - ;" H - Hinh 7.7 MQ dong Thanh than Mn02 dupe trpn vol than chi trpn vol ho dac V6 kem Hmh 7.8 "-»^^- '- - - Dung dich «P ^ Khi ndi hai cue cua pin Vdn-ta thanh maeh kin (Hinh 7.7), thi ddng dien d maeh ngoai la ddng cac electron tu do chay tir cue kem tdi cue ddng, lam mat bdt dien tieh am eua cue kem va giam dien tieh duong ciia cue ddng. Tae dung hoa hge lai biit eae ion kem Zn^^ khdi thanh kem, keo chiing di vao dung dich, ddng thdi eae ion duong H"^ tir ben trong dung dich chay tdi cue ddng, thu lay eae electron d cue ddng. Ket qua la ed mdt ddng dien chay lien tue d maeh ngoai va maeh trong eiia pin. Tie dung hoa hge ddng vai trd eiia lire la tao ra va duy tri su tieh dien khac nhau d hai cue eiia pin, do dd duy tri hieu dien the giira chiing va tao ra suat dien ddng ciia pin. b) Pin La-clan-se (Leelanehe) Pin La-clan-se la loai pin hien nay cdn dang duoc sir dung klia phd bien. Cue duang ciia pin la thanh than duoc hoc xung quanh bing chat mangan didxit (MnOj) cd trdn them than chi de khir bot khf hidro bam vao cue than va tang dp din dien. Dung dich chat dien phan la amdni clorua (NH^Cl) duoc trdn vdi mot loai hd dac va dugc ddng trong hop kem diing lam v6 pin va vd kem nay ddng thdi la cue am ciia pin (Hinh 7.8). Do tac dung hoa hoc, thanh than va vd kem dugc tich dien khac nhau va giija chung cd mot hieu dien the. Hieu dien the nay vao khoang 1,5 V va dd cung la gia tri cua suat dien ddng cua pin. Mangan dioxit la chat dxi hoa manh, tac dung vdi kfii hidro xuat hien d cue than khi pin hoat ddng, nhd dd han che sir tang nhanh dien trd trong ctia pin. Trong thdi gian pin phat dien, vd kem mon dsn, mangan didxit va dung dich amdni clorua bi bien doi thanh chat khac, lugng nude tao thanh trong pin tang dan. Dien trd trong ciia pin tang len dang ke, nen cudng do ddng dien ma pin sinh ra trong maeh dien kin giam dang ke, tdi miic pin khong diing dugc nua. 2. Acquy a) Acquy chi Acquy chi gdm ban cue duong bing ehi didxit (Pb02) va bin cue am bing ehi (Pb) (Hinh 7.9). Chit dien phan la dung dich axit sunfuric (H2SO4) loang. 42

45 Do tac dung vdi dung dich dien phan, hai ban cue cua acquy dugc tfch dien khac nhau va hoat ddng gidng nhu mdt pin dien hoa. Suit dien ddng ciia acquy axit vao khoang 2 V. Khi cho acquy phat dien, do tac dung hoa hgc, eae bin cue ciia acquy bi bien doi. Ban cue duong cd Idi la chi didxit nhung dugc phii mdt Idp ehi sunfat. Ban cue am ed Idi la ehi ciing dugc phii mdt Idp ehi sunfat. Sau mdt thdi gian sir dung, hai ban cue ciia acquy ed Idi vin khac nhau nhung cd Idp vd ngoii gidng nhau, deu la ehi sunfat. Do dd suit dien ddng cua acquy giam din. Khi suit dien ddng nay giim xud'ng tdi 1,85 V thi ngudi ta phai nap dien eho acquy de tie'p tue sir dung. Khi nap dien cho acquy, ngudi ta dung mdt ngudn dien khac de tao ra ddng dien mdt chieu di vao bin cue duong (Pb02) va di khdi cue am eiia nd (Pb) (Hinh 7.10). Khi dd, Idp ehi sunfat d hai ban cue mat dan, ban cue duong ciia acquy bien doi trd lai thanh Pb02 va bin cue am cua nd trd lai thanh Pb. Khi qua trinh bien ddi nay ket thiic, acquy lai cd khi nang phat dien nhu trude. Nhu vay, acquy la ngudn dien cd the nap lai de sir dung nhieu lin dua tren phin ung hoa hgc thuan nghich : nd tfch trii nang lugng dudi dang hoa nang khi nap va giai phdng nang lugng ay dudi dang dien nang khi phat dien. Hinh 7.9 Hmh 7.10 b) Acquy kiem Mdt loai acquy kiem dugc dung pho bien la acquy cadimi - kfin. Nd CO cue duong dugc lam bang ken hidrdxit Ni(0H)2, con cue am dugc lam bang cadimi hidrdxit Cd(0H)2 ; cac cue nay dugc ngam trong dung dich kiem KOH hoae NaOH. Acquy nay co suat dien dong la 1,25 V. Acquy kiem cd suat dien dong va hieu suat nhd hon so vdi acquy axit, nhung nhe hon, thdi gian su dung lau hon va dac biet la chiu dugc ddng dien co cudng dp Idn (vi du nhu khi khdi d6ng xe may, 6 to...). 43

46 Dong dien la dong cac dien tich (cac hat tai dien) djch chuyen co hudng. Chieu quy Udc cua dong dien la chieu djch chuyen co huorng cua cac dien tich duong. CUdng do dong dien duoc xac dinh bang thuong so cua dien luong Aq djch chuyen qua tiet dien thang cua vat dan trong khoang thori gian At va khoang thdi gian do. Aq At Dong dien khong doi la dong dien co chieu va cudng do khong thay doi theo thdi gian. q Cudng do cua dong dien khong doi dudc tinh bang cong thufc :!=--. Cac luc la ben trong nguon dien co tac dung lam cho hai cuc cua nguon dien duoc tich dien khac nhau va do do duy tri hieu dien the gicta hai cuc cua no. Suat dien dong cua nguon dien dac trung cho kha nang thuc hien cong cua nguon dien va duoc do bdng cong cua luc la khi djch chuyen mot don vj dien tich duong ngudc chieu dien trudng ben trong nguon dien. Dien trd cua nguon dien dudc goi la dien trd trong cua no. Cau tao chung cua cac pin dien hoa la gom hai cuc co ban chait hoa hoc khac nhau, duoc ngam trong chat dien phan (dung dich axit, bazo hoae muoi...). Do tac dung hoa hoc, cac cuc cua pin dien hoa duoc tich dien khac nhau va giuta chung co mot hieu dien the bdng gia trj cua suat dien dong cua pin. Khi do nang luong hoa hoc chuyen thanh dien nang dutruf trong nguon dien. Acquy la nguon dien hoa hoc hoat dong dua tren ph^n Ung hoa hoc thuan nghjch: no tich tru nang luorng luc nap dien va giai phong nang luorng nay khi phat dien. CAU HOI VA BAI TAP Khi cd ddng dien chay qua vat dan thi cac hat 3. Cudng dd^ddng dien dupe xac dinh bang cdng mang dien tham gia vao chuyen ddng cd ^"^^ "^ hudng dudi tac dung cua luc nao? 4, Bang each nao ma cac nguon dien duy tri sy Bang nhung cach nao de biet cd ddng dien ^ich dien khac nhau d hai cue cua nguon dien chay qua mdt vat dan? va do do duy tn hieu dien the giua hai cue ciia nd? 44

47 5. Dai lugng nao dac trung cho kha nang Ihyc 10. Trong cac pin dien hoa co sir chuyen hoa tu hien cdng cue luc la ben trong nguon dien? nang lugng nao sau day thanh dien nang? Dailudng nay dugc xac djnh nhu the nao? A. Nhiet nang. B. The nang dan hoi. W C. Hoa nang. D. Co nang. 6. Cudng dp ddng dien dugc do bang dung cu 11. Suat dien dong dugc do bang don vj nao nao sau day? sau day? A. Luc ke. B. Cdng td dien. A. Culdng (C). B. Vdn (V). C. Nhiet ke. D. Ampe ke. C. Hec (Hz). D. Ampe (A). 7. Do cudng dp ddng dien bang don vj nao 12. Tai sao cd the ndi acquy la mot pin dien hoa? sau day? Acquy hoat ddng nhu the nao de cd the sir A. Niuton (N). B. Ampe (A). dung dugc nhieu lan? C. Jun (J). D. Oat (W). 13. Mot dien lugng 6,0 mc djch chuyen qua tiet dien thing ciia day dan trong khoang thdi 8. Chpn cau dung. gian 2,0 s. Tfnh cudng dp ddng dien chay qua Pin dien hoa co day din nay. A. hai cue la hai vat dan cung chat. 14. jrong khoang thdi gian ddng cdng tac de B. hai cue la hai vat din khac chat. chay mot tu lanh thi cudng dp ddng dien trung C. mdt cue la vat din va cue kia la vat each dien. ^'"^ ^ '^^^^ '^ ^ A. Khoang thdi gian dong,..,',,,.',,..' cong tac la 0,50 s. Tinh dien luong dich D. u. iia. hai cue V.UO deu ucu a,a cac v.av. vat VOL cach V^OM, dien. uicii. chuyeh,.' qua i--i tiet dien - i.^ thang cua >'.-.= day dan noi - 9. Hai cue cua pin dien hoa dugc ngam trong vdi dong cocua tu lanh. chat dien phan la dung dich nao sau day? ^^ guat dien dong cua mdt pin la 1,5 V. Tinh cdng A. Chi la dung dich mudi. cua luc la khi djch chuyen dien tfch +2 C tu cue B. Chi la dung djch axit. anfi ^^ cue duong ben trong nguon dien. C. Chi la dung djch bazo. D. Mot trong cac dung djch ke tren. 45

48 8 DIEN NANG CONG SUAT DIEN O THCS, ta da biet ve dien nang ma doan maeh tieu thu khi cd ddng dien chay qua va cdng suai tieu thu dien nang cua doan maeh dd. Trong bai nay, ta se tim hieu qua trinh thuc hien cdng khi cd ddng dien chay qua, tim hieu mdi lien he giua cdng cua nguon dien va dien nang tieu thu trong maeh dien kin. I - DIEN NANG TIEU THU VA CONG SUAT DIEN Hinh 8.1 -^ u ^^ I CB Hay cho biet don vi cua cae dai lugng cd mat trong cong thu'c(8.1). B^ Hay neu cac tac dung ma ddng dien cd the gay ra. CE Dung cu gi dugc dung de do dien nang tieu thu? Moi sd do cua dung cu dd cd gia tri la bao nhieu jun (J)? R 1. Dien nang tieu thu cua doan maeh Khi dat mot hieu dien the U vao hai dau doan maeh tieu thii dien nang, eae dien tieh tu do eo trong doan maeh chiu tac diing ctia luc dien. Sir ehuyen doi eo huong eiia eae dien tieh nay tao thanh dong dien chay qua doan maeh va khi do lire dien thire hien cong. Neu dong dien co cucmg do / thi sau mot thdi gian / se co mot dien lugng q = It di ehuyen trong doan maeh (Hinh 8.1) va khi do lire dien thire hien mot cong la : RI A = Uq = Ult (8.1) Dong dien chay qua doan maeh gay ra cac tae dung khac nhau va khi do co su chuyen hoa tir nang lugng dien thanh cae dang nang lugng khac. I^ Vi vay, lugng dien ndng md mot doan maeh tieu thu khi cd ddng dien chay qua de chuyen hod thdnh cae dang ndng lugng khde duge do bdng cdng cua luc dien thuc hien khi dich chuyen cd hudng cdc dien tich. 46

49 2. Cong suat dien Cdng suat dien cua mot doan mqch Id edng suat tieu thu dien ndng eua doan mqch dd vd cd tri sd bdng dien ndng md doan mqch tieu thu trong mot dan vi thdi gian, hodc bdng tieh eua hieu dien the gida hai dau doan maeh vd cudng dp ddng dien chay qua doan mqch dd. ^=^=UI (8.2) H! BE Hay cho biet don vi cua cac dai lugng c6 mat trong cdng thdc (8.2). II - CONG SUAT TOA NHIET CUA VAT DAN KHI CO D6NG OIEN CHAY QUA 1. Djnh luat Jun - Len-xO Nhu da biet o THCS, ne'u doan maeh (hoae vat dsn) chi co dien trd R (voi R = p ) thi dien nang ma doan maeh tieu thu duge bien doi hoan toan thanh nhiet nang. Ket qua la doan maeh nong len va toa nhiet ra moi trucmg xung quanh. Tir cong thuc (8.1), suy ra cong thiic tfnh nhiet lugng Q toa ra a doan maeh chi co dien trd khi CO ddng dien chay qua va nhu da biei d THCS, mdi quan he nay duge Jun - Len-xo phat bieu thanh dinh luat: Nhiet lugng toa ra a mdt vat ddn ti le thuan vdi dien trd eua vat ddn, vdi binh phuang eudng dp ddng dien vd vdi thdi gian ddng dien chay qua vat ddn dd. B5 Hay chutig to I Q = RI^t (8.3) rang, cong suat toa ' - nhiet d vat dan khi CO ddng dien chay 2. Cong suat toa nhiet cua vat dan khi co dong dien chay qua qua dugc tfnh bang Cdng suat tod nhiet ^ a vat ddn khi cd ddng dien chay qua ^ dqe trung eho toe dp tod nhiet ciia vat ddn dd vd dugc xde dinh bdng nhiet lupng toa ra a vat ddn trong mot dan vi thdi gian. p/j= 0 = R/2 = LL t va hay cho biet ddn I ~ t (8-4) lugng c6 mat trong «cong thdc tren. ES 47

50 Ill - CONG VA CONG SUAT CUA NGUON DIEN 1. Cong cua nguon dien O bai 7, ta da biet cac lue la ben trong nguon dien thirc hien cdng lam dich ehuyen eae dien tfch de tao ra su tich dien khac nhau d hai cue eua ngudn dien. Ket qua la giua hai cue cd mdt hieu dien the' va mdt dang nang lugng nao dd (ehsng han nhu nang lugng hoa hgc trong cae pin dien hoa) dugc bien ddi thanh dien nang du tro ben trong ngudn dien. Khi tao thanh maeh dien kin, ngudn dien thue hien cdng khi di chuyen cac dien tfch tu do trong toan maeh de tao thanh ddng dien. Khi dd, dien nang duge ehuyen hoa thanh eae dang nang lugng khac. Theo dinh luat bao toan nang lugng, dien ndng tieu thu trong todn mqch bang cdng cua cdc luc la ben trong ngudn dien. TiT cdng thiic (7.3), ta cd edng thiic tinh cdng A eua ngudn dien khi tao thanh ddng dien ed cudng do / chay trong toan maeh sau mdt khoang thdi gian t la : A^^ = q'^ = mt ^^^^^ ^ ^ (85) 2. Cdng suat cua nguon dien Cdng suat '^ ciia ngudn dien dac trung eho td'c do thuc hien edng eiia ngudn dien dd va dugc xac dinh bang cdng ciia ngudn dien thue hien trong mdt don vi thdi gian. Cdng suat cp nay ciing chinh bang edng suat tieu thu dien nang cua toan maeh. ^.= 4^ = ^ %8.6) Dien nang tieu thu cua mot doan maeh bang tich cua hieu dien the giuta hai dau doan maeh vdi cudng do ddng dien va thdi gian ddng dien chay qua doan maeh do. Cong suat dien cua mot doan maeh bang tich eua hieu dien the giuta hai dau doan maeh va cudng do dong dien chay qua doan maeh dd. 48

51 Cong suat toa nhiet d vat dan khi co ddng dien chay qua luong toa ra d vat dan dd trong mot don vj thdi gian. L/2 duoc xac dinh bang nhiet Cong cua nguon dien bang dien nang tieu thu trong toan maeh. ng ^ Cong suat cua nguon dien bang cong suat tieu thu dien n ang cua toan maeh. K,=^j m 1. Dien nang ma mot doan maeh tieu thu dupe do bang cdng do luc nao thuc hien? Viet cdng thuc tinh dien nang tieu thu va cong suat dien ciia mot doan maeh khi cd ddng dien chay qua. 2. Hay neu ten mot dung cu hay mot Ihiet bj dien cho moi trudng hop dudi day ; a) Khi hoat dong, bien ddi dien nang thanh nhiet nang va nang lupng anh sang. b) Khi hoat dong, bien ddi toan bp dien nang thanh nhiet nang. c) Khi hoat ddng, bien ddi dien nang thanh co nang va nhiet nang. d) Khi hoat ddng, bien ddi dien nang thanh nang lupng hoa hoc va nhiet nang. 3. Cdng suat toa nhiet ciia mot doan maeh la gi va dupe tinh bang cdng thuc nao? 4. Cdng ciia ngudn dien cd mdi lien he gi vdi dien nang tieu thu trong maeh dien kin? Viet cdng thuc tinh cdng va cong suat ciia ngudn dien. 5. Chpn cau dung. Dien nang tieu thu dupe do bang CAU HOI VA BAI TAP A. vdn ke. B. cdng to dien. C. ampe ke. D. tinh dien ke. Cdng suat dien dupe do bsng don vj nao sau day? A. Jun (J). B. Oat (W). C. Niuton (N). D. Culdng (C). Tinh dien nang tieu thu va cdng suat dien khi ddng dien cd cudng dp 1 A chay qua day dan trong 1 gid, biet hieu dien the giua hai dau day din nay la 6 V. Tren nhan ciia mot am dien co ghi 220 V W. a) Cho biet y nghia cac sd ghi tren day b) Su dung am dien vdi hieu dien the 220 V de dun sdi 2 lit nude tii nhiet dp 25 C. Tinh thoi gian dun nude, biet hieu suat cua am la 90% va nhiet dung rieng ciia nude la J/(kg,K). Mdt ngudn dien cd suat dien ddng 12 V. Khi mic ngudn dien nay vdi mdt bdng den de thanh maeh dien kin thi no cung cap mot ddng dien cd cudng dp 0,8 A. Tinh cdng ciia ngudn dien nay san ra trong thdi gian 15 phut va tinh cdng suat ciia ngudn dien khi do 4-VATLl 11.(C)-A 49

52 9 DINH LUAT OM DOI vdi TOAN MACH Nhu da biei, khi pin La-clan-se (pin thudng dung) duoc su dung mdt thdi gian dai thi dien tro trong cua pin tang len dang ke va ddng dien ma pin sinh ra trong mach dien kin trd nen kha nhd. Vay cudng dp ddng dien chay trong mach dien kin cd moi quan he nhu the nao voi dien tra trong cua nguon dien cung nhu vdi cac yeu td khac cua mach dien? Bai hoc nay se chi ra mdi quan he dd. A Hmh 9.1 A*. - B e 1 ( ^ I [^ Toan mach la maeh dien kin dcm gian nhat cd so dd nhu Hinh 9.1, trong dd ngudn dien ed suat dien ddng e va dien trd trong r, cdn R^ la dien trd tuong duong cua mach ngoai bao gdm cac vat dsn ndi lien hai cue ciia ngudn dien. Dinh luat Om ddi vdi toan maeh bieu thi mdi lien he giqa eudng do ddng dien / chay trong mach dien kin ndi tren vdi suat dien ddng f ciia ngudn dien va vdi dien trd toan phan R^ + r ciia mach dien kin nay. Iflo ' 1 1 Hinh 9.2 K I-THI NGHIEM Mac maeh dien nhu so dd Hinh 9.2, trong dd ampe ke (cd dien trd rat nhd) do cudng do / ctia ddng dien chay trong mach dien kin, vdn ke (eo dien trd rat Idn) do hieu dien the maeh ngoai U^ va bien trd cho phep thay ddi dien trd mach ngoai. Thi nghiem dugc tien hanh vdi mach dien nay eho cac gia tri do / va ^^ nhu Bang 9.1 va dugc the hien tren dd thi Hinh 9.3. Bang 9.1 O Hinh 9.3 0,1 0,2 0,3 0,4 0,5 /(A) /(A).(V) 0 3,05 0,10 2,90 0,15 2,80 0,20 2,75 0,25 2,70 0,30 2,55 0,35 2,50 0,40 2, VATLI 11.(C)-B

53 II - DINH LUAT OM DOI VCJl TOAN MACH Thf nghiem tren day va nhidu thi nghiem khac cho ket qua tuong tu. Tii' dd thi Hinh 9.3, cd the viet he thiic lien he giua hieu dien the maeh ngoai U^ va cudng do ddng dien chay qua mach dien kin la : U^ = UQ-aI = ' al (9.1) trong do, a la he sd ti le duong va ^Q la gia tri Idn nhat cua hieu dien the maeh ngoai va nhu da neu d bai 7, no diing bang suat dien ddng ctia ngudn dien. ^11 Dd tim hieu y nghia ctia he sd a trong he thiie (9.1), ta hay xet maeh dien kin ed so dd Hinh 9.2. Ap dung dinh luat 6m eho mach ngoai chi ehira dien trd tuong duong R^, ta ed : ^N = ^AB = ^^N (9.2) Tich cua cudng do ddng dien vd dien trd dugc ggi Id dp gidm dien the, do dd, tich IR^ cdn dugc ggi la do giam dien the maeh ngoai. Tir eae he thiic (9.1) va (9.2), ta cd : f = U^ + ai = I{R^ + a) Dieu nay cho tha'y a ciing ed dcm vi ctia dien trd. Ddi vdi toan mach, R^ la dien trd tucmg duong ciia mach ngoai, nen a chinh la dien trd trong / eiia ngudn dien. Do dd : HI Trong thf nghiem d tren, maeh dien phai nhu the nao de cudng dp ddng dien / = 0 va tudng dng U= UQ? Tai sao khi dd L/Q cd gia tri Idn nhat va bang suat dien dong # cua nguon dien : Cg = r^? '=I{R^ + r)=ir^ + Ir (9.3) Nhu vay, suat dien ddng eua ngudn dien ed gid tri bdng tdng edc dp gidm dien the a mqch ngodi vd maeh trong. Tir he thiie (9.3), suy ra : U^ = IR^= 'i-ir (9.4) ^ TU he thdc (9.4), hay cho biet trong nhijog trudng hop nao thi hieu dien the L/^g giua hai cue cua nguon dien bang suat dien dong 'c cua nd? (9.5) I^ 51

54 Tdng R^ + r la tdng dien trd tuong duong R^ ciia maeh ngoai va dien trd trong r eiia ngudn dien, duge ggi la dien trd todn phdn ciia mqch dien kin. He thiie (9.5) bieu thi dinh luat 6m ddi vdi toan maeh va duge phat bidu nhu sau : f^ Mdt pin cd sd ghi tren v6 la 1,5 V va cd dien trd trong la 1,0 Q. Mdc mot bdng den cd dien trd R = 4,0 Q. vao hai cuc ciia pin nay de thanh mach dien kfn. Tfnh cudng dp ddng dien chay qua den khi dd va hieu dien the giua hai dau cua n6. Cuong dp ddng dien chay trong mqch dien kin ti le thuan vdi suat dien ddng cua ngudn dien vd ti le nghich vdi dien trd todn phdn cua mach dd. fm NHAN XET 1. Hien tugrng doan mach Tir he thiie (9.5) ta thay, cudng do ddng dien chay trong maeh dien kin dat gia tri Idn nhat khi dien trd R^ ciia maeh ngoai khdng dang ke (R^ = 0), nghia la khi ndi hai cue eua ngudn dien bang day dan cd dien trd rat nhd. Khi dd ta ndi rang ngudn dien bi dodn mach va / = (9.6) Pin Lo-clan-se ed dien trd trong kha Idn (khoang vai dm) nen khi bi doan mach, ddng dien chay qua pin khdng qua Idn, nhung se lam hong pin ne'u 6.i doan mach trong thdi gian dai. 15? Hay cho biet vi sao se rat nguy hiem ne'u hien tugng doan mach xay ra doi vdi mang dien d gia dinh. Bien phap nao dugc sir dung de tranh khong xay ra hien tugng nay? Acquy ehi ed dien trd trong kha nhd, vao khoang vai phan tram dm, nen khi bi doan maeh lau, ddng dien chay qua acquy cd hang tram ampe se lam hdng acquy. Chang han acquy eua xe may hay d td, bi doan maeh khi khdi ddng hoae khi bdp cdi. Do dd. de sii' dung acquy ben lau thi ehi duge a'n edng tae khdi ddng hoae bdp cdi mdi lan trong khoang vai giay va khdng qua hai, ba lan. HI 52

55 2. Djnh luat Om doi vdi toan mach va djnh luat bao toan va chuyen hoa nang luqrng Theo cdng thilc (8.5), edng eiia ngudn dien san ra trong mach dien kin khi ddng dien khdng ddi ed cudng do / chay qua trong thdi gian t \a : A = ^It (9.7) Trong thdi gian dd, theo dinh luat Jun - Len-xo, nhiet lugng toa ra d mach ngoai va mach trong la : Q = {R^ + r)lh (9.8) Theo dinh luat bao toan va ehuyen hoa nang lugng thi A = Q, do dd, tir eae edng thiie (9.7) va (9.8), suy ra eae he thiie (9.3) va (9.5) bieu thi dinh luat 6m ddi vdi toan maeh da thu dugc d tren :? = /(/?N--)va/=- Nhu vay, dinh luat 6m ddi vdi toan maeh hoan toan phii hgp vdi dinh luat bao toan va ehuyen hoa nang lugng. 3. Hieu suat cua nguon dien Cac he thiie (9.7) va (9.8) eho thay rang, cdng ciia ngudn dien bang tdng dien nang tieu thu d maeh ngoai va d mach trong, trong do dien nang tieu thu d maeh ngoai la dien nang tieu thu ed ich. Tir dd, ta ed edng thirc tinh hieu suat H ciia ngudn dien la : m H = )ich _ IN _ IN r/f (9.9) PF! TU cdng thuc (9.9), hay chung to rang, trong trudng hgp mach ngoai chi gom dien trd R^ thf hieu suat cua nguon dien cd dien trd trong r dugc tinh bang cong thuc : H- RK, RN+^ Djnh luat 6m doi vdi toan mach : Cudng do dong dien chay trong mach dien kin ti le thuan vdi suait dien dong cua nguon dien va ti le nghjch vdi dien trd toan phan cua maeh do. «M+r 53

56 Tich cua cudng do dong dien chay qua mot doan mach va dien trd cua nd dudc goi la do giam dien the tren doan mach do. Suat dien dong cua nguon dien cd gia tri bang tong cac do giam dien the d mach ngoai va mach trong. i = /R^ + Ir riien tuong doan mach xay ra khi noi hai cuc cua mot nguon dien chi bdng day dan cd dien trd rait nhd. Khi do^n mach, ddng dien chay qua mach cd cudng do Idn va cd hai. Dinh iuat 6m ddi vdi toan mach hoan toan phu hop vdi dinh luat bao toan va chuyen hoa nang ludng. m CAU HOI VA BAI TAP 1. Dinh luat Om ddi vdi toan mach de cap tdi loai 5. Mac mdt dien trd 14 Q vao hai cue ciia mot mach dien kin nao? Phat bieu dinh luat va viet ngudn dien cd dien trd trong la 1 Q thi hieu he thiic bieu thi dinh luat dd. dien the giua hai cue ciia ngudn la 8,4 V. 2. Op giam dien the tren mot doan mach ia gi? a) Tinh cudng dp ddng dien chay trong mach Phat bieu mdi quan he giua suat dien dong ciia va suat dien ddng ciia ngudn dien. ngudn dien va cac dp giam dien the ciia cac doan mach trong mach dien kin. b) Tinh cdng suat mach ngoai va cdng suat ciia ngudn dien khi dd. 3. Hien tuong doan mach xay ra khi nao va cd the e. Dien trd trong ciia mdt acquy la 0,06 Q va tren gay ra nhung tac hai gi? Co each nao de tranh ^5 cua nd cd ghi 12 V. Mac vao hai cue cua dupe hien tuong nay? acquy nay mot bdng den cd ghi 12 V - 5 W. a) Hay chiing td rang bdng den khi dd gan nhu sang binh thudng va tinh cdng suat tieu thu 4. Trong mach dien kin, hieu dien the mach ngoai f^ien thuc te ciia bdng den khi dd. U^ phu thude nhu the nao vao dien trd R^ ciia b) Tinh hieu suat ciia ngudn dien trong trudng mach ngoai? hop nay A. Uf^ tang khi R^^ tang. 7. Ngudn dien cd suat dien ddng la 3 V va cd dien B. U, tang khi R, giam. ''t 'T '' ^ "' ^?- '?^ r'^j^"' ^'"^ *" N '^i Nii nhu nhau co cung dien tro la 6 Q vao hai cue C. Uf^ khdng phu thude vao R^. ciia ngudn dien nay D. Uf^ luc dau giam, sau do tang dan khi R,^j a) Tinh cdng suat tieu thu dien ciia mdi bong den. tang dan tu 0 tdi v6 cung. b) Neu thao bd mdt bdng den thi bdng den con lai sang manh hon hay yeu hon so vdi trude dd? 54

57 10 GHEP CAC NGUON OIEN THANH BO Khi giai cac bai tap ve bd nguon dien, ta thudng gap cac doan mach chua nguon dien. Vi vay, trude khi hoc ve bp ngudn dien, ta hay tim hieu moi quan he giua hieu dien the va cuong dp ddng dien trong doan mach chua ngudn dien. I - DOAN MACH CHCA NGUON DIEN (NGUON PHATDIEN) Doan mach AWrRB chira ngudn dien la mdt phan eua mach dien kin don gian (Hinh 10.1) da hgc d bai 9. 6 bai dd, ta da cd he thile lien he giiia suat dien ddng 'f vdi cudng do ddng dien / va cac dien trd /, R, R^ ddi vdi mach dien kin nay. ^B Co the hinh dung mach dien kin nay gdm hai doan maeh nhu Hinh 10.2a,b. Ddi vdi doan mach Hinh 10.2b chi chiia dien trd, dinh luat 6m da hge d THCS eho ta he thijc lien he giiia hieu dien the t/^g, eudng do ddng dien / va dien trd ^j. E Ddi vdi doan mqch cd chifa ngudn dien (ngudn phdt) ddng dien cd chieu di ra td cue duang vd di tdi cue dm (Hinh 10.2a). Tuong tu he thirc (9.4) d bai trude, ta ed he thiie lien he giiia hieu dien the t/^g, eudng do ddng dien / va cac dien trd r, R : hay U.^ = ^~l{r + R) 'AB r + R f- U AB R AB (10.1) (10.2) Hinh 10.1 isn Hay viet he there lien he giu'a suat dien dong f vdi cudng do ddng dien I va cac dien trd r, R, R^ ciia mach dien kin. a) A * b) A 0 R^ R Hinh 10.2 trong dd R^^ =r + RVa dien trd tdng edng cua doan ^ Hay viet he thdc lien he giua maeh nay. Cae he thiie (10.1) va (10.2) bieu thi eae hieu dien the L/^g, eudng do mdi quan he giiia hieu dien the va eudng do ddng ddng dien I va dien trd R., ddi vdi dien ddi vdi doan maeh ed ehiia ngudn phat. doan mach Hinh 10.2b. 55

58 Can luu y chidu tinh hieu dien the t/^g la tir A tdi B : Ne'u di theo chi6u nay ma gap cue duang cua ngudn dien trude thi sud't dien ddng ^ dugc lay vai gid tri duang, ddng dien cd chieu tu: B tdi A nguge vdi chieu tinh hieu dien the' thi tdng do gidm dien the'i(r + R) duge lay vdi gid tri dm. B^ BI Hay viet he thdc tinh Wg^ doi vdi doan mach Hinh 10.2a va tfnh hieu dien the nay khi cho bietc'=6 V;/ = 0,5A;r=0,3Q va R = 5,7 Q. II - GHEP CAC NGUON DIEN THANH BO Cd thd ghep eae ngudn dien thanh bd (bd ngudn dien) theo mdt trong eae each dudi day. 1. Bo nguon ndi tiep ^i,ri ^2.''2 'S,r Bd ngudn ndi tie'p la bd ngudn gdm cac ngudn ^^ * *-] r ""l h> ^ h * (lien ( ^v ''i)' ( *2' ' 2)'-' ^ ^n' '"n) ^^^^ ghep ndi tie'p A M N Q e y^j nhau, trong dd circ am ciia ngudn dien trude dugc ndi bang day din vdi cue duong cua ngudn ^x + _ + _ dien tie'p sau de thanh mdt day lien tie'p nhu so dd fy ^'1' 1' g Hinh 10.3a hoae 10.3b. Nhu vay, dau A la cue %,ri %,r2 'g,r duong va dau B la cue am ctia bd ngudn. Hmh 10.3 ^r-, ~ *., -,.,, Vi hieu dien the giua hai cue A, B eua bd ngudn khi maeh hd ed tri sd bang sua't dien ddng ciia nd va ap dung mdi quan he giiia hieu dien the va eudng do ddng dien ddi vdi doan maeh ehira cae ngudn dien, ta thu duge cdng thiic tinh suat dien ddng f^ ctia bd ngudn ghep ndi tie'p nhu sau : Ta ed ^y^g = U^y^ + Uy^j, U^^, do do : 56 ^b = ^1 + ^2+ +^n (10.3) Suat dien ddng cua bp ngudn ghep noi tiep bdng tdng cdc suat dien ddng cua ede ngudn cd trong bd.

59 Dien trd trong r^^ cua bd ngudn dien ghep ndi tiep bdng tdng ede dien trd trong cua ede ngudn ed trong bp. ''b = ^1 + ^2 + + r (10.4) Trong trudng hgp rieng, ne'u n ngudn dien cd ciing sua't dien ddng ^ va dien trd trong / dugc ghep ndi tie'p thi bd ngudn nay ed suat dien ddng va dien trd trong la : 2. Bo nguon song song m va r^^ = nr (10.5) Bd ngudn song song la bd ngudn gdm n ngudn dien giong nhau dugc ghep song song vdi nhau, trong dd ndi cue duong cua eae ngudn vao ciing mdt diem A va ndi cue am ciia cae ngudn vao ciing diem B nhu so dd Hinh Dien the eiia diem A Idn hon dien the eua diem B nen A la cue duong va B la cue am eua bd ngudn. Khi maeh ngoai hd, hieu dien the f/^g bang suat dien ddng ciia mdi ngudn va bang suat dien ddng eiia bd ngudn, cdn dien trd trong cua bd ngudn la dien trd tuong duong cua n dien trd r mac song song. Do dd : r '"" = «3. Bo nguon hdn htfp doi xutng (10.6) Bd ngudn hdn hgp ddi xiing la bd ngudn gdm n day ghep song song vdi nhau, mdi day gdm m ngudn dien gidng nhau ghep ndi tiep nhu so dd Hinh Tijr cdng thiic (10.5) va (10.6), ta cd edng thiic tinh suat dien ddng va dien trd trong ciia bd ngudn ghep hdn hgp ddi xung cac ngudn gidng nhau cd ciing suat dien ddng c^ va dien trd trong r Ya.: ^^ = m^ ; /"b = mr n (10.7) %r %r m r^-^ n,.- i'^'" B Hinh 10.4 ^ >n Hmh

60 Ooi vdi doan mach cd chua nguon dien (nguon phat), ddng dien cd chieu di ra tu cuc duong va di tdi cue am. Hieu dien the U^g giqa hai dau AvaB cua doan mach, trong dd dau A ndi vdi cuc duong cua nguon dien : L/^g = ^ - /fr + R). Suat dien dong eiia bo nguon ndi tiep bang tong cac suait dien ddng cua cac nguon dien cd trong bo : qp qp q^ ap Oien trd trong r^ cua bo ngudn ndi tiep bdng tong cac dien trd trong cua cac nguon cd trong bo: ' l+'-2 + ' + r_ Ghep song song n nguon dien cd ciing suat dien ddng ^ va dien trd trong r tao thanh bo nguon song song cd suat dien dong '^^-?^ va dien trd trong r^ = CAU HOI VA BAI TAP 1. Dong dien chay qua doan mach chiia ngudn dienco chieu nhu the nao? 2. Trinh bay cac mdi quan he ddi vdi doan mach chua ngudn dien. 3. Trinh bay each ghep cac ngudn dien thanh bp ngudn ndi tiep va thanh bp ngudn song song, Trong tiing trudng hop, hay viet cdng thiic tinh suat dien ddng cua bp ngudn va dien trd trong ciia no. Mdt acquy cd suat dien ddng va dien trd trong la r = 6 V va r = 0,6 f2. Sii dung acquy nay de thap sang bong den co ghi 6 V - 3 W. Tinh cudng dp dong dien chay trong mach va hieu dien the giiia hai cue ciia acquy khi dd. Hai ngudn dien cd suat dien ddng va dien trd trong lan lupt la "i = 4,5 V r, = 3Q Mac hai ngudn dien thanh mach dien kin nhu so dd Hinh Tinh cudng dp ddng dien chay trong mach va hieu dien the U^g. Trong mach dien cd so dd nhu Hinh 10.7, hai pin cd Cling suat dien ddng o? = 1,5 V va dien trd trong r = 1 Q. Hai bdng den gidng nhau Cling cd sd ghi tren den la 3 V - 0,75 W. Cho rang dien trd ciia cac den khdng thay ddi theo nhiet dd. Hmh 10.7 a) Cac den cd sang binh thudng khdng? Vi sao? b) Tinh hieu suai ciia bp ngudn. c) Tinh hieu dien the giua hai cue ciia mdi pin. d) Neu thao bdt mot den thi den cdn lai cd cdng suat tieu thu dien nang la bao nhieu? 58 ^. = 3V fj = 2 f^. 32-''2 Hinh 10.6

61 11 PHI/ONG PHAP GIAI MOT S6 BAI TOAN VE TOAN MACH I - NHCNG LUU Y TRONG PHU'ONG PHAP GIAI 1 Toan mach la maeh dien gdm mdt ngudn dien cd suat dien ddng f va dien trd trong r, hoae gdm nhieu ngudn dien duge ghep thanh bd ngudn ed sua't dien ddng f^, dien trd trong r^ va maeh ngoai gdm cac dien trd. Can phai nhan dang loai bd ngudn va ap dung cdng thiic tuong ting dd tinh suai dien ddng va dien trd trong eua bd ngudn. '2. Mach ngoai cua toan mach cd the la cac dien trd hoae eae vat dsn dugc coi nhu cac dien trd (vi du nhu cae bdng den vdi day tde ndng sang) ndi lien hai cue eiia ngudn dien. Can phai nhan dang va phan tieh xem cac dien trd nay dugc mac vdi nhau nhu the'nao (ndi tiep hay song song). Tii dd ap dung dinh luat 6m ddi vdi timg loai doan mach tuong ung ciing nhu tinh dien trd tuong duong cua mdi doan mach va cua mach ngoai. H] ; ra 3. Ap dung dinh luat 6m ddi vdi toan mach de tinh eudng do ddng dien maeh chinh, sua't dien ddng eua ngudn dien hay ctia bd ngudn, hieu dien the maeh ngoai, edng va cdng sua't eua ngudn dien, dien nang ti6u thu eua mdt doan maeh,... ma dd bai yeu eau. 4. Cae cdng thiie can sir dung : (r / = R^+r ; f = I{R^ +/ ) U = IR^^f-Ir; A = fit; PA, = fi;a = UIt\ ^= UI. ng ng a) Hay eho biet cudng do ddng dien chay qua doan mach gom cae dien trd mac ndi tie'p ed dac diem gi. b) Viet cdng thiie tfnh dien trd tuang duong cua doan mach gdm cac dien trd R.,, Rj va R3 mac ndi tie'p. c) Hieu dien the U.,, L/j va L/3 gicra hai dau cac dien trd R.,, Rj va R3 mac ndi tie'p cd mdi quan he nhu the nao? IS a) Hay cho biet hieu dien the giua hai dau cac dien trd R.,, R2 va R3 mac song song cd dac diem gi. b) Cudng do ddng dien / chay qua mach chfnh va /.,, I2, Ij, chay qua cac mach re cua mot doan mach gom cac dien trd R.,, Rj, R3 mac song song cd mdi quan he nhu the nao? c) Viet cong thiic tfnh dien trd tuong dudng ciia doan mach gdm cae dien trd R.,, Rj va R3 mac song song. 59

62 II - BAI TAP VI DU Hmh 11.1 BI Hay phan tfch va cho biet cac dien trd mach ngoai cua mach dien cd so do nhu Hinh 11.1 dugc mac vdi nhau nhu the nao. TU dd neu each tfnh dien trd tudng duong cua mach ngoai nay. Bai tap 1 Mdt mach dien cd so dd nhu Hinh 11.1, trong dd ngudn dien cd suat dien ddng ^ = 6 V va cd dien trd trong r = 2 Q, cae dien trd /?, = 5 Q, ^2 ~ ^^ ^ va /?3 = 3 n. a) Tinh dien trd R^ ciia maeh ngoai. b) Tinh cudng do ddng dien / chay qua ngudn dien va hieu dien thd mach ngoai U. c) Tinh hieu dien the f/j giiia hai dau dien trd R^. Hifdng dan giai a)l«e Dien trd maeh ngoai lar^= 18 Q. b) Ap dung dinh luat 6m cho toan mach, tinh dugc ddng dien mach chinh chay qua ngudn dien la 7 = 0,3 A. Tiir dd tinh duge hieu dien the maeh ngoai la (7 = 5,4 V. e) Ap dung dinh luat 6m, tinh dugc la t/, = 1,5 V. Hmh 11.2 >i HI Nhan dang cac den D.,, 2 v^ bien trd R,, dugc mac vdi nhau nhu the nao d mach ngoai cua mach dien kfn da cho. Bai tap 2 Mdt mach dien cd so dd nhu Hinh 11.2, trong dd ngudn dien cd sua't dien ddng ' = 12,5 V va cd dien trd trong /' = 0,4 Q. ; bdng den )j cd ghi sd 12 V - 6 W ; bdng den D^ loai 6 V - 4,5 W ; 7?j, la mdt bien trd. a) Chiing td rang khi dieu chinh bie'n trd R^ cd tri sd la 8 Q thi cac den )j vad2 sang binh thudng. b) Tinh cdng suat 'P va hieu suat H eua ngudn ng didn khi dd. HU&ng ddn giai a)hl 60

63 De cac den sang binh thudng thi hieu dien the mach ngoai phai la t/ = 12 V. Ap dung dinh luat 6m, ta tim duge ddng dien chay qua ngudn dien cd cudng dd/= 1,25 A. TCr dd suy ra ddng dien chay qua mdi den cd cudng do diing bang cudng dd dinh miic /j = 0,5 A; /j = 0,75 A. Vay cae den sang binh thudng. h)fsl Cdng suat eiia ngudn dien khi dd la 3^ = 15,625 W. Hieu suat lah = 0,96 = 967o. s*^ Tfnh cudng do djnh miic /.,, I2 cua dong dien chay qua mdi den khi cac den sang binh thudng. C«t? Tfnh dien trd R., va Rj tuong img cua cac den khi sang binh thudng. B3 Viet cdng thifc tinh cdng suat.^ va hieu sua't H cua ngudn dien. Bai tap 3 Cd tam ngudn dien ciing loai vdi ciing suat dien ddng ^ = 1,5 V va dien trd trong r = 1 Q. Mac cac ngudn nay thanh bd ngudn hdn hgp ddi xung gdm hai day song song de thap sang bdng den loai 6 V - 6 W. Coi rang bdng den cd dien trd nhu khi sang binh thudng. a) Ve so dd mach dien kin gdm bd ngudn va bdng den mach ngoai. b) Tinh cudng do / eua ddng dien thuc su chay qua bdng den va cdng sua't dien l^ciia bdng den khi dd. c) Tinh cdng sua't 3^^ eiia bd ngudn, cdng sua't S^j eiia mdi ngudn trong bd ngudn va hieu disn the U^ giiia hai cue cua mdi ngudn dd. Hudng ddn gidi a) Ve so dd mach dien nhu de bai yeu cdu. b)k' Ap dung dinh luat 6m cho toan mach, ta tinh duge : / = 0,75 A;3^ = 3,375 W. C)E: Ap dung cae edng thiirc phii hgp, tinh dugc : ^b = 4,5W; P/>. = 0,5625 W;U- = 1,125 V. G^ Tfnh suat dien dong f^ va ^ ciia bg ngudn nhude bai da cho. Be! Viet cac cong thifc tfnh.5^^,, 3^ va U, theo nhu de bai da neu. 61

64 CAU HOI va BAI TAP Cho mach dien cd so dd nhu Hinh 11.3, trong dd ngudn dien cd suat dien ddng (^ = 6 V va co dien trd trong khong dang ke, Cac dien trd R, -R2 30 D.;R^ = 7,5 Q. a) Tinh dien trd tuong duong R^^ ciia mach ngoai, b) Tinh cudng dp ddng dien chay qua mdi dien trd mach ngoai. Hinh 11.3 Cho mach dien cd so dd nhu Hinh 11,4, trong dd cac acquy cd suat dien ddng?^ = 12 V ; ff2 = 6 V vaco dien trd trong khdng dang ke, Cac dien trd R^ = 4 Q ; R2 = 8 Q. a) Tinh cuong dp dong dien chay trong mach, b) Tinh cong suat tieu thu dien ciia mdi dien trd, c) Tinh cdng suat ciia mdi acquy va nang lupng ma mdi acquy cung cap trong 5 phut. Hmh *. Cho mach dien cd so dd nhu Hinh 11,5, trong dd ngudn dien cd suat dien ddng? = 12 V va dien trd trong r = 1,1 D.; dien trd R = 0,1 Q, a) Dien trd x phai cd tri sd la bao nhieu de cdng suat tieu thu d mach ngoai la Idn nhat? b) Dien trd x phai cd tri sd la bao nhieu de cdng suat tieu thu d dien trd nay la Idn nhat? Tinh cdng suat Idn nhat dd. %r 'A^ R zm X cz Hinh

65 12 Thi/c hanh : XAC OINH SUAT DIEN O6NG VA OIEN TRd TRONG CUA M6T PIN Oliisi HOA Pin dien hoa ludn cd dien trd trong r khac 0. Khi cd ddng dien / chay qua pin thi hieu dien the U giua hai cue cua pin nay bao gid cung nhd hon suai dien ddng ^ cua pin. Han nua, neu cudng dp ddng dien / Ion thi pin dien hoa se bi phan cue manh (do chai khu cue tac dung khdng kip) nen dien trd trong rcua pin se tang. Khi dd, hieu dien the Ugiua hai cue cua pin dien hoa cang nhd so vdi suai dien dong e cua pin, dong thdi gia tri cua cudng do ddng dien / chay qua pin khdng on dinh. Vay ta phai lua chpn phuong phap va cac dung cu do nhu the nao de cd the xac dinh duoc gia tri cua suat dien ddng 'f va dien trd trong r cua pin dien hoa? I-MUC DiCH THI NGHIEM 1. Ap dirng he thiie hieu dien the eiia doan maeh ehu'a ngudn dien va dinh luat 6m ddi vdi toan mach de xac dinh suat dien ddng va dien trd trong ctia mdt pin dien hoa. 2. Sir dung eae ddng hd do dien da nang hien sd (Digital Multimeter) de do hieu dien the va cudng do ddng dien trong cac mach dien. II-DUNG CU THI NGHIEM Bd thiet bi thi nghiem "Xac dinh suat dien ddng va dien trd trong cua mdt pin dien hoa" dugc bd tri nhu Hinh Hmh

66 I M +,?> ' ( ^ T "s,r i I flo Hinh 12.2 W ^J m Hay ndi rd chcrc nsng hoat ddng ciia miliampe ke A, bien trd R, va dien trd bao ve RQ mac trong mach dien tren Hinh I Hmh 12.3 M C^ Tai sao khi mac mdt vdn ke V cd dien trd khdng Idn vao hai dau doan mach MN thi cudng dp ddng dien / trong doan mach lai tsng len va hieu dien the U giofa hai dau doan mach nay lai giam nhd? Pin dien hoa (loai pin "Con thd"). 2. Bien trd niim xoay R (loai 10 Q x 10). 3. Ddng hd do dien da nang hien sd (DT-830B) diing lam chiic nang miliampe ke mdt ehidu A. 4. Ddng hd do dien da nang hien sd (DT-830B) diing lam chiic nang vdn ke mdt chidu V. 5. Dien trd bao ve RQ. 6. Bd day dsn ndi mach dien cd hai dau phich csm. 7. Khoa ddng - ngat dien K. Ill-CO sd LI THUYET Xet mach dien kin gdm mdt pin dien hoa ed sua't dien ddng ^ va dien trd trong r mac ndi tiep vdi dien trd bao ve RQ, miliampe ke A va bien trd niim xoay R (Hinh 12.2). HI Ap dung he thiic (10.1) ddi vdi hieu dien the cua doan mach MN chiia ngudn dien, ta cd the viet : Uy^^^U = f-i{r, +,-) (12.1) Mudn xac dinh gia tri cua sua't dien ddng? va dien trd trong r cua ngudn dien, ta phai mac vdn ke V vao hai dau doan mach MN de do hieu dien the U (Hinh 12.3). Nhung neu vdn ke V ed dien trd khdng Idn, thi khi mdc nd vao hai dau doan mach MN, cudng do ddng dien / chay trong doan mach se tang len va hieu dien the U se bi giam nhd so vdi gia tri can do.i^ De khac phuc khd khan tren, ngudi ta dung vdn ke hien so V ed dien trd trong Idn (cd megadm) sao eho khi mdc nd vao hai dau doan maeh MN, thi eudng do ddng dien I trong doan maeh khdng bi thay ddi (do cudng do ddng dien chay qua vdn ke V cd eudng do ra't nhd, ed the bd qua). Nhu vay, ta ed thd mdc vdn ke hien sd V vao hai ddu ctia mdt doan maeh bat ki trong mach kin ma khdng lam anh hudng den eudng dd ddng dien va hieu dien the cua doan maeh dd.

67 Hon nua, cdn phai chgn gia tri thich hgp cua dien trd 7?^ de ddng dien chay qua pin dien hoa ed eudng do dii nhd, sao eho chdt dxi hoa cd the khir kip su phan cue cua pin. Khi dd, gia tri dien trd trong r hau nhu khdng bi thay ddi. Ne'u thay hieu dien the U - I{R + R^^) doi vdi doan mach MN chua cdc dien trd R cua bien trd va R^ ciia miliampe kca vao he thiie (12.1), ta se nhan dugc he thiic cua dinh luat 6m ddi vdi toan mach cd dang : / = R + Rj^ + R^ + r (12.2) IV - GlCri THIEU DUNG CU DO 1. Dong ho do dien da nang hien so Ddng hd do dien da nang hien so DT-830B (Hinh 12.4) la dung eu do dien hien dai, gdm 2000 diem do cd the hien thi bang 4 chir sd tir 0000 den 1999 nhd cac tinh the long (LCD). 6 mat sau, ben trong ddng hd cd mdt pin 9 V cdp dien cho ddng hd hoat ddng va mdt cau chi bao ve 0,2 A. Loai ddng hd nay cd nhieu thang do ung vdi cac ehu'c nang khac nhau nhu : do dien ap mdt ehidu (DCV), do dien dp xoay ehidu (ACV), do cudng do ddng dien mdt chieu (DCA), do dien trd {Q.),... DT.830B "fi "- mm. mmm +iicat.n" Hinh Nhiirng diem can chu y thiic hien a) Khi su dung ddng hd DT-830B, ta van niim xoay eua nd den vi tri tuong ung vdi ehiic nang va thang do can chgn. Sau dd ndi edc cue eiia ddng hd vao mach dien. Gat niim bat - tdt (ON - OFF) sang vi tri "ON" de cac chu sd hidn thi tren man hinh eiia nd. b) Ne'u chua biet rd gid tri gidi han ciia dai lugng cdn do, ta phdi chgn thang do cd gid tri Idn nhat phu hgp vdi chiie nang da chgn. 5-VATLI 11.(C)-A 65

68 c) Khdng do eudng do ddng dien va hieu dien the vugt qud gidi han thang do da chgn. d) Khdng ehuyen ddi chiic nang thang do eiia ddng hd khi dang cd ddng dien chay qua nd. L*J Tai sao khdng dugc phep dung nham thang do cudng dp ddng dien ciia ddng ho do dien da nang hien sd de do hieu dien the trong mach dien? e) Khdng diing nhdm thang do eudng do ddng dien de do hieu dien the. B3 f) Khi thue hien xong edc phep do, phdi gat niim bat - tat ciia ddng hd ve vi tri "OFF" dd tat dien trong ddng hd. g) Phai thay pin 9 V ben trong ddng hd khi d gdc tren ben trai man hinh ctia nd hien thi ki hieu + -. h) Phai thdo pin 9 V nay ra khdi ddng hd neu trong thdi gian ddi (khoang vai thdng) khdng sir dimg no. V - TIEN HANH THI NGHIEM BE Trong mach dien Hinh 12,3, ne'u de bien trd R hd mach, thi so chi cua vdn ke V se bang bao nhieu? Sd chi nay cd dung bang gia tri sua't dien ddng f ctia pin dien hoa mac trong mach dien khdng? 1. Mac pin dien hod ^ vdo mach dien Hinh 12.3, trong dd chgn dien trd RQ~20D. de eudng do ddng dien chay qua pin dien hod khdng vugt qud 100 ma va ehii y dat diing : - Khoa K avi tri ngdt dien (OFF) ; - Bien trd Ravi tri 100 Q ; - Miliampe ke hien sd A d vi tri DCA 200m, circ duong (+) la Id cdm "VQmA", cue am (-) la Id edm "COM" ; - Vdn ke hien sd V a vi tri DCV 20, cue (+) la Id cdm "VQmA", cue (-) la Id cdm "COM". 2. Gat niim bat - tdt eua miliampe ke A va ciia vdn ke V sang vi tri "ON". Ddng khoa K. Ghi gia tri dn dinh cua cudng do ddng dien / tren miliampe ke'a va ctia hieu dien the' U tren vdn kev vao Bang thuc hanh Hi 66 5-VATLI1i.(C)-B

69 3. Thuc hien lai ddng tde (2) neu tren ling vdi mdi gid tri dien trd eiia bien trd R, bdng cdch van niirn xoay cua nd sang vi tri tiep sau de giam ddn dien trd eiia bien trd R til 100 i^ xud'ng tdi 30 Q, mdi Idn giam 10 Q. 4. Diing vdn ke hien sd dat d vi trf thang do DCV 2000m, Idn lugt mdc song song vdi dien trd R^ va R^ trong maeh dien Hinh 12.2 de do hieu dien the U' d hai ddu mdi dien trd ting vdi cudng do ddng dien / chay qua edc dien trd. Tu dd suy ra gid tri ciia U' RQ va 7?^ theo cdng thirc : R = Ghi cdc gid tri ciia RQ va R^ vao Bang thuc hanh Xde dinh gid tri sua't dien ddng f va dien trd trong / eua pin dien hod theo mdt trong hai phuong dn sau day : O Hinh PhUCng an thtirnhat Can cii cac gid tri tuong ting ciia I va U trong Bang thuc hanh 12.1: a) Ve dd thi (J = f(i) bidu didn su phu thude ciia hieu dien the JJ ciia doan mach MN chiia ngudn dien vdo eudng do ddng dien / trong doan mach (Hinh 12.5) dd nghiem lai he thiic (12.1). CE b) Xac dinh toa do U^ va I^ ciia cdc didm tai dd dudng keo dai eua dd thi U = /(/) cdt true tung va true hoanh : / = 0 = t/ (12.3) tmi Phai ve dudng bieu dien cua dd thi U = f(i) nhu the nao de phu hgp vdi phep tinh gia tri trung binh (thong ke) ddi vdi cac gia tri I vail ghi dugc trong Bang thuc hanh 12,1? U = 0 RQ+r (12.4) Tu (12.3) va (12.4), suy ra gid tri suat dien ddng va dien trd trong / eiia pin dien hod. 67

70 Phuong an thiir hai Cd the viet he thiie (12.2) dudi dang : ^ = ^{R + R^ + R^ + r) hay y=^{x + b) (12.5) voi y= Y,x = R;b = R^ + R^^r. /o Hmh 12.6 Can cii cac gid tri tuong ling cua R va I trong Bang thuc hdnh 12.1 : a) Tinh cdc gid tri tuong ling cua y va x. b) Ve dd thi y =f{x) bieu diin gidn tiep su phu thude ciia cudng do ddng dien / trong mach kin vao dien trd cua bien trd R (Hinh 12.6) de nghiem lai dinh luat 6m ddi vdi toan mach theo he thiic (12.2). c) Xac dinh toa do y^ va x^ cua cae diem tai dd dudng keo dai cua dd thi y = f{x) cdt true tung va true hoanh : y = 0=^x^ = -b (12.6) (12.7) Tii (12.6) va (12.7), suy ra gid tri sua't dien ddng va dien trd trong / cua pin dien hod. 68

71 Ho va ten BAO CAO THl/C HANH Ldp.Td 1. Ten bai thuc hanh : 2. Bang thuc hanh 12.1 Giatri:Ro = (^);RA = (^) x = R(Q) /(10-3A) U{V) y=7(a-^) i 1 1 i 1!. Phuang an thijr nhat a) Ve dd thi U =f{i) tren giay ke d vudng (khd A4) vdi ti xfeh thich hgp, hoae ve tren mdy vi tfnh, trong Microsoft Excel. b) Nhan xet va ket luan : - Dang ciia dd thi U =f{i) cd gidng vdi Hinh 12.5 khdng. - He thiic (12.1) ddi vdi doan mach chiia ngudn dien ed dugc nghiem diing khdng. c) Xde dinh toa do U^^ va I^ eiia ede diem tai dd dudng keo dai eua dd thi U =f{i) cdt true tung va true hodnh : / = 0 ^ t/o = (V) RQ+, (A) Tir dd suy ra : "f = (V) ; r = {Q) 69

72 . PhUdngan thorhai a) Tfnh cdc gia tri tuong ling ciia v va.v trong Bang thuc hdnh b) Ve dd thi y =/(.v) tren giay ke d vudng (khd A4) vdi ti xfeh thfeh hgp, hoae ve tren may vi tfnh, trong Microsoft Excel. c) Nhan xet va ket luan : - Dang eiia dd thi y = /(.v) ed gidng vdi Hinh 12.6 khdng. - Dinh luat 6m ddi vdi toan mach (he thiic (12.2)) cd duge nghiem diing khdng. d) Xac dinh toa do x^ va y,, ciia cae diem tai dd dudng keo dai eua dd thi y -f{x) cdt true tung va true hoanh : y = 0 ^.v, = -b = -(R^ + R, + r) = (Q).V = 0 ^ Vn = - = (Q/V) e Tir do suy ra : r = (V) ; r = (Q) CAU HOI 1. Ve mach dien va mo ta phuong phap xac dinh 4. Tai sao cd the mdc nd'i tiep vdn ke vdi pin dien suat dien ddng va dien trd trong ciia pin dien hoa hoa thanh mach kin de do hieu dien the U giua theo phuong an thii nhat ciia thi nghiem nay hai cue ciia pin, nhung khdng dupe mdc noi tiep miliampe ke vdi pin nay thanh mach kin de do cudng dd ddng dien chay qua pin? 2. Ve mach dien va md ta phuong phap xac dinh suat dien dong va dien trd trong ciia pin dien hoa theo phuong an thii hai trong thi nghiem nay 5. Tai sao can phai mdc them dien trd bao ve RQ noi tiep vdi pin dien hoa trong mach dien? 3. Mudn sii dung dong ho do dien da nang hien sd lam chuc nang miliampe ke hoae vdn ke e. Vdi cac dung cu thi nghiem da cho trong bai mot chieu, ta phai lam nhu the nao? nay, ta cd the tien hanh thi nghiem theo nhung Neu nhung diem can chu y thuc hien khi sii phuong an nao khac nua? dung ddng hd nay 70

73 Em CO biet? CACH TiNH SAI SO CUA D6NC H6 OO OIEN HIEN SO Ne'u /^ la gia tri gidi han cua thang do cudng do dong dien thi do phan giai cua thang do tfnh bang : / (A/digit) Gia su M^ la sai sd tuyet ddi cua I^. Khi dd, sai sd ti ddi cua/^ bang 6 = M va goi la cap chinh xac cua thang do. Trudng hap nay, sai sd tuyet ddi cua cudng do ddng dien / hien thi tren dong hd do dien da nang hien sd duac tinh theo cdng thuc : A/ = 51 + na trong dd, ca'p chinh xac 5 va so digit n duac quy dinh bai nha che tao ddi vdi moi thang do (xem Bang 12.1). Vi du : Neu chon thang do DCA 200 ma cua dong ho hien sd DT-830B va do duac / = 26,0 ma, thi ta cd : A/= 1,2%.26, ~ 0,5 ma nghia la cudng do ddng dien / do duac nlm trong khoang cac gia tri : hay (26,0-0,5) ma < / < (26,0 + 0,5) ma / = (26,0 ±0,5) ma Bang 12.1 Cac thong so kl thuat cua dong ho DT-830B Chuc nang '\ DCV DCA Thang do 200 mv mv 20 V 200 V 1000 V 200 na ia 20 ma 200 ma 10A 5 (%) 0,5 0,8 1,0 1,2 2,0 n

74 Tong ket chuang II DONG DIEN KHONG DOI 1. Dong dien Cudng do ddng dien / = Aq_ At. Ddng dien khdng ddi la ddng dien cd chieu va eudng do khdng thay ddi theo thdi gian : / = 7; 1A=^ = 1C/S / Is Cdng ciia ngudn dien ' ^n^-'sq = ^It. ng Cdng suat ciia ngudn dien : ng - ^ = ^ 1 3. Djnh luat 6m doi v6i toan mach. Cudng do ddng dien chay trong mach : 2. Nguon dien Suat dien ddng ctia ngudn dien dac trung cho kha nang thuc hien cdng eiia nd va dugc do bang cdng cua luc la khi dich chuydn mdt don vi dien tfch duong nguge ehidu dien trudng ben trong ngudn dien. «. Cdc pin dien hod cd cau tao chung gdm hai cue cd bdn chat hoa hgc khde nhau? dugc ngam trong chat dien phan. Do tde dung hod hgc, edc cue eiia pin dien hod duge tfch dien khde nhau vd giua chiing cd mdt hieu dien the. o Acquy la ngudn dien hod hgc hoat ddng dua tren phdn ung hod hgc thuan nahieh. / = R\+r «Sua't dien ddng ctia ngudn dien bdng tdng cac do giam dien the d mach ngoai va mach trong : = //?N + /r 4. Ghep cac nguon dien thanh bo Bd ngudn ndi tie'p : ^ = ^1 + ''2 + - > Bd ngudn song song : + ''n Neu n ngudn dien ed ciing suat dien ddng c^ va dien trd trong r dugc mdc song song thi : ^b = ^ 5 /"b = - 72

75 CHUONG Dong dien trong cac moi trifdng Ban mach dien tii Idp bsng cac mach to hop Trong Ijch su ciia nhan loai, moi thdi kl phat trien dupe danh dau bang mdt loai vat lieu. Ta da trai qua thdi ki do da, thdi ki do dong, thdi ki do sdt. Nhung gid day rat khd neu len mot vat lieu dac trung cho nen van minh hien dai. De phuc vu cho nen cong nghiep dien tii, ngudi ta khong nhiing da tan dung mpi loai vat lieu sdn cd trong tu nhien, ma cdn dang co gdng thiet ke va che tao cac loai vat lieu theo yeu cau ciia minh, Chinh vi the, can phai tim hieu cac dac diem cua dong dien trong cac moi trudng khac nhau moi co co hoi hieu dupe nguyen li co sd ciia cac cong nghe hien dai. Chuong nay de cap den ddng dien trong cac moi trudng, bdt dau bdng viec nghien ciiu ddng dien trong kim loai, sau dd nghien ciiu chi tiet dac diem cua ddng dien trong chat dien phan, chat khi, chan khdng va chat ban dan, ddng thdi de cap cac ap dung tuong ung. 73

76 13 DONG DIEN TRONG KIM LOAI Trong cac bai trude, ta da ndi ddng dien trong kim loai la ddng cac electron chuyen ddng cd huang. Nhung nhu tai ca cac vat lieu khac, kim loai cung do cac nguyen td lien kei vdi nhau tao nen. Nguyen tu lai gom hat nhan tich dien duong va cac electron mang dien am quay xung quanh. Vay cac electron trong kim loai cd dac diem gi va nd chi phdi tfnh chai cua ddng dien trong kim loai ra sao? Dd chinh la noi dung cua bai hoc nay. 1 - BAN CHAT CUA DONG DIEN TRONG KIM LOAI ^ 0 / 0 0 : Gf k er- \ 0 0^0 ^ -^ f : 0 0, 0 ' 0 f ^ Hinh 13.1 Mang tinh the tao bdi cac ion duong sdp xep CO trat tu va cac electron tu do chuyen dong hpn loan trong mang. Ban chat ciia ddng dien trong kim loai duge neu ro trong mdt li thuyet tdng qudt ggi la thuyet electron vi tfnh ddn dien cua kim loai. Thuyet dd cd ndi dung nhu sau : 1. Trong kim loai, cac nguyen tu bi mat electron hod tri trd thdnh edc ion duong (Hinh 13.1). Cdc ion ducng lien ket vdi nhau mdt cdch trat tu tao nen mang tinh the kim loai. Chuyen ddng nhiet cua cdc ion (dao ddng cua ion quanh vi tri can bdng) ed the pha huy trat tu nay. Nhiet do eang cao, dao ddng nhiet cang manh, mqng dnh tlie cdng trd nen mdt trat tu. 2 Cdc electron hoa tri tdch khdi nguyen tir, trd thdnh edc electron tu do vdi mat do n khdng ddi {n = hang sd). Chiing chuyen ddng hdn loan tao thanh khi electron tu do choan toan bd the tfch eua khdi kim loai va khdng sinh ra ddng dien nao. 3. Dien trudng " do ngudn dien ngoai sinh ra, day khf electron trdi nguge chieu dien trudng, tao ra ddng dien. 74

77 4. Su mat trat tu ciia mang tinh the cdn trd chuyen ddng cua electron tu do, la nguyen nhan gay ra dien trd ctia kim loai. Cdc loai mat trat tu thudng gap la chuydn ddng nhiet (dao ddng nhiet) eiia cae ion trong mang tinh the, su meo mang tinh thd do bien dang eo hge vd edc nguyen tti la Idn trong kim loai. Dien trd ciia kim loai rat nhay cdm vdi cae yeu to tren. Thuyet electron vd tfnh ddn dien cua kim loai cho tha'y hat tdi dien trong kim loai Id electron tu do. Mat dp ciia cluing rdt cao nen kim loai ddn dien rat tdt (Bdng 13.1). Nhieu tfnh chat khac eua ddng dien trong kim loai ciing cd thd suy ra tii thuyet nay. Vay, ddng dien trong kim loai Id ddng chuyen ddi cd hudng cda ede electron tu do dudi tac dung ciia dien trudng. Bang 13.1 Bac Chat Bach kim Dong Nhom Sdt Silic Vonfam Po l^' 1,62.10" 10,6.10-1, , , ,25.10" 5, a (K-1) 4, , , , , , i Tren bang nay cd silic khong phai kim loai. Dien tra sua't cua chiing Idn hon dien trd suat ciia kim loai vai bac. II - SU" PHU THUOC CUA DIEN TRd SUAT CUA KIM LOAI THEO NHIET DO Khi nhiet do tang, ehuyen ddng nhiet eua cac ion trong mang tinh thd tang, lam cho dien trd cua kim loai tang. Thi nghiem chiing td dien trd suat p eua kim loai tang theo nhiet do gan dung theo ham bae nhat: p = p^[l + a{t-t^)] (13.1) trong dd p^ la dien trd suat d rq C (thudng lay la 20''C) ; a la he sd nhiet dien trd, don vi do la K"'. Gid tri cua p^ vd a eiia mdt so kim loai dugc ghi tren Bdng Tuy nhien, neu lam thf nghiem mdt cdch chfnh xde, ta tha'y he sd nhiet dien trd eiia mdi kim loai khdng nhiing phu thude vao nhiet do, ma vao ed do saeh vd che do gia cdng vat lieu dd. Ngay nay, he sd nhiet dien trd ciia bach kim (platin) da dugc nghien eiiu rat cdn than, vi ngudi ta thudng diing day bach kim de lam nhiet ke diing trong cdng nghiep. HI T(K) Su bien thien dien trd suat cua dong theo nhiet do Rl Vi sao ngudi ta chpn day bach kim de lam nhiet ke dien trd dung trong cdng nghiep? 75

78 Ill - DIEN TRd CUA KIM LOAI 6 NHIET DO THAP VA HliN TUONG SiEU DAN Bang 13.2 Nhiet do toi han cua mot so chat sieu dan Nhom ( Thuy ngan i Chi Thiec Kem NbgSn 1 NbgAl NbgGe Ten vat lieu j DyBa2Cu307 ' HgBa2Ca2Cu30g 1 7"c(K) 1,19 4,15 7,19 3,72 0, , ,5 134 EP Vi sao ddng dien chay trong cuon day sieu dan khong cd ngudn dien lai cd the duy tri lau dai? Cd the dcing ddng dien ay lam cho dong co chay mai dugc khdng? Khi nhiet do cang giam, mang tinh the eang bdt mat trat tu nen su edn trd ciia nd den chuyen ddng eua electron edng ft, dien trd suat ciia kim loai gidm lien tue. Den gdn 0 K, di6n trd ciia cdc kim loai saeh deu rat be. Do thi bieu didn dien trd suat ciia ddng theo nhiet do dugc ve tren Hinh Mdt so kim loai nhu Hg, Pb..., mdt sd hgp kim nhu NbjSn, NbjGe..., va ca mdt sd gdm dxit kim loai nhu DyBa2Cu307 khi nhiet do thap hon mot nhiet do tdi han T^ thi dien trd sudt dot ngdt gidm xudng bang 0. Nhiet do tdi han cua mdt sd chat dugc ghi tren Bang Nhieu tfnh cha't khac nhu tii tfnh, nhiet dung ciing thay ddi dot ngdt d nhiet do nay. Ta ndi rdng cae vat lieu a'y da chuyen sang trang thdi sieu ddn. Ngay nay cac cudn day sieu ddn duge diing de tao ra cdc tii trudng rdt manh ma cae nam cham dien thudng khdng thd tao ra dugc. Cho ddng dien chay qua cdc cudn day kim loai sieu ddn rdi bd ngudn dien di, ddng dien vdn tiep tue chay trong nhieu nam ma khdng yeu di. Trong tuong lai, ngudi ta du kie'n ed the diing day sieu ddn de tdi dien, vd tdn hao nang lugng tren dudng day khdng cdn nira. BE Ti T,>T^ IV - HIEN TUONG NHIET DIEN ;) Hmh 13.3 Electron khuech tan tu dau nong qua dau lanh lam dau nong tich dien duong. Thuyet electron vd tfnh ddn dien eiia kim loai cdn cho thdy, neu sgi day kim loai cd mdt ddu ndng va mdt dau lanh, thi chuyen ddng nhiet cua electron se lam cho mdt phan electron tu do d ddu ndng ddn vd ddu lanh. Ddu ndng se tfch dien duong, ddu lanh tfch dien am (Hinh 13.3). 76

79 Giira ddu ndng va ddu lanh cd mdt hieu dien the nao da'y. Neu lay hai day kim loai khac loai nhau va han hai ddu vdi nhau, mdt mdi han giii d nhiet do cao, mdt mdi hdn d nhiet do thap, thi hieu dien the gioa ddu ndng vd ddu lanh cua timg day khdng gidng nhau, khien trong maeh cd mdt sua't dien ddng ^ (Hinh 13.4). f ggi Id sudt dien ddng nhiet dien, vd bd hai ddy ddn hdn hai ddu vdo nhau gpi la cap nhiet dien. Thf nghiem ehiing td rdng "f = aj (7, - Tj), trong dd Tj - ^2 la hieu nhiet do d ddu ndng vd dau lanh ; (Zp la he sd nhiet dien ddng, phu thude vdo bdn chat cua hai loai vat lieu diing lam cap nhiet dien, den vi do la V.K"'. Suat dien ddng nhiet dien tuy nhd nhung rat dn dinh theo thdi gian va didu kien thf nghiem, nen cap nhiet dien dugc dimg pho bien dedo nhiet do. Ba loai cap nhiet dien thudng ddng la : Cap platin - platin pha rddi cd o^ = 6,5 J.V/K Cap crdmen - alumen cd o^ = 41 lv/k Cap ddng - constantan cd (Zp = 40 J.V/K. Day (Jong Nuoc da Von ke Ngon nen chay Hmh 13.4 Cap nhiet dien dong - constantan : - Nhiet dp ngpn nen chay 7^: - Nhiet dp nude da dang tan Tg = 273 K (tue 0 C). Hat tai dien trong kim loai la electron tu do. Mat do cua chung rait cao nen kim loai dan dien tot. Dong dien trong kim loai la dong chuyen ddi co hudng cua cac electron tu do du6i tac dung cua dien trudng. Chuyen dong nhiet cua mang tinh the can trd chuyen dong cua hat tai dien lam cho dien trd cua kim loai phu thuoc nhiet do. Den gan 0 K, dien trd cua kim loai rat nhd. Vat lieu sieu dan cd dien trd dot ngot giam den bang 0 khi nhiet do T < T^. Cap nhiet dien la hai day kim loai khac ban chait, hai dau han vao nhau. Khi nhiet do hai moi han T.^, T^ khac nhau, trong mach cd suait dien dong nhiet dien ^=: 0^(7, - T^), Oj la he so nhiet dien dong. 77

80 CAU HOI VA BAI TAP ' 1. Hat tai dien trong kim loai la loai electron nao? B: electron d Idp trong ciing ciia nguyen ti). Mat dp cua chiing vao cd nao? C. cac electron hoa tri da bay tu do ra khoi 2. Vi sao dien trd ciia kim loai tang khi nhiet dp tinh the., J *^"9 '^ 3. Dien trd ciia kim loai thudng va sieu dan khac mang tinh the. nhau the nao? D. cac electron hoa tri chuyen dong lu do trong 7_ [^pt ^opg ^en 220 V W khi sang binh 4. Do dau ma trong cap nhiet dien cd suat dien thudng thi nhiet dp ciia day tde den la C. ddng? Xac dinh dien trd ciia den khi thdp sang va khi khdng thap sang, biet rdng nhiet dp mdi trudng la 20 C va day toe den lam bang vonfam. 6 bai tap 5 va 6 dudi day, phat bieu nao la s. Khdi lupng moi nguyen tii ciia dong la ^'^'"'^ ^^^ ' kg/mol. Khoi lupng rieng ciia dong la 5. Cac kim loai deu 8,9.103 kg/m^. Biet rang mdi nguyen tu dong A. ddn dien tot, cd dien trd suat khdng thay ddi. ddng gop mot electron dan. B. ddn dien tot, cd dien trd suat thay ddi theo a) Tinh mat dp electron tu do trong dong. "hietdp. b) Mot day tai dien bang dong, tie't dien C. dan dien tdt nhu nhau, cd dien trd suat thay 10 mm^, mang ddng dien 10 A. Tinh td'c dp troi doi theo nhiet dp. ciia electron ddn trong day ddn dd. D. dan dien tdt, cd dien trd suat thay doi theo 9. De mac dudng day tai dien tii dia diem A den nhiet dp giong nhau. dia diem S, ta can kg day dong. Muon 6. Hat tai dien trong kim loai la ^^V ^^y ^ "9 '^^^9 day nhdm ma van dam bao chat luong truyen dien, it nhat phai dung A. cac electron cua nguyen tu. b^o ^hieu kildgam day nhdm? Cho biet khoi lupng rieng ciia dong la kg/m^, ciia nhdm la kg/m',3 78

81 14 DONG OIEN TRONG CHAT DIEN PHAN Nhung nam gan day, nhdm ngay cang duoc su dung rdng rai trong cac nganh cdng nghiep nhu cdng nghiep dien, dien tu, cdng nghiep hang khdng, cdng nghiep xay dung, cdng nghiep che tao dd gia dung,... Oe san xuai nhdm can cd ngudn dien nang ddi dao. Quy trinh luyen nhdm dua tren hien tugng nao ma ddi hdi nhieu dien nhu vay? I-THUYET DIEN LI Cho nude tinh khie't (nude cat hai Idn) vdo mdt cdc cd hai dien cue bdng kim loai rdi ndi vdi mdt bd pin, ta thay ddng dien chay qua rdt nhd (Hinh 14.1a). Dieu dd ehiing td trong nude tinh khidt cd rat ft hat tai dien. Cho them vdo trong nude mdt lugng nhd axit, hoae bazo, hoae mudi thi ddng dien tang manh (Hinh 14.1b), chiing td mat do hat tai dien trong dd tang len. Su tang sd hat tai dien trong ede dung dich nhu the ed the gidi thfeh dua tren mdt If thuyet ggi Id thuyet dien li : Trong dung dich, ede hgp chat hod hpc nhu axit, baza vd mudi bi phdn li (mdt phdn hodc todn bd) thdnh ede nguyen tu (hodc nhdm nguyen tii) tieh dien gpi Id ion (Hinh 14.2); ion ed the ehuyen ddng tu do trong dung dich vd trd thdnh hat tdi dien. I»Q Hmh 14.1 Khi trong coc ia nuoc tinh khiet, dong dien rat nho, Cho them axit vao nuoc, dong dien tang manh.. Axit phan li thanh ion am (gdc axit)" va ion duong H"*^.. Bazo phan li thanh ion am (OH)" va ion duong (kim loai)"^.. Mudi phan li thanh ion am (gdc axit)" va ion duong (kim loai)"^.. Mdt sd bazo nhu nude amdniac (NH4)0H hoae mudi nhu phan dam amdni clorua (NH4)C1 khdng chiia ion kim loai. Trong dung dich, chiing cung bi phan li thanh edc ion (OH)", CI" vd {nw^y. Phan tu nuoc Phan tu chat tan Hinh 14.2 h/16 hinh dung dich dien phan 79

82 Mdi ion mang mdt sd nguyen dien tich nguyen td. Khi ion Id mdt nguyen tu tfch dien, sd dien tfch nguyen td ciia ion Id hod tri ciia nguyen td ay. Cae ion duang vd dm vdn dd tdn tai sdn trong cdc phdn tir axit, baza vd mudi. Chiing hen ket chat vdi nhau bdng luc hut Cu-ldng. Khi tan vao nude hoae mdt dung mdi khac, luc hiit Cu-ldng yen di, lien ket trd nen long leo. Mot sd phdn tit bi chuyen ddng nhiet tdch thdnh cdc ion tu do. Chuyen ddng nhiet manh trong cdc mudi hoae bazo ndng chay ciing lam cdc phan tir chat nay phan li thdnh cae ion tu do nhu cdc dung dich. Ta ggi chung nhiing dung dich vd chat ndng chay nhu tren la chdt dien phdn.,a e^* ' e- h?l Anion Cation Hmh 14.3 Khi dong dien chay qua binh dien phan, ion am (anion) di ve phia anot, ion duong (cation) di ve phia catot. II - BAN CHAT DONG DIEN TRONG CHAT DIEN PHAN Lay mdt binh dung chat dien phan (vf du dung dich CuSO^) va cdm vao dd hai dien cue ddn dien (vf du bdng kim loai ddng) nhu Hinh Ta dugc mdt binh dien phan. Ndi hai dien cue vdi mot ngudn dien (vf du pin hoae acquy) qua mdt dien trd bao ve va mdt ampe ke. Dien cue ndi vdi cue duong cua ngudn dien ggi la andt, dien cue kia ggi la catot. Trong mach ed ddng dien chay qua. Ddng dien trong Idng chat dien phdn Id ddng ion duang vd ion dm ehuyen ddng cd hudng theo hai chieu nguge nhau. Ion duong chay ve phfa eatdt nen ggi la cation. Ion am chay vd phfa andt nen ggi la anion. Mat do cac ion trong chat dien phan thudng nhd hon mat do electron tu do trong kim loai. Khdi lugng va kfch thude cua ion Idn hon khdi lugng vd kfch thude ctia electron nen tde do cua chuyen ddng cd hudng cua ehiing nhd hon. Mdi trudng dung dich lai rat mat trat tu nen can trd manh chuydn ddng eiia cdc ion. Vi the, chdt dien phdn klidng ddn dien tdt bdng kim loai. 80

83 Ddng dien trong chat dien phan khdng chi tdi dien lugng md cdn tdi cd vat chdt (theo nghia hep) di theo. Tdi dien cue ehi cd electron cd the di tiep, edn lugng vat chat dgng lai d dien cue, gay ra hien tugng dien phdn. Tuy ban chat hod hgc ciia chdt lam dien cue, ma qua trinh trao ddi dien tfch giira ion vd dien cue se kem theo nhijng phan ung hod hgc phu, lam cho hien tugng dien phan trd nen phiic tap them. GD MU De phan biet mdi truong dan dien c6 phai la chat dien phan hay khong, ta c6 the lam each nao? Ill - CAC HIEN TUONG DIEN RA 6 DIEN Cl/C. HIEN TU'gfNG DUONG Cl/C TAN Ta xet chi tiet nhirng gi xdy ra d dien cue ciia binh dien phan da ve tren Hinh Binh dien phan nay thude loai don gian nhat, vi chat tan la mudi cua kim loai diing lam dien cue (trudng hgp nay la ddng). Khi cd ddng dien chay qua, cation Cu^"^ chay ve catot, va nhan electron tii ngudn dien di tdi. Ta cd : Cu2+ + 2e"^Cu Ddng hinh thdnh d catdt se bdm vao cue ndy. O andt, electron bi keo ve cue duong ctia ngudn dien, tao didu kien hinh thanh ion Cu^^ tren bd mat tiep xtic vdi dung dich : Cu -^ Cu2+ + 2e- Khi anion (SO^)^" chay ve andt, nd keo ion Cu^"*" vao dung dich. Nhu vay, ddng d andt se tan dan vao trong dung dich. Dd la hien tugng duang cue tan. Hinh 14.4 Binh dien phan dung dich CUSO4 voi dien cue bang dong. Khi co dong dien chay qua, nguyen tii dong d anot bien thanh ion Cu^^ va tan vao dung dich. lon Cu^+ d gan catot nhan electron cua catot, bien thanh nguyen tu dong va bam vao cue nay. Cac hien tugng didn ra d andt va eatdt trong binh dien phan nay la ciing mdt phan ung can bdng nhung xay ra theo hai chieu nguge nhau : Cu^ 2e" Cu Neu phdn ling didn ra theo ehidu nay thu nang lugng, thi phdn ung didn ra theo chieu nguge lai tod nang lugng, nen tdng edng lai dien nang khdng bi tieu hao trong cac qua trinh phan tfch edc chat md ehi hi tieu hao vi toa nhiet. Binh dien phan khdng khde si mdt dien trd. 6-VATLI 11-(C)-A 81

84 o, H2SO4 +H2O r-\ K Tinh hinh se khac hdn khi ta xet ddng dien qua mdt binh dien phan dugc ve tren Hinh Chat dien phan la dung dich H^^SOj vd cdc dien cue lam bdng graphit (hoae inde). Phan tii H2SO4 bi phan li thanh ion H+ vd ion (SO^)-". Graphit (caebon) ddn dien nhung khdng tao thanh ion cd the tan vdo dung dich khi dien phan, nen cac phdn d'ng 6 dien cue phiie tap hon. Hmh 14.5 Binh dien phan dung dich HjSG^ voi dien cue bdng graphit. Luc dau, trong hai ong nghiem up ngupc ehua day dung djch H2SO4. KhiCO dong dien chay qua, 6 anotco Oj bay len, eon 6 catot co Hj bay len, day ept dung dich tut xudng. Khi ed dien trudng trong binh dien phan, ion H"^ bi ddy vd phfa catdt, cdn ion (SO^)-" bi ddy ve phia andt, gay ra mat can bdng vd ndng do ede ion d gdn dien cue. Quanh catdt thua ion H"^ nen tao di6u kien huy ion H"^. Cac ion H"^ se nhan electron d catdt theo phan ung : va hidro bay ra d catdt. 4H++4e"^2H2 T Quanh andt thieu ion H"^ nen tao di6u kien sinh ion H*. Nude phan 11 thanh H"^ va (0H)~. Cac ion (OH) se nhucmg electron cho andt theo phan ung : 4(0H)" -> 2H2O + O2 T + 4e" va 0x1 bay ra d andt. Cac ion (SO^)" khdng trao doi dien tfch vdi dien cue. Ket qud Id chi cd nude bi phan tach thanh hidro vd dxi. Hidrd bay ra d catdt. cdn dxi bay ra d anot. Nang lugng W diing de thuc hien viec phan tdch lay tir nang lugng ciia ddng dien, nen nd ti le vdi dien lugng chay qua binh dien phan. Ta cd thd viet: W = c It. trong dd c ggi la sudt phdn dien ciia binh dien phan. Gid tri eua nd phu thude vdo bdn chat ciia dien cue va chat dien phan, va dugc do bdng vdn. Trudng hgp cua binh dien phan duong cue tan thi sua't phan dien bdng khdng. IV - CAC DjNH LUAT FA-RA-DAY Vi ddng dien trong chat dien phan tdi dien lugng ciing vdi vat chat (theo nghia hep) nen khdi lugng chat di den dien cue :. ti le thuan vdi dien lugng chay qua binh dien phan ; 82 6-VATLI 1,(C)-B

85 . ti le thuan vdi khdi lugng cua ion (hay khdi lugng moi nguyen tir A ciia nguyen td tao nen ion dy);. ti le nghich vdi dien tfch ciia ion (hay hod tri n ciia nguyen td tao ra ion ay). Fa-ra-day da tdng qudt hod edc nhan xet tren, va md rdng cho ea trudng hgp edc chat duge gidi phdng d dien cue la do cdc phan ling phu sinh ra, thanh hai dinh luat Fa-ra-day. E B^ Vi sao cac dinh luat Fa-ra-day. Djnh luat Fa-ra-day thii nhat c6 the ap dung ca Khdi luang vat chdt duac gidi phdng a dien cue cua binh ^'^,' ^^'^, ^^^l ^^^"^...,. \i /t J- 1 1 ' L- I J' giai phong 0 dien dien phan ti le thuan vol dien luong chay qua binh do., \ ~,, ^., '^ = ^'i V. (14.1) P^- trong dd k ggi la duang lugng dien hod ciia chat dugc gidi phdng d dien cue.. Dinh luat Fa-ra-day thii hai Duang luang dien hod k eiia mdt nguyen td ti le vdi duang A > ' - ' lugng gam cua nguyen td dd. He sd ti le la -j^, trong dd F gpi la sd Fa-ra-ddy. * = 4-- (14.2) F n ^ ^ Thf nghiem cho thay, neu / tinh bdng ampe, t tinh bdng giay thi: F = C/mol (tfnh todn ta thudng lay chsn la C/mol). BE El C6 the tinh sd Ket hop hai dinh luat Fa-ra-day, ta duoc cdng thiic Fa-ra-day :.,,,.,.,?, ^.?'. to J mot moi kim loai tu 1 4 sd Fa-ra-day duoc m = j It (14.3) khong? m la khdi lugng eua chat duge giai phdng d dien cue, tfnh bdng gam. V - OfNG DUNG CUA HIEN TU'gfNG DIEN PHAN Hien tugng dien phan ed nhieu ling dung trong thue te san xudt va ddi sdng nhu luyen nhdm, tinh luyen ddng, didu ehd elo, xiit, ma dien, due dien,... Dudi day, ta ehi ndi qua vd cdng nghe luyen nhdm va ma dien. 83

86 1. Luyen nhom Cdng nghe luyen nhdm chu ydu dua vao hien tugng dien phan quang nhdm ndng chay. Quang nhdm phd bien Id bdxit giau nhdm dxit AloO^. Nhiet dd ndng chay cua AI2O3 rat cao. r^ = C. Ngudi ta pha them vao quang nhdm mdt ham lugng quang crydlit NajAlF^ de ha nhiet do ndng chdy xudng cdn khoang 950 C. Bd dien phan cd dien cue bdng than, ddng dien chay qua khoang lo'^ A. Nang lugng dien tod ra trong be dien phan giii cho hdn hgp quang ludn ludn ndng chay. Cdng nghe luyen nhdm tieu thu mdt dien nang Idn nen gia thanh eiia nhdm cao, vao khoang 2 dola mdt kildgam. 2. Ma dien SI Tai sao khi ma De tang ve dep vd chdng gi cho cdc dd diing thudng ngay dien, mudn Idp ma bdng kim loai, ngudi ta thudng ma len ehiing mdt ldp kim loai '^f ^' 1^ '^'^^' '^^^^ ti'o'- ^di vdi cac vat dung Idn bang thep thi thudng ma niken, edn vat can ma trong ^^- ^^ ^j ^IQ thi ma bac, vang. Cdng nghe ma thudng diing la luc dien phan?, w^-' u- '-o-^^- t-,-? ' \^ u-' - -. cong nghe dien phan. Be dien phan lue nay ggi la be ma eo anot la mdt tdm kim loai dd ma, eatdt la vat can ma. Chat dien phan thudng la dung dich mudi kim loai de ma (neu ma niken ta diing NiSO^ tan trong nude, edn ndu ma bac thi diing mudi AgNOj) trong dd cd them mdt sd chat phu gia de lam cho ldp ma bam vao bd mat dugc chdc, ben vd bdng dep. Ddng dien qua bd ma dugc chgn mdt cdch thfeh hgp dd ddm bdo chat lugng eua ldp ma. Khi ma cac vat dung phiic tap, ngudi ta cdn phai quay vat trong liic ma dd ldp ma duge ddu. E! Trong dung djch, cac axit, bazcr va muoi bj phan II thanh lon (thuyet dien li): Anion mang dien am la goc axit hoae nhom (OH), con cation mang dien duong la ion kim loai, ion H+ hoae mot so nhom nguyen tu khac. Dong dien trong chat dien phan la dong chuyen ddri co huomg cua cac ion trong dien trudng. Hien tuong ducrng cuc tan xay ra khi cac anion di tdi andt keo cac ion kim loai cua dien cuc vao trong dung djch. Khoi luqfng cua chait duoc giai phong ra d dien cuc khi dien phan cho bofi cong thuc : 1 A n It 84

87 trong do m tinh bang gam, A la khoi luong moi nguyen tu cua chait, / tinh bang ampe, t tinh bang giay, n la hoa trj cua nguyen to tao ra ion. Hien tuong dien phan dudc ap dung trong cac cong nghe luyen kim, hoa chat, ma dien... cau HOI va BAI TAP 1. Noi dung ciia thuyet dien li lagi? Anion thudng 8. Dong dien trong chat dien phan la ddng la phan nao ciia phan tu? chuyen ddi cd hudng ciia 2. Ddng dien trong chat dien phan khac ddng A, cac chat tan trong dung dich. dien trong kim loai nhu the nao? B. cac ion duong trong dung dich. 3. Hay ndi rd hat tai dien nao mang dong dien C. cac ion duong va ion am dudi tac dung ciia tren cac phan khac nhau ciia mach dien cd dien trudng trong dung djch. chiia binh dien phan : Q ^ac ion duong va ion am theo chieu dien a) Day dan va dien cue kim loai. trudng trong dung dich. b) d sat be mat hai dien cue. 9. Kei qua cudi ciing ciia qua trinh dien phan c) d trong Idng chat dien phan. ^^"9 dich CuSO, vdi dien cue bang dong la 4. Chat dien phan thudng dan dien tot hon hay A, khdng cd thay doi gi 6 binh dien phan. kem hon kim loai? Tai sao?,. B. anot bj an mon. 5. Hai be dien phan : be A de luyen nhom, be 6 c. dong bam vao catdt. de ma niken. Hoi be nao cd duong cue tan? r^.-,, ,...,... ^ D. dong chay tu anot sang catot. Be nao co suat phan dien? \ 10. Toe do chuyen ddng cd hudng ciia ion Na"^ va 6. Phat bieu dinh luat Fa-ra-day viet cdng thiic n,~, ' ' *u-'. u *i, - *u-..,.,, '.,, ^, CI trong nuoc co the tinh theo cong thuc : Fa-ra-day va don VI dung trong cong thuc nay,-. J- rrr ^-^ - * '. a a a y ^ _ ^ ^ {^Qiig ^Q g cygng dp dien truong, 7. Khi dien phan dung dich HjSO^ vdi dien cue ^^ ^o gia tn lan luot la 4,5.10"^ m2/(v.s) va bang graphit, ta thu dupe khi oxi bay ra d andt. 6,8.1 Q-^ m2/(v,s). Tinh dien trd suat ciia dung Co the diing cdng thuc Fa-ra-day de tinh khdi dich NaCI ndng dp 0,1 moi//, cho rdng'toan bp lupng dxi bay ra dupe khdng? cac phan tii NaCI deu phan li thanh ion, W 11. Ngudi ta mudn bdc mot Idp dong day d = 10 p m,... tren mdt ban dong dien tich S = 1 cm^ bang 0 bai tap 8 va 9 sau day phat bieu nao la p^^^^g p^^p ^.^^ p^-^ ^^^^^ ^. ^^^^ ^.-^ chinh xac? la 0,010 A. Tinh thoi gian can thiet debdc dupe Idp ddng. Cho biet ddng cd khdi lupng rieng la p = kg/m^. 85

88 t-m fsm DONG DIEN TRONG CHAT KHI Ngay nay, de tiei kiem nang luong dien dung de thap sang, ngudi ta khuyen khong nen dung den cd day tde ndng dd. Trong gia dinh nen dung den ong, ngoai dudng phd thi dung den thuy ngan va den natri (den vang). Cac loai den nay hoat ddng theo nguyen li nao ma lai tiei kiem dien? I - CHAT KHI LA MOI TRU'dNG CACH OIEN HI Ne'u khong khi dan dien thi : a) Mang dien trong gia dinh cd an toan khong? b) O to, xe may cd chay dugc khong? c) Cac nha may dien se ra sao? Thuc te ddi sdng cho thay khdng khi ndi rieng (hay chat khf ndi chung) khdng ddn dien. Vi thd, tren edc dudng day tdi dien, ngudi ta chi dimg cdc cgc sii de ngan khdng cho dien truyen tii day ddn dien vao cdt dien, ma khdng cdn lam gi de ngan dien truyen tir day nay sang day khde qua khdng khf. Cdc edng tde dien trong gia dinh, khi cdt dien ngudi ta eung ehi can tao ra mdt khe khdng khi rdng khoang vai milimet giira hai tiep diem la du. HI Chat khf khdng ddn dien vi cac phan tir khf deu d trang thai trung hod dien, do dd trong chdt khf khdng ed hat tai dien. ' ^ A Hinh 15.1 Goc giua hai la kim loai cua dien nghiem giam dan theo thoi gian, chung to dien tich tru trong dien nghiem mat dan. M - Sir DAN DIEN CUA CHAT KHI TRONG DIEU KIEN THLTOfNG Thue ra, chdt khf khdng phai tuyet ddi khdng ddn dien. Tfch dien vdo mdt cdi dien nghiem, ta thdy hai Id kim loai cua cdi dien nghiem xoe ra. Theo ddi gdc cua hai la kim loai theo thdi gian, ta tha'y nd gidm ddn, ehiing td dien tfch trij trong dien nghiem mat dan (Hinh 15.1). Mdt trong edc nguyen nhan lam suy giam dien tfch cua dien nghiem la dien da truydn qua khdng khf d didu kien thudng den edc vat khac. De cd thd ket luan mdt cdch chfnh xac hon, ngudi ta cd thd diing mdt dien ke rat nhay de do true tie'p ddng dien qua chat khf. 86

89 FRnh 15.2 ve so dd thf nghiem dd phdt hien vd do ddng dien qua chat khi. A, B \a hai bdn cue kim loai, f la ngudn dien ed sua't dien ddng khoang vai chuc vdn, G la mdt dien ke nhay, V la vdn ke, D Id nggn den ga (dat gioa hai bdn cue). Chinh con chay eua bien trd R dd cho vdn ke V chi mdt gid tri nao ddy va quan sat dien ke G, ta thay : - Khi khdng ddt den ga, kim dien kehau nhu chi sd 0. Vay binh thudng chat khf hdu nhu khdng ddn dien, trong chat khf ed sdn rdt ft hat tai dien. - Ddt den ga, kim dien ke lech dang kd khdi vi trf sdo. - Keo den ga ra xa, diing quat thdi khi ndng di qua giiia hai bdn cue, kim dien kd vdn lech. - Tdt den, chat khi lai hdu nhu khdng ddn dien. - Thay den ga bdng den thuy ngan (tia tir ngoai) vd lam thf nghiem tuong tu nhu trude, ta ciing tha'y nhiing ket qud tuong tu. Tir do, ta riit ra ket luan la nggn lira ga vd biic xa ciia den thuy ngan da lam tang mat do hat tai dien trong chat khf. B^ Hinh 15.2 l[/1ach do true tiep dong dien qua chat l<h! bang dien lie nhay Ifl^ VI sao ngay tu liic chua ddt den ga hoae chieu den thuy ngan, chat khi cung dan dien it nhieu? Ill - BAN CHAT DONG DIEN TRONG CHAT KHI 1. SU lon hoa chat khi va tac nhan ion hoa Nggn lira ga (nhiet do rat cao), tia tii ngoai eiia den thuy ngan trong thf nghiem tren dugc ggi la eae tac nhan ion hod. Nhd ed nang lugng cao, chiing ion hoa chat khf, tdch phan tir khf trung hod thanh ion duong va electron tu do. Electron tu do lai cd the ket hgp vdi phan tir khf trung hoa thanh ion am (Hinh 15.3). Cae hat tfch dien nay la hat tdi dien trong chat khf. Qua trinh ion hoa do tac nhan ion hoa ; Hinh 15.3 a) Ban dau chat khi gom cac phan tu trung hoa, b) Tia til ngoai lam phan tii bien thanh ion+ va e", c) e" ket hop voi phan tii trung hoa thanh ion". ^ u o o o o o Olon+ r~^ - o O o o o lon+ - O o o o o o o O O o e~ O O o o o '0 o'-- O b) 87

90 11 Ddng dien trong chdt khi Id ddng ehuyen ddi eo hudng eiia ede ion duang theo chieu dien trudng vd edc ion dm, ede electron nguge chieu dien trudng. Cdc hat tdi dien ndy do chat khi bi ion hod sinh ra. Khi mat tde nhan ion hoa, cdc ion duong, ion am va electron trao ddi dien tfch vdi nhau hoae vdi dien cue de trd lai thanh eae phan tir khf trung hoa, nen chat khf trd thdnh khdng ddn dien. 2. Qua trinh din dien khong t\i life cua chat khi Qua trinh ddn dien eua chat khf ma ta vira md ta ggi la qud trinh ddn dien (phdng dien) khdng tuluc. Nd chi tdn tai khi ta tao ra hat tdi dien trong khdi khi a giqa hai bdn cue vd bien mdt khi ta ngitng viec tao ra hat tdi dien. \ Thay ddi hieu dien the U giira hai ban cue va ghi lai Q ' ' -^ ddng dien / chay qua chat khi, ta thay qud trinh ddn U nhd U du Idn U qua Idn dien khdng tu luc khdng tudn theo dinh luat Om. Hinh 15.< )^ tl^j ^j^y dig^i su phu thude eiia eudng dd ddng Su phu thuoc cua I theo U trong,.., ' u~-» i u^ i u- u ' J-- I U- *, i,.,.,,^ ^ -, u-,,,, ^ dien / qua chat khi khi phong dien khong tu luc, qua tnnh dan dien l<hong tuluc cua ^ F fe. &.. > ctiat khi theo hieu dien the U giira hai dien cue, dugc ve tren Hinh Nd ed ba doan rd ret : - Doan Oa : U nhd, ddng dien tang theo U. - Doan ab : U du Idn, ddng dien / dat gid tri bao " "':' Trong qua trinh din dien hod. i#-] khdng tu luc cua khi, khi nao ^, ^,,,,,,,,,.rr ddng dien dat gia tri bao hoa? " ^ ^" ^^ ' ^ 1"^ l'^' ' ^^ng nhanh khi U tang. Didu dd chung td, khi hieu dien thd da qua Idn, su tang hieu dien the lam cho dien trd cua chat khi gidm, mat do hat tdi dien tang. 3. Hien tuorng nhan so hat tai dien trong chat khi trong qua trinh dan dien khong tii \\ic Hien tugng tdng mat dp hat tdi dien trong chdt khi do ddng dien chay qua gay ra gpi Id hien tugng nhan so hat tdi dien. 88 Nd didn ra nhu sau : Nhirng hat tdi dien ddu tien ed trong chat khi la cac electron va ion duong do tac nhan ion hod sinh ra.

91 Electron kich thude nhd hon ion duong, nen di dugc quang dudng dai hon ion duong trude khi va cham vdi mdt phan tir khf. Nang lugng ma electron nhan dugc tir dien trudng ngodi trong quang dudng bay tu do Idn hon nang lugng ma ion nhan duge khodng 5-^6 Idn. Khi dien trudng dii Idn, ddng nang eiia electron eung du Idn de khi va cham vdi phan tir trung hoa thi ion hoa nd, bien nd thanh electron tu do vd ion duong. Qua trinh didn ra theo kieu thac lii ("tuyet Id") nhu da ve tren Hinh 15.5 lam mat do hat tai dien tang manh cho tdi khi electron den andt. Chdt khf trd nen ddn dien tdt hon, vd ddng dien chay qua chat khf tang. Vi mdt electron ban ddu chi sinh ra dugc mdt sd hiiu han hat tdi dien tren dudng di den dien cue, nen tuy ddng dien cd tang nhung no vdn phu thude vao sd hat tdi dien md tde nhan ion hoa tii ben ngoai da sinh ra trong chai khf. RT! IV - QUA TRINH DAN DIEN TU" Ll/C TRONG CHAT KHI VA DIEU KIEN DE TAO RA QUA TRiNH DAN DIEN Tl/LLrC Qud trinh ddn dien eiia chdt khi ed the tit duy tri, khdng cdn ta chu ddng tao ra hat tdi dien, gpi Id qud trinh ddn dien (phdng dien) tu luc. Mudn cd qua trinh ddn dien tu lue thi trong he gdm chat khf va cae dien cue phdi tu tao ra cdc hat tai dien mdi dd bu lai so hat tai dien da di den dien cue va bien mat. Sd hat tdi dien sinh ra ban ddu cd the khdng nhieu nhung nhd qua trinh nhan sd hat tdi dien da ndi d tren ma mat do hat tdi dien tang manh, khien mdi trudng trd nen ddn dien tdt. Cd bdn each chfnh dd ddng dien cd the tao ra hat tdi dien mdi trong chdt khf : 1, Ddng dien chay qua chat khf lam nhiet do khf tang rat cao, khien phan tir khf bi ion hod. 2. Dien trudng trong chat khf rdt Idn, khien phan tir khf bi ion hoa ngay khi nhiet do thap. t -»-- --*-- ^ '-S--0--S -,1 a Hinh 15.5 Qua trinh nhan so hat tai dien theo kieu thac lu (tuyet Id) CF KhiCO qua trinh nhan sd hat tai dien thi cudng do dien truong tai cac diem khac nhau d giija hai ban cuc co gidng nhau khong? Vi sao? 89

92 Su hinh thanh tia lira dien disn ra nhu sau : Gia sir giua hai dien circ A va. B cd hieu dien the U dii Idn, va dien cue A cd mot mui nhon (Hinh 15.6). Dien trudng manh nhat d gsn cac miii nhon, vi the chat khi d day d6 bi ion hoa nhat (Hinh 15.6a). Nod chat khi hi ion hoa trd thanh mdi trudng din dien tdt. Mui nhon tua nhu duoc keo dai den het mifin nay. Noi chat khi chua bi ion hoa van cdn la mdi trudng each dien, nen hieu dien thd' U tap trung d mien a'y (Hinh 15.6b). Dien tnidng d noi xung yeu nha't trong mien nay se tang vuot gia tri ngudng va qua tnnh phdng dien xay ra, tao nen da lua dien (Hinh 15.6c). Ne'u tia lira didn hinh thanh trong khdng khi, cac nguyen tit dxi cd th^ ket hop vdi nhau thanh dzdn (O3), nguyen tir nito va dxi ket hop vdi nhau thanh nito dxit. Cac hop chat nay tao ra mui khet rat dac trung ma trong dan gian hay goi la "mui dien". u u e 3, Catdt bi ddng dien nung ndng dd, lam cho nd cd kha nang phdt ra electron. Hien tugng nay ggi la hien tugng phdt xa nhiet electron. 4, Catdt khdng ndng do nhung bi cdc ion duong cd nang lugng Idn dap vao, lam bat electron ra khdi eatdt va trd thanh hat tai dien. Tuy eo che sinh hat tdi dien mdi trong chat khi ma ta cd edc kieu phdng dien tu luc khac nhau. Hai kieu phdng dien tu luc thudng gap nhdt la tia Ilia dien va. hd quang dien. V - TIA LCTA DIEN VA DIEU KIEN TAO RA TIA LOTADIEN I.Djnh nghta Tia Ilia dien Id qud trinh phdng dien tit lite trong chdt khi ddt giiia hai dien cue khi dien trudng du manh de bien phdn tu khi trung hod thdnh ion duang vd eletron tu do. 2. Dieu kien tao ra tia lira dien Tia lua dien cd thd hinh thanh trong khdng khf d didu kien thudng, khi dien trudng dat den gid tri ngudng vao khoang 3.10^ V/m. Hieu disn the dii de phdt sinh tia lira dien trong khdng khf giiia hai dien cue dang khde nhau, d cdc khoang each khde nhau dugc ghi tren Bang Bang 15.1!! Hieu dien the U (V) Khoang each danh tia dien. Cue phang (mm) Mui nhon (mm) ,1 15,5 Hinh 15.6 Qua tnnh hinh thanh tia lira dien : a) Thoat dau, khi 6 gan mui nhon bi ion hoa. b) Vung khi bi ion hoa lan rpng ra. c) Tia Ilia dien xuat hien, ,7 45, ,7 75,

93 3. D'ng dung Tia lira dien dugc dung phd bien trong ddng eo nd dd ddt hdn hgp nd (la hoi xang Idn khdng khi) trong xilanh. Bd phan dd tao ra tia lira dien la bugi (Hinh 15.7), thuc chat dd chi la hai dien cue dat each nhau vao ed vai phdn mudi milimet tren mdt khdi sir each dien. Khi cd con gidng, cdc ddm may gan mat dat thudng tich dien am va mat dat tich dien duong. GiGa dam may va mat dat cd hieu dien the Idn. Nhiing ehd nhd cao tren mat dat gidng nhu nhiing miii nhgn la noi ed dien trudng manh nhat. Set Id tia lira dien hinh thanh gioa ddm may mua va mat dat nen thudng danh vdo cdc md dat cao, nggn cay... BE VI - HO QUANG DIEN VA DIEU KIEN TAO RA HO QUANG DIEN Su each dien iiililili^ Dien cue 2 Oien cue 1 Hinh 15.7 Cau tao cua bugi dung trong dong ca no (6 to, xe may) M-IVi sao khi di dudng gap mua gidng, sam set du doi ta khong nen dung tren nhung gd dai cao hoae tru dudi gdc cay ma nen nam dan ngudi xudng dat? I.Djnh nghia Hd quang dien Id qud trinh phdng dien tu lue xdy ra trong chdt khi a dp sudt thudng hoae dp sudt thdp ddt giiia hai dien cue cd hieu dien the khdng lan. Hd quang dien cd the kem theo tod nhiet va tod sang rat manh. 2. Dieu kien tao ra ho quang dien De mdi hd quang dien, thoat ddu ngudi ta phai lam eho hai dien cue ndng dd den miic cd the phat ra dugc mdt lugng Idn electron bdng su phdt xa nhiet electron. Sau dd, ta tao ra mdt dien trudng du manh gioa hai dien cue dd ion hod chat khf, tao ra tia lira dien giira hai dien cue. Khi da cd tia lira dien, qud trinh phdng dien tu luc se vdn tie'p tue duy tri, mac dii ta gidm hieu dien the giiia hai dien cue den gid tri khdng Idn. Nd tao ra mdt cung sdng ehdi nhu nggn lira ndi hai dien cue, md ta ggi la hd quang dien (Hinh 15.8). Hinh 15.8 Ho quang dien 91

94 Trong hd quang dien, ddng dien chay qua chat khi chu ydu la ddng electron di tijr catdt ddn andt, nhung cung cd mdt phdn la ddng ion duong di ttr andt den catdt. Khi ede ion duong dap vao catdt, chiing truydn cho cue nay nang lugng ma ehiing da nhan tir ngudn dien, lam eho catdt duy tri dugc trang thai ndng dd vd ed khd nang phdt ra cdc electron (hien tugng phat xa nhiet electron). Bien the h^n Hmh 15.9 Cdc electron phdt ra vdi so lugng Idn, di nguge ehidu dien trudng den andt, truyen cho andt nang lugng da nhan tii ngudn dien lam nd ndng len, nhidt do cd the tdi tren C. Nhiet do nay ciing lam eho hdu het cdc vat lieu bi ndng chdy, vd tham chf bay hoi, nen andt thudng bi 1dm xud'ng. Chat khf trong viing hd quang dien d nhiet do rat cao, do dd ciing hi ion hod va ddn dien tdt, khidn dien trd cua chat khf trong hd quang dien rat nhd. Den d'ng diing trong gia dinh, den thuy ngan, den natri (den vang) diing trong chieu sang cong cdng cung la ho quang dien sinh ra trong mot khdi hoi thuy ngan hoae natri d ap sua't thap chira trong mot bdng kin. Ho quang dien ciing co th6 ngsu nhien xay ra tren cac mang dien cii nat hoae lap dat khong dung kl thuat: Neu hai day dien khdng may cham nhau, khi chiing rdi nhau se tao ra ho quang dien va day chinh la nguyen nhan gay ra nhieu vu hoa hoan tai cac dd thi. 3. Cng dung Hd quang dien cd nhieu ting dung nhu han dien, lam den chieu sang, dun chdy vat lieu,... May han dien la mdt ngudn dien cd dien dp khodng vai chuc vdn, dien trd trong rat nhd de cd the sinh duge ddng dien rat Idn, hang tram ampe. Mdt cue ciia ngudn dien ndi vao vat can han, cue kia ndi vdi que han (Hinh 15.9). Khi han, thoat ddu ngudi thg cham que han vao vat cdn han. Mach dien bi ndi tdt, diem tiep xiic hi ddt ndng dd. Sau dd, ngudi ta nhdc que han len mdt chiit. Khi que han viia rdi khdi vat can hdn, ddng dien hi ngdt dot ngdt, sudt dien ddng tu cam (se hgc trong phdn Dien tir hgc) rat Idn, tao ra tia lira dien mdi hd quang dien va hd quang dien phat sinh. Chat khi von khong dan dien. Chat khi chi dan dien khi co hat tai dien (electron, ion) do tac nhan ion hoa sinh ra. Dong dien trong chat khi la dong chuyen ddi co hudrng cua electron va cac ion trong dien trucrng. Qua trinh dan dien khong tuluc cua chat khi xay ra khi ta phai dijng tac nhan ion hoa tu ben ngoai de tao ra hat tai dien trong chat khi. 92

95 Khi dung nguon dien ap Idn de tao ra su phong dien qua chat khi, ta thay co hien tuong nhan so hat tai dien. Qua trinh phong dien tu luc trong chat khi la qua trinh phong dien van tiep tue giiif duo'c khi khong con tac nhan ion hoa tac dong tu ben ngoai. Tia lira dien la qua trinh phong dien tu luc hinh thanh trong chat khi khi co dien trudng du manh de lam ion hoa chait khi. Ho quang dien la qua trinh phong dien tu luc hmh thanh khi dong dien qua chat khi CO the giu duoc nhiet do cao cua catot de no phat duoc electron bang hien tuong phat xa nhiet electron. CAU HOI VA BAI TAP 1. Mo ta thi nghiem phat hien, do ddng dien qua chat khi va each tao ra hat tai dien trong chat khi. 2. Trinh bay hien lugng nhan sd hat tai dien trong qua trinh phdng dien qua chat khi. 3. Trinh bay nguyen nhan gay ra ho quang dien va tia Ilia dien. 4. VI sao ddng dien trong hd quang dien lai chii yeu la ddng electron chay tit catdt den andt? 5. Trinh bay thao tac han dien va giai thich vi sao phai lam the. w 6 bai tap 6 va 7 dudi day, phat bieu nao la chinh xac? 6. Ddng dien trong chat khi chi cd the la ddng chuyen ddi cd hudng ciia A. cac electron ma ta dua vao trong chat khi. B. cac ion ma ta dua tii ben ngoai vao trong chat khi. C. cac electron va ion ma ta dua tii ben ngoai vac trong chat khi. D. cac electron va ion dugc tao ra trong chat khi hoae dua tii ben ngoai vao trong chat khi. 7. Hd quang dien la qua trinh phdng dien ty luc ciia chat khi, hinh thanh do A. phan tti khi bj dien trudng manh lam ion hoa. B. catdt bi nung ndng phat ra electron. C. qua trinh nhan sd hat tai dien kieu thac lu trong chat khi. D. chat khi bi tac dung cua cac tac nhan ion hoa. 8. Tii Bang 15.1, cac em hay udc tinh : a) Hieu dien the da sinh ra tia set giua dam may cao 200 m va mot nggn cay cao 10 m. b) Hieu dien the tdi thieu giua hai cue ciia bugi xe may khi xe chay binh thudng. c) Diing each xa dudng day dien 120 kv bao nhieu thi bat ddu cd nguy co bi dien giat, mac dii ta khdng cham vao day dien. 9. Cho phdng dien qua chat khi d ap suat thap, giua hai dien cue each nhau 20 cm. Quang dudng bay tu do ciia electron la 4 cm. Cho rdng nang lugng ma electron nhan dugc tren quang dudng bay tu do du de ion hoa chat khi, hay tinh xem mot electron dua vao trong chat khi cd the sinh ra tdi da bao nhieu hat tai dien. 93

96 Em CO biet? NGUYEN TAC HOAT OONG CUA DEN ONG Den d'ng (cdn ggi la den huynh quang) la loai den thudng dung de thsp sang trong nha. Nd dugc ca'u tao bdi mot ong thuy tinh dai khoang 0,6 m -;- 1,2 m, ben trong chua hai thuy ngan va mot loai khi tro 6 ap suai thap. Thanh trong cua d'ng thuy tinh phu mot Idp bot huynh quang cd mau trsng, khi bi tia tu ngoai rgi vao thi phat ra anh sang tring. Hai dau den la hai sgi day tde bing vonfam, cd phu mot loai dxit dac biet de tang kha nang phat xa nhiet electron. Vi day tde rai manh, nen chi can cung cap cho nd mot nang lugng khdng Ion cung du lam nd ndng do. Mach msc den ong duoc ve tren Hinh Chan luu la mot cudn day cd do tu cam Idn, nd tao ra mot hieu dien the cao de mdi den va de han che ddng dien. De moi den ngudi ta dung mot den khdi dong, thudng ggi la "stacte". Stacte hoat dong nhu mot cdng tde dien tu dgng Kjj : Khi cd dien, thoat dau cdng tic Kjj noi tat. Khoang vai giay sau, cdng tic /Cp- se hd mach. Khi bat den, cdng tsc Kjj ddng, ddng dien chay qua hai day tde mdc ndi tie'p, lam chung ndng dd va phat electron. Khi cdng tde Kjj trong stacte ngdt dien, thi mot day tde tra thanh andt, day tde kia thanh catdt. Suai dien dgng tu cam xuai hien khi mach dien bi ngdt, tao ra tia lua dien giua andt va catdt, moi cho hd quang dien phat sinh. Ddng dien cua qua trinh phdng dien hd quang giu cho hai day tde tie'p tue ndng dd. Chan luu trong mach dien giu cho ddng dien khdng tang qua Chan luu cao. Trong den ong, hai thuy ngan bi ion hoa phat ra tia td ngoai rat manh. Ldp bdt huynh quang (mau trdng) trang ben trong ong, hap thu cac tia nay va phat ra anh sang trdng. Den ong rai sang nhung khong ndng. Nd la loai den tiet kiem nang lugng. K^ Khi su dung, den ong thudng bi hdng do mot trong hai nguyen nhan sau : Stacte a) Mot trong hai day tde bi ddt : Khi dd, trong mach khdng cd ddng dien nung ndng day tde nen khdng the tao ra ho quang dien. Ta cd the ndi tdt hai chan day tde bi ddt, chi su dung mot day tde cdn tdt, den vdn hoat ddng dugc binh thudng. b) Den dung lau ngay bi "gia", hai dau d'ng xam den ; Od la do Idp dxit phu ngoai day tde da bay hei, nen du ndng dd nd cung khdng phat ra du electron de tao thanh ho quang dien. Khi den bi gia hoae dut ca hai day tde, ta cd the dung mot nguon dien the cao cho su phdng dien qua den va den van phat sang. Qua trinh phdng dien bay gid khdng phai la hd quang dien va khdng the duy tri khi ta ha hieu dien the cua nguon dien xudng ca hieu dien the cua mang dien thdng thudng. Chan luu Kj- ^b) Stacte Hinh So do mach mdc den ong : a) Khi cong tde dien Kjj trong stacte dong, day toe den nong do, b) Vai giay sau, Kj^ md, den bung sang. Ho quang dien lam day toe tiep tue nong do. 94

97 16 DONG DIEN TRONG CHAN KHONG I - CACH TAO RA DONG OIEN TRONG CHAN KHONG 1. Ban chat dong dien trong chan khong Chan khong la moi trudng da duoc lay di tdt ca cae phan tii khi. Nd khdng chua hat tdi dien nen khdng ddn dien. Mudn tao ra ddng dien chay giira hai dien ciic dat trong chan khong, ta phai dua hat tdi dien la cdc electron vao trong dd. Ddng dien trong chdn khdng Id ddng ehuyen ddi cd hudng eiia edc electron dugc dua vdo khodng chdn khdng do. Hinh 16.1 So d6 thi nghiem nghien ccfu ddng dien trong chan khong 2. Thi nghiem Lay m6t den diot chan khong D, cdu tao bed mot bdng thuy tinh da hiit chan khong, ben trong co mot catot K (la day toe vonfam FF') va mot anot la ban circ kim loai A. Catot dugfc ddt nong bdng dong dien (maeh dien gdm mot bo pin fp vd mot bien trd R). Von ke V dimg de do hieu dien the U^^^ giiia anot va catot. Anot duoc ndi vdd ngudn dien dp bien ddi va mot dien ke G (Hinh 16.1). Ddt ndng catot d cac miic do khac nhau, cho hieu dien the U^^ giiia anot va catot thay ddi tii gid tri am den gid tri duong va ve cdc dd thi bieu didn dong dien /^ (chay tiir A den FF') theo U.. Cac dd thi thu duoe, goi la dac tuyen von - ampe ciia diot D, duoc ve tren Hinh IA (ma) > ' ( c) b) I a) c(v) Hinh 16.2 Do thi bieu di^n /^ theo U^^^: a) Khi day toe khong duoc ddt nong, b) Khi day toe dugc dot nong do. e) Khi day toe dugc dot nong d nhiet do cao hon. 95

98 Sn Tren dd thi c) Hinh 16.2, ddng bao hoa vao khoang bao nhieu? a) Khi day toe FF' khong duoc ddt nong, ddng /^ = 0, chan khong khong ddn dien (duong a)). b) Khi day toe nong dd nhung hieu dien the U^^ < 0, ta thay /^ khong dang ke ; khi U^^ > 0, dong /^ tang nhanh theo U^^ rdi dat den gid tri bao hoa (dudmg b)). e) Khi day toe nong hon, ta duoc duong cong c) eo dang gidng nhu dudng b), nhung gid tri cua dong bao hod 16n hem. HI Ta giai thich do thi 6 Hinh 16.2 nhu sau : Khi dot nong catdt, chuyen dong nhiet cua nguyen tu trong catdt lam mot sd electron cd ths biit ra khdi hi mat catdt va bay vao chan khdng vdi mot td'c do ban dau nao dd. Td'c do nay khdng deu nhau, mot sd it electron cd the cd td'c dp Idn. a) Khi t/^j, am va nhd, cac electron cd tde do ban dau Idn vin thdng dugc luc day ciia andt va tdi andt, gay ra mot ddng andt nhd chay vi catdt. b) Khi t/^j, duong, andt hut cac electron va gay ra ddng andt Idn. c) Khi sd electron phat ra tu catdt trong mot giay bang sd electron den andt trong mot giay thi ddng dien dat den gia tri bao hoa. Vi the, nhiet do catdt cang cao, ddng bao hoa cang Idn. Dac tuyen von - ampe ve tren Hinh 16.2 chung td diot chan khdng cd tinh chinh luu. Trude khi cd diot ban dan, ngudi ta vsn ddng nd 66 lap bo chinh luu ddng dien xoay chi6u. II-TIA CATOT De tao ra ddng dien trong chan khong, trude day, ngudi ta diing mot hieu dien the 16n giiia anot vd catot dat trong mot ong thuy tinh ndi voi bom chan khong, rdi nit khi cho den khi trong ong la chan khong. 1. Thi nghiem Hinh 16.3 minh hoa mot thi nghiem tao ra dong dien trong chan khong bdng cdch riit ddn khi trong ong. Ong thuy tinh dai chiing 30 cm, ngudn dien ed hieu dien the khoang vdi ngdn von. Rut l<hi Cot sang anot Khoang toi catot H ^ a) b) Hinh 16.3 Tao tia catot bang qua trinh phong dien tu luc qua khi: a) 6 ap suat thap, ta quan sat thay cot sang anot va khoang toi catot, b) d ap suat rat thap (khoang 10-^ mmhg), trong ong co tia catot lam huynh quang ong thuy tinh. 96

99 a) Khi dp suat ciia khi trong ong bdng dp sudt khi quyen, ta khong thay qua trinh phong dien. b) Khi dp suat da dii nho, tiong dng co qua trinh phdng dien tu lire (Hinh 16.3a), ta thay mot cot khi phdt sang keo ddi tir anot de i gdn catot (cot sdng anot), cdn d gdn catot eo mot khodng tdi (khodng tdi catot). ^ e) Tiep tue gidm dp suat, khoang tdi catot md rong. Den khi ap suat vdo khoang 10"^ mmhg, khodng tdi catot chie'm toan bo dng nen khong edn thdy dng phat sdng. Qud trinh phong dien vdn duy tri va d phia ddi dien vdi catdt, thanh d'ng thuy tinh phdt ra anh sdng mau vang luc (Hinh 16.3b). Ta goi tia phdt ra tir catdt lam huynh quang thuy tinh Id tia catdt hay da dm cue. d) Tiep tire riit khf de dat chan kh^g tdt hon nira thi qua trinh phdng dien bien mat. Vi sao khi ap suat cdn Idn ta khdng thay qua trinh phdng dien qua khi, va khi ap suai da du nho lai cd qua trinh phdng dien tu luc? Vi sao khi rut khi de duoc chan khong tdt hon thi tia catot lai bien mat? 2. Tinh chat cua tia catot Dd tim hieu bdn chat ciia tia catdt, ngudi ta 1dm thf nghiem tren cdc d'ng phdng dien hinh dang khde nhau, trong d'ng cd dat cdc vat va cdc dien cue khde nhau de tim hieu cdc tfnh chat cua nd. Ngudi ta thay tia eatdt cd cdc tfnh chat sau : a) Nd phdt ra til catdt, theo phuong vudng gdc vdi ba mat catdt. Gap mot vat can, nd bi chan lai va lam vat dd tich dien am. b) Nd mang nang luong Idn : nd ed the lam den phim anh, lam huynh quang mot sd tinh the, lam kim loai phat ra tia X, 1dm ndng edc vat ma nd roi vao va tac dung lire len ede vat dd. e) Tii- trudng lam tia catdt lech theo hudng vudng gdc vdi phuong lan truyen va phuong eiia tir trudng (Hinh 16.4), edn dien trudng lam tia eatdt lech theo chieu nguge vdi ehidu eiia dien trudng. Hinh 16.4 Til trudng lam lech tia catot theo phuong vuong goc voi phuong lan truyen va phuong tu truong. 7-VATLI 11.(C)-A 97

100 3. Ban chat cua tia catot Nhung tfnh chat tren ehiing td tia catdt la mdt ddng cae electron phdt ra tii catdt ; do dp sua't eua khf thap, chi mot ti le rat nhd eiia edc electron nay va chain vdi phan tir khf va lam ion hod chiing. Cdc ion duong nhan nang lugng ciia dien trudng, dap vao eatdt, sinh ra edc electron mdi de duy tri qud trinh phdng dien. Dai bd phan ede electron edn lai, khdng bi va cham vdi cae phan tu khf. Chiing chuydn ddng nhu cae electron tu do trong chan khdng. Nhu vay, tia eatdt thuc chdt la ddng electron phdt ra tit eatdt vd bay gdn nhu tu do trong dng thi nghiem. Tuy trong dng vdn edn khf, nhung tia catdt khdng khac gi mdt ddng electron trong chan khdng. Ku-^m G ^-1 A: 2, A "X" 4. CTng dung Tia catdt cd nhidu tfnh chat ed the dp diing vao thue te. IJhg diing phd bien nhat la de lam dng phdng dien tii vd den hinh. Dd tao duge tia catdt manh vd dap ting dugc ede yeu cdu eiia ki thuat, ngudi ta khdng diing phdng dien qua chat khf d dp sudt thap nhu da md td d tren, ma diing mot diot chan khdng vdi eatdt dugc nung ndng va andt ed Id thiing dd eho ddng electron bay ra (ggi la siing electron). Sting electron dugc sir dung trong d'ng phdng dien tu va den hinh. Hinh 16.5 Sung electron Sting electron (Hinh 16.5) co cue catdt K la day toe FF'. cue ludi G la mot Judi kim loai bao quanh catdt. va andt la mot bo gom ba dng kim loai. Hai dng ngoai ndi vdi cue A^, cdn dng d giira ndi vdi cue A^- Catot duoc ddt nong. phat ra electron. Anot /i d dien the duong so vdi catot. lam nhiem vu gia tde chilm electron. Anot A^ ddien the co the' dicu chinh dugc. dcing de hgi tu chijm electron tai diem mong mudn. Ludi C a dien the am so vdi catot.se chan mot phan dong electron, cho phep ta difiu chinh cudng do dong nay. Sting electron dugc dung de' tao ra chum tia electron trong dng phong dien ttr \'d den hinh VATLI 11.(C)-B

101 Chan khong chi dan dien neu ta dua electron vao trong do. Dong dien trong chan khong la dong chuyen dori co hudng cua cac electron. Diot chan khong vdi catot nong do co tinh chinh luu. Tia catot la mot dong cac electron phat ra tu catot, co nang luong Idn va bay tu do trong khong gian, duqrc sinh ra khi phong dien qua chat khi d ap suat thap. No cung c6 the tao ra bang mot sung electron. Tia catot co kha nang lam huynh quang cac chat va bj lam lech bang dien trudng va tu trudng. No duoc dung trong den hinh va ong phong dien tcr. CAU HOI VA BAI TAP 1. Vi sac chan khdng khdng dan dien? Bang each nao ta tao duoc ddng dien trong chan khong? 2. Diot chdn khdng cau tao nhu the nao va cd tinh chat gi? 3. Tia catdt la gi? Co the tao ra no bang each nao? 4. Tai sao khi phdng dien qua khi d dp suat thap lai sinh ra tia catdt? 5. Ke vai tinh chat ciia tia catdt chiing to nd la dong cac electron bay tu do. 6. Sung electron tao ra tia catot theo nguyen tde nao? 7. Hay ke hai ling dung ciia tia catdt ma em biet. 6 bai tap 8 va 9 duoi day phat bieu nao la chinh xac? 8. Dong dien trong chan khong sinh ra do chuyen dong ciia A. cac electron phat ra tii catot. B, cac electron ma ta dua tii ben ngodi vao giua cac dien cue dat trong chdn khdng. C. cac electron phat ra tii anot bi ddt ndng do. D, cac ion khi cdn du trong chan khdng. 9. Ngudi ta ket ludn tia catdt Id ddng hat tich dien am vi A. nd cd mang nang luong. B. khi roi vao vat nao, nd lam cho vat ay tich dien am. C. nd bi dien trudng lam lech hudng. D. nd lam huynh quang thuy tinh. 10. Catdt ciia mot diot chan khdng cd dien tich mat ngoai S = 10 mm^. Ddng bao hoa /i jj(^ = 10 ma. Tinh sd electron phat xa tu mdt don vi dien tich ciia catdt trong mdt giay 11. Hieu dien the giua andt va catdt ciia mot siing electron la V, tinh toe dp ciia electron ma sung phat ra. Cho biet khdi lupng ciia electron la 9, ^ kg. 99

102 Em CO biet? ONG PHONG OIEN TU VA DEN HINH 1. Ong phdng dien tu Ong phdng dien td duac minh hoa tren Hinh Chum tia electron do sung electron phat ra, dtroc didu chinh cho di qua khoang khdng gida hai bo ban cue V^, Yj va X,, Xj rdi dap vao man huynh quang gido dien ap cao, de lai a dd mot cham sang M. Dung dien trudng gicra hai ban cue V^, Yj, ta lam lech dugc chum electron theo phuang thdng ddng. Tuang tu, dung dien trudng giua hai ban cue Xp Xj, ta cd the lam nd dich chuyen theo phuang ngang. Diem M di chuyen ve mot dudng sang tren man huynh quang. Ong phdng dien tu duoc dung trong dao dong ki dien tu. Sung electron Dien ap cao. Hinh 16.6 Ong phong dien tcr Dien ap cao < 2. Den hinh Oen hinh dugc minh hoa tren Hinh16.7a. Chum tia electron do sting electron phat ra dugc dieu chinh cho di qua khoang khdng gida hai cuon day y va X(dugc cudn theo dang dac biet va gpi la cudn lai tia), rdi hgi ttj tren man huynh quang giu 6 dien ap cao, de lai d dd mot cham sang M. Dung tu trudng tao bdi hai ddng dien bien doi theo thdi gian theo quy luat thich hgp chay qua hai cudn day Y va X, ta lam lech chum electron theo phuang thdng dung va phuang ndm ngang, cho M ve nen nhdng dudng ngang, lam sang toan bg man huynh quang. Cudng dp cua tin hieu anh cd ehd yeu, ehd manh, lam man huynh quang cd cac diem tdi, sang khac nhau tao ra hinh anh (Hinh 16.7b). Oen hinh dugc dung trong tivi va may vi tinh. b) Sung electron Hmh 16.7 Den hinh 100

103 17 DONG DIEN TRONG CHAT BAN DAN Ngay nay, ta hay ndi den si.f bung no cua cdng nghe thdng tin. Vay su bung no' ay bit nguon tu dau? I - CHAT BAN DAN VA TINH CHAT Khi nghien eiiu edc vat Heu, ngudi ta thdy nhieu chat khdng the xem la kim loai hoae'dien mdi. Trong sd nay ed mot nhdm vat lieu ma tieu bieu Id gemani va silic, duoc goi la chdt bdn ddn hoae goi tdt la bdn ddn. Nhung bieu hien quan trong dau tien ciia chat bdn ddn la : 1. Dien trd sudt cua chat bdn ddn ed gia tri ndm trong khoang trung gian giqa dien trd suat ctia kim loai vd dien trd sudt cua dien mdi. (J nhiet do thdp, dien trd sudt eiia chdt bdn ddn sieu tinh khiet rdt Idn. Khi nhiet do tdng, dien trd sudt gidm nhanh, he sd nhiet dien trd ed gid tri dm. Ta goi dd la su ddn dien rieng ciia chat bdn ddn. Dieu nay nguoc vdi sir phu thuoc ctia dien trd suat cua cdc kim loai vao nhiet do. 2. Dien trd sudt ciia chdt bdn ddn phu thuoc manh vdo tap chdt. Chi can mot luong tap chat nhd (khodng 10"^% den 10"^%) ciing dii lam dien trd suat eiia nd d lan can nhiet do phong gidm rat nhieu lan. Luc ndy, ta ndi su ddn dien ciia chat ban ddn la ddn dien tap chdt. 'i-dien tra sudt ciia chdt bdn ddn cdng gidm ddng ke khi nd bi chieu sdng hodc bi tde dung ciia cdc tde nhan ion hod khac. II - HAT TAI OIEN TRONG CHAT BAN DAN. BAN DAN LOAI n VA BAN DAN LOAI p 1. Ban dan loai n va ban dan loai p Dd hidu duoc tinh chat dien ciia chat bdn ddn, trude het edn xac dinh hat tai dien trong chat bdn ddn mang dien tieh gi. Dieu nay cd the thuc hien bdng cdch Idy mot thdi ban ddn va giu mot ddu d nhiet do cao, mot ddu d nhiet do thdp. Chuyen ddng nhiet cd xu hudng ddy hat tdi dien ve phfa ddu lanh, nen ddu lanh se tich dien cung ddu vdi hat tai dien. 101

104 '^:c ^:Csi) «e Q)iQ):Q) Si) s (sj): (sj) Hinh 17.1 Lien ket cua mot nguyen tii Si vdi mot nguyen tii Si 6 ben canh duoc thuc hien bang 'mot cap electron chay quanh hat nhan cua hai nguyen tu nay Sii 11 sij; I Si vsij:\sij:isi b* (i):(sj):(si) Hmh 17.2 Chuyen dong nhiet lam dut mot moi lien ket giua hai nguyen tii silic, tao ra mot electron tu do va mot 16 trong. Thf nghiem vdi mdu silic pha tap phdtpho (P). asen (As), hoae antimon (Sb), chiing td hat tdi dien trong do mang dien dm. Ta goi mau silic nay la loai n. Vdi mdu silic pha tap bo (B), nhdm (Al), hoae gali (Ga), thf nghiem chirng td hat tdi dien mang dien duang. Ta goi mdu silic nay la loai p. 2. Electron va 16 trong Trong cd hai loai ban ddn /; va /;, thuc ra ddng dien deu do chuyen dong cua electron sinh ra. Khi tao thanh tinh the silic, mdi nguyen tir silic cd bdn electron hod tri nen vira dii de tao ra bdn lien kei vdi bdn nguyen tu lan can. Cdc electron hod tri deu bi lien kei (Hinh 17.1), nen khdng tham gia vao viec ddn dien. Khi mot electron bi nit khdi mdi lien kei, nd trd nen tu do va thanh hat tai dien goi la electron ddn. hay goi tdt la electron. Chd lien ket diit se thieu mot election nen mang dien duong. Khi mot electron tir mdi lien ket cua nguyen tir silic lan can chuyen tdi ddy thi mdi lien ket diit se di chuye'n nguoc lai. Chuyen ddng ciia cdc electron lien ket bay gid cd the xem nhu ehuyen ddng cua mot dien tfch duong theo chieu nguoc. Nd cung duoe xem Id hat tdi dien mang dien duong, vd goi la Id trdng (Hinh 17.2). Vay, ddng dien trong chdt bdn ddn Id ddng cdc electron ddn chuyen ddng nguge chieu dien trudng vd ddng cae Id trdng ehuyen ddng eung chieu dien trudng. ' -H ^. isy; ^si;..si) vsi) vsi) I (si) I (s\) Hinh 17.3 Nguyen tu tap chat hoa tri nam (P) chi can bdn electron hoa tri de lien ket voi bon nguyen tu silic lan can. Electron thu nam trd thanh electron tu do, con nguyen tu P tro thanh ion P+. 3. Tap chat cho (dono) va tap chat nhan (axepto) Khi pha tap P. As,... la nhfrng nguyen td ed nam electron hod tri vao trong tinh the silic, chiing chi can dimg bdn electron hod tri de lien kei vdi bdn nguyen tir silic lan can. Electron thir nam rat dd trd thanh electron tu do, nen mdi nguyen tu tap chat nay cho tinh thd mot electron ddn. Ta goi chiing la tap chdt cho hay ddno (Hinh 17.3). Tap chdt ddno sinh ra electron ddn nhung khdng sinh ra Id trdng. Mat khac, chuyen ddng nhiet eung tao ra mot sd electron vd Id trdng nhung sd luong nhd ban. Vi the, hat tdi dien trong bdn ddn loai n chii yeu Id electron. Tuong tu. khi pha tap B, Al,... la edc nguyen tu cd ba electron hod tri vao tinh the' silic, chiing phdi lay mot electron '.'-! 102

105 cua nguyen tu silic lan can dd cd du bdn mdi lien ket (Hinh 17.4). Chiing nhan mot electron lien ket va sinh ra mot Id trdng, nen duge goi la tap chdt nhan hay axepto. Tap chat axepto sinh ra Id trdng ma khdng sinh ra electron tu do. Hat ddn dien trong hdn ddn loai p chii yen Id Id trdng. Dien trd sudt p. mat do electron va Id trdng trong gemani sieu tinh khiei, gemani pha tap gali vdi ti le nong do nguyen tu 10*'^% vd 10"^% d nhiet do phong duge cho tren Bang CU Bang 17.1 Dien trd suat va mat do hat tai dien cua 1 gemani pha tap gali K Ti le tap chat 0% 10-6% % i I Dien tro suat 0,5 Q.m 10^Tim IQ-^Q-m so:(so:(si Hmh 17.4 Nguyen tu tap chat hoa tn ba (B) can bon electron hoa tri de lien ket voi bdn nguyen tu silic lan can. Nd lay mot electron cua nguyen tii silic lan can, trd thanh ion B~ va sinh ra mot Id trdng. K l So sanh dien trd suat cua gemani tinh khiei, gemani pha tap gali vdi ti le 1Q'^ % va 1Q-^ % d nhiet dp phdng vdi dien trd suai cua cac kim loai. Mat do l6 trong Mat do electron 2,5.10^9 m-3 : 3, m-3 ^ 3,7.1023m-3 i 1 '! 2,5.10^9m-3 ^ 1,7.10^8m-3 ]J.W^m-'^ 1 i i Ill-LdP CHUYEN TIEP p-n Ldp chuyen tiep p-n Id chd tiep xiic ciia mien mang tinh ddn p vd mien mang tinh ddn n dugc tao ra tren mot tinh.the bdn ddn. 1. Ldp ngheo Vi trong mi6n bdn ddn loai p hat tdi dien chii yeu la Id trdng, trong mien bdn ddn loai n hat tai dien ehii yeu la electron tu do, nen tai ldp chuyen tie'p p-n, chiing tra trdn vao nhau. Khi electron gap Id trdng (la ehd lien kei bi thieu electron), nd se ndi lai mdi lien ket ay, vd mdt cap electron - Id trdng se bien mat. 0 ldp chuydn tie'p p-n, se hinh thdnh mdt ldp khdng cd hat tdi dien ggi la Idjj ngheo. 6 ldp ngheo, ve phfa bdn ddn /; ed edc ion ddno tfch dien duong va vd phfa ban ddn p cd cdc ion axepto tfch dien am (Hinh 17.5). Dien trd ciia ldp ngheo rat Idn. 151 OOQ Oo Oo oo o o + p Lop ngheo n Hinh 17.5 Ldp chuyen tiep p-n CP Vi sao d hai ben Idp ngheo lai cd cac ion duong va ion am? 103

106 ^4- P n <^^~^0 I(n la) o J 1 Ui Hinh 17.6 Dac tuyen von - ampe cua diot ban dsn Mach chinh Itru thudng dtrac mac bang bdn diot. thanh cau chinh luu nhu Hinh Nguon dien xoay chi6u dugc ndi vao cac diem I va 3 ; tai tieu thu dien mot ehidu dirge ndi vao cac diem 2 va 4. Dong dien ludn di qua tai theo mot ehidu ttr 2 den 4, nen di6m 2 la cue duong. didm 4 la cue am cua bg chinh luu. Bg chinh luu dugc diing pho bien trong cac thiet bi dien tir dan dung nhu radio, tivi. may nap acquy. 2. Dong dien chay qua ldp ngheo Ne'u dat mdt dien trudng ed ehidu hudng tii bdn ddn p sang bdn ddn ii thi Id trdng trong ban dan p se chay theo dien trudng vdo ldp ngheo ; electron trong bdn ddn n se chay n-ugc chieu dien trudng vao ldp, dd. Liic nay, ldp nglicc ed hat tai dien va trd nen ddn dien. Vi vay se ed li'!"g dien chay qua ldp ngheo tir mienp sang mien /;. ivhi dao ehidu dien trudng ngodi, ddng dien khdng thd chay tir midn n sang midn p, vi khi dy khdng ed hat tdi dien nao den ldp ngheo, dien trd eiia nd trd nen rat Idn. Ta ggi chieu ddng dien qua dugc ldp ngheo {tiip sang n) Id chieu thuan. chieu kia (tir n sang p) la chieu nguge. 3. Hien tuorng phun hat tai dien Khi ddng dien chay qua ldp chuyen tiep p-n theo chieu thuan, cae hat tai dien di vdo ldp ngheo ed the di tie'p sang mien ddi dien. Ta ndi rdng cd hien tugng phun hat tai dien tir miin ndy sang mien khac. Tuy nhien, chiing khdng the di xa qud khodng 0,1 mm, vi ca hai midn p va n liic nay ddu ed electron va Id trdng nen ehiing de gap nhau vd bien mat tirng cap. IV - OIOT BAN DAN VA MACH CHJNH LLTU DUNG DIOT BAN DAN Didt ban ddn thuc chat la mdt ldp chuyen tie'p /;-/;. Kf hieu ciia didt vd dac tuyen vdn - ampe eua didt dugc ve tren Hinh Vi ddng dien chii yeu chi chay qua didt theo chieu tu p den n. nen khi ndi nd vao mach dien xoay ehidu, ddng dien cung chi chay theo mdt chieu. Ta ndi didt bdn ddn cd tfnh chinh luu. Nd duge diing dd ldp mqch chinh hai, bien dien xoay ehidu thdnh mot chieu. Hinh 17.7 Cau chinh luu : Du diem 1 6 dien the duong hay am so voi diem 3, dong dien ludn di qua tai theo mot chieu tu 2 den 4. V - TRANZITO LLTdNG Cl/C n-p-n. CAU TAO VA NGUYEN LI HOAT DONG 1. Hieu lirng tranzito Xet mdt tinh the' ban ddn tren dd cd tao ra mdt mienp, vd hai miin /?, va /j^- Mat do electron trong 104

107 midn «2 rdt Idn so vdi mat do Id trdng trong midn p. Tren edc mien nay cd hdn cdc dien cue C, B, E. Dien the d cac cue E, B, C giii d cdc gid tri Vg = 0, Vg vira dii de ldp ehuyen tie'p p-«, phan cue thuan, VQ cd gia tri tuong ddi Idn (cd 10 V). a} Gid sit mien p rdt ddy, /?, vd n2 cdch xa nhau Ldp ehuyen tie'p n^-p phan cue nguge, chi cd ddng dien rdt nhd do electron chay tixp sang «,, va 16 trdng chay tir n, sang p sinh ra. Dien trd i?^g giira Cvafi rat idn (Hinh 17.8a). Ldp chuydn tie'p p-«2 phan cue thuan, ddng dien chay qua chu yeu la ddng electron phun tir Uj sang midn p. Cac electron ndy khdng tdi dugc ldp chuyen tie'p /?-«,, do dd khdng anh hudng tdi R,^. b) Gid sit mien p rdt mdng, n j rdt gdn /?2 Dai bd phan ddng electron tir «2 phun sang p ed the di tdi ldp chuyen tie'p n^-p, rdi tie'p tue chay sang «] den cue C (Hinh 17.8b) lam cho dien trd RQQ gidm dang ke. Hieu dng ddng dien chay tit B sang E lam thay doi dien trd RQ^ gpi la hieu dng tranzito. Vi dai bd phan electron tir «2 phun vao p khdng chay vd B ma chay tdi cue C, nen ta ed /g «/^ va IQ X /g. Ddng /g nhd (do ngudn dien dat vdo B cung cap) sinh ra ddng /^ Idn (do ngudn dien dat vao C eung cdp), chiing td cd su khuech dai ddng dien. 2. Tranzito ludng cuc n-p-n Tinh the bdn ddn duge pha tap de tao ra mot mien p rdt mdng kep gida hai mien n^vd Uj da md td a tren gpi la tranzito ludng cue n-p-n (Hinh 17.9). Bl" Tranzito cd ba cue : - Cue gop hay colecta, ki hieu Id C. - Cue ddy hay cue gdc, hodc baza, ki hieu Id B. - Cue phdt hay emita, ki hieu Id E..- Mien ngheo Electron tu n^ phun vaop Electron tu n^ phun vao p va lan sang n. E,OV r^ Hmh 17.8 Minh hoa hieu ting tranzito : a) Khi mien p day : khdng cd hieu ung tranzito. b) Khi mien p mdng : cd hieu ijng tranzito. B5 Tinh the ban din dugc pha tap de tao ra mot mien n mong kep gicra hai mien p cd the goi la tranzito dugc khong? a) b) c) Tranzito ludng cue: a) Md hinh. b) Cau true thuc. c) Ki hieu cua tranzito n-p-n. Hinh

108 Tranzito ed kha nang khuech dai tin hieu dien, vd la linh kien chii lire da ddn den su bdng nd eiia edng nghe dien tir vd thdng tin ngay nay. IJhg dung phd bien nhdt ciia tranzito la de' ldp mach khuech dai va khod dien tir. Chat ban dan la mot nhom vat lieu ma tieu bieu la gemani va silic. Dien trd suat cua cac chat ban din co gia tri niim trong khoang trung gian giua kim ioaiva dien moi. Dien trd suat cua chat ban dan phu thuoc manh vao nhiet do va tap chat. Chat ban din co hai loai hat tai dien la electron va lo trong. Dong dien trong chait ban dan la dong chuyen ddri co hudng cua cac electron tu do va 16 trong dudi tac dung cua dien trucrng. Ban dan chua ddno (tap chat cho) la loai n, co mat do electron rat Idn so vdi mat do lo trong. Ban dan chua axepto (tap chait nhan) ia loai p, cd mat do Id trdng rat Idn so vdi mat do electron. Ldp chuyen tiep p -n la cho tie'p xuc giiira hai mien mang tmh dan dien p va n tren mot tinh the ban dan. Dong dien chi chay qua duorc Idp chuyen tiep p-n theo chieu tup sang n, nen Idp chuyen tiep p-n duoc dung lam didt ban dan de chinh luu ddng dien xoay chieu. Mot Idp ban dan loai p rait mdng kep giua hai Idp ban dan loai n thuc hien tren mot tinh the ban din (Ge, Si,...) la mot tranzito n-p-n. Tranzito cd kha nang khuech dai tin hieu dien, va diing de lap bo khuech dai va cac khoa dien tiir. CAU HOI VA BAI TAP ^eg«r 1. Tinh chat dien ciia ban ddn va kim loai khac nhau the nao? 2. Diem khac nhau chinh giua nguyen tii ddno va axepto doi vdi silic la gi? 3. Mo ta each sinh ra electron va lo trong trong ban dan tinh khiet. ban dan n va p. 4. Ddng dien chi chay qua Idp chuyen tiep p-n theo chieu nao? 5. Khi nao thi mot Idp ban ddn p kep giua hai Idp ban dan n tren mot tinh the duoc xem la mot tranzito n-p-n? 6. Phat bieu nao dudi day la chinh xac? Ngudi ta goi silic la chat bdn ddn vi A. nd khdng phdi la kim loai, cung khdng phai la dien mdi. B. hat tdi dien trong dd cd the la electron va lo trdng. C. dien trd suat cua nd rat nhay cam vdi nhiet do, tap chat, va cac tac nhan ion hoa khac. D. Ca ba li do tren. 7. Phat bieu nao dudi day ve tranzito la chinh xac? 106

109 A. Mdt Idp ban ddn loai p kep giua hai Idp ban dan loai n la tranzito n-p-n. B. Mot Idp ban dan loai n mdng kep giua hai Idp ban dan loai p khdng the xem la tranzito. C. Mot Idp ban dan ioai p mong kep giiia hai lop ban dan loai n ludn cd kha nang khuech dai. D. Trong tranzito n-p-n, bao gio mat dp hat tai dien mien emito cung cao hon mien bazo. Em CO biet? MACH KHUECH DAI DUNG TRANZITO So do nguyen li cua mach khuech dai dung tranzito n-p-n (cdn goi la tang khuech dai kieu emita chung hay emita ndi dat) duac ve tren Hinh Suai dien dong cua nguon i^ thcrdng vao khoang tu 6 V den 1 2 V, Cac dien tra /?, va R, dugc chon de cho hieu dien the cua Ug^ vao khoang 0,7 V, du de phan cue thuan Idp chuyen tie'p B - E, vdi Rj vao khoang 5^10 kq. Oien tra tai Rj duac chon sao cho hieu dien the giua colecta va emita vao cd -^. Tin hieu dien can khuech dai dua vao chan baza va emita (Idi vao) va lay ra tren dien trd tai hoae giua chan colecta va emita (Idi ra). Cac tu dien C, va C2 duac dung khi chi mudn khuech dai tin hieu dien xoay ehidu. De khuech dai nhcrng tin hieu rai yeu, ta cd the mdc noi tiep nhieu tang khuech dai vdi nhau, loi vao cua tang sau ndi vdi Idi ra cua tang trude. Ngay nay, ngudi ta da che tao nhung vi mach khuech dai hoan chinh bang tranzito tren mot manh silic dien tich khoang 1/4 mm-^ va gpi la bo khuech dai thuat toan (viei tdt la bd KOTT). Bd KDTT pho bien la vi mach ia 741. Hinh ve hinh dang ben ngoai cua vi mach KOTT, ki hieu thudng dung cua nd, va mach do nhiet do dung cap nhiet dien lip bang bo KOTT. Mach nay dung hai ngudn dien 9 V mdc ndi tie'p, diem giua ndi dat. Chan 7 a dien the + 9 V, chan 4 d dien the - 9 V. Tin hieu can khuech dai dua vao cac chan 2 va 3, tin hieu lay ra duac dua vao milivdn ke Vrndc giua chan 6 va dai. He so khuech dai (ti sd cua hieu dien the d loi ra va hieu dien the d Idi vao) la p k =, va khdng phu thuoc loai bo KOTT. Neu dung cap nhiet dien dong - constantan, iaj = 40 av/k), ta cd the chpn R. = 250 kn, R-, = ]0 kq thi mdi do chia tren milivdn ke se tuang ung vdi 1 "C. Hinh Sa do nguyen li cua mach khuech dai dung tranzito n-p-n Nuoc da c) Hinh Bo KOTT va ung dung : a) Hmh dang ben ngoai cua bd KDTT, b) Kl hieu thuong dung cua bo KDTT. c) So dd may do nhiet dp dung cap nhiet dien ddng - constantan lap bang bd KDTT. 107

110 Thirc hanh : KHAO SAT OAC TINH CHINH Ll/U CUA OIOT BAN DAN VA OAC TINH,. ^UECH OAI CUA TRANZITO Cac loai linh kien ban din cd dac tinh rat khac nhau, tuy thuoc sd lugng va cau tao cua cac Idp chuyen tiep p-n dugc hinh thanh trong mdi loai linh kien. Thuc vay, didt cd dac tinh chinh luu ddng dien chi do tac dung cua mot Idp chuyen tie'p p-n, tranzito cd dac tfnh khuech dai ddng dien (hoae dien ap) do tac dung cua hai lap chuyen tiep p-n dugc hinh thanh bdi mot midn p rat mdng kep giua hai midn n, hoae bai mot midn n rat mdng kep giua hai mien p. Nhung dac tinh nay se dugc lan lugt khao sat trong thi nghiem dudi day. A - KHAO SAT DAC TINH CHJNH Ll/U CUA DIOT BAN DAN I - MUC DICH THI NGHIEM 1. Khao sat dac tinh chinh luu ciia diot. 2, Ve dac tuyen von - ampe eiia diot. II-DUNG CU THI NGHIEM Bo thiet bi thi nghiem "Khao sdt dac tinh chinh luu cua diot ban ddn" duoc bo trf nhu Hinh Hmh Diot chinh luu (loai D 4007). 2. Nguon dien U (AC - DC : V/3A). 3. Dien tro bdo ve RQ = 820 Q. 4= Bien tro niim xoay R (loai 10 Q x 10 ). So Dong ho do dien da nang hien so (DT-830B) diing lam chiic nang miliampe ke m6t chi6u A.

111 6. Dong h6 do dien da nang hien so (DT-830B) dung lam chiic nang von ke mot chieu V. 7. Bang ldp rap mach dien. 8. Bo day ddn noi mach dien co hai dau phich cdm. 9. Khoa dong - ngdt mach dien K. a) K Ill-CO sd LI THUYET Diot chinh luu la linh kien ban ddn duoc eau tao hoi mot ldp ehuyen tie'p p-n hinh thdnh tai eh6 tie'p xiic giija hai mien mang tinh ddn p vd tinh ddn n tren mot tinh the ban ddn. Dien cue noi v6i midn p goi la anot A, dien cue noi vcfi mien n goi la catot K. Diot chinh luu duoc ki hieu nhu Hinh 18.2a. Do tde dung ctia ldp ehuyen tie'p p-n nen diot bdn ddn eo dac tinh chinh luu dong dien, tiic la no chi eho dong dien chay qua theo chieu thuan tii midn p sang midn n (xem muc IV, bai 17). Trong thi nghiem nay, ta sir dung ede dong ho do dien da nang hien so DT-830B dd khao sat dac tfnh chinh luu dong dien eua didt bdn ddn. b) Anh ehup didt Hinh 18.2 EMI Chieu thuan cua diot ban dan ve tren Hinh 18.2 hudng theo chieu tu andt A sang catot K hay theo chieu nguoc lai? IV - Gidl THIEU DUNG CU DO D6ng ho do dien da nang hien so kieu DT-830B la dung eu do dien hien dai, eo nhieu thang do vcd cdc chiic nang khde nhau (xem muc IV, bai 12). : 1 V - TIEN HANH THI NGHIEM 1. Khao sat dong dien thuan chay qua diot a) Mdc diot AK vd dien trd bdo ve RQ theo so do mach dien Hinh 18.3, trong do chii y dat diing : - Khoa Kavi tri ngdt dien (OFF) ; - Nguon dien U a vi tri 6 V mot chieu ; - Bien trd R noi vdi hai cue ciia nguon dien U theo kieu phan dp; ^ Hay cho biet chuc nang va thang do cua dong ho do dien da nang hien sd DT-830B khi num xoay cua nd duoc dat d cac vi trf sau : DCV 20, DCV 2000m, DCA 200m, DCA200 i. Hinh

112 Hay ndi ro chdc nang hoat dong ciia bien trd R, miliampe ke A, von ke V va dien trd bao ve RQ mac trong mach dien Hinh Diot AK phan cue thuan : anot A noi vdi cue ducmg, catot K noi v6i cue am ciia nguon dien U ;,/:,.. >o - Von ke V 6 vi tri DCV 20, mdc song song vcd diot AK ; : ' - Miliampe ke A d vi trf DCA 20m, mdc ndi tie'p vdi doan mach chiia didt AK va von ke. ^ b) Cdm phich lay dien cua nguon dien U vao 6 dien ~ 220 V. Gat cong tde ciia ngudn dien U vi ben phdi : den tin hieu LED phdt sang, bdo hieu ngudn dien da boat dong. e) Gat niim bat - tdt ciia miliampe ke A va vdn ke V sang vi tri "ON" de cdc chii sd hien thi tren man hinh. d) Ddng khod K vd van niim xoay ciia bien trd R den vi tri sao eho hieu dien the giira hai cue eiia didt AK hiin thi tren vdn ke V ed gid tri f/ = 0. Sau dd, thay ddi vi trf niim xoay cua bien trd R de tang dan hieu dien the U (tdi gid tri khodng 0,70 V). Ghi cac gia tri cudng do ddng dien I^ hien thi tren miliampe ke A tuong ling vdi cac gid tri hieu dien the U vao Bdng thuc hdnh r Hinh Khao sat dong dien ngitofc chay qua diot ' a) Gat cdng tde ctia ngudn dien U vi ben trdi de ngdt dien. Mdc didt AK, miliampe ke A va vdn ke V theo Hinh 18.4, trong do chii y dat diing : - Khoa A' o vi trf ngat dien (OFF) ; I!?? I - Ngudn dien U d vi tri 6 V mot chi6u ; - Bien trd R ndi vdi hai cue cua ngudn dien U theo kieu phan dp ; R U - Didt AK phan cue nguge : anot A ndi vdi cue am, catot K ndi vdi cue duong ctia ngudn dien U ; - Miliampe kea a vi trf DCA 200 a, mdc ndi tie'p vdi didt AK ; " - Vdn kev^ d vi trf DCV 20, mdc song song vdi doan mach chiia diot AK va miliampe ke A.,,, b) Gat cong tde eua ngudn dien U vi ben phdi de ddng dien. Ddng khod K vd van niim xoay ciia bien trd R den vi trf sao cho hieu dien the giua hai cue ciia didt AK hien thi tren von ke V ed gia tri f/ = 0. e) Tliay ddi vi trf niim xoay ciia bien trd R de tang dan hieu dien the U.

113 Ghi cae gid tri eudng do ddng dien nguge I^^ hien thi tren miliampe ke A tuong ung vdi cdc gid tri hieu dien the U vdo Bdng thuc hanh d) Gat cong tde eua ngudn dien U ve ben trdi de ngdt dien. CE B - KHAO SAT DAC TINH KHUECH DAI CUA TRANZITO I-MUC DICH THI NGHIEM 1. Khao sat dac tinh khuech dai ciia tranzito bdng mot mach dien don gian. 2. Xac dinh he so khuech dai ddng ciia maeh tranzito. H! So sanh each mac miliampe ke A va von ke V trong hai so do : - Didt phan cuc thuan (Hinh 18.3); - Didt phan cuc nguoc (Hinh 18.4). Giai thich tai sao. II-DUNG CU THI NGHIEM Bo thiet hi thf nghiem "Khdo sdt dac tfnh khuech dai eiia tranzito" dugc bd tri nhu Hinh Tranzito ludng cue n-p-n (loai C 828). 2. Ngudn dien U (AC-DC : V/3A). 3. Bien trd niim xoay R (loai 10 Q x 10). 4. Dien trd : RQ = 300 kq. 5. Dientrd7?(^ = 820Q. 6. Ddng hd do dien da nang hien sd (DT-830B) diing lam chiic nang micrdampe ke mot chieu A j. 7. Ddng hd do dien da nang hien sd (DT-830B) ddng 1dm chiic nang miliampe ke mdt chieu A2. 8. Bang ldp rap mach dien. 9. Bd day ddn ndi maeh dien cd hai ddu phich cdm. 10. Khod ddng - ngdt mach dien K. Hinh 18.5 m

114 E n p n a) c) Anh ehup tranzito Hinh 18.6 RB C ''Re Up ^ + III-CdSdL! THUYET Tranzito (ludng cue) n-p-n la dung cu ban dan, dugc cdu tao tir mot tinh the ban ddn ed mot mien mang tfnh ddn p rat mdng kep gioa hai mien mang tfnh ddn n (Hinh 18.6a). Dien cue ndi vdi mien n ed mat do electron rat Idn ggi la cue emito E, dien cue ndi vdi miin n cdn lai ggi la cue eolecto C, dien cue ndi vdi mien p d giira ggi la cue baza B. Tranzito n-p-n duge kf hieu nhu Hinh 18.6b. De tranzito hoat dgng, ta phdi dat ngudn dien ed hieu dien the U^ vao giiia hai cue B-E va phdi dat ngudn dien cd hieu dien the U2 (vdi t/2 > U^) vdo giira hai cue C-E, sao cho ldp chuyfin tie'p B-E phan cue thuan va ldp chuyen tie'p C-B phan cue nguge (Hinh 18.7). Tranzito ed tde dung khuech dai cudng do ddng dien hoae hieu dien the - ggi chung la khuech dai tin hieu dien (xem muc V, bai 17). Trong thi nghiem nay, ta sir dung cdc ddng hd do dien da nang hien sd DT-830B de khao sdt dac tfnh khuech dai ddng dien ciia tranzito n-p-n bdng mdt mach dien don gian (Hinh 18.8). -I Hmh 18.7 IV - TIEN HANH THI NGHIEM 1. Mdc tranzito n-p-n va cdc ddng hd do dien da nang hien sddt-830b theo Hinh 18.8, trong dd chii y dat diing : - Khod Kavi tri ngdt dien (OFF) ; - Ngudn dien U avi tri 6 V mot chilu ; - Bien trd R ndi vdi hai cue ducfng va am cua ngudn dien mgt ehidu U theo kidu phan dp ; - Micrdampe ke'aj d vi tri DCA 200 i, mdc ndi tie'p vdi dien trd R^ = 300 kq vd cue bazo B ciia tranzito ; - Miliampe ke A2 d vi tri DCA 20m, mdc ndi tie'p vdi dien trd RQ ~ 820 Q va cue colecta C eiia tranzito.

115 m 2. Gat cdng tde ciia ngudn dien U ve ben phai. Ddng khod K va van niim xoay cua bien trd R den vi tri sao cho micrdampe ke'aj ehi cudng do ddng dien /g Idn nhat. Ghi gia tri tuang ting ciia eudng do ddng dien /g tren micrdampe kea^ va cudng do ddng dien /^ tren miliampe ke'i42 vao Bang thuc hdnh Thuc hien nam lan dgng tae tren, mdi lan lai thay ddi vi tri niim xoay eiia bien tra R td 100 Q den 50 Q (mdi Idn gidm 10 Q) de gidm ddn cudng do ddng dien /g. Ghi gid tri tuang ling eiia cudng do ddng dien /g va cudng do ddng dien I^^ vao Bang thuc hanh Tdt dien ciia cac ddng hd hien sd Aj, A2 vd ngudn dien mdt chieu U khi thuc hien xong cac phep do. B5 Trong thf nghiem nay, tai sao phai dung micrdampe ke dat d vi tri DCA 200 i de do cudng do ddng bazo /g va dung miliampe ke dat d vi tri DCA 20m de do ddng eolecto /Q? Hg vd ten 1.Ten bai thuc hanh : BAO CAO THl/C HANH Ldp.Td 2. Bang thiic hanh 18.1 : Khdo sdt dac tinh chinh luu eua didt bdn ddn Diot phan cue thuan, Diot phan cue nguoc U(V) 0,00 /,h(ma) U(V). /ng( ja) 0,00 a) Ve dd thi / =/(60 bieu didn eudng do ddng dien / chay qua didt ban ddn phu thude hieu dien the U giiia hai cue eua nd. b) Nhan xet va ket luan : - Cudng do ddng dien chay qua diot phan cue thuan ed gid tri trong khoang hieu dien the U tii 0 den vd nd ehi bdt ddu manh khi hieu dien the L^ tie'p tue tang den gid tri Idn ban 8-V.A.TL! 11.(G)-A 113

116 Cudng do ddng dien chay qua diot phan cue nguge cd gid tri bdng vdi mgi gid tri ciia hieu dien the U til 0 den khodng Cac ket qud neu tren ehufng td didt bdn ddn cd dac tinh tlie la chi cho ddng dien chay qua nd theo chieu tii cue sang cue Bang thitc hanh 18.2 ikhdo sdt dac tinh khuech dai eua tranzito 1 c: Vdi Re = 820 a 1 1 Lan do j /B(^^A) 1 /c(ma) 1-1 ^ a) Tfnh he sd khuech dai ddng p eua mach tranzito ling vdi mdi lan do. b) Tfnh gid tri trung binh eua (3 va sai sd Idn nhat {^P)^^^ ' ^.' ^ = (A^max = c) Ghi ket qud cua phep do : /?=^±(A^Ux- ± d) Ve dd thi /^ -/{IQ) bieu didn su phu thuoc cua cudng do ddng colecta I^^ vao cudng do ddng /g trong maeh tranzito. CAU HOI 1. Md ta nguyen tac cau tao ciia didt chinh luu. Ve ki hieu ciia didt nay kem theo ten goi cac dien cug ciia nd. 2. Didt chinh luu cd dac tinh gi? Hay ndi rd chieu cua ddng dien chay qua didt nay Giai thich tai sao. 3. Ve so do mach dien diing khao sat dac tinh chinh luu ciia didt ban dan trong hai trudng hop : a) Didt phan cue thuan. b) Didt phan cue nguoc. Md ta nguyen tac cau tao ciia tranzito (ludng cue) n-p-n. Ve ki hieu ciia tranzito nay kem theo ten goi cdc dien cue ciia nd. Tranzito cd dac tinh gi? Mudn diing tranzito n-p-n de khuech dai ddng dien, la phai noi cac dien cue ciia nd vdi cac ngudn dien nhu the nao? Ve so dd mach dien diing khao sat dac tinh khuech dai cua mach tranzito n-p-n. Ndi ro chieu ciia cac ddng dien chay trong mach dien cua tranzito dd VATLI 11.(C)-B

117 Tong ket DONG DIEN TRONG chironglll CAC MOI TRl/OfNG I.Kim loai. Hat tai dien la electron tu do vdi mat do n - hdng sd.. Ddng dien trong kim loai la ddng chuyen ddi ed hudng ciia cdc electron tu do dudi tde dung ciia di6n trudng. Dien trd suat ciia kim loai tang khi nhiet do tang : p = Pf)[l + au-t^)] 2. Chat dien phan La ede dung dich axit, bazo, mudi hoae cdc hgp chat nay ndng chdy. Hat tai dien la cac ion ducmg va ion am hi phan li tir phan tir chat dien phan. Ddng dien trong chdt dien phan la ddng chuyen ddi cd hudng ciia cac ion trong dien trudng.. Hien tugng dien phan la hien tugng ddng dien tdch cac hgp chat thdnh cdc thanh phdn hod hge va dua ehiing den ede dien cue.. Khdi lugng cua chdt dugc gidi phdng d dien cue tuan theo dinh luat Fa-ra-day : 1 m = " It i Ung dung : Didu che elo, xut, luyen kim (nhom), ma dien, Chat khi. Vdn khong cd hat tdi dien. Cdc hat tdi dien (electron, ion) dugc tao ra nhd tac nhan ion hod. Ddng dien trong chat khi la ddng chuyen ddi cd hudng ciia ede electron va cae ion trong dien trudng.. Ddn dien khong tu luc : Bien mat khi khdng cdn tde nhan ion hod.. Ddn dien tu luc : Duy tri duge nhd tu tao ra hat tdi dien ban ddu va nhan sd hat tdi dien dy len nhidu lan nhd ddng dien chay qua. - Hd quang dien : Tu tao ra electron nhd phdt xa nhiet electron tii catdt ndng. Nhiet dg eatdt dugc duy tri nhd ddng dien. Ung dung : 1dm den d'ng, hdn dien. - Tia lira dien,: Tu tao ra electron vd ion duong nhd ion hod chat khi bdng dien trudng manh. Xdy ra trong tia set. IJhg dung : lam bugi d td, xe mdy. 115

118 4. Chan khong. Vdn khong ed hat tdi dien. Ddn dien duge khi dua electron vao.. Ddng dien trong chan khong la ddng chuyen ddi cd hudng ciia cdc electron.. Didt chan khdng ed tinh chinh luu.. Tia catdt (tia am cue) la ehiim electron bay tu do. Tia catdt mang nang lugng cao. Tia catdt cd the tao ra bdng phdng dien qua chat khf d dp sudt thdp hoae bdng Sling electron.. IJhg dung : lam didt chan khdng, dng phdng dien tir vd den hinh. 5. Chat ban dan. Gid tri ciia dien trd sudt ndm trung gian giira dien trd suat eua kim loai va dien trd sudt cua dien moi.. Hat tdi dien trong chat ban ddn : - la electron nhung the hien dudi hai dang : electron tu do (tfch dien am) vd 16 trdng (tich dien duong). - la do ehuyen dgng nhiet hoae cdc tac nhan ion hod khde sinh ra.. Ddng dien trong chdt ban ddn la ddng chuyen ddi ed hudng ciia cac electron tu do vd Id trdng dudi tac dung cua dien trudng.. Ban ddn loai n : ehiia tap chdt ddno, mat do electron rat Idn so vdi mat do 16 trdng.. Ban ddn loai p : chiia tap chat axepto, mat do Id trdng rat Idn so vdi mat dd electron.. Ldp chuyen tiep p-n cd tinh chinh luu, diing lam didt ban ddn.. Cdu triic n-p-n vdi mi6n p rat mdng cd hieu ung tranzito va kha nang khuech dai ddng dien, dugc dung lam tranzito. 116

119 CHUONG IV TCr trirdng Tau dien chay tren dem tir truong Trong phan Dien hpc, ta da nghien ciiu dien trudng do cac dien tich diing yen gay ra. Bdt dau tii chuong nay ta nghien ciiu tii trudng do cac hat dien tich chuyen ddng va cdc nam cham gay ra, cu the ia :. Tii trudng cua nam cham. Tii trudng cua ddng dien Tii trudng ciia Trai Dat. Tac dung ciia tii trudng len day ddn cd ddng dien. Tac dung ciia tii trudng len hat dien tich chuyen dong 117

120 ly TaTRl/dNG Trong chuong I, chung ta da nghien cuu luc dien - luc tuong tac giua cac dien tich dung yen. Nguon gdc cua luc dien la dien trudng. Mot van de tu nhien duac dat ra la khi cac dien dch chuyen dong thi luc tuong tac giua chung ra sao? Chung gay ra loai trudng gi? I - NAM CHAM m Vat lieu nao sau day khong the lam nam cham? A. Sat non. B. Dong dxit. C. Sat dxit. D. Mangan dxit. 1. Tir rdt lau trong lich sir, loai ngudi da nhan tha'y mdt vai loai quang sdt cd khd nang hiit dugc sdt vun. Loai quang sdt dd dugc ggi la nam cham. Vi sau ngudi ta nhan thdy vat lieu diing de lam nam cham thudng la ede chdt (hoae la edc hgp chat eiia ehiing) : sdt, niken, cdban, mangan, gaddlinium, disprdsium. Bil Hinh 19.1 Kim nam cham 2. Tren mdt nam cham, cd nhijng mien hiit sdt vun manh nhdt : dd Id cdc cue ciia nam cham. Mdi nam chdm bao gid ciing cd hai loai cue phdn biet. Mdt kim nam cham nhd dugc dat tu do vd cd the quay xung quanh mdt true thdng dijng di qua trgng tam ciia kim (Hinh 19.1), ne'u khong ed mot nam cham nao khde (hoae mdt ddng dien nao) dat gdn kim nam cham ay, thi ta tha'y nd ludn ndm theo hudng Nam - Bde. Do vay, hai cue ciia nam cham cung dugc dat ten la cue Nam vd cue Bde, ki hieu la S (South) va N (North). 118

121 3. Thuc nghiem chiing td rdng, giiia cac nam cham cd tuong tac vdi nhau thdng qua cae lue dat vdo cdc cue. Cu the la hai cue cua hai nam cham dat gdn nhau se day nhau khi ehiing cung ten va hiit nhau khi chiing khac ten. Luc tuong tac dd dugc ggi la luc tit vd cac nam cham duge ggi Id cd tit tinh. Iffi M Hmh 19.2 II - TCT TINH CUA DAY DAN CO DONG DIEN 1. Thuc nghiem chiing td rdng, day ddn cd ddng dien (ggi tdt la ddng dien) ciing cd tir tfnh nhu nam chdm. Cu the la : a) Ddng dien ed the tac dung luc len nam cham ; b) Nam cham cd the tac dung luc len ddng dien ; e) Hai ddng dien cd the tuang tde vdi nhau. Tren Hinh 19.3, ddng dien ed eudng do / chay trong day ddn cd dinh dat song song vdi mdt nam cham. Dudi tac dung ciia luc tir do ddng dien gay ra, cue Bde eiia nam cham dich ehuyen ve phfa trude hinh ve, cue Nam ciia nam cham dich chuyen ve phfa sau. Tren Hinh 19.4, nam cham cd dinh tde dung luc tii F len doan day ddn cd ddng dien /. O day, doan day ddn cd mdt ddu nhiing vao mot dung dich ddn dien de khep kin ddng dien, ddng thdi doan day ddn dy cung cd the xe dich tuy theo tac dung cua luc tii do nam cham gay ra. RP Mpt thanh nam cham /Wdugc gid thang bang nam ngang bang mot sgi day thing ddng di qua trong tam cua nd (Hinh 19.2). Ngudi quan sat cam mot thanh nam cham thd hai sao cho khdng dugc cham vao thanh nam cham /W. Hoi phai dat thanh nam cham thii hai nhu the nao de cho cuc Bac cua thanh nam cham /W : a) di len? b) di xudng? c) chuyen ddng theo dudng trdn trong mat phing nam ngang? 05 D6ng (Jien Hinh 19.3 Luc tu do dong dien tac dung ten nam cham Hinh 19.4 Luc tcfdo nam cham tac dung ten dong dien Dung djch dan dien Tren Hinh 19.3, ki hieu 0 cd nghia la luc F, hudng vi phia sau mat phing hinh ve ; ki hieu 0 cd nghta la luc Fj hudng vi phia trude mat phing hinh ve. 119

122 J, /s ~~Hur~ Tren Hinh 19.5, hai day ddn song song cd cae ddng dien /j, I2 tac dung len nhau luc hiit khi I^ vd I2 cung ehidu, luc day khi /j vd I2 nguge chi6u. 2. Ket luan Giiia hai day ddn cd ddng dien (ggi tdt la hai ddng dien), giiia hai nam cham, giira mot ddng dien va mot nam cham deu cd lue tuong tde ; nhiing lue tuong tde ay ggi la luc td. Ta ciing ndi ddng dien va nam cham cd td tinh. Day Hmh 19.5 Luc tuang tac giua hai ddng dien thing song song lll-tctrlrcfng 1. Trong chuang I, de gidi thich su xuat hien ciia luc dien, ngudi ta dua ra khai niem dien trudng. Trong ehucmg nay, chung ta dung phuang phap so sanh tuong tu de gidi thich su xudt hien ciia luc tii. Xung quanh mdt ddng dien hay mdt nam cham tdn tai mdt tii trudng. Chfnh tir trudng nay da gay ra luc tii tac dung len mdt ddng dien khac hay mdt nam cham khde dat trong dd. 2. Djnh nghta Td trudng Id mot dang vdt chdt tdn tai trong khdng gian md bieu hien cu the Id su xudt hien eua lite tu tde dung len mpt dong dien hay mpt nam chdm ddt trong dd. 3. De phat hien su tdn tai eua tir trudng trong mdt khoang khdng gian ndo dd, ngudi ta sir dung kim nam cham nhd, dat tai nhiing vi tri bat ki trong khoang khong gian ay. Ne'u khong ed tac dung cua tii trudng cua mdt ddng dien hay mgt nam cham thi kim nam cham ndi tren ludn ndm theo hudng Nam - Bde. Khi cd tae dung cua tii trudng ciia mgt ddng dien hay mdt nam cham, kim nam cham ndi tren se quay den mdt vi trf can bdng xac dinh ; vi tri nay tuy thude vdo ehd dat kim nam cham trong tir trudng. Ngudi ta quy udc : Hudng cua tu trudng tai mdt diem Id hudng Nam -Bac cua kim nam chdm nhd ndm edn bdng tai diem dd. 120

123 IV - Ol/CfNG SU'C TU" De bieu didn ve mat hinh hgc sir tdn tai ciia tii trudng trong khong gian, ngudi ta dua ra khdi niem dudng sue td. I.Djnh nghia Dudng site td Id nhung dudng ve a trong khdng gian cd tit trudng sao cho tiep tuyen tai mdi diem cd phuong trung vdi phuang eiia tu trudng tai diem dd. Ddng thdi, ngudi ta ciing quy udc chieu ciia dudng siic tdtai mdt diem la chifiu eiia tii trudng tai diem dd. Hmh 19.6 Dudng suc tit Cd the quan sdt hinh dang cua nhiing dudng siic tii bdng thf nghiem tdphd: rdc mat sdt len mgt tam kfnh (hay nhua trong) nhdn vd dua vao trong tii trudng can quan sdt. Do tac dung eiia tii trudng dd, cdc mat sdt trd thdnh nhiing nam chdm nlid (bi td hod). Cdc nam cham nhd dd se sdp xep theo nhirng dudng siie tif. 2. Cac vi du ve difdng siifc tii Vi du 1 : Td trudng cua ddng dien thang rdt ddi Thi nghiem tir pho eho ket qua ve cac dudng siie tir gay bdi mdt ddng dien thdng rdt ddi cd cudng do / (Hinh 19.7a) : a) La nhiing dudng trdn ndm trong nhung mat phdng vudng gdc vdi ddng dien va cd tam ndm tren ddng dien ; b) Cd ehidu dugc xac dinh bdi quy tac ndm tay phdi sau day (Hinh 19.7b) : a) Dudng suc tu cue ddng dien thang b) Quy tac nam tay phai Hmh

124 a) Dong dien thing cd chieu hudng ve phia sau mat phang hinh ve. b) Ddng dien thing cd chieu hudng ve phia trude mat phing hinh ve. Hmh 19.8 DUQng suc tu cua dong dien thing De bdn tay phdi sao eho ngdn cdi ndm dpe theo ddy ddn vd ehi theo chieu ddng dien, khi dd cdc ngdn kia khum lai cho ta chieu eiia ede dudng sue td. Hinh 19.8 bieu disn dudng sire tir cua ddng dien thdng. Vi du2 -.Td trudng ciia ddng dien trdn Thf nghiem tir phd cho ta hinh dang cdc dudng siic tir CLia ddng dien trdn nhu Hinh 19.9a. Cdc dudng siic tir eua ddng dien trdn d6u ed chieu ciing di vao mdt mat va di ra mat kia cua ddng dien trdn a'y. De cd the phdt bieu quy tde vi ehidu cua cdc dudng siic tir dd, ta dinh nghia mat Nam cua ddng dien trdn la mat khi nhin vao ta thay ddng dien chay theo chieu kim ddng hd, cdn mat Bac thi nguge lai (Hinh 19.9b). Khi dd cd the phdt bieu : Cdc dudng sue tdciia ddng dien trdn ed chieu di vdo mat Nam vd di ra td mat Bac cua ddng dien trdn dy. Hmh 19.9 Mat Nam Mat Bac a) Dudng sdc td cua dong dien trdn b) Hinh 19.9b cho mot phuang phap xac dinh nhanh chi6u dong dien cua mot dong dien trdn tai mat Nam hay mat Bic. Tai mat Nam (South): viet chu S roi danh dau miii ten vao hai dau chu 5. Tai mat Bic (North): viet chq N rdi danh dau mui ten vao hai diu chii A'. Chieu clia mui ten d hai dau chcr 5 va chu N chi chieu cua ddng dien trdn tuong ung. 3. Cac tinh chat cua 6\idng site tii Cac dudng siic tii ed nhiing tfnh chat sau : a) Qua mdi didm trong khong gian chi ve dugc mdt dudng siic tir. b) Cdc dudng sufc ttr Id nhirng dudng cong khep kfn hoae vo ban d hai ddu. c) Chieu eua cdc dudng siic tir tuan theo nhirng quy tde xac dinh (quy tde ndm tay phai, quy tde vao Nam ra Bde). 122

125 d) Ngudi ta quy udc ve cdc dudng su'c tii sao cho ehd nao tir trudng manh thi ede dudng siic tir mau va chd nao tii trudng yeu thi cdc dudng siic hi thua. B3 BE Xac djnh chieu ddng dien chay trong vdng trdn (C) d Hinh Cho biei dudng suc tu cd chieu hudng ve phia trude mat phang chua vdng trdn (C). V - lis TRU'CfNG TRAI DAT Tii thdi cd, loai ngudi da biet sir dung la ban de xde dinh phuang hudng. Bd phan chfnh ciia la bdn la mgt kim nam cham ed the quay tu do xung quanh mgt true ed dinh di qua trgng tam cua nd. Dat la ban tai mdt vi trf xde dinh, xa cdc nam cham khde vd cdc ddng dien, kim nam cham ciia la ban ludn ludn ndm theo mdt hudng xac dinh khdng ddi, gdn triing vdi hudng Nam - Bde. Xe dich la ban sang nhiing vi trf khde (khdng qua xa vi trf cii), ta tha'y hudng ciia kim nam cham vdn khdng ddi. Dd la do kim nam cham ludn ludn chiu tde dung cua td trudng Trdi Ddt (dia til trudng). Phan tfch su bien thien ciia tir trudng Trdi Dat tai mdt vi tri xac dinh trong mdt khodng thdi gian ddi, ngudi ta nhan thdy, tir trudng Trdi Ddt thay ddi va cd the viet dudi dang tdng hgp cua hai thanh phdn. Thanh phdn thii nhdt dugc coi la khdng ddi ggi la dia td trudng trung binh. Nam 1839, Gao-xo da chiing minh rdng dia tir trudng trung binh cd the coi la tir trudng gay bdi mdt thanh nam cham khdng Id ndm trong Idng Trdi Ddt, hai ddu nam cham nay hudng vi hai dia cue td. Gdc tao bdi true quay eiia Trdi Ddt vd nam cham khdng Id dd bdng 11 (Hinh 19.11). Thanh phan thii hai bien thien phure tap va ciing nhd han thanh phdn thii nhat nhieu, nen khdng xet d day. (C) Hmh Nht'mg kie'n titicc dd biei : True quay cua Trai Dat ndi lifen hai dia ct/c : Bac ci/c va Nam cue. Xet mpt diem tren mat dat thi : a) Ducng thdng diing la dudng ndi di6m do den tam cua Trai Dat. b) Mat phdng Idnh tuyen la mat phing chiia di6m dd va true quay cua Trai Dat. Nam cue Dia cuc^ tu Hinh Bic cue Mat phang kinh tuyen tu TU trudng Trai Dat 123

126 Xung quanh mot nam cham hay mot dong dien ton tai mot tu trudng. TU trudng la mot dang vat chait, ma bleu hien cu the la suxua't hien luc tcrtac dung ten mot nam cham hay mot dong dien dat trong khoang khong gian co tu trudng. Tai mot diem trong khoang khong gian co tu trudfng, hudng cua tu trudng la hudng Nam Bac cua kim nam cham nho nam can bang tai diem do. CAU HOI VA BAI TAP 1. Phat bieu dinh nghia tu trudng. 2. Phat bieu dinh nghla dudng siic tit. 3. So sanh nhung tinh chat ciia dudng siic dien vd dudng stic tii. 4. So sanh ban chat ciia dien trudng va tii trudng. 5. Phdt bieu nao dudi day la sai? Luc tii la luc tuong tac A. giiia hai nam cham. B. giua hai dien tich diing yen. C. giua hai ddng dien. D. giua mot nam cham va mot ddng dien. Phat bieu nao dudi day la dung? Tu trudng khdng tuong tac vdi A. cac dien tich chuyen dong. B. cac dien tich diing yen. C. nam cham diing yen. D. nam cham chuyen dong. Oat mot kim nam chdm nho tren mat phang vudng gdc vdi mot ddng dien thang. Khi can bang, kim nam chdm dd se nam theo hudng nao? Hai kim nam cham nhd dat xa cac ddng dien va cac nam cham khac ; dudng noi hai trong tam cua chung nam theo hudng Nam - Bde. Khi can bang, hudng ciia hai kim nam cham dd se nhu the nao? 124

127 20 Ll/C TCr CAM UfNG TCr Nhu da biei trong chuang I, dai luong dac trung cho tac dung cua dien trudng la cudng do dien trudng. Vay dai luong dac trung cho tac dung cua tu trudng la gi? I - Ll/C TU" De dd dang khao sat va do dac luc tii, trude het ta hay tao ra mdt tir trudng deu. 1. Tii trucfng deu Td trudng deu Id td trudng md dac tinh eua nd gidng nhau tai mgi diem ; edc dudng sue td Id nhung dudng thdng song song, ciing chieu vd cdch deu nhau. Tir trudng d6u cd the dugc tao thdnh giiia hai cue ciia mdt nam cham hinh chii U (Hinh 20.1). Hinh 20.1 TCf trudng deu 2. Xac djnh life tii do tii trudng deu tac dung len mot doan day dan co dong dien Trong mdt tir trudng diu cd cdc dudng siie tir thdng diing (tao bdi mdt nam cham hinh chir U, Hinh 20.2a), ta dat mdt doan day ddn M^M2 = I vuong gdc vdi cdc dudng siic tii. Gia sir MjM2 dugc treo ndm ngang nhd hai day ddn manh ciing do ddi OjM] = 0-,M2, CO hai ddu O^ vd ^2 <5Wc giii cd dinh. Ddng dien di vdo (9, vd di ra O2 qua day ddn M.^M2 theo ehidu tir M, den M2. Khi ehua cd ddng dien qua MjM2 thi OjM, va O2M2 cd phuang thdng diing, do tac dung eua trgng luc mg cua M^M2 can bdng vdi tde dung cua cdc luc cang. Hinh 20.2a Dong dien / di vao 0^ va di ra Og qua doan day dan M^tJI^^l dat vuong goc voi cac dudng sue tu thang dung cua nam cham hinh chu U. 125

128 Hmh 20.2b Huong tu trudng Xac dinh luc tu F tac dung len dong dien / (huong vao phia trong). Khi eho ddng dien cd cudng do / chay qua M^M2 thi xudt hien luc tii F tac dung len M^M2- Thuc nghiem ehiing td rdng : F± M[M2 va F vuong gdc vdi dudng siic tir. Ket qud la F ed phuang ndm ngang vd cd ehidu nhu Hinh 20.2b. Dudi tde dung eua trgng lue mg va luc tir F, khi can bdng, tdng mg -i- F true ddi vdi lue cang T ciia hai day treo. Hai day 0,Mj vd O2M., lech gdc 6 so vdi phuang thdng diing. Luc F cd cudng do dugc xac dinh bdi cong thiic : HI Hay thiet lap he thiic (20.1). HI F = mgtand (20.1) up Nghiem lai nhan xet: Hudng cua ddng dien, tu trudng va luc tu tao thanh mdt tam dien thuan. Dd dang nhan thay, hudng ddng dien M^M^, hudng cua tii trudng (kf hieu la B) vd hudng ciia luc F tao thanh mdt tam dien thuan. CE Tam dien thuan : Ba veeto M^Mj, B vd F Idiong dong phdng tao nen mot tam dien thuan khi chung thoa man quy tac ban tay trdi (Hinh 20.3): De ban tay trai sao cho B huong vao long ban tay. chieu tir co tay den ngon giiia la chieu M^M^, khi dd chigu ngdn cai choai ra chi chieu cua F. II - CAM OTNG TCT 1. Thf nghiem mo ta d muc tren cho phep xde dinh lire tirf do tir trudng tac dung len doan day ddn MjM, = / ed ddng dien cudng do / chay qua. Tie'p tue tien hanh thf nghiem trong dd cho / vd / 1 P thay ddi, ket qua cho thay thuong sd khdng thay ddi. Thuang sd dd chi phu thuoc vdo tde dung ciia tir trudng tai vi tri dat doan day ddn M^M2. Ndi each khac, cd the coi thuang sd dd dac trung cho tac dung cua tir trudng tai vi trf khdo sat. Ngudi ta dinh nghia thuang so dd Id cdm dng td tai vi tri dang xet, kf hieu Id B : Hinh 20.3 Quy tic ban tay trai f-v B -- F li (20.2) 126

129 Trong cong thiic (20.2), ta da chgn dan vi do cdc dai lugng sao cho he sd ti le bdng Don vj cam ufng tii Trong he SI, don vi cam ung tir Id tesla (T). Trong edng thiic (20.2), F do bdng niuton (N), / do bdng ampe (A) vd / do bdng met (m). 3. Veeto cam ijfng tii Ngudi ta bi6u didn cdm ling tir bdng mgt vecta ggi la vecta cdm dng td, kf hieu la B^^'>- Veeto cdm img td B tai mdt diem : - Cd hudng trung vdi hudng eua td trudng tai diem dd ; - Cd dd lan Id : B = F U Vai vi du ve cd dp Idn ciia cam ling til 6: Tir trudng \ B(T) - Nam cham dien sieu ddn 20 - Tren be mat ciia Mat Trdi 5 - Nam cham dien Idn 2 - Nam cham thong thudng 10"^ - Kim nam cham -Trai Dai 10"'* Bleu thiirc tong quat cua litc ti^ F theo B Trude het, ta dinh nghla veeto phdn tu ddng dien II la veeto IM^M^, ciing hudng vdi ddng dien vd cd do Idn bdng //. Dua vao nhiing ket qud thuc nghiem da neu d tren, cd the xde dinh luc tir F tac dung len mdt phdn tir ddng dien IM^M^ = II khi dat trong mdt tii trudng deu, cdm ling til Idfi : Lite tdf cd diem ddt tai trung diem cua M^M2, CO phuang vudng gdc vdi I vd B, cd chieu tudn theo quy tde bdn tay trdi vd cd dp lan : F = IlBsina (20.3) trong dd a Id gdc tqo bdib vd I. (I) Sau nay, ngudi ta thudng noi tdt: huong cua tcr trudng va do Idn cua tit trudng. Ta hieu dd chinh hudng ciia B va do Idn ciia B. 127

130 Tai moi diem trong khong gian cotu trudng xac dinh mot vector cam Ung tub : Co hudng triing vdi hudng cua tu trudng ; Co do Idn bang, vdi F la do Idn cua luc tu tac dung len phan tu ddng dien cd do dai /, cudng do /, dat vuong gdc vdi hudng cua tu trudng tai diem dd. LUc tu F tac dung len phan tcr ddng dien it dat trong tu trudng deu, tai dd cam Ung tir la 6: Cd diem dat tai trung diem cua /; Cd phucrng vuong gdc vdi fva 6; Cd chieu tuan theo quy tac ban tay trai; Cd do Idn : F-IlBs'ina CAU HOI VA BAI TAP 1. Phat bieu cac djnh nghla : a) Tir trudng deu ; b) Luc tcr; c) Cam irng tu. 2. Phat bieu djnh nghla don vj tesla. 3. So sanh luc dien va luc tir. 4. Phat bieu nao dudi day la sai? Luc tu tac dung len phan tir ddng dien A. vudng gdc vdi phan ttr ddng dien. B. ciing hudng vdi tir trudng. C. ti le vdi cudng do ddng dien. D. ti le vdi cam irng tu. 5. Phat bieu nao dudi day la dung? Cam irng tir tai mot diem trong tu trudng. A. vuong gdc vdi dudng sire tu. B. nam theo hudng cua dudng sire tir. C. nam theo hudng cua luc tu., D. khdng cd hudng xac djnh. 6. Phan tir ddng dien //"nam trong tir trudng deu cd cac dudng suc tu thang dirng. Phai dat ij nhu the nao de cho luc tu a) nam ngang? b)bango? 7. Phan tii ddng dien //"dugc treo nam ngang trong mot tu tn/dng deu, Hudng va do Idn cua cam img tu e phai nhu the nao de luc tu can bang vdi trong luc mg cua phan tir ddng dien? 128

131 TRl/dNG CUA DONG DIEN TRONG CAC DAY DAN CO HlNH DANG DAC BIET Xung quanh mdt day ddn cd ddng dien tdn tai mdt tu trudng. Tai mdt diem trong khdng gian dd, vecta cam ung tu 6 xac dinh tu trudng phu thuoc vao nhung yeu to nao? Thue nghiem va If thuyet da xac dinh dugc cam ung tir B tai mdt diem cho trude trong tii trudng eua mdt ddng dien chay trong mdt day ddn ed hinh dang nha't dinh. Ket qud cho thdy rdng, cam ting tir B tai mdt diem M : - Ti le vdi eudng do ddng dien / gay ra tif trudng ; - Phu thude vdo dang hinh hgc cua day ddn ; - Phu thude vao vi tri ciia diem M ; - Phu thude vdo moi trudng xung quanh. Dudi day, ta gid thiet moi trudng xung quanh la chan khdng ; mdt each gdn diing, nhiing ket qua thu dugc ciing dp dung dugc cho mdi trudng xung quanh Id khdng khf. I - Tir TRLTdNG CUA DONG OIEN CHAY TRONG DAY DAN THANG DAI Ta hay xde dinh cam ling tii B tai mdt diem M gay bdi ddng dien cd cudng do / chay trong day ddn thdng ddi PQ. Trude het, ta xde dinh dudng siic tii di qua M. Theo bdi 19, dudng siie tir di qua M la dudng trdn ndm trong mat phdng di qua M vuong gdc vdi day ddn, cd tam O ndm tren day ddn. Veeto cdm ting tir B tiep xiic vdi dudng trdn dd tai M (Hinh 21.1). Hinh 21.1 Cam Ung tir ccia dong dien thing 9-VATLI 11.(C)-A 129

132 B B -<x) Dl ddng tha'y rdngb lom (ti_e'p tuyen vudng gdc vdi bdn kinh tai tie'p die'm) va B vuong gdc day ddn (vi B ndm trong mat phdng vudng gdc vdi day dan). Ket qua Id B vuong gdc mat phdng tao bdi M vd day ddn. B Dong dien b) Oe Hinh 21.2 HI Hay xac dinh chieu ddng dien tren Hinh 21.2b. Mat khde, cd chieu xde dinh bdi quy tde ndm tay phdi. Ne'u lay mat phdng hinh ve la mat phdng xac dinh bdi M va day ddn thi chieu ciia 5 dugc xde dinh tren Hinh 21.2a. HI Ni do Idn ciia cdm ling tir, thuc nghiem vd li thuyet da chiing minh dugc rdng : cam ling tir B cua ddng dien chay trong day ddn thdng ddi (cd the coi la dai vd ban) ti le thuan vdi cudng do ddng dien / vd ti le nghich vdi khodng cdch r = OM tir M den day ddn : B = k I Trong he SI, he sd ti le k cd gid tri bdng 2.10 ^. Vay: 5 = 2.10-'^^ (21.1) He qud : Khi cd hai ddng dien /j va 12 chay trong hai day ddn thdng dai, song song, each nhau mot doan r thi tir trudng cua ddng /j se tac dung len moi doan / ciia dong /j mpt lye tii la : F = B^l^l sin 90 = 2.10-^-L?- trong dd, / tinh ra ampe (A), /- tfnh ra met (m), B tfnh ra tesla (T). Vidu: /= loa; r = 0,l m 5 = 2.10-^.^ = T II - TU" TRU'CfNG CUA DONG OIEN CHAY TRONG DAY DAN UON THANH VONG TRON Hmh 21.3 TU trudng cua dong dien trdn Theo bdi 19, cdc dudng siic tir cua ddng dien trdn la nhiing dudng cong cd chieu di vdo mat Nam, di ra mat Bde cua ddng dien trdn ay (Hinh 21.3). Trong sd dd, cd dudng siic tir di qua tajn O la dudng thdng v6 ban d hai ddu. Cdm ling tir fi tai tam O cd phuang vuong gdc vdi mat phdng ehiia ddng dien vd cd chieu di vao mat Nam, di ra mat Bde ciia ddng dien trdn dd. Theo ket qua tfnh todn, do Idn cam ling tii tai O dugc xac dinh bdi cong thiic : VATLI 11.(C)-B

133 B^2K.\0-^ I_ R (21.2a) vdi R la bdn kfnh cua khung day trdn. Ne'u khung day trdn tao bdi A^ vdng day sit nhau thi : A (21.2b) III - Tir TRl/dNG CUA D6NG DIEN CHAY TRONG 6NG DAY DAN HINH TRU Trong vat If vd ki thuat, ngudi ta thudng sir dung d'ng day ddn hinh tru tao thdnh bdi mdt day ddn qudn ddu quanh mdt Idi hinh tru (thudng cd chieu dai Idn ban nhidu so vdi dudng kinh tiet dien). Khi cho ddng dien cudng do / di vdo day ddn, thue nghiem ehiing td rang, trong d'ng day eae dudng siic tir la nhirng dudng thdng song song ciing chieu vd each deu nhau. Ndi cdch khac, tif trudng trong Idng dng day la ddu. Theo ket qud tinh todn, cam ling tii trong Idng d'ng day dugc cho bdi cong thiic : Hmh 21 '< TU trudng cua ong day hinh tru 1 N B^An.lQ-^ I (21.3a) I trong dd A'^ la tdng sd vdng day, / Id do ddi hinh tru. A' Chii y rang -n\a sd vdng day quan tren mdt dan vi ddi eiia loi, vay ciing cd the viet : B = 47t.l0~'nl (21.3b) Chilu cac dudng siic tii ciia dng day ddn hinh tru ciing cd the dugc xac dinh bdng quy tde ndm tay phdi : Tudng tugng dung ban tay phdi ndm Idy dng day sao cho cdc ngdn trd, ngdn giiia... hudng theo chieu ddng dien ; khi dd ngdn cdi choai ra eho ta ehidu ciia dudng stic tir. BE f^ Dua vao quy tac "vao Nam ra Bac", nghiem lai rang, chieu cac dudng suc tu cua d'ng day dien hinh tru cung dugc xac djnh bang quy tac nam tay phai. 131

134 IV - Tir TRl/dNG CUA NHIEU DC)NG OIIN Phuang phdp tfnh todn tuang tu nhu ddi vdi cudng do dien trudng gay bdi nhieu dien tfch diem. Nghia la tir trudng do nhidu ddng dien gay ra tuan theo nguyen If chdng chdt: Vecta cdm img td tai mdt diem do nineu ddng dien gdy ra bang tdng cdc vecta cdm dng td do tdng ddng dien gdy ra tai diem dy. Bai tap vi du Cho hai ddng dien /j = /, = 6 A chay trong hai day din dai, song song, each nhau 30 em theo ciing mot chieu. Xac dinh vecto cam ung tir tdng hop tai diem M nam trong mat phang chli;a hai day din, each hai day lan luot la MO, = r, = 0,1 m ; MO2 = ''2 = 0.2 m. Hmh 21.5 HI Tim mdt diem tren doan 0^02 trong dd cam ung tu tong hgp bang 0. Gidi Tai M cd hai vecto cam img tir B, va Bj lin luot do /, va /^ gay ra. Vi M nim trong mat phing chira hai dong disn n6n S] va B-i cung phuong (vi vudng gdc vdi mat phing chiia M va hai day din). Ap dung quy tic nim tay phai, ds dang thay tai Mhai vecta B[ vab^ nguoc hudng (Hinh 21.5). Vay vecto cam ijng tir tdng hop tai M cho bdi : cd do Idn trong dd : B= B, + BJ '. i; B Bi B-> -6 '-p. B = (12-6).10"^ = 6.10" Bcung hudng vdib HI '1 -va- B] = 2.10" 7/L = 2.10" 'o.i 12.10" B2 = 2.10" -7/1 = A = 6.10" '2 '0,2-6 -T^ -6 rp 'H. Cam ufng tii cua dong tfien thing dai: S = 2.10-^-. Cam Ung tu tai tam cua khung day dien trdn : 8 =,NI Cam Ung tu trong long ong day dien hin I1 tru dai: B = 4n.^0-^nI. 132

135 cau H6I VA BAI TAP 1. Cam ung tir tai mpt diem trong tit trudng cua ddng dien phu thuoc vao nhung yeu to nao? 2. Dp idn cua cam iing tit tai mpt diem trong lit trudng cua ddng dien thing dai thay doi the nao khi diem ay dich chuyen a) song song vdi day? b) vudng gdc vdi day? c) theo mpt dudng siic lis xung quanh day? A. ludn bang 0. B. ti le vdi chieu dai ong day C. la dong deu. D. ti le vdi tiei dien ong day 5. So sanh cam itng tii ben trong hai dng day dien sau : Ongi i 5A vdng i dai 2 m 1 3. Phat bieu nao dudi day la diing? 6ng2 2 A vdng dai 1,5 m Op Idn cam img tii tai tam mpt ddng dien trdn A. ti le vdi cudng dp ddng dien. B. ti le vdi chieu dai dudng trdn. C. ti le vdi dien tich hinh trdn. D. ti le nghich vdi dien tich hinh trdn. 4. Phat bieu nao dudi day la diing? Cam iing ti; trong Idng dng day dien hinh tru Hai ddng dien dong phang : ddng thii nhat thdng dai, /, = 2 A ; ddng thii hai hinh trdn, tam O2 each ddng thu nhat 40 cm, ban kinh R2 = 20 cm, /j = 2 A. Xac dinh cam img tir tai O2. Hai ddng dien /^ = 3 A, /g = 2 A chay trong hai day dan thang dai, song song each nhau 50 cm theo ciing mpt chieu. Xac dinh nhung diem tai dd 6 = 0, Em CO biet? DINH NGHIA DON VI AMPE Theo nhung tinh toan a tren ve tuong tac tu giira cac ddng dien, ta thay : hai ddng dien, cudng do tuong ung la /^ va Ij, chay trong hai day ddn thing dai, song song, cung chieu thi hut nhau va nguoc chieu thi day nhau. Luc tuong tac tren mot do dai MN = I cua mdi day ddn cho bdi : F=2.10-7J-^ f trong dd r la khoang each giua hai day ddn. Cdng thuc tren cho thay, ne'u/, =/^ = 1 A; /= 1 m ; r= 1 m thi F= 2.10"''N. Tu dd, ngudi ta dua ra dinh nghta dan vi ampe cua cudng do ddng dien, mot don vi co ban cua he SI nhu sau : Ampe la cuang do cua dong dien khong doi khi chay trong hai day din thing dai, song song, CO tiet dien nhd, dat each nhau 1 m trong chan khong, thi mdi met chieu dai cua mdi day chiu tac dung cua mot li/c tir bdng 2.10~^ N. 133

136 JLu LUCLO-REN-XO Ddng chuyen ddi cd huong cua cac hat tich dien tao thanh ddng dien. Vay khi hat tich dien chuyen dong trong mot tu trudng thi hat ay cd chiu tac dung cua luc tu khdng? 134 I - Ll/C LO-REN-XO 1. Djnh nghta luc Lo-ren-xcr Ta biet rdng, ddng dien trong kim loai la ddng chuyen ddi eo hudng ciia cdc electron. Khi day ddn cd ddng dien duge dat trong mdt tir trudng, ngudi ta giai thfeh luc tiir tac dung len day ddn chfnh la tdng hgp cdc luc do tir trudng tae dung len eae electron chuyen ddng tao thanh ddng dien. Mdt each tdng quat : Mgi hat dien tieh chuyen dgng trong mot td trudng, deu chiu tde dung cua luc td. Luc tir nay dugc ggi la luc Lo-ren-xa (Lorentz). Cd the lam nhiing thf nghiem chiing minh hien tugng nay. Chang ban khi dat mdt nam cham lai gdn mgt mdy thu hinh dang boat ddng, thi luc Lo-ren-xa tde dung len chiim electron dang rgi vao man hinh 1dm lech quy dao cua ddng electron. Do dd, hinh dnh trdn man hinh bi nhi6u loan. 2. Xac djnh luc Lo-ren-xor Tuy rdng, ddng dien trong kim loai la ddng ehuyen ddi nguge chigu ddng dien cua cdc electron (mang dien - e = -1,6.10"^^ C), nhung de tien If gidi va de ed the md rong ket qua tim duge cho mgi trudng hgp, ta coi rdng ddng dien trong day ddn la ddng chuyen ddi theo chieu ddng dien ciia cdc hat dien tfch qq--\- e. Theo bai 20, luc tii F tac dung len phdn tir ddng dien ll = IM^^. ed phuang vudng gdc vdi / va B, cd ehidu tuan theo quy tde ban tay trai vd cd do Idn dugc xde dinh bdi cdng thiic : F = IlBsina

137 6 day, ta gid thiet tir trudngfi la deu. Luc tir F Id tdng hgp cac luc Lo-ren-xa tac dung len cdc hat dien tfch ^Q chuydn dgng vdi eung van tde v tao thanh ddng dien theo ehidu tj (Hinh 22.1). Nhu vay, luc tir tdng hgp phan chia deu cho cdc hat dien tfch. Ne'u A' Id tdng sd hat dien tfch trong phan tir ddng dien thi lire Lo-ren-xa tde dung len mdi hat dien tfch eho bdi : / = L-IL N ~ N a la gdc tao bdi Bval = M^M^ Bsina (22.1) Gid sir UQ Id mat do hat dien tfch trong day ddn, S la tiei dien day ddn thi : N = UQX thi tich day ddn = UQ X SI Hinh 22.1 Xac dinh luc Lo-ren-xa Mat khac, cudng do ddng dien / bidu thi lugng dien tfch chuyen qua tie't dien S trong thdi gian mdt giay (Hinh 22.2). Trong mdt giay, cdc hat dien tfch di dugc doan dudng bdng v, vay cudng do ddng dien / ciing dugc tfnh bdng lugng dien tich chiia trong thd tfch Sxv mang sd hat SVUQ, nghia la : / = qqisvuq) II _ qqsvuql va %v N ~ UQSI Vay (22.1) cho ta edng thiie xde dinh lue Lo-ren-xa: /= f/glibsina (22.2) So sdnh ve hudng, ta nhan tha'y /' vd V ciing hudng khi qq> 0 va nguge hudng khi qq < 0. Vay cd the ket luan : Luc Lo-ren-xa do td trudng ed edm ung td B tac dung len mpt hat dien tieh q^ ehuyen ddng vdi van tde v : a) Cd phuang vudng gdc vdi v vds ; Hinh 22.2 Xac dinh cudng do ddng dien qua tiet dien S 135

138 qo>0 b) Cd chieu tudn theo quy tde bdn tay trdi : De bdn tay trdi md rpng sao eho td trudng hudng vdo long bdn tay, chieu td cd Uiy den ngdn giita Id chieu cua V khi qq>0 vd nguge chieu v khi q^ < 0. Liic dd, ehieu eua lue Lo-ren-xa Id chieu ngdn cdi ehodi ra; c) Cd dp lan :f= Iq^lvEsina (22.3) trong dd a la gdc tqo bdi v vdb (Hinh 22.3). Hinh 22.3 Xac dinh luc Lo-ren-xo tac dung len dien tich : a) qg > 0, b) q^ < 0. IfU Khi nao luc Lo-ren-xd bang 0? BB Xac dinh luc Lo-ren-xa tren Hinh 22.4.' q< 0 Hinh 22.4 II - CHUYEN D6NG CUA HAT DIEN TfCH TRONG TLTTRUdNGDEU 1. Chu y quan trong Gia sir mdt hat dien tfch qq khdi lugng m chuyen ddng dudi tac dung duy nhat ciia luc Lo-ren-xo. Khi dd, lire tac dung/luon ludn vudng gdc vdi van td'c D, do dd cdng suat tiic thdi ciia luc tde dung : ludn bdng 0. Vay ddng nang cua hat (theo dinh If bien thien ddng nang) dugc bdo toan, nghia la dp Idn van td'c ciia hat khdng ddi, chuyen dgng ciia hat Id chuyen ddng deu. 2. Chuyen dong cua hat dien tich trong tii trudng deu Bay gid ta hay khao sat ehuyen dgng ciia mdt hat dien tfch qq, khdi lugng m trong mdt tir trudng ddu 5 vdi gid thiet la van tde ban ddu ciia hat vudng goc vdi td trudng. Gia thiet hat chiu tac dung duy nhdt cua tir trudng, phuong trinh chuyen dgng ciia hat duoc viei : ma - f vdi/duge xde dinh theo Hinh (22.4) 136

139 Chgn he quy chieu qudn tinh la Oxyz, sao cho cdm ling tiis hudng dgc theo true Oz (Hinh 22.5). Khi dd, neu ggi thdnh phdn cua gia tde theo phuang 2 la a^ thi theo (22.4), vi a 1 5 nghla lad 10:, nen : a^ = 0, suy ra : y^ = const Ket qud cho tha'y thanh phan cua van td'c v theo phuang z khong thay ddi. Vi liic ddu {t = 0) : v^ = 0 (van td'c ban ddu vuong gdc vdi B ) nen ta ludn cd v^ = 0, nghia la vecto van td'c ij ludn ndm trong mat phdng Oxy : Chuyen dgng eiia hat dien tich Id chuyen dong phdng trong mat phdng vudng gdc vdi td trudng. Trong mat phdng dd, lire Lo-ren-xa ludn vuong gdc vdi van td'c rj, nghia la ddng vai trd luc hudng tam : qo>0 Hmh 22.5 ChuySn dong ccia hat di$n tich trong tit trudng deu r mv I I D (22.5) vdi R Id bdn kfnh cong cua quy dao. 155 Vi do lon eua van td'c khdng ddi nen bdn kfnh cong R cua quy dao khong ddi, ndi cdch khde cpiy dao Id mgt dudng trdn. B! Hinh 22.6 la quy dao trdn cua mot electron trong mot mat phang vudng gdc vdi tu trudng deu 6. Xac dinh chieu ciia B. Ket luan : Quy dao ciia mdt hat dien tich trong mpt td trudng deu, vdi dieu kien van td'c ban ddu vudng gdc vdi td trudng. Id mpt dudng trdn ndm trong mat phdng vudng gdc vdi tit trudng, ed bdn kinh (eho bdi cong thiie (22.5)) : R = mv ko[b (22.6) Luc Lo-ren-xa cd nhidu umg dung trong khoa hge vd cdng nghe : do ludng dien tir, dng phdng dien tii trong truyen hinh, khdi phd ke, cdc mdy gia td'c,... Hinh 22.6 CE TU cong thuc (22.6), hay tfnh chu ki cua chuyen ddng trdn deu cua hat. Chirng to rang, chu ki dd khong phu thuoc van tde hat (trong khi ban kinh quy dao ti le vdi van td'c hat). 137

140 Lire Lo-ren-xcr tac dung len mot hat dien tich q^ chuyen dong trong mot tu trudng B co phuong vuong goc vdi v va B, co chieu tuan theo quy tac ban tay trai, va co do \dn : f= 4g vbsina Hat dien tich q^, khoi luofng m bay vao mot tu trudng deu S vdi van toe ban dau vuong goc vdi tcr trudng, co quy dao la mot dudng trdn nam trong mat phang vuong gdc vdi tu trudng vdi ban kinh : mv CAU HOI VA BAI TAP g 5. Mpt ion bay theo quy dao trdn ban kinh R trong mpt mat phang vuong gdc vdi cac dudng siic 1. Luc Lo-ren-xo la gi? Viet cong thiic ciia luc ciia mpt tii trudng deu. Khi dp Idn van toe tang Lo-ren-xo. gap ddi thi ban kinh quy dao la bao nhieu? 2. Phat bieu quy tde ban tay trai cho luc Lo-ren-xo. ^ R^ g ^ C 2R D 4R 2 6. So sanh luc dien va luc Lo-ren-xo ciing tac dung len mpt dien tich. 3. Phat bieu nao dudi day la sai? 7. Hat prdtdn chuyen dong theo quy dao trdn ban kinh 5 m dudi tac dung ciia mpt lii trudng deu Luc Lo-ren-xo e = 10-2 T. Xac djnh: A. vudng gdc vdi tii trudng a) Toe dp cua protdn. B. vudng gdc vdi van tde. b) Chu kl chuyen ddng ciia prdtdn. C. khdng phu thuoc vao hudng ciia tii trudng. ^^^ ^ ^. g.^2 io-27 kg D. phu thuoc vao dau ciia dien tich..^ ^.,,,......^..^.. i, ^ 8*. Trong mpt tu truong deu co 6 thang dung, cho Phat bleu nao sau day la diing? mpt ddng cac ion bat dau di vao tij trudng tii Hat electron bay vao trong_mpt tii trudng deu ^^^^ ^,^ ^i ^^ ^^j c, sao cho AC la - dudng theo hudng cua tii trudng B thi, 2 trdn trong mat phang ngang. Cac ion cd ciing A. hudng chuyen ddng thay ddi. ^jien tich, cung van toe dau. Cho biet khoang B. dp Idn CLia van toe thay doi. each AC giua diem di vao va diem di ra ddi vol C. dong nang thay doi. 'o^^ C2H5O+ la 22,5 cm, xac dinh khoang each D. chuyen ddng khdng thay doi. AC doi vdi cac ion C2H5OH+ ; CjH^ ; 0H+; CH2OH+; CH+; CH+. 138

141 Em CO biet? KHOI PHO KE Khdi pho ke la mot ung dung true tie'p cua hien tuong ndi tren. Od la mot thiei bi cd tac dung tach rieng cac hat tfch dien (cac ion) cd cung dien tfch nhung khoi luong khac nhau. Mudn vay, ta cho ddng cac ion bay vao mot tu trudng deu theo hudng vudng gdc vdi cac dudng sue. Khi dd cac ion ciing dien tfch cd khoi luong khac nhau se bay theo nhung nua dudng trdn cd ban kfnh khac nhau. CAC MAY GIA TOC De thuc hien cac phan ung hat nhan, ngudi ta phai tang tde cho cac chum hat dien tfch sao cho nang luong cua cac chum hat nay dat tdi nhung gia tri ngay cang Idn. Mudn dat muc dfch dd, ngudi ta su dung cac may gia tde, trong dd cac hat dien tfch duoc tang td'c nhd cac luc dien. Trong cac may gia tde thing, cac hat dien tfch duoc tang td'c nhd luc dien manh. Chdng han trong may gia td'c thing cd chieu dai 4 km cua phdng thf nghiem Stan-fot, cac hat electron duoc tang td'c den nang luong dat gia tri 50 GeV'". Trong cac may gia tde trdn, hat dien tfch chuyen dong theo cac quy dao trdn dudi tac dung cua mot tu trudng deu cd hudng vudng gdc vdi van td'c cua hat (Hinh 22.7). Dong thdi hat chuyen ddng trong mot hop hinh trdn gom hai nua hop rdng hinh chu D ndi vao mpt hieu dien the xoay chieu. Tai ca d&u nam trong chan khdng. Khi dd, dien trudng xoay chieu giua hai hinh D cd tac dung tang tde cho hat trong qua trinh chuyen ddng : Van td'c hat ngay cang tang len ciing vdi ban kfnh quy dao. Khi dong nang cua hat tang len den gia tri du lon thi ngudi ta cho chum hat ban vao mpt tam "bia" de tao ra cac phan ung hat Hinh 22.7 May gia td'c trdn nhan. Hien nay, may gia td'c (LEP LHC) Idn nhai the gidi da dupe xay dung tai trung tam nghien cuu hat nhan chau Au (CERN) vao cudi nhung nam tam muoi cua the ki trude. Trong "nha may" khong 16 nay, cac hat dien tich bay theo nhcrng quy dao trdn ndm trong mpt dudng ham hinh trdn, cd chu vi tdi 27 km, ndm sau dudi long dai 100 m, giua hai nude Phap va Thuy ST. (1) ev (electron vdn), dcm vi do nang luong hat. 1 ev= 1,6.10"''* J; 1 GeV = lo'^ev. 139

142 Tong ket _ chirotiglv TCr TRl/OfNG 1. Luc tir la luc tuong tac giua hai nam cham, giira mgt nam cham va mdt day ddn cd ddng dien, hay giua hai day ddn cd ddng dien. Trong khodng khong gian xung quanh mdt nam cham hay xung quanh mdt ddng dien, tdn tai mdt tir trudng. Bieu hien cua tir trudng trong mgt khodng khong gian ndo dd la su xudt hien lire tir tac dung len mgt nam cham hay mgt doan day ddn cd ddng dien dat tai mgt diem bdt ki trong khoang khdng gian ay. e Hudng ciia tu trudng tai mgt diem la hudng Nam - Bac ciia kim nam cham nhd ndm can bang tai didm dd.» Dudng siic tir la nhung dudng ve d trong khoang khong gian cd tir tixrdng sao cho tie'p tuyen tai mdi diem cd phuang triing vdi phuang ciia tir trudng tai diem dd. 2. De dac trung cho tir trudng tai mgt diem trong khong gian xung quanh mgt ddng dien, ngudi ta dinh nghia mgt dai lugng ggi la cam img tir, ki hieu B. Dd la mgt vecto : - Cd hudng trung vdi hudng ciia tir trudng tai diem dd ; - Cd do Idn ti le vdi cudng do ddng dien sinh ra tir trudng, phu thuge vdo hinh dang ciia day ddn mang ddng dien vd ciing phu thude vi tri^ua diem dang xet. 3. Mgt sd bieu thiic ciia do Idn cam d'ng 140 tir B do mgt vdi ddng dien cd hinh dang dac biet gay ra : Ddng dien chay trong day ddn thdng ddi Ddng dien chay trong khung day ddn trdn! Ddng dien chay : trong d'ng day i ddn hinh tru I B^2.\0 -ll B = 2n.\0-7/y/ R (tai tam khung trdn) B = 4K.\0-^nl (trong Idng d'ng day) 4. Luc tir tae dung len phdn tu ddng dien if dat trong tir trudng d6u : - Chidu cua luc : xde dinh theo quy tde ban tay trdi ; - Do Idn ciia luc : F - BIhma. 5. Luc Lo-ren-xa (lue tii tae dung len hat dien tfch {qq, v) chuyen ddng) : - Chidu eiia lire : tuan theo quy tde ban tay trdi khi qq>i>; - Do Idn cua luc : F = l^qlubsina. e Ban kinh quy dao trdn cua hat dien tich {qq,v) chuyen ddng trong jnat phdng vuong gdc vdi tir trudng ddu B : mv R = Kl«

143 CHL/ONG V Cam ufng dien tii May bien ap 220 kv-180 MVA Trong chuong trude, ta da xet mdi quan he giua ddng dien va tii trudng do dong dien sinh ra. Trong chuong nay ta xet bai toan ngupc lai ; trong dieu kien nao tii trudng gay ra ddng dien? Cu the la cac van de sau :. Hien tuong cam iing dien tii. Dinh luat Len-xo (Lentz) ve chieu ddng dien cam img, Suat dien ddng cam img, Ty cam. Suat dien dong tu cam. Nang lupng tii ciia cudn day ty cam 141

144 23 TQTHONG CAM CTNG DIEN TU* Ddng dien gay ra tu trudng. Cau hdi nguge lai : Trong dieu kien nao tu trudng gay ra ddng dien? (Cau hoi do Fa-ra-day dat ra)..f^ I-TCTTHONG Hinh 23.1 Dinh nghta tif thong I.Djnh nghia Gia su mdt dudng cong phdng kin (C) la chu vi gidi ban mdt mat cd dien tich S (gia thiet la phdng) (Hinh 23.1). Mat dd dugc dat trong mdt tir trudng ddu B. Tren dudng vudng gdc vdi mat 5, ta ve vecto d cd do dai bdng dan vi theo mgt hudng xde dinh (tuy y chgn),at dugc ggi la vecta phdp tuyen duang. Ggi a la gdc tao bdi /fva B, ngudi ta dinh nghia tir thdng qua mat 5 la dai lugng, ki hieu O, cho bdi : <& = BS cosa (23.1) Cdng thiic dinh nghla tren day chiing td rdng ttr thdng la mdt dqi lugng dqi so. Khi a nhgn (cosa > 0) thio>0vakhio;tii (cosa < 0) thi O < 0. Dac biet khi a = 90 (cosa = 0) thi 0 = 0. Ndi each khac, khi edc dudng sue td song song vcfi mat S thi td thdng qua S bang 0 (Hinh 23.2). Trudng hgp rieng, khi a = 0 thi: <D = 55 (23.2) Hmh 23.2 TU thong qua S bang 0 2.0ofn vjdoti/thong * Trong he SL dan vi do tir thong la vebe (Wb). Trong cong thiic (23.2) ne'u 5 = 1 m^, fi = i T thi : O = 1 Wb. 142

145 II - HIEN Tl/ONG CAM CTNG DIEN TU" 1. Thi nghiem Mdt mach kin (C) hai ddu ndi vao dien ke G (cd nhiem vu xac dinh chisu va cudng do ddng dien). Gia sir (C) dat trong tir trudng ciia mdt nam cham SN (Hinh 23.3). Ta chgn ehidu duong tren mach kin (C) phu hgp vdi chieu cua dudng siic tit cua nam cham SN theo quy tde ndm tay phdi: Dat ngdn tay cai ndm theo chieu eua dudng sire tir thi chieu ciia cac ngdn tay kia khum lai ehi chieu duang tren mach (C). a) Thi nghiem I. Cho nam cham SN dich chuyen lai gdn (C). Quan sat thdy kim dien ke'g lech di, chiing td rdng trong (C) xuat hien ddng dien / chay theo chieu nguge vdi chieu duong da chgn. Khi nam cham ngimg chuyen ddng thi ddng dien / tdt. b) Thi nghiem 2. Cho nam cham SN dich chuyen ra xa (C). Kim dien ke'lai chi mdt ddng dien / trong (C) nhung theo ehidu nguge vdi ehidu d thi nghiem 1. e) Thi nghiem 3. Ciing thu duge ket qud tuang tu neu eho nam cham diing yen va mach (C) dich chuyen lai gdn hay ra xa nam cham, hoae eho (C) quay xung quanh mdt true song song vdi mat phdng chiia mach hoae lam bien dang (C). d) Thi nghiem 4. Thay nam cham SN bdng mdt nam cham dien. Khi thay ddi cudng do ddng dien qua nam cham dien, trong (C) vdn xuat hien ddng dien /. HI ;l^ Hinh 23.3 Thi nghiem cam Ung dien tu BD Hay giai thfeh su bien thien tu thong qua mach kfn (C) trong tung thf nghiem. Mo ta va giai thfeh thf nghiem Fa-ra-day duoc ve tren Hinh'23.4. Hinh 23.4 Thi nghiem Fa-ra-day 143

146 2. Ket luan a) Tdt ea cdc thi nghiem trdn day deu cd mgt dac diem chung la tir thdng qua mach kin (C) bien thien. Dua vao cong thiic dinh nghia rtr thong (23.1), ta nhan thay, khi mdt trong cac dai lugng B, S hoae a thay ddi thi tir thong O bien thien. b) Ket qua ciia cdc thi nghiem ay vd ciia nhidu thi nghiem tuong tu khac ehiing td rdng : - Mdi khi tir thdng qua mach kin (C) bien thien thi trong maeh kin (C) xuat hien mdt ddng dien ggi la ddng dien cdm dng. Hien tugng xuat hien ddng dien cam ting trong (C) ggi la hien tugng cdm itng dien td. - Hien tugng cam ting dien tir chi tdn tai trong khodng thdi gian td thdng qua mqch kin bien thien. Ill - DINH LUAT LEN-XO VE CHIEU DONG DIEN CAM l/ng l.ta hay khdo sat quy luat xde dinh chieu ddng dien cam ting xuat hien trong mgt maeh kin khi tii thong qua maeh kin dy bien thien. Ta quy udc ehidu duang tren (C) phu hgp vdi chieu eiia dudng siic tir eiia nam cham (hoae d'ng day dien) qua (C) theo quy tde ndm tay phdi d tren. 0 thi nghiem Hinh 23.3a, tir thdng qua (C) tang : Ddng dien cam ling / trong mach kin (C) cd chi6u nguge vdi ehidu duang tren (C). O thi nghiem Hinh 23.3b, tir thdng qua (C) gidm: Ddng dien cam ling / trong mach kin' (C) cd ehidu triing vdi chieu duang tren (C). 2. De dd dang so sdnh, ta chii y rdng khi ddng dien cam iing xudt hien thi cung sinh ra tir trudng, ggi la td trudng cdm dng. Can phan biet tir trudng cdm iing vdi tir trudng eua nam cham hay nam cham dien - dugc ggi la td trudng ban ddu. Chidu cua tir trudng cam iing va ehidu eiia ddng dien cam iing lien quan chat che vdi nhau. 3. Qud trinh phan tich cdc ket qua thi nghiem md td tren Hinh 23.3 vd cdc thi nghiem tuong tu ddn tdi ket luan sau : Ne'u xet edc dudng sde td di qua mqch kin, td trucmg cam img nguge chieu ven td trudng ban ddu khi td thdng qua mqch kin tdng vd ciing chieu vcfi td trudng ban ddu khi td tiidng qua mach kin gidm.

147 Ndi each khac : Ddng dien cdm dng xudt hien trong mqch kin CO chieu sao cho td trudng edm dng cd tde dung chdng lai sit bien thien cua td thdng ban ddu qua mqch kin. Phat bieu tren day la ndi dung eiia dinh luat Len-xa, nd eho phep ta xde dinh chieu ddng dien cdm Ung xudt hien trong mqch kin. CE 4. TrUdng hcrp tir thong qua (C) bien thien do chuyen dong Xet thi nghiem dugc mo ta tren Hinh 23.3a, khi nam cham SN dich chuyen lai gdn (C), ddng dien edm ung chay theo ehidu am va mat cua (C) ddi dien vdi cue Bde eiia nam cham la mat Bde, mat ndy gay ra luc tir ddy cue Bde ciia nam cham. Trong trudng hgp d Hinh 23.3b, nam cham SN dich ra xa (C), ddng dien cam iing chay theo chieu ducmg va mat cua (C) ddi dien vdi cue Bde ciia nam cham Id mat Nam, mat nay gay ra luc tir hiit cue Bde cua nam cham. Trong ea hai trudng hgp, lue tir ddu nguge hudng vdi ehuyen ddng ciia nam cham. Vay ed the phdt bieu mgt dang khac cua dinh luat Len-xa : Khi td thdng qua (C) bien thien do ket qua cda mot chuyen ddng ndo dd thi td trudng cdm dng cd tde dung ehdng lai ehuyen ddng ndi tren. fecho nam cham SN rdi thing dirng chui qua mach kfn (C) cd dinh (Hinh 23.5), Hay xac dinh chieu ddng dien cam irng xuat hien trong (C). Hinh 23.5 IV - DONG DIEN FU-CO (FOUCAULT) Thuc nghiem chung td rdng ddng dien cam ung eung xudt hien trong cdc khdi kim loai khi nhung khdi nay chuyen ddng trong mdt tir trudng hoae dugc dat trong mdt tir trudng bien thien theo thdi gian. Nhiing ddng dien cam ting dd duge ggi la ddng dien Fu-ed. 10-VATLI 11.{C)-A 145

148 1. Thi nghiem 1 Mgt banh xe kim loai (ddng hoae nhdm) cd dang mdt dia trdn quay xung quanh true O ciia nd trude mdt nam cham dien (Hinh 23.6). Khi chua cho ddng dien chay vao nam cham, bdnh xe quay binh thudng. Khi cho ddng dien chay vao nam cham, bdnh xe quay cham va bi ham dimg lai. Hinh Thi nghiem 2 Mdt khdi kim loai (ddng hoae nhdm) hinh lap phuang dugc dat giiia hai cue cua mdt nam chapi dien (Hinh 23.7). Khdi ay dugc treo bdng mdt srri day cd mdt dau cd dinh ; trude khi dua khdi kim loai vao trong nam cham dien, sgi day treo duge xodn nhidu vdng. Ne'u chua ed ddng dien di vao nam cham dien, khi thd ra, khdi kim loai quay nhanh xung quanh minh nd. Ne'u cd ddng dien di vao nam cham dien, khi tha ra, khdi kim loai quay cham vd bi ham diing lai. Hinh 23.7 S.. 3. Giai thich O cdc thi nghiem tren day, khi bdnh xe va khdi kim loai (ddng hoae nhdm) chuyen ddng trong tit trudng thi trong the tich cua chiing xuat hien ddng dien edm irng - nhirng ddng dien Fu-cd. Theo dinh luat Len-xa, nhirng ddng dien cdm iing nay ludn eo tac dung chdng lai su chuyen ddi, vi vay khi chuyen ddng trong tii trudng, tren bdnh xe va tren khdi kim loai xuat hien nhiing luc tii cd tac dung can trd ehuyen ddng ciia chiing, nhiing luc ay ggi la luc ham dien td Tfnh chat va cong dung cua dong dien Fu-cd a) Do tac dung eua ddng Fu-cd, mgi khdi kim loai chuyen dgng trong tii trudng d6u chiu tde dung cua nhiing lire ham dien tir. Tinh chat nay dugc iing dung trong cac bg phanh dien tir eua nhirng d td hang nang. -iatli 11.(C)-B

149 b) Ddng dien Fu-co cung gay ra hieu iing toa nhiet Jun - Len-xa : Khdi kim loai ehuyen ddng trong tir trudng hoae dat trong hi trudng bien thien se ndng len. Tinh chat nay dugc ting dung trong cdc Id cam ung de nung ndng kim loai. Trong nhi6u trudng hgp, su xuat hien ddng Fu-ed gay nen nhiing tdn hao nang lugng v6 ich. De' gidm tac dung cua ddng Fu-cd, ngudi ta cd the tang dien trd cua khdi kim loai. Chdng han, trong thi nghiem 1 (Hinh 23.6), ngudi ta khoet nhiing Id tren bdnh xe ; trong thi nghiem 2 (Hinh 23.7), khdi kim loai nguyen ven dugc thay bdng mgt khdi gdm nhieu la kim loai xep lien nhau, each dien ddi vdi nhau. Bdng nhung cdch dd, ngudi ta tha'y tde dung eua ddng Fu-ed giam rd ret. Ddng Fu-cd ciing duge iing dung trong mdt sd Id tdi kim loai. TU thong qua mot dien tich 5 dat trong mot tu truorng deu : e O = BScosa Khi tir thong qua mot mach kin (Q bien thien th) trong (C) xuait hien dong dien cam Ung. Dong dien cam Ung co chieu sao cho tu trudng cam Ung co tac dung chdng lai su bien thien cua tu thong ban dau qua (Q. Noi rieng, khi tu thong qua (C) bien thien do mot chuyen dong nao do gay ra th) tutrudng cam Ung co tac dung chong lai chuyen dong do. CAU HOI VA BAI TAP n deu B. Hdi trudng hpp nao dudi day, tii thdng qua mach bien thien? Phat bieu cac dinh nghla : - Ddng dien cam ung ; A. (C) chuyen ddng tinh tien. - Hien tuong cam ung dien tii; B. (C) chuyen ddng quay xung quanh mdt tryc CO dinh vudng goc vdi mat phang chiia mach. Tij trudng cam iing. C. (C) chuyen ddng trong mdt mat phang 2. Ddng dien Fu-cd la gi? ^^o^g g^^^ y^, g ' D. (C) quay xung quanh tryc co dinh nam ^ trong mat phdng chiia mach va true nay 3. Mach kin (C) khdng bien dang trong tii trudng khdng song song vdi dudng sue tii. 147

150 4. Mach kin trdn (C) nam trong ciing mat phdng P voi dong dien thdng / (Hinh 23.8). Hdi trudng hpp nao dudi day tii thdng qua (C) bien thien? Tjnh tien A. (C) dich chuyen trong mat phdng P lai gan / hoae ra xa /. B. (C) dich chuyen trong mat phdng Pvdi van toe song song vdi ddng /. C. (C) cd dinh, day dan thdng mang ddng / chuyen ddng tinh tien doc theo chinh nd. D. (C) quay xung quanh ddng dien thdng /. Hinh Xac dinh chieu ciia ddng dien cam img trong cac thi nghiem dudi day : a) Nam cham chuyen dong tinh tien (Kinh 23.9a). b) Mach (C) chuyen dorg tinh tien (Hinh 23.9b). C) Quay c) Mach (C) quay (Hinh 23.9c). d) Nam cham quay lien tue (Hinh 23.9d). Quay lien tue d) Hinh

151 24 SUAT DIEN DONG CAM QNG Trong cac bai tren, ta da khao sat hien tuong cam ung dien tu chu yeu vd mat dinh tfnh. Vd mat dinh luong, cudng dp ddng dien cam ung duac xac dinh nhu the nao? I - SUAT DIEN DONG CAM OTNG TRONG MACH KIN I.Djnh nghla Su xuat hien ddng dien cam iing trong mdt mach kin (C) chiing td tdn tai mdt ngudn dien trong mach dd. Suat dien ddng eua ngudn nay duge ggi la sudt dien ddng cdm dng. Vay ed the dinh nghia : Sudt dien ddng cdm dng Id sudt dien ddng sinh ra ddng dien cdm dng trong mqch kin. HI 2. Djnh luat Fa-ra-day Gid sir tai maeh kin (C) dat trong mdt tir trudng (Hinh 24.2), tir thdng qua mach bien thien mdt lugng AO trong mdt khodng thdi gian At. Gid sir sir bien thien tir thdng ndy dugc thuc hien qua mdt dich chuyen ndo dd ciia mach. Trong dich chuyen nay, luc tii tde dung len mach (C) da sinh mdt cdng AA. Ngudi ta da chiing minh duge rdng : R] a) Nhac lai dinh nghia sua't dien dgng cua mgt nguon dien. b) Trong cac so dd mach dien, nguon dien If tudng mgt chieu dugc kf hieu nhu Hinh 24.1a. Ngoai ra, nguon dien cdn dugc ki hieu nhu Hinh 24.1b, trong dd, diem nggn cua mui ten chi vao cue duong cua ngudn ; chieu mui ten dudc ggi la chieu cua sua't dien dgng. Tinh u^g theo so dd Hinh 24.1c. c) Tfnh UQQ theo sd do Hinh 24.1d. d) Tfnh u^g theo so do Hinh 24.le vdi mgt ngudn co r^o. e) Nhac lai bleu thirc cua dien nsng do mdt ngudn dien san ra trong mgt khoang thdi gian At. '-\^ a) A^ = /Ad) vdi / la cudng do ddng dien cam iing. Theo dinh luat Len-xa, luc tir tac dung len mach (C) luon cdn trd chuyen ddng tao ra bien thien tir thong. Do dd, AA la mdt edng can. Vay, de thuc hien su dich ehuyen ciia (C) (nhdm tao ra sir bien thien ciia 0) phdi cd ngoai luc tde dung len (C) vd trong chuyen ddi ndi tren, ngoai lue nay da sinh cdng thdng cdng can ciia luc tir: AA'= - AA = - ia(i> (24.1) 'g s D e-^ s b) c) d) Hmh

152 Cdng AA' cd do Idn bdng phdn nang lugng do ben ngodi cung cap eho maeh (C) va dugc chuyen hod thanh dien nang cua suat dien dgng cam iing e^ (tuong tu nhu dien nang do mgt ngudn dien san ra) trong khodng thdi gian At. Theo cdng thiic (8.5), ta cd : AA' = ejat (24.2) So sdnh hai cong thiic ciia AA' la (24.1) va (24.2), ta suy ra cong thiic ciia suat dien ddng cam iing : Hmh 24.2 Sua't dien dong cam img trong mach kin e^ = ^ AO At (24.3) Ne'u chi xet do Idn cua e^ (khdng ke dau) thi : re = At (24.4) CP Nghiem lai rang, trong cdng thuc (24.4), hai ve deu cd cung ddn vi. Thuang sd AO bieu thi do bien thien tir thdng Ar qua mach (C) trong mdt don vi thai gian, thuang sd nay dugc ggi la td'c do bien thien tir thdng qua mach. Vay cong thiic (24.4) dugc phdt bieu nhu sau : Dp Idn ciia sudt dien dpng cam dng xudt hien trong mqch kin ti le vdi tde dp bien thien td thdng qua maeh kin dd. ^E Phdt bieu nay dugc ggi la dinh luat co ban ciia hien tugng cam iing dien tir - dinh luat Fa-ra-day. II - QUAN HE GIU'A SUATDIEN DONG CAM CTNG VA DjNH LUAT LEN-XO Su xudt hien ddu trir (-) trong cong thiic (24.3) la de phil hgp vdi dinh luat Len-)ia. 150

153 Trude het mach kin (C) phdi dugc dinh hudng. Dua vao ehidu da chgn tren (C), ta chgn chieu phdp tuyen duang de tinh tir thong O qua mach kin (C) (O Id mgt dai lugng dai so). Neu O tang thi c^ < 0 : Chieu cua suat dien ddng cdm ting (ehidu eua ddng dien cam ting) nguge vdi chieu ciia mach. Neu O gidm thi e^>0 : Chieu ciia sudt dien ddng edm ling (ehidu ciia ddng dien cam iing) la chieu cua mach. K] 151 Xac dinh chieu cua suat dien dgng cam dng xuai hien trong mach kfn (C) tren Hinh 24.3 khi nam cham : a) di xudng. b) di len. Ill - CHUYEN HOA NANG LUOfNG TRONG HIEN TUONG CAM l^ng DIEN TU" Trong hien' tugng cam iing dien tir tren day, de tao ra sir bien thien tir thdng qua mach (C), phdi ed ngoai luc tde dung vao (C) vd ngoai luc nay da sinh mdt edng co hgc. Cdng co hgc nay lam xuat hien sudt dien ddng cdm iing trong mach, nghia la da tao ra dien nang. Vay ban chat cua hien tugng cam ung dien tir da neu d tren la qud trinh chuyen hod ca nang thanh dien nang. Fa-ra-day la ngudi ddu tien khdm phd ra hien tugng cam dng dien tir va dinh luat co bdn ve hien tugng ndy. Ddng gdp ciia Fa-ra-day da md ra mdt trien vgng to Idn trong the ki XK ve mgt phuang thiic sdn xudt dien nang mdi, lam ndn tang eho edng cudc dien khf hod - cudc Cdch mang khoa hgc edng nghe Idn thii hai trong lich sir tien hod ciia nhan loai. Hinh KhitUthongqua mot mach ki n (C) bien thien thi trong mach kin do xuat hien suatd en ^H dong cam Ung va do do tao ra dong dien (:am Ung. 1 B J Suait dien dong cam Ung co gi a tri cho bdi : AO e = - c At 15^1

154 CAU HOI VA BAI TAP 1. Phat bieu cac dinh nghla : - Suat dien ddng cam img ; - Toe dp bien thien tii thdng. 2. Neu it nhat ba img dung ciia hien tuong cam img dien tii. Phat bieu nao dudi day la dimg? Khi mpt mach kin phdng quay xung quanh mpt tryc nam trong mat phdng chua mach trong mpt til trudng, thi suat dien dpng cam iing doi chieu mpt lan trong A. 1 vdng quay B. 2 vdng quay -I C. - vdng quay D. - vdng quay 4 Mdt mach kin hinh vudng, canh 10 cm, dat vudng gdc vdi mpt tu trudng deu cd dp Idn thay doi theo thdi gian. Tinh toe dp bien thien cua cam img tu, biei cudng dp ddng dien cam iing / = 2 A va dien trd ciia mach r = 5 Q. 5. Mdt khung day dan hinh vudng, canh a = 10 cm, dat cd dinh trong mpt tu truong deu co vecto cam img tu B vudng gdc vdi mat khung. Trong khoang thoi gian Af = 0,05 s. cho dp Idn ciia 8 tang deu tu 0 den 0,5 T, Xac dinh dp Idn ciia suat dien dpng cam img xuat hien trong khung. 6*. Mpt mach kin trdn (C) ban kinh R, dat trong til trudng deu, trong dd vecto cam img tii B liic dau cd hudng song song vdi mat phdng chiia (C) (Hinh 24.4). Cho (C) quay deu xung quanh tryc A co dinh di qua tam ciia (C) va nam trong mat phdng chiia (C); toe dp quay la (0 khdng doi. Xac dinh suat dien dpng cam img eye dai xuat hien trong (C). Hmh

155 25 Tl/CAM Trong bai nay, chung ta xet mdt loai hien tuong cam irng dien tu dac biet la hien tuong tu cam : dd la hien tuong cam ung dien tu xay ra trong mach cd ddng dien bien thien theo thdi gian. Trude hei, hay xet tu thdng cua mot mach kfn da cd san ddng dien. I - TCT THONG RIENG CUA MOT MACH KIN Gid sir cd mdt mach kin (C), trong dd cd ddng dien eudng do /. Ddng dien i gay ra mgt tir trudng, tir trudng nay gay ra mdt tir thdng O qua (C) duge ggi la td thdng rieng cua mach. Ngudi ta da chirng minh dugc rdng, tir thdng ndy ti le vdi cam iing tir do / gay ra, nghia la ti le vdi /. Ta cd the viet : 0 = Li (25.1) L la mdt he sd, chi phu thude vao cau tao va kfch thude cua mach kin (C) ggi la dp tu cdm ciia (C). Trong cong thirc (25.1), ; tinh ra ampe (A), O tinh ra vdbe (Wb), khi dd do tu cam L tinh ra henry (H). Vi du : Mdt d'ng day dien chieu dai /, tiet dien S, gdm tat ca A^ vdng day, trong cd ddng dien cudng do / chay qua gay ra tir trudng deu trong long d'ng day dd. Cam iing tir B trong Idng d'ng day cho bdi ; N B = 47C.lO-^~i I De dang tfnh dugc tir thong rieng ciia d'ng day dd vd suy ra do tu edm (viet trong he don vi SI) : -7 N^ wr%, L = 4n.l0 - S (25.2) I Hay thiei lap cdng thiic (25.2). BI 153

156 CIni y : Trong cac so do mach dien, cudn cam dugc ki hieu nhu tren ffinh25.1. Hinh ^MMOT^ Cong thiic nay dp dung ddi vdi mgt dng day dien hinh tru cd chieu ddi / khd Idn so vdi dudng kfnh tiet dien 5. Ong day cd do tu cam L ddng ke, dugc ggi la dng ddy tu cdm hay cudn cam. Chii thich : De cd dugc dng day vdi do tu cam L lan, trude hei dng day phai cudn nhidu vdng (A^ Idn), sau dd dng day phdi ed mdt loi sdt. Do tu cam cua dng day cd loi sdt duge tfnh theo cong thuc 2 L = 4;7r. 10"^/J S, trong dd p la mdt he sd (gid tri eo 10^) ggi la dp td tham, dac trung cho tir tfnh ciia loi sdt. ll-hientuofngtucam I.Djnh nghta Trong mach kfn (C) cd ddng dien cudng do / : Neu do mdt nguydn nhan ndo dd cudng do / bien thien thi ttr thdng rieng ciia (C) bien thien ; khi dd trong (C) xay ra hien tugng cam iing dien tir; hien tugng nay ggi la hien tugng tu edm. Hien tugng tu cdm Id hien tugng cdm dng dien tif xdy ra trong mot mqch cd ddng dien md su bien thien td thdng qua mqch dugc gdy ra bdi sit bieit thien ciia eudng dp ddng dien trong mqch. Trong cdc mach dien mdt chieu, hien tugng tu cam thudng xdy ra khi ddng mach (ddng dien tang len dot ngdt) va khi ngdt mach (ddng dien giam xud'ng 0). Trong cdc mach dien xoay chieu, ludn ludn xay ra hien tugng tu cam, vi eudng do ddng dien xoay chieu bien thien lien tue theo thdi gian. Hinh Mot so vi du ve hien tiiong tu" cam a) Vi du I Thi nghiem Trong mach dien ve tren Hinh 25.2, hai den 1 vd 2 gidng nhau ; dien trd R va dng day tu cam L ed cung gia tri dien trd. Khi ddng khod K, den 1 sdng len ngay edn den 2 sdng len tir tir. 154

157 Gidi thich Khi ddng khod K, ddng dien qua dng day va den 2 tang len dot nggt, khi dd trong d'ng day xay ra hien tugng cam iing dien tir - hien tugng tu cam. Sudt dien ddng cam iing xudt hien ed tac dung cdn trd nguyen nhan sinh ra nd, nghia la can trd su tang ciia ddng dien qua L. Do dd ddng dien qua L vd qua den 2 tang len tir tir, khong tang nhanh nhu ddng dien qua den 1. b) Vi du 2 Thi nghiem Trong mach dien ve tren Hinh 25.3, dieu chinh bien trd R de do sdng eiia den yeu, vira dii de trdng rd dugc sgi day tde. Neu dot ngdt ngdt khod K, ta tha'y den sdng bdng len trude khi tat. IS Gidi thich Ban ddu ed ddng dien /j^ chay qua d'ng day (theo chieu miii ten). Khi ngdt K, ddng dien i.^ gidm ddt nggt xudng 0. Trong d'ng day xdy ra hien tugng tu cam : Hien tugng nay cd tac dung ehdng lai su giam cua i^ ; trong dng day xudt hien ddng dien cam itng ciing chieu vcfi i^ ban ddu, ddng dien edm irng nay chay qua den vd vi ngdt K dot ngdt nen eudng do ddng cdm iing khd Idn, lam cho den sdng birng len trude khi tdt. L r" I ' R -HI I. Den K Hmh 25.3 K' Trong mach dien ve tren Hinh 25.4, khoa K dang ddng 6 vi tri a. Neu chuyen K sang vi tri b thi dien trd R ndng len. Hay giai thfeh. l- R Ill - SUAT DIEN DONG TU CAM 1. Khi cd hien tugng tu cdm xay ra trong mgt maeh dien thi sudt dien ddng cam iing xuat hien trong mach dugc ggi la sudt dien dpng tu cam. Gid tri cua nd dugc tfnh theo cong thiic tdng qudt (24.3) : - _ AO_ ^'^ Ar trong dd O la tir thong rieng dugc eho bdi : O = Li. Vi L khdng ddi, nen AO = LAi. Hmh

158 Vay, suat dien ddng tu cam ed cong thiic : ^tc = -L~ (25.3) ^^ At Sudt dien ddng tu edm cd dp lan ti le vdi tde dp Men thien eua eudng dp ddng dien trong mqch. Dau trir trong (25.3) pho hgp vdi dinh luat Len-xa. 2. Nang luorng tit trucrng cua ong day tu cam Trong thi nghiem md ta d Hinh 25.3, khi ngdt K, den sdng bimg len trude khi tdt. Dieu nay chiing td da cd mdt nang lugng giai phdng trong den. Nang lugng nay chfnh la ndng lugng dd dugc tich luy trong dng ddy tu cdm khi cd ddng dien chay qua. Ngudi ta chiing minh dugc rdng, khi cd ddng dien cudng do / chay qua d'ng day tu cam thi dng day tfch luy dugc mdt nang lugng cho bdi : CB Chiing to BI W = -Li^ (25.4) 2 r5no h^i \/^ f^ii3» ^ ^ T (25 4) cd cung ddn ^^^^ ^^ ^"" ^^^^ "^^"^ ^""^^ ""^"S' " " " ^^ ^^^ "^"^ vi la jun (J). ilroftg "^y chfnh Id nang lugng cua tii trudng tdn tai trong d'ng day khi cd ddng dien chay qua. IV-CTNG DUNG Hien tugng tu cam cd nhieu iing dung trong cac mach dien xoay chieu. Cudn cdm la mdt phdn tir quan trgng trong cac mach dien xoay chieu cd mach dao ddng vd cac may bien dp... Khi trong mach dien co cudng do dien dong tucam : dong dien bien thien th' trong mach xuat hien suat, A*- Khi cuon cam co dong dien cudng dudi dang nang lucrng tu trudng dofchayquathi trong cuon cam tich luy nang ludng W = ' Li' 2 156

159 CAU HOI VA BAI TAP 1. Trong nhirng trudng hgp nao cd hien tugng tu cam? 2. Phat bieu dinh nghla tir thdng rieng, dp ty cam cua mot mach kfn. 3. Op Idn cua suat dien dpng ty cam phy thuoc vao nhirng dai lugng nao? Chpn cau dung. Mpt dng day cd dp tu cam L ; ong day thir hai CO sd vdng day tang gap doi va dien tfch mdi vdng day giam mpt niia so vdi ong day thir nhat. Neu hai dng day cd chieu dai nhu nhau thi dp ty cam coa ong day thir hai la C. ddng dien cd gia tri Idn. D. ddng dien bien thien nhanh. Tfnh dp ty cam ciia mpt d'ng day hinh try cd chieu dai 0,5 m gdm vdng day, mdi vdng day cd dudng kinh 20 cm, Suat dien dpng ty cam 0,75 V xuat hien trong mpt cuon cam cd L = 25 mh ; tai dd cudng dp ddng dien giam tu gia tri ig xudng 0 trong 0,01 s. Tinh ig. Trong mach dien Hinh 25.5, cuon cam L cd dien tro bang 0. Ddng dien qua L bang 1,2 A ; dp ty cam L = 0,2 H. Chuyen K sang vi tri b, tinh nhiet lygng toa ra trong R. A. L B.2L. -i D.4L. Phat bieu nao dudi day la sai? Suat dien dpng ty cam co gia tri Idn khi A. ddng dien tang nhanh. B. ddng dien giam nhanh. Hinh

160 T ong ket chuang V CAM LTNG OIEN TU' 1. Tir thong qua mdt mat 5 (cd chu vi la (O) dat trong mgt tir trudng ddu B {til thong qua mach kfn (C)) : O = BScosa 2. Hien tugng cam iing dien tir : Khi tir thdng qua mach kin (C) bien thien thi trong maeh kin (C) xuat hien ddng dien cam ling. Hien tugng cam ung dien tir chi tdn tai trong khoang thdi gian tir thdng qua maeh kin (C) bien thien. 3. Dinh luat Len-xa : Ddng dien cam ting xuat hien trong maeh cd chieu sao cho tir trudng edm ting cd tac dung chdng lai sir bien thien cua tir thdng ban dau qua mach kin. 4. Dinh luat Fa-ra-day : Do Idn ciia suat dien ddng cam iing xuat hien trong mach kfn ti le vdi td'c do bien thien tii thdng qua mach kin dd : c.. = AO Ar 5. Hien tugng tu cam : la hien tugng cam ling dien tii xdy ra trong mdt mach dien cd cudng do ddng dien bien thien. Khi trong mach dien ed eudng do ddng dien bien thien thi trong mach xuat hien sua't dien ddng tu cam : -L A[ Ar Khi tir thdng qua mach kin bien thien do ket qud ciia mdt chuyen ddng ndo dd thi tir trudng cdm ting cd tde dung ehdng lai chuydn dgng ndi tren. 158

161 PHAN HAI QUANG HINH HOC Mot hien tuong quang hoc : Cau My Thuan soi bong tren song Tien Anh sang la doi tupng nghien cuu ciia Quang hpc. Quang hinh hpc la phdn Quang hpc nghien ciiu sy truyen anh sang qua cac mdi trudng trong sudt, va nghien ciiu sy tao anh bdng phuong phap hinh hpc. Nhd cac nghien ciiu ve Quang hinh hpc, ngudi ta da che tao ra nhieu dyng cy quang can thiei cho khoa hpc va ddi sdng. 159

162 QUANG HINH HOC Khucxaanh sang Mat. Cac dung cu quang 160

163 CHUONG VI Khuc xa anh sang Cac chum tia sang trong mot le hoi dem Anh mpt cai thuoc nhiing trong nuoc Ba dinh luat co ban ciia Quang hinh hpc la : Oinh luat truyen thdng anh sang ; - Ojnh luat phan xa anh sang ; - Dinh luat khiic xa anh sang. 6 THCS, ta da khao sat so bp ve cdc dinh luat nay ciing vdi mpt sd img dyng ciia guong phang, guong cau, thau kinh, mdt,... Khiic xa anh sang la hien tupng quan trong cd nhieu iing dung. Trong chuong nay chiing ta se nghien ciiu day dij hon ve su khiic xa, ddng thdi tim hieu them mpt hien tupng cd lien quan : hien tupng phan xa toan phan. m Cap quang dijng trong Y hgc 11-VATLI 11.(C)-A 161

164 KHUC XA ANH SANG O ldp 9, ta da buac dau tim hieu hien tupng khuc xa anh sang ve mat dinh tfnh. Trong bai hpc sau day, chung ta se khao sat ddy du hon hien tupng nay ve mat dinh luong tiinn ^6.1 Do hien tupng khiic xa anh sang, ta thay thia trong coc nhu bi gay 6 mat nuoc. Xnen (Willebrord Snell) giao su toan va vat li tai Dai hpc Lay-den (Leyden), ngudi da kham pha ra dinh luat khiic xa anh sang dong thdi vdi De-cac (Descartes). I - SI/ KHUC XA ANH SANG 1. Hien tifcrng khiic xa anh sang Khuc xq dnh sdng Id hien tugng lech phuang (gdy) eiia cdc tia sdng khi truyen xien gdc qua mat phdn cdch giiia hai mdi trudng trong sudt khde nhau. 2. Djnh luat khuc xa anh sang 6 Hinh 26.2, ta ggi :, SI : tia tdi ; / : diem tdi ;. N'lN : phdp tuyen vdi mat phan cdch tai / ;, IR : tia khiic xa ;, i : gdc tdi ; / : gdc khiic xa. 11-VATLM1.(C)-B

165 Khi thay ddi gdc tdi i, thue nghiem cho ket qud sau day, dugc ggi la dinh luat khiic xa dnh sdng : - Tia khue xq ndm trong mat phdng tdi (tqo bdi tia tdi vd phdp tuyen) vd a phia ben kia phdp tuyen so vdi tia tdi. - Vdi hai mdi trudng trong sudt nhdt dinh, ti sd giua sin gdc tdi (sini) vd sin gdc khuc xq (sinr) ludn khdng ddi : sini = hang sd (26.1) sinr Thuoc do do II - CHIET SUAT CUA MOI TRUOfNG 1. Chiet suat ti doi sinr Ti sd khdng doi ^ trong hien tugng khiic xa sinr duge ggi Id chidt sudt n ddi «,, ciia mdi trudng (2), (chira tia khiic xa) ddi vdi moi uudng (1) (ehira tia tdi): sini sinr = "21 (26.2) Ne'u «2i > 1 thi r < i Tia khiic xa bi lech lai gdn phdp tuyen hon. Ta ndi moi trudng (2) chidt quang /!0'/7 mdi trudng (1). - Neu «T, < 1 thi r > i: Tia khiic xa bi lech xa phdp tuyen han. Moi trudng (2) chidt quang kem moi trudng (1). 2. Chiet suat tuyet ddi Chief sudt tuyet ddi (thudng gpi tdt la chiet sudt) eiia mot mdi trudng Id chiet sudt ti ddi cua mdi trudng dd ddi vcfi chdn khdng. Nhu vay, chiet sua't eiia chan khdng Id 1. Chiet suai eua khong khf Id 1, (rat gdn vdi chiet suat eiia chan khong) nen thudng dugc tfnh trdn Id 1, neu khong cdn do chfnh xac cao. Oen chieu t laze Khoi nhira ban tru trong suot Hinh 26.3 Dung cu do cac goc /' va rde nghiem lai dinh luat khiic xa anh sang. Bang 26.1 Kei qua do goc toi / va goc khuc xa r tuong ung trong thi nghiem 6 Hinh ' 0 j ' 0 6, ,5 25, ,5 sin/ 0 0,174 0,342 0,500 0,643 0,766 0,866 0,940 0,985 Sinr 0 0,113 0,225 0,334 0,431 0,515 0,574 0,629 0,

166 Mgi moi trudng trong sud't deu cd chiet sua't tuyet ddi Idn ban 1. Cd the thie't lap dugc he thiic : «2 «21 = «1 (26.3) '-' / Hinh 26.4 Do thi bieu di n su phu thuoc cua goc r vao gdc i theo Bang 26.1 trong dd : «2 Id chiet sudt (tuyet ddi) ciia mdi trudng (2); «, la chiet suat (tuyet ddi) ciia mdi trudng (1). vay edng thiie ciia dinh luat khiic xa cd the viet theo dang ddi xiing : Hu ; E ; BJ njsini = nisinr (26.4) O 0,2 0,4 0,6 0,8 1 Sin; Hmh 26.5 Do thi bieu dien su phu thuoc ciia sinr vao sini theo Bang 26.1 III - TINH THUAN NGHJCH CUA SU TRUYEN ANH SANG Ml Viet cdng thirc cua dinh luat khiic xa vdi cac gdc nho (< 10 ). *3fA Ap dung dinh luat khuc xa cho trudng hop / = 0 - Ket luan. 1*5 Hay ap dung cdng thdc ciia dinh luat khuc xa cho su khuc xa lien tiep vao nhieu mdi trudng cd chiet suat lan lugt la n.,, Hg.--- "n va cd cac mat phan each song song vdi nhau. Nhan xet. Thf nghiem cho thay : O Hinh 26.2, ne'u dao ehidu, cho anh sang truyen tir nude ra khdng khi theo tia RI thi nd khiic xa vao khdng khf theo tia IS. Nhu vay, dnh sdng truyen di theo dudng ndo thi ciing truyen nguge lai theo dudng dd. Day la tinh thuan nghich ciia su truydn anh sang. Tir tfnh thuan nghich, ta suy ra ; «i2=:^ 21 (26.5) Tfnh thuan nghich nay cung bieu hien d su truyen thdng va su phdn xa. 164

167 Bdi tap vi du Tia sang truydn tir mot chat trong sudt co chiet suat /( tdi mat phan each vdi moi trudng khdng khi. Goe khuc xa trong khong khf la 60. Tia phan xa d mat phan each co phuotig vuong gdc vdi tia khuc xa (Hinh 26.6). Tfnh chiet suat /;. Gidi Theo di bai :/' + ; = 90" Ta suy ra : / + r = 90" Ap dung dinh luat khuc xa : iisini = sinr sin;- Tir do : // =.sin/ VI sin/ = cosr. nen : /( = tanr Thay sd, ta dugc : n = tan 60" = V? = Bang Chiet suat ciia mpt so moi trudng'^i I Chat rdn (20 C) u I i Kim cuong 2,419 Chiet suat I Thuy tinh crao 1,464 ^ 1,532 i Thuy tinh flin Nuoc da 1,309 Chat long (20 C) 1,603-^1,865 Chiet suat Chat rdn (20 C) Chiet suat Muoi an (NaCI) 1,544 Ho phach 1,546 Polistiren 1,590 Xaphia 1,768 Chat long (20 C) Chiet suat Gill cini : Nguyen nhan ciia hien tuang khuc xa la su thay ddi tde do truygn anh sang. Ngudi ta thie't lap duoc he thire v^ chiet suat tuyet ddi n ciia mot moi trudng nhu sau : c ll = u trong do : ( ia toe do anh sang trong chan khdng ; ll la tde do anh sang trong moi trudng. Nuoc ' 1,333 Benzen 1,501 Chat khi,.-. -, man ^, ^ Chiet suat (0 C; 1 atm) Rupu etilic Glixerol Chat khi (0 C ; 1 atm) 1,361 1,473 Chiet suat Khong khi 1, Khi cacbonic 1,00045 Djnh luat khuc xa anh sang : Tia khuc xa nam trong mat phang tdi va or phia ben kia phap tuyen so v6i tia tdi. Vdi hai moi trudng trong suot nhat dinh, ti so giua sin goc tdi (sin/) va sin goc khiic xa (sinr) luon khong doi: smi = hang sd smr (1) Xac dinh vdi anh sang vang do natri phat ra (xem bai Lang kinli). 165

168 ,"*!-; # ' " ' i '-,1 4& Chiet suat:,..., sin/ Chiet suat ti ddi: n,, = sinr Chiet sua't tuyet doi: + Chiet suait ti ddi ddi vdi chan khdng "2 + Ta co : n,., = "1 Cdng thuc cua dinh luat khuc xa anh sang viet dudi dang ddi xung : n^sin/ = n^sinr. CAU HOI VA BAI TAP A. Tia Sd- 1. The nao la hien tuong khuc xa anh sang? Phat bieu dinh luat khiic xa anh sang. 2. Chiet suat ti doi n^^ ciia moi truong (2) doi voi moi trudng (1) la gi? 3. Chiet suat (tuyet doi) n ciia mpt moi trudng la gi? Viet he thiic lien he giua chiei suat ti doi va chiet suat tuyet doi. 4. The nao la tinh thuan nghich ciia su truyen anh sang? Chung to ; ni2 1 '21 NuocCO chiei suat la -. Chiet suat ciia khong khi doi voi nude la bao nhieu? 5. Mpt tia sang truyen den mat thoang ciia nude. Tia nay cho mpt tia phan xa d mat thoang va mpt tia khuc xa. B. Tia S^. C. Tia S3/. D. Sd ; S^I ; S3/ deu cd the la tia tdi. Tia sang Hinh 26.7 truyen tii nude va khuc xa ra khdng khi. Tia khiic xa va tia phan xa d mat nude 4 vudng gdc vdi nhau. Nude cd chiet suat la - Gdc tdi cua tia sang la bao nhieu (tinh trdn so)? A. 37. B. 42. C. 53. D. Mdt gia tri khac A, B, C. Cd ba mdi trudng trong sudt t,?, ^3". Vol cung gdc toi;, mpt tia sang khiic xa nhu Hinh 26.8 khi truyen tit ^ vao 2 vatu 1 vao ^,. Ngudi ve cac tia sang nay quen ghi lai chieu Injyen trong Hinh Tia nao dudi day la tia tdi? 166 Hinh 26.8

169 Van vdi gdc toi /, khi tia sang truyen ti; 2 vao -1- thi gdc khiic xa la bao nhieu (tinh trdn sd)? A. 22. B. 31. C. 38. D. Khdng tinh dupe, vi thieu yeu td. 8. Mdt cai thude dupe cam thdng dung vao binh nude cd day phdng, ngang. Phan thude nhd khoi mat nude la 4 cm. Chech d tren cd mdt ngpn den. Bong ciia thude tren mat nude dai 4 cm va d day dai 8 cm. Tinh chieu sau ciia nude trong binh. Chiet. 4 suat cua nuoc la TT. Mdt tia sang dupe chieu den diem giua ciia mat tren mdt khdi lap phuong trong sudt, chiet suat n = 1,50 (Hinh 26.9). Tim gdc tdi / Idn nhat de tia khuc xa vao trong khdi cdn gap mat day ciia khdi. / ^ ^ / / Hmh 26.9 Em CO biet? SL/TAO ANH QUA LUONG CHAT PHANG Trong dai song, ta thuong gap truong hgp nhin anh cua mot vat do khuc xa anh sang ma co, chdng han nhu nhin mot con ca bai loi trong h6 nuac, nhin hon soi a day suoi,... (Hinh 26.10). Khi do, anh sang da khuc xa qua mat phdng phan each hai moi truong trong suot. He hai moi truong nay tao thanh mot kr&ng chat phing. Anh cua vat dugc tao bai mot chiim tia sang rat hep di vao mst. Neu quan sat theo phuang vuong goc vai mat phdng phan each, ta co the thiet lap dugc cong thirc xac dinh vi tri anh (cong thijc ciia luang chat phdng). That vay, theo Hinh 26.11, ta co : HI = /-/S2tanr= HS.sinr HS.Xani = /^5,sin/ Hmh Ban the nao de mui ten triing con ca? Dodo Vay HS^ sin/ HS sinr n^ HS^ HS^ Neu nhin tir khong khi vao nuac thi n, = 1 ;ni = ^- '^ L^wMw,,-.2 Do do HS,= /^S, 2 ' - I 3 Anh dugc "nang" len gan mat nuac so vai vat. (26.6) H r /. ly,-' y' S, Si / Hir}h / 167

170 27 PHAN XA TOAN PHAN Ngay nay, mpi nguai d^u nghe noi den cap quang diing trong Cong nghe thong tin, trong Y hoc, Hien tuong ca ban dugc ap dung trong cap quang la phan xa toan phan. Phan xa toan phsn la gi? Chum tia laze Tia phan xa I - SLT TRUYEN ANH SANG VAO MOI TRl/OfNG CHIET QUANG KEM HON («, > nd Hinh 27.1 Tia khuc xa l.thi nghiem CT Tai sao d mat cong ciia ban tru, chiim tia tdi hep truyen theo phcrcing ban kinh lai taiyen thing? PP Van dung tinh thuan nghich cua su" truyen anh sang, hay neu ra cac ket qua khi anh sang truyen vao moi trudng chiet quang han. Ta cho mot chiim tia sang hep truysn tir khoi nhira trong suot hinh bdn tm vdo Ichong khf v6i cdc diing cii bo trf theo so d6 a Hinh CT Thay d6i do nghieng cua chdm tia toi (thay doi goc toi /) vd quan sdt chum tia khiic xa ra khong khf. K^ Kdt qud : Gdc tdi Chiim tia khiic xa Chiim tia phan xa Nho Co gia tri dac biet / f, Lech xa phap tuyen (so vdi tia tdi) Rat sang Gan nhu sat mat phan each Rat md Rat mo Rat sang Co gia tri lon hon gia tri i^^. Khdng con i Rat sang 168

171 2. Goc gidi han phan xa toan phan - Khi chiim tia sang khiic xa a mat phan each hai moi trirdng, ta co : Suy ra : /? Sinz = «2Sin/" >H.. Sinr = sin? "2 Vi Hj > n-, nen : sin/- > sin/. Do do r > i. Chiim tia khiic xa lech xa phdp tuyen hon so voi chiim tia tdi. - Khi goc / tang thi goc / cung tang (vod / > /). Do do, khi / dat gid tri circ dai 90" thi / dat gid tri i^ goi Id gdc gidi han phdn xa todn phdn (Hinh 27.2), con goi Id gdc tdi hqn. Khi do ta co : "jsin/ j^ = «2sin90 Chum tia laze Tia phan xa (rat ma) Hinh 27.2 Suy ra: sini, *8h = n. (27.1) - V6i / > / [^, neu dp dung dinh luat khiic xa dnh sang, ta co : "I smr = sinr > 1 (v6 If) Dieu ndy phdn dnh thuc te la khong c6 tia khiic xa, toan bo tia sdng bi phdn xa o mat phan each. Do la hien tuong phdn.xq todn phdn. II - HIEN TUgfNG PHAN XA TOAN PHAN I.Djnh nghia Phdn xq todn phdn Id hien tugng phdn xq todn bd tia sdng tdi, xdy ra a mat phdn cdch giua hai mdi trudng trong sudt. Hmh 27.3 Ao tuang Luc trua ndng, mat ducmg nhua kho rao, nhung nhin ttr xa co ve nhu ucft nuoc (Hinh 27.3). Do la vi cac tia sang phan xa toan phdn tren lop khong khf sat mat duong va di vao mat. 169

172 Khi CO phan xa todn phdn thi khong con tia khiic xa. Ta goi la todn phdn de' phan biet vcfi phdn xa mpt phdn luon xdy ra di kem v6i sir khiic xa. 2. Dieu kien de co phan xa toan phan a) Anh sdng truyen td mpt mdi trudng tdi mdi trudng chiet quang kem han n2<«i b) Gdc tdi Idn han hoae bdng gdc gidi hqn : Hinh 27.4 Kim CUdng sang long lanh do phan xa toan phan Bdi tap vi du Co hai tia sang song song nhau, truy6n trong nude. Tia (1) gap mat thoang ciia nude. Tia (2) gap mot ban thuy tinh hai mat song song, dat sat mat nude (ITmh 27.5a). Neu tia (1) phan xa toan phan. thi tia (2) co 16 ra khong khf dupe khong? I -' n' Gidi Dat n va li lan lupt la chiei suai cua nuoc va thuy tinh. Vi tia (1) phan xa toan phdn nen : sin/ >. /) Xet tia (2) khuc xa vao thuy tinh voi goc khuc xa /. Ta co ; /(. /!sin/ = /j'sinr hay sinr = sin/ /;' Tia nay tdi mat phan each voi khong khf vdi goc tdi la r. n.. n \ sin/- = sin; > sin; gh ;; n ii n Suy ra : ; > i'^^^ (l'^^^: goc gidi han giiia thuy tinh va khong khq Tia (2) phan xa toan phan va khong khiic xa ra khong khf dupe (ffinh 27.5b).

173 Ill - LTNG DUNG COA HIEN TUONG PHAN XA TOAN PHAN : CAP QUANG 1. Cau tao Cap quang la bo soi quang. M6i soi quang Id mot day trong suot co tfnh ddn sdng nho phdn xa toan phdn (Hinh 27.6). Soi quang gom hai phdn chfnh (Hinh 27.7) : - Phdn 15i trong suot bdng thuy tinh sieu saeh co chiet sudt Idn (n^). - Phan v6 boc ciing trong suot, bdng thuy tinh co chiet suat nj nhd han phdn loi. Phdn xa todn phdn xdy ra a mat phan cdch giira loi vd v6 lam cho dnh sang truyen di duoc theo soi quang. Ngoai ciing la mot so ldp v6 boc bdng nhua deo de tao cho cap do hin va do dai co hoc. 125 urn fmh 27.6 Dudng truyen cua tia sang trong sdi quang 50 jm (loi) Hinh 27.7 Cau tao ciia sai quang 2. Co'in Himri Tir nhirng nam 80 ciia the ki XX, cap quang da duoc ling dung vao viec truyen thong tin. Cdp quang co nhieu uu diem so v6i cdp bdng dong : - Dung luong tin hieu Idn. - Nho va nhe, di van chuyen, de udn. - Khong bi nhliu bdi cdc btrc xa dien ttr ben ngodi, bao mat tdt. - Khdng cd riii ro chdy (vi khdng cd ddng dien). Cap quang cdn duoc diing de ndi soi trong Y hoc (Hinh 27.8 vd 27.9). Loai cap nay gdm cdc soi quang rdt nhd. Mot cdp quang thudng diing cd the gdm hang tram soi quang. Hinh 2.-^.8 Cap quang dung trong phep noi soi Hinh 27.9 Thie't bi noi sol 171

174 i' Phan xa toan phan la hien tuong phan xa toan bo tia sang tdi, xiiy ra d mat phan each giufa hai moi trucing trong suot. '^ Dieu kien de CO phan xa toan phan : '^ "' (sin/ = "^) Cap quang la day dan sang ufng dung phan xa toan phan de truyen tin hieu trong thong tin va de noi soi trong Y hpc. CAU HOI VA BAI TAP 1. The nao la phan xa toan phan? Neu dieu kien deco phan xa toan phan. 2. So sanh phan xa toan phan vdi phan xa thong thudng. 3. Cap quang la gi? Hay cho biet cau tao ciia cap quang. Neu mot vai irng dung. 4. Giai thfeh tai sao kim cuong (Hinh 27,4) va pha le sang long lanh, Ngudi ta tao ra nhieu mat cho vien kim cuong hay cac vat bang pha le de lam gi? Mpt chiim tia sang hep truyen tir moi trudng (1) chiet suat n^\6\ mat phang phan each vdi moi trudng (2) chiet suat 02- Cho biet n^ < 02 va / CO gia tri thay ddi, Trudng hgp nao sau day co hien tugng phan xa toan phan? A, Chum tia sang gan nhu sat mat phang phan each, B, Goc tdi / thoa man dieu kien sin/ >. "2 C, Goc tdi /thoa man dieu kien sin/ < "1 D, Khong trudng hgp nao da neu, 6. Mpt chiim tia sang s hep Si truyen trong mat phang tie't dien vuong goc cua mpt khdi trong sudt nhu Hinh 27,10, Tia sang phan xa toan phan d mat AC. Hmh Trong dieu kien do, chiet suat n ciia khdi trong sudt co gia trj nhu the nao? A, n > V2, B, n < V2, C. 1 < n < >/2, D. Khong xac dinh duac. 172

175 7. Co ba moi truong trong sudt. Vdi cung goc tdi: 9. Mpt soi quang hinh tru, loi co chiet suat - Neu tia sang truyen tir (1) vao (2) thi goc r7, = 1,50. Phdn vd bpc co chiet suat khiic xa la 30. ^2 = 1,41 = \/2. Chum tia toi hoi tu d mat trude - Neu tia sang truyen tii (1) vao (3) thi goc khiic xa la 45. Goc gidi han phan xa toan phari 6 mat phan cdch (2) va (3)CO gia tri nhu the nao (tinh tron sd)? A. 30. C. 45. B. 42. D. Khong tinh dupe. CLia soi vdi goc 2a nhu Hinh Xac dinh a de cac tia sang ciia chiim truyen di dupe trong dng. \ / a/ y:-',^^'/^'"^/^'^^'/'^ Mpt khdi ban tru trong sudt co chiet suat Hmh n = 1,41 = 72, Mpt chum tia sang hep nam trong mpt mat phang ciia tiet dien vuong goc, chieu toi khdi ban tru nhu Hinh Xac dinh dudng di cua chum tia sang vdi cac gia trj sau day cua Hinh gdc a. a) a = 60 ; b) a = 45 ; c) a =

176 I KHUC XA ANN SANG Hien tuong Cdc ndi dung chfnh...,_ IJhg dung 1.Khuc xa anh sang " Cdng tilde : «,sini = /j,sinr ; Chiet sudt : 1 ", "l2 "l Hau het cac dung cu quang deu dp diing hien tuong khiic xa anh sang. 2. Phan xa toan phan : Toan bd dnh sang tdi phdn xa (khdng cdn khiic xa).» Dieu kien : Cdp quang (diing trong Cdng nghe thdng tin va Y hoc). gh Hj 174

177 CHL/ONG VII Mat Cac dung cu quang Mat nguoi ^^^ ''' Kinh hien vi Ngay nay cac dung cu quang diing trong khoa hpc va trong ddi sdng rat da dang. Cac dung cu nay deu ap dung cac hien tugng phan xa va khiic xa anh sang. Trong chuong nay ta se tim hieu mpt sd dung cu quang thuong diing :, Lang kinh. Thau kinh. Kinh lup. Kinh hien vi. Kinh thien van B^H ^' «f --asi^^p ^L^^^^_*JB ^^^-^H Kinh thien van 175

178 ~r~" J\j LANG KINH Lang kfnh la bp phan chinh ciia may quang pho, mot dung cu diing de phan tich anh sang. Hmh 28.1 M at ben Hmh 28.2 ABC la tiet dien thang cua lang kfnh Mat b n I - CAU TAO CUA LANG KINH Lang kinh Id mot khdi chdt trong sudt, ddng chdt (thuy tinh, nhua...), thudng cd dqng lang tru tam gidc (Hinh 28.1). Khi sir dung lang kfnh, chdm tia sang hep dugc chieu truyen qua lang kfnh trong mot mat phdng vudng gdc vdi canh ciia khdi lang tru. Do dd, lang kinh dugc bieu didn bdng tam gidc tiet dien thdng (Hinh 28.2). Cac phan tir ciia lang kfnh gdm : canh, ddy, hai mat ben. Ni phuong dien quang hoc, mot lang kfnh dugc dac tnmg bdi : Gdc chiet quang A ; Chiet sudt n. Ta se khdo sdt lang kfnh dat trong khdng khf. II - DLTCfNG TRUYEN CUA TIA SANG QUA LANG KINH 1. Tac dung tan sac anh sang trang Hinh 28.3 Lang kinh tan sac anh sang 176 Tim d ldp 9, ta da biet, anh sang trdng (dnh sdng mat trdi) gdm nhieu anh sang mau vd lang kfnh cd tde dung phan tfch chiim sang trdng truyen qua nd thdnh nhiiu chiim sang mau khac nhau (Hinh 28.3). Dd la su tdn sac dnh sdng bdi lang kfnh do Niu-ton khdm pha ra nam 1669.

179 Dudi day, ta chi xet su truydn ciia mdt chiim tia sang hep don sdc (cd mot mdu nhdt dinh) qua mot lang kfnh. 2. OUcrng truyen cua tia sang qua lang kfnh Chieu den mat ben cua lang kfnh mot chum tia sang hep don sdc SI nhu d Hinh Tai / : tia khuc xa lech gdn phdp tuyen, nghla Id lech v6 phfa day lang kfnh. Kl Tai / : tia khiic xa lech xa phdp tuyen, tiic la Wl Tai sao khi anh sang truyen cung lech vi ddy lang kfnh. tir khong khf vao lang kfnh, luon vay, khi cd tia Id ra khdi lang kfnh thi tia Id bao c6 su khuc xa va tia khuc xa lech gid cung lech ve ddy lang kfnh so vdi tia tdi. S^" P^aP *uyen hon so vdi tia tdi? Gdc tao bdi tia Id vd tia tdi goi la gdc lech D cua tia sdng khi truydn qua lang kfnh. Hinh 28.4 III - CAC CONG THlJC LANG KINH Xet dudng truydn eua tia sdng qua lang kfnh nhu d Hinh Ap dung dinh luat khiic xa dnh sdng va mot sd *^'" ''"' dinh If hinh hoc ve gdc, ta thid't lap duoc cdc cdng Ne'u cac goc /, va A nho (< 10") thi thli:e lang kfnh sau day : cac cong thiic nay c6 the viei : /] = ni] ; ij = ni'~, sin/j - nsinrj ; A = TJ + TJ A = /, +,2 sini2 = nsinr2,d = iy + i^-a ^^^-' ^ D = (n-\)a E^ Bdi tap vi du ^ Hay thiet lap cac cong thirc lang kfnh. Mot lang kfnh thuy tinh c6 chiei suai // = 1.41 = v2. Tiei dien thdng cua lang kinh la tam giac deu ABC. Chieu mot tia sang nim trong mat phang ciia tiei dien thang. tai AB vai goc loi /, = 45". Xac dinh duang truy6n ciia tia sang. 12-VATLI 11.(C)-A 177

180 Gidi - Tai / (luon co tia khiic xa), ta co Hmh 28.5 Tai / : sin/, = nsinr. 1 sin 45 sin/'i = n r, = 30" = = 30 Ap dung tinh thuan nghich ciia su truydn anh sang, ta suy ra O y CO tia khiic xa voi goc khiic xa la : /2 = 45. I IV - CONG DUNG CUA LANG KINH Lang kfnh cd nhieu cdng dung trong khoa hpc va kl thuat. Cd the kd' : Hinh 28.6 May quang pho Giii chii : Ngay nay, phln lan may quang pho diing cdcfi til thay vi diing lang kinh. Hmh May quang pho Lang kfnh la bo phan chfnh cua may quang pho (Hinh 28.6). May ndy phan tfch anh sang tii ngudn phat ra thdnh cac thanh phdn don sdc, nhd dd xac dinh dupe cdu tao cua ngudn sdng. May quang phd cd the gdm mdt hoae hai lang kfnh. 2. Lang kinh phan xa toan phan Lang kfnh phan xa toan phan la lang kfnh thuy tinh cd tiet didn thang la mdt tam gidc vudng can (Hinh 28.7). Lang kfnh phan xa toan phan dupe sir dung de' tao anh thuan ehidu (dng nhdm, may anh...). r«] " Giai thich su phan xa toan phan d hai mat ben cua ISng kfnh d Hinh 28, VATL1I1(C)-ST-B

181 Mpt lang kinh ditcrc dac trung bdi goc chiet quang A va chiet suait n. Tia 16 ra khoi lang kinh luon lech ve day lang kinh so vdi tia tdi. Cong thijfc lang kinh : sin/., = nsinr, sin#2 = nsinrj A = r,+r2 D = 1.^+12-A Lang kinh la bo phan chinh cua may quang pho. CAU HOI VA BAI TAP 1. Lang kinh Id gi? Neu cau tao va cac dac trung quang hpc ciia lang kinh. 2. Trinh bay tac dung ciia lang kinh doi vdi su truyen anh sang qua no. Xet hai trudng hop : - Anh sang don sdc ; - Anh s^ng trang. 3. Neu cdc cong dung ciia lang kinh. 4. Co ba trudng hop truyen tia sang qua lang kinh nhu Hinh Hinh 28.8 d (cac) trudng hpp nao sau day lang kinh khong lam lech tia 16 ve phia day? A. Trudng hpp T). B. Hai trudng hpp 2 va f). C. Ba trudng hpp, (?) va (D. D. Khong trudng hpp nao. Cho tia sang truyen tdi lang kinh nhu Hinh Tia 16 truyen di sat mat BC. G6c lech tao bdi lang kinh CO gia tri ndo sau day? A. 0. B. 22,5. C. 45. D. 90. Tiep theo bai tap 5. Hmh 28.9 Chiet suat n ciia lang kinh c6 gia tri nao sau day? (Tinh trdn voi mpt chii so thap phan). A. 1,4. B. 1,5. C. 1,7. D. KhacA, B, C. Lang kinh thuy tinh c6 tiet dien thdng la tam giac can ABC dinh A. Mot tia sang don sdc dupe chieu vuong g6c toi mat ben AB. Sau hai lan phdn xa toan phan tren hai mat AC va AB, tia sang 16 ra khoi ddy BC theo phuong vuong goc vdi BC. a) Ve duong truyen ciia tia sang va linh goc chiet quang A. b) Tim dieu kien ma chiet suat n ciia lang kinh phai thoa man. 179

182 EfiTi CO biet? CAU VONC Truac va sau can mua, hoae ben canh thac nuoc, khong khf chiia rat nhieu nhung giot nuac nho hinh cau. Anh sang til Mat Trai khiic xa vao ben trong mdi gipt nuac, phan xa d mat cau phan each nuac vai khong khf roi khuc xa tra ra (Hinh 28.10). Qua hai lan khuc xa vao va ra khoi giot nuac, cac chiim anh sang mau bi tach roi nhau. Diing 6 vi trf thi'ch hap, mat ta nhan dugc cac chiim sang mau nay theo mot hinh vong cung. Do la cau vdng (Hinh 28.11). Do duoc tao thanh nhu trinh bay 6 tren ma cdu vdng luon xuat hien 6 phia nguge vai Mat Trai va thanh vong cung, CO huang nhin ti; mdt tao gdc 41 -H 42 so vai phuang anh sang tai ciia Mat Troi. Anh sang mat tr6i Hinh Su tao thanh cau vong wiit!.. - Hmh Cau vong 180

183 29 THAU KINH MONG Thau kinh la bg phan ca ban ciia hau het cac dung cu quang quan trgng : may anh, kfnh hien vi, kfnh thien vsn,... De ca dugc cac tfnh nang tdi uu, nguai ta thuang ghep nhieu thau kfnh thanh he thau kfnh. Trong bai hgc nay, ta se tim hieu ve thau kfnh mong, bo sung cho nhung di^u da hoc 6 lop 9. I - THAU KINH. PHAN LOAI THAU KINH Thdu kinh la mdt khdi chdt trong sudt (thuy tinh, nhua...) gidi hqn bdi hai mat cong hodc bdi mot mat cong vd mot mat phdng (Hinh 29.1). (!) phd thdng, ta chi xet thdu kfnh mdng mat cdu (mdt trong hai mat cd th^ la mat phang). Theo hinh dang, thdu kfnh gdm hai loai : Thdu kfnh loi (cdn dupe gpi la thau kinh ria mdng);. Thdu kfnh Idm (cdn dupe gpi la thdu kfnh ria ddy). HI Trong khdng khf: - Thdu kfnh loi tao ra chiim tia Id hdi tu khi chdm tia tdi la chdm song song (Hinh 29.2a). - Thau kfnh 1dm tao ra chum tia Id phan ki khi chiim tia tdi la chiim song song (Hinh 29.2b). Do dd, trong khdng khf: - Thdu kfnh Idi la thdu kinh hdi tu. - Thdu kfnh 1dm la thdu kinh phdn ki. ^ ^ (D _ a) Hinh bo doc thau kfnh loi V7 ^ b) Hinh bd doc thau kfnh 16m Hmh 29.1 ni Hay gpi ten phan biet ba loai thau kfnh loi va ba loai thau kfnh lomd Hinh Hinh

184 II - KHAO SAT THAU K(NH H6I TU 1. Quang tam. Tieu diem. Tieu dien Hmh 29.3 Thau kfnh (mong) hoi tu Mpt true --, phu a) Quang tdm Thau kfnh mdng ed be day chfnh giu'a rat nhd so vdi ban kfnh mat cdu. Ddi vdi thau kfnh mdng, thue nghiem va If thuyet eho thay ed mdt diem O ciia thau kfnh ma mpi tia sang tdi O deu truyen thing qua thau kfnh. Cd the coi O la didm chfnh giira thau kfnh. O gpi la quang tdm cua thau kfnh (Hinh 29.3). - Dudng thang di qua quang tam O va vudng gdc vdi mat thau kfnh la true chinh ciia thau kfnh. - Cac dudng thdng khac qua quang tam O la true phu. Mgi tia tdi qua quang tdm cua thdu kinh deu truyen thdng. True chfnh Hinh 29.4 Tieu diem anh chinh ccia thau l<inh hoi tu llp Coi chum tia song song nhu xuat phat hay hoi tu d mpt diem rat xa (vd cue), hay neu mdi quan he gida diem nay vdi : - tieu diem anh ; - tieu diem vat cua thau kfnh hdi tu. b) Tieu diem. Tieu dien - Chieu den thdu kfnh hdi tu mdt chum tia tdi song song. Chiim tia Id cdt nhau (hdi tu) tai mdt diem trdn true tuong ting vdi chum tia tdi. Diem nay la tieu diem dnh cua thau kinh. Trdn mdi true ed mdt tidu diem dnh : + Tieu diem dnh chinh dupc kf hieu F' (ITmh 29.4). + Tieu diem dnh phu dupc kf hieu F^ (n = 1,2, 3...). Cdc tieu diem anh cua thau kfnh hdi tu deu hiing dupc trdn man. Dd la tieu diem dnh that. - Trdn mdi true ciia thau kfnh hdi tu edn cd mdt diem ma ehiim tia tdi xuat phdt tijr dd se eho chiim tia Id song song. Dd la tieu diem vdt eua thdu kfnh. fm 182

185 + Tieu diem vdt chinh dupe kf hieu F. + Tieu diem vdt phu duoe kf hieu F^{n = \,2, 3,...) (Hinh 29.5). Tidu diem dnh va tidu diem vat trdn mdt true ndm ddi xdng vdi nhau qua quang tam. Vi tri eiia chiing tuy thude chidu truyen anh sang. - Tap hpp tat ca cac tieu diem tao thanh tieu dien. Mdi thdu kfnh cd hai tidu dien : tieu dien dnh vd tieu dien vdt. Cd the coi tidu dien la mat phdng vudng gdc vdi true chfnh va qua tidu diem ehfnh (Hinh 29.6). True phu Hinh 29.5 Tieu dism vat phu Chieu truyen 6nh sang 2. Tieu cu. Dotu De thid't lap cae edng thire vd thau kfnh, ngudi ta dat ra hai dai lupng quang hpc la tieu eu va do tu. Tieu cu ciia thdu kfnh dupc dinh nghia nhu sau : O Hinh 29 6 Hai tieu dien that (vat va anh) cue thau idnh hoi tu Ta quy udc/> 0 ddi vdi thdu kfnh hdi tu, iing vdi tidu diem anh F' that (sau thau kfnh). Thau kfnh ed kha nang hdi tu chiim tia sdng edng manh khi/eang nhd. Do dd, ngudi ta dinh nghia dp tu cua thdu kfnh nhu sau : ' D = (29.1) trong dd :/ tfnh bdng met (m); D tfnh bdng didp (dp). Mpt true phu ill - KHAO SAT THAU KINH PHAN Kl Quang tam ciia thdu kfnh phan ki cd cdng tfnh chat nhu quang tam ciia thdu kfnh hdi tu (Hinh 29.7). Hmh 29.7 ThSu l<inh (mdng) phan ki 183

186 f, _, ' *-P_ >= fc, m Cdc tidu diem eung nhu tidu didn (anh vd vat) eua thau kfnh phan ki eung dupc xac dinh tucmg tu nhu vdi thau kfnh hdi tu (Hinh 29.8 va 29.9). Diem khac biet la chung ddu do, dupc tao bdi dudng keo ddi cua cdc tia sdng. f^ Hinh 29.8 Tieu dism anh chinh cua thau kinh phan ki Ve dudng truyen cua chum tia sang minh hoa tinh chat ciia tieu diem vat cua thau kfnh phan kl. Chieu truyen ^nh s^ng V A Hmh 29.9 Hai tieu dien ao (anh va vat) cue thau kinh phan ki Cac edng thiic dinh nghla tidu cu vd dp tu van dp dung dupc ddi vdi thau kfnh phan ki. Tidu cu vd dp tu ciia thau kfnh phan ki cd gid tri am (ling vdi tidu diem anh F' do). IV - SI/ TAO ANH Bdi THAU KINH ^' nh Anh ao tao bdi gudng phang (chiim tia Id phan ki) Minh Anh that tao bdi thau kinh hoi tu (chiim tia Id hoi tu).s' 1. Khai niem anii va vat trong Quang hoc O ldp 7 va ldp 9, chiing ta da quan sat va dung dnh cua vat tao bdi guong phdng, guong cau, thdu kfnh. Chung ta da nhan thdy : - Anh do chi cd thi quan sat bdng mdt dat d vi tri thu nhan dupc chiim tia phdn xa hoae khiic xa (Hinh 29.10). - Anh that cd the hiing dupc trdn man anh (Hinh 29.11). a) De tdng quat hod khdi niem anh, ta quy udc gpi chum tia sang truydn ra khdi bd mat sau ciing ciia he quang hpc la chiim tia Id. 184

187 Cd the dinh nghla tdng quat nhu sau ve dnh trong Quang hpc : -Anh diem Id diem ddng qui cua chiim tia Id hay dudng keo ddi ciia chung. - Mot dnh diem Id : + that neu chum tia Id la chum hdi tu ; + do neu ehiim tia Id Id chiim phdn ki. b) Tuong tu, ta ciing cd the' tdng quat hod khai niem vat. Thdng thudng, vat phdt ra chcim tia tdi. Dd la vat that. Mdt each tong quat : - Vdt diem Id diem ddng qui cua chum tia tdi hay dudng keo ddi ciia chung. - Mot vdt diem Id : + that neu chum tia tdi la chiim phdn ki; + do neu chum tia tdi Id chum hdi tu. Ta khdng xet vat do trong chuong tiinh hpc. S' A F A O ~\. ^'^^'^"^^ >' \s.^ Hmh Anh ao tao bdi thiu kinh hdi tu 2. Cach dung anh tao bdi thau kinh a) Thuat ngii dung dnh (ve anh) ed nghla la ve dudng truydn cua mdt chum tia sdng bieu didn su tao anh cua mdt vat diem (didm B a Hinh 29.12). BE Ta thudng ve cdc tia tdi sau day : - Tia tdi qua quang tam O ciia thdu kfnh. - Tia tdi song song vdi true chfnh ciia thdu kfnh. - Tia tdi qua tieu diem vat chfnh F (hay cd dudng keo dai qua F). HI Khi tao anh ^o, th^'u kfnh hoi tu cho chum tia Id phan kl. Ket qua nay c6 mau thuan vdi tfnh chat cua thau kfnh khong? Giai thich. F; Trgcphy b) Trong trudng hpp phai ve mdt tia bdt ki thi ta xac dinh true phu song song vdi tia tdi. Tia Id tuong iing (hay dudng keo dai eua nd) se qua tidu diem anh phu trdn true phu dd (Hinh 29.13). 185

188 8..^^^-.^.^^ A I Hmh A/A F O \F' A "-- ^\ 1 r B' Di cd anh rd (ddng dang vdi vat), vat phai cd dang phdng, nhd, dat vudng gdc vdi true chfnh vd dupe bidu didn tupng tnmg bdi mdt mui tdn AB liin net (vat that). Trong di^u kien dd, dnh A'B' cua vat cung vudng gdc vdi true chfnh. Anh dupc bieu didn bdng miii tdn lien net neu la anh that va miii ten diit net neu la anh do (Hinh va 29.15). 3. Cac trudng hop anh tao bcri thau kinh Anh ciia mdt vat tao bdi mdi loai thdu kfnh cd nhiing dac diem xac dinh vi tfnh chat (that, do), chieu va dp Idn. Bdng each thay doi vi tri ciia vat, ta cd the dung anh tuong iing va nhan ra cac dac diem nay. BANG T6M TAT (chi xet vat that) \ Thau \ kinh H6itu(f>0) Phanki(f<0) \ I F O F' r O F Anh (Oi=or = 2f) Tinh chat (that, do) t Anh That: vat ngoai OF Ac : vat trong OF Anh luon luon ao : Do Idn i (so vdi vat) Anh ao > vat [ > vat: vat trong FI Anh that: = vat; vat o / (^nh 6 /'; [ < vat: vat ngoai FI i Anh < vat Chieu (so vdi vat) I Vat va anh cung chieu <-» trdi tfnh chat cung tinh chat <^ trai chieu Anh cung chieu so vol vat 186

189 V - CAC CONG THCrc VE THAU KINH Cdc cdng thiic anh dupc thid't lap dd' xde dinh vi tri, tfnh chdt (that, do), chidu va dd Idn ciia dnh tao bdi thau kfnh. Xet hai trudng hpp cua dnh nhu ve d cac hinh vd a) De thid't lap edc cdng thiic tdng quat dp dung cho mpi trudng hpp, ngudi ta dat cdc gid tri dai sd cho khodng each nhu sau : 0A=dv6i quy udc vat that :rf>0 vat ao : </ < 0 (khdng xet) OA' =rf'vdi quy udc anh th$t: rf' > 0 anh ao:d' <0 b) Ngodi ra, chieu vd dp Idn ciia dnh dupc xde dinh bdi ti so : JB = k k dupe gpi la so phdng dqi dnh. - Ne'u k > 0 : v&t va anh ciing chieu. - Ne'u ^ < 0 : vat va anh ngupc chieu. Lap cdc ti sd theo tfnh ddng dang ciia cdc tam gidc (OAB va OA'B') cung nhu cdc tam gidc {F'ON va FAB), ddng thdi xem xet tat cd cdc trudng hpp ciia anh, ta ed hai kdt qua : 1. Cdng thuc xac dinh vj tri anh m :.-Ai>.'''" d d' f (29.2) ^E Dung cdng thiic xac djnh v trf anh, hay chdng to rang, ne'u giijr thau kfnh cd dinh va ddi vat doc theo true chfnh thi dnh va vat ludn di chuyen ciing chieu. Bdi tap vi du vat va man dat each nhau doan a. X6 dich mdt tha'u kinh hoi tu giua vat va man de hiing anh cua vat hien trfin man. Khoang each a phai thoa man di6u kien nao? Gidi Dat: d + d' = a TaCO the viet : a = d + d'> iddd'. Suy ra : ^d + d' >2 _dd_ d + d' Dodo: -Jd + d' > 2^ vay : a > 4/ Khoang each giiia vat va man phai 16n hon hay bang b6'n lan tieu cu cua thsiu kfnh. 187

190 2. Cong thuc xac dinh so phong dai anh d' (29.3) Hinh Thau kinh diing lam vat kinh ccia may ghi hinh (camera) VI - CONG DUNG CUA THAU KINH Thdu kfnh cd nhieu cdng dung hiju feh trong ddi sdng va trong khoa hpc. Tha'u kfnh dupc diing lam : - Kfnh khde phuc tat ciia mdt (can, vidn, lao); - Kinh liip ; - May anh, may ghi hinh (camera) (Hinh 29.16); - Kfnh hiin vi; - Kfnh thidn van, d'ng nhdm ; - Den chidu ; - Mdy quang phd. Vdi vat lieu lam thdu kfnh ngay cang hoan thien, vdi cdng nghe ehd'tao tinh vi, ngudi ta da chd'tao dupc cae dung cu quang cho dnh cd chdt lupng rdt cao. Moi tia sang qua quang tam ciia thau kinh deu truyen thang. Tia tdi song song vdi true cua thaiu kinh se cho tia 16 truyen qua (hay co dudng keo dai cua tia 16 qua) tieu diem anh tren true d6. Tia tdi (hay dudng keo dai cua n6) qua tieu diem vat tren true se cho tia 16 song song vdi true do. Hai tieu diem vat va anh nam doi xdng vdi nhau qua quang tam. Moi thau kinh cd hai tieu dien anh va vat la hai mat phang vuong gdc vdi true chinh va di qua cac tieu diem chinh. f-thaiu kinh hoi tu<=>f> 0. Tieu eu: f =0F' \ -Thau kinh phan k 06 tu : - ; Cong thdc ve thaiu kinh : - VI tn anh :. +. -, d d t d' - So ph6ng dai anh ^ = ~ ^ 188

191 CAU HOI VA BAI TAP 1. Thau kinh la gl? Ke cac loai thau kinh. Tiep theo bai tap 5. Cho biet doan ddi vat la 12 cm. 2, Neu tinh chat quang hoc ciia quang tam, tieu diem anh, tieu diem vat. Minh hoa bang dudng truyen ciia tia sang cho m6i trudng hpp. Tieu cy ciia thau kinh la bao nhieu? A.-8 cm. B. 18 cm. C cm. D. Mpt gia trj khac A, B, C. 3. Tieu cu, do tu cua thau kinh la gl? Don vi ciia tieu cu va do tu? 4. Chon phat bieu dung vdi vat that dat trude thau kinh. A. Thau kinh hoi tu ludn tao chiim tia Id hoi tu. B. Thau kinh phan ki luon tao chiim tia Id phan ki. C. Anh ciia vat tao bdi thau kinh khong the bang vat. D. Ca ba phat bleu A, B, C deu sai. Xet thau kinh hoi tu. Lay tren true chinh cdc diem / va /' sao cho 0/ = 20F, 0/' = 20F' (Hinh 29.17). Ve anh cua vat AB va nhan xet ve dac diem ciia anh trong m6i trudng hpp sau : - Vat that d ngoai doan 01. -Vat that taf/. - Vat that trong doan FI. - Vat that trong doan OF. F' /' Hinh Mpt vat sang dat trude mpt thau kinh, tren true chinh. Anh cua vat tao bdi thau kinh bang ba lan vat. Ddi vat lai gan thau kinh mpt doan. Anh ciia vat 6 vi tri mdi van bang ba lan vat. Co the ket luan gl ve loai thau kinh? A. Thau kinh la hoi tu. B. Thau kinh la phan kl. C. Hai loai thau kinh deu phu hpp. D. Khdng the ket luan dupc, vl gia thiet hai anh bang nhau la v6 li. 8. Ngudi ta dung mpt thau kinh hoi tu co dp tu 1 dp de thu anh ciia Mat Trang. a) Ve anh. b) Tinh dudng kinh ciia anh. Cho goc trdng Mat Trang la 33'. Lay 1' «3.10"'* rad. 9. Vat sang AB dupc dat song song voi man va each man mpt khoang co dinh a. Mpt thau kinh hoi tuco true chinh qua diem A va vuong goc vdi man, dupc di chuyen giua vat va man. 189

192 a) Ngudi ta nhan thay co mdt vi tri ciia thau kinh cho anh ro net ciia vat tren man, anh Idn hon vat. Hay chiing to rang, con mpt vi tri thii hai ciia thau kinh d trong khoang giua vat va man cung cho anh ro net ciia vat tren man. b) Dat / la khoang each giua hai vj tri tren ciia thau kinh. Hay lap cdng thiic ciia tieu cu thau kinh f theo a va /. Suy ra mpt phuong phap do tieu cu ciia thau kinh hoi tu. 12. Trong Hinh 29.18, xy la true chinh ciia thau kinh L, A la vat diem that, A la anh ciia A tao bdi thau kinh. Vdi moi trudng hpp, hay xac djnh ; a) A la anh that hay do. b) Loai thau kinh. c) Cac tieu diem chinh (bang phep ve). A. 10. Mpt thau kinh hoi tu cd tieu cu f = 20 cm. Vat sang AB dupc dat trudc thau kinh va cd anh AB. Tim vj tri ciia vat, cho biet khoang each vat - anh la: a) 125 cm. b)45cm. 11. Mpt thau kinh phan ki co dp tu -5 dp. a) Tinh tieu cy cua kinh. b) Neu vat dat each kinh 30 cm thi anh hien ra 6 dau va co so phdng dai bao nhieu? Hmh

193 GIAI BAI TOAN VE HE THAU KINH Cac dung cu quang d^u co cau tao phuc tap va gom nhieu bo phan nhu thau kinh, guong,... ghep voi nhau tao thanh mot he quang hpc. Noi chung, viec giai bai toan he quang hoc bao gdm hai buoc : - Phan tfch qua trinh tao anh va bieu thi bdng mot so do. - Ap dung cac cong thuc lien quan cho mdi khau cua so do de giai bai toan. Trorig bai nay, ta se xet cac vf du ve he hai thau kfnh. I - LAP sa DO TAO ANH 1. He hai thau kinh donq true ghep each nhau Xet he quang hpc ddng true gdm hai thdu kfnh L[ vd L2. Gid str vat that AB dupe dat trdn true cua he va d trudc Lj. N at AB cd anh A\B\ tao bdi Lj. Anh nay do ehiim tia Id ra khdi Lj tao ndn. Cae tia sdng truyen ddn Lj ed th^ coi la do A\B\ ma cd. Bdi vay A\B\ la vdt ddi vdi L2. - Ndu A[B[ a trudc L^, dd la vat that. - Ndu A\B\ a sau Lj, dd la vat do (khdng xet). Tha'u kinh Lj tao anh A^j ^ua vat A[B[. Anh A^2 tao bdi Lj la dnh sau ciing (Hinh 30.1). Toan bd qua trinh tao anh dupc tdm tdt bdi so dd : Hmh 30.1 He hai thau kinh hoi tu ddng true ghep each nhau ^^-^^ ^^ -^^^^^ 2. He hai thau kinh dong true ghep sat nhau Vdi he nay, phuong phdp diing thdu kinh tuang duang giup ta giai bai toan rat tien Ipi. 191

194 B A Ll L, Xet trudng hpp hai thdu kfnh cd cdc tieu cu/,,/2 dupc ghep sat nhau (vf du nhu trdn Hinh 30.2). Ta cd so dd tao dnh AB- L >A,B:- L, d.; d] d-. d\ -^ A,B' d, B\ Hmh 30.2 H hai thiu kinh hdi tu dsng tnic ghep sat nhau m ChCmg to rang, vdi he hai thau kfnh dong true ghep sat nhau ta ludn cd : a) Ap dung cdng thiie vd tha'u kfnh, ta dupe : ± _L-_L ^ ± ^ = -L d\ d[ f\ ^2 d'l fl Ta ludn cd tij - "" d^ ndn : = ^1 di A Suy ra : + = + d\ dj f\ fl ra = di dj fi (1) b) Tha'u kfnh tupng ducfng vdi hd ed tidu cu /, nghidm so dd tao anh : AB- Ta CO : h = d\ dj f L ^,;^;^5^^ (2) Tit (1) vd (2) suy ra : j = j + j hay D = D, + D, (30.1) 192 Day la cdng thiic tfnh dp tu eua he hai thau kfnh mdng ddng true ghep sat nhau. Dp tu eua he hai thdu kinh mdng ddng true ghep sdt nhau bdng tdng dqi sd ede dp tu cua tifng thdu kinh ghep thdnh he. Dac diem anh ciia vat AB tao bdi he hai thau kfnh ghep la dac die'm anh ciia vat AB tao bdi thdu kfnh tuong duong.

195 II-THl/C HIEN TINH TOAN Ndi dung khdo sat mdt he quang hpc rat da dang. Nhung nhin chung, ed hai ydu cdu chfnh : - Xde dinh cdc dac diem ciia dnh sau cdng. - Xac dinh cac dac diem cdu tao eiia he. Trong qua trinh thuc hien cdc tfnh todn, cd hai kdt qua can Itru y : 1. Quan he giufa hai vai tro anh va vat cua A\B\ Anh A\B\ cd cdc dac didm xac dinh bdi d[. Nhung khi nd ddng vai trd vat vdi Lj thi cdc dac diem ciia nd dupc xac dinh bdi Jj- Trong mpi trudng hpp, ta ludn cd : d2 = l-d[ hay d[ + d2 = I (30.2) (/ la khodng cdch giiia hai thdu kfnh). ^ 2. So phong dai anh sau cung Sd phdng dai nay dupc xde dinh bdi : AjB-y AB *^ Hay xet cac trudng hdp khac nhau va thiet lap he thurc : dj = / - d\ Xet trudng hop / = 0. Cd the vidt k = ^4=i-.^J- = k^k, AB ^ ' Ajfii Vay: #C ^ Kr'yn-t (30.3) III - CAC BAI TAP VI DU Bdi tap 1 Cho thau kinh hoi tu Lj co tieu cir/2 = 24 cm va vat AB dat tren true chinh each thau kinh mot doan khiong doi a = 44 cm. Thau kinh phan ki L, co tieu cu/, = -15 cm dugc dat giua vst AB va LT, each Lj khoang / sao cho hai true ehfnh triing nhau (Hinh 30.3). Hinh VATLI 11.(C)-A 193

196 Hinh 30.4 Xac dinh vi tri va so phong dai l< cua anh sau ciing A^S; trong trucmg hop / = 34 cm. Gidi Sa do tao anh : AB ~ >A\B:- d,\d, ' ' Ta CO 10 em : ^1 = - 6 cm L, > A.B\ dj = I - d\ = 40 cm => C/T = 60 cm Anh A'^B'-, that, each L, 60 em. Ta cung co : k = li.,l<^ Anh nguge ehi6u vat va bang Bdi tap 2 'A '' J V 9_ vat. 10 Mgt thau kinh mong phing - lom bing thuy tinh, co tieu cir/ = -20 cm. Thau kfnh duge dat sao cho true chinh thing dung, mat 16m hudng len tren. Mot diem sang 5 nim tren true ctiinh va each thaiu kfnh mgt doan d (Hinh 30.4). a) Anh S cua 5 tao bdi thau kfnh each thiu kfnh 12 em. Tfnh d. b) Giii 5 va thau kfnh cd dinh. D6 mgt chit long trong sudt vao mat lom. Bay gio anh S eua S la anh ao va each tha'u kfnh 20 em. Tfnh tieu eu/, eiia thau kfnh chat long phang - I6i. Gidi a) Tinh d S CO anh ao tao bdi thau kfnh phan ki : lij = -12 em. Dodo; Suy ra : d= 30 cm. b) Tieu cif /, d' I l l f\ d\ He gom thau kfnh chai long va thau kfnh thuy tinh ghep dong true, sat nhau. Thau kfnh tuong duong co tieu cir / Ta CO : Ddi voi thau kfnh tuong duong : d Vay : Suy ra ~7 1 ~7^ 30 cm 1 d' ~ 1 J ' ~ " cm VATLI 11.(C)-B

197 BAI TAP 1. Mpt hpc sinh bo tri thi nghiem theo so do Hinh Hinh 30.5 /-1 V A O, i = 70 cm Man Thau kinh phan kl L^ co tieu cu f, = -10 cm. Khoang cach tii anh S\ tao bdi L^ den man co gia tri nao? A. 60 cm. B. 80 cm. C. Mot gia tri khac A, B, D. Khong xac djnh dupc, vi khong co vat nen L, khong tao dupc anh. Tiep theo cdc gia thiet cho d bai tap 1. Dat giua L^ va H mot thau kinh hoi tu L^. Khi xe dich Lg, hoc sinh nay nhan thay chi co mot vi tri duy nhat ciia Lg tao dupc diem sang tai H. Tieu cu cua L^ la bao nhieu? A, 10 cm. B. 15 cm. C. 20 cm. D. Mot gia tn khac A, B, C. Hai thau kinh, mot hoi tu (f, = 20 cm), mot phan ki (fj = -10 cm),co Cling true chinh. Khoang each hai quang tam la / = 30 cm. Vat AB vuong goc vdi true chinh dupc dat ben trdi /.., va each L^ mot doan dy H a) Cho d, = 20 cm, hay xac dinh vi tri va tinh so phong dai anh cur.i cung cho bdi he hai thau kinh. Ve anh. b) Tinh d, de anh sau cung la anh do va bang hai lan vat., 4. Mot he gom hai thau kinh /.^ va L, dong true CO tieu diem anh chinh ciia L, triing vdi tieu diem vat chinh ciia Lj. Chieu mpt chum tia sang song song toi L, theo phuong bat ki. a) Chung minh chum tia 16 ra khoi L^ cung la chuni tia song song. b) Ve duong di cua chijm tia sang iing voi cac trudng hpp :. L^ va /.2 deu la thau kinh hoi tu. «L, la Ihau kinh hoi tu ; L^ la thau kinh phan ki.. L^ la thau kinh phan ki; Lj la thau kinh hoi tu. 5. Mpt thau kinh mong phdng - loi L, co tieu cu f, = 60 cm dupc ghep sat dong true voi mpt thau kinh mong phdng - loi khac L^ c6 tieu cu fj = 30 cm. Mat phdng cua hai thau kinh sat nhau. Thau kinh L^ co dudng kinh ria gap doi dudng kinh ria cua thau kinh L^. Mpt diem sang S ndm tren true chinh cua he, trudc L,. a) Chung to co hai anh ciia S dupc tao bdi he. b) Tim dieu kien ve vi tri ciia S de hai anh deu that va hai anh deu ao. 195

198 IVIAT Mit ia bp phan thu nhan anh sang giup nguai nhin thay mpi vat xung quanh. Mat la he quang hpc het sue phuc tap va tinh vi. Trong bai hpc nay, ta se tim hieu m^t nguai ve phuang dien quang hpc. I - CAU TAO QUANG HOC CUA MAT L6ng den vs con nguoi Hinh 31,1 Mk ngudi "*«S^ Mdt Id mot he gdm nhieu mdi trudng trong sud't tiep giap nhau bdng cdc mat edu. Chidt sudt eua ede mdi trudng ndy cd gid tri d trong khoang 1,336+ 1,437. Tir ngodi vdo trong, mdt cd edc bd phan sau (ffinh 31.2) : a) Mdng gidc (gidc mac): Ldp mang ciing trong sud't ed tac dung bdo ve cho cac phdn tir phfa trong vd lam khuc xa cdc tia sang truydn vdo mdt. b) Thuy dich : chdt Idng trong sud't cd chid't sudt xdp xi bdng chidt sudt cua nude. e) Long den : man chdn, d giira cd Id trdng dd didu chinh chdm sang di vdo trong mdt. Ld trdng nay goi la con nguoi. Con nguoi cd dudng kfnh thay doi tu dpng tuy theo eudng do sang. Con naudi Wang giac Thuy dich Ot^m mil Dich thuy tinh d) The thuy tinh : khdi chat dac trong sud't (gidng nhu thach) cd hinh dang thdu kinh hai mat Idi. Hint.IT 2 Cau tao ctja mat e) Dich thuy dnh : chat long gidng ehat keo loang, lap ddy nhan edu phia sau thd' thuy tinh. f) Mdng ludi (vdng mac) : ldp mdng tai dd tap trung ddu edc soi thdn kinh thi gidc. 196

199 6 mang ludi cd mdt chd rat nhd mdu vang la nd cam nhan dnh sang nhay nhat duoc goi Id diem vdng V. - Khi mdt nhin mot vat, dnh that cua vat dirgfc tao ra d mdng ludi. Nang lugng dnh sang thu nhan d day dugc chuyen thdnh tin hieu thdn kinh va truyen tdi nao, gay ra cam nhan hinh dnh. Do dd mdt nhin thdy vat. - 0 mang ludi cd mdt vi trf tai dd, cac sgi than kinh di vdo nhan cdu. Tai vi trf nay, mdng ludi khdng nhay cam vdi dnh sang. Dd la diem mil. Trong Quang hoe, mdt dugc bieu didn bdi so dd tirgng trung nhu ffinh 31.3 ggi la mdt thu ggn, trong dd he quang hge phdc tap cua mdt dugc coi tuong duong vdi mdt thdu kfnh hdi tu. Thau kfnh tuong duong nay duge ggi Id thdu kinh mdt. Tidu eu cua thdu kfnh mdt thudng dugc ggi tdt la tieu cu ciia mdt. Tdng qudt, mdt hoat ddng nhu mdt may anh, trong dd : Thdu kfnh mat ed vai trd nhu vat kfnh ;. Mdng ludi ed vai trd nhu phim. II - SU" OIEU TIET CUA MAT. DIEM Cl/C VIEN, DIEM Cl/C CAN Khoang each tit tha'u kfnh mdt den mang ludi (diem vang) OV cd gid tri nha't dinh d'. Neu tidu eu eua thdu kfnh mdt cung cd gid tri nhdt dinh/thi mdt chi nhin thdy vat d mdt vi trf nhat dinh. Tuy nhidn, ta cd the quan sat duge nhiing vat tir rat xa (ehdng han mdt ngdi sao) eho ddn nhijng vat rat gdn (ehdng han mdt trang sdch). 6 ldp 9, chung ta da biet didu nay dugc thuc hien bdi su didu tiet cua mdt. 1. Sir dieu tiet Didu tie't la hoat ddng eiia mdt lam thay ddi tidu cir ctia mdt de eho dnh ciia cdc vat d cdch mdt nhiing khoang khde nhau vdn dugc tao ra d mdng ludi. Hinh 31.3 Sd do mst thu gon Bdi tap vi du 1 Mot ngucri co mdt binh thudng (khong tat) nhin tha'y duac cac vat a rax xa ma khong phai dieu tie't. Khoang cue can ciia nguoi nay la OC^ = 25 cm. D6 tu ciia mat ngucri nay khi dieu tie't tdi da tang them bao nhieu? Gidi Ta CO cac phuong trinh tao anh : 1 1 I D, min (1) OC, OV /n, 1 1 D (2) OC OV fn Lay (2) trir(l), ta duoc D -D =AD = max mm g^. g^ Vi OC., -^ 00 nen = 0. OC. Vay : AD: 1 OC 0.25 :4dp. 197

200 Viec ndy dugc thuc hien nhd cdc co vdng cua mat. Khi bdp lai, eae co ndy Idm the thuy tinh phdng Idn, gidm ban kfnh cong, do dd tieu cu cua mdt giam.. Khi mdt d trang thai khdng dieu tiet, tidu cu ctia mdt Idn nhdt {f[^^j. Khi cdc CO mdt bdp tdi da, mdt d trang thdi dieu tiet tdi da va tieu cu cua mdt nhd nhat {f^^^). Bang 31.1 Tuoi Khoang cach OC^ tu mat toi diem cue can 7 cm 10 cm 14 cm 22 cm 40 cm 2. Diem cuc vien. Oiem cuc can Khi mdt khdng dieu tie't, diem tren true cua mdt md dnh dugc tao ra ngay tai mang ludi ggi la die'm cite visn C^, (hay vien diem) eua mdt. Dd ciing la diem xa nhdt ma mdt ed thd nhin rd. Ddi vdi mdt khdng cd tat, didm circ vidn d xa vd cung (vd cue). Khi mdt dieu tiet tdi da, didm trdn true ciia mdt ma dnh cdn dugc tao ra d ngay tai mang ludi ggi la diem cue can C^ (hay can diem) cua mdt. Dd cung la didm gan nha't ma mdt cdn nhin rd. Cang Idn tudi, diem cue can cang lui ra xa mdt (xem Bang 31.1). Khodng cdch giua did'in cue vidn va didm cue can ggi la khodng nhin rd cua mdt. Cac khoang each OC^ va D = OC^ til mdt tdi cac didin cue vidn va cue can ciing thudng dugc ggi tuong iing la khodng cifc vien. khodng cite can. 198 Ill - NANG SUAT PHAN LI CUA MAT Mudn eho mdt nhin tha'y mdt vat thi anh that eua vat tao bdi mdt phdi hien ra d mdng ludi, nghia la vat phdi cd vi trf d trong khoang nhin rd eiia mdt. Tuy nhien, trong nhidu trudng hgp cdn cd nhu cdu la quan sat dugc cdc chi tiet nhd eua vat, ehdng han dgc dugc chu ctia mdt trang saeh bdo hoae nhan ra ngudi quen trong mdt tdm dnh nhd chiip nhidu ngudi,...

201 Vide nhin thdy dugc mdt vat nhd AB chdng han, tuy thude vao kich thude dnh A'B eiia vat dd trdn mdng ludi. Kfch thude ndy phu thude gdc trdng vat (Hinh 31.4). Kl Dd mdt ed the phan biet duge hai diem AvaB thi goc trdng vat khdng the nhd hon mdt gid tri tdi thieu ggi la ndng sudt phdn li e cua mdt. Khi dd, dnh cua diem ddu va diem cudi cua vat dirge tao ra d hai te bdo thdn kinh thi giac ke can nhau. Nang sudt phan li thay ddi tuy theo timg ngudi, nhung gid tri trung binh Id : e= a V Hinh 31.4 Gdc trong vat m Gdc trdng mot vat la gi va phu thuoc vao cac yeu td nao? IV - CAC TAT CUA MAT VA CACH KHAC PHUC Ta chi xet cac tat phd bien nha't Id : mat can. mdt vien vd mdt lao. 1. Mat can va each khac phuc a) Mdt can cd do tu lon hon do tu ciia mdt binh thudng. Mdt chum tia sdng song song truydn den mdt can se eho chum tia Id hdi tu tai mdt diem d trude mdng ludi (ffinh 31.5). Hinh 31.5 Sa dd minh hoa dac diem quang hoc ciia mat can Cae he qua :, Khodng each OC^ huu han.. Diem C gdn mdt hon binh thudng. Tat can thi cd the do bdm sinh, nhung ciing cd thd do dgc sdch hay hge bdi d ehd khdng du do sang hoae dat saeh qud gdn mdt mdt thdi gian ddi. 199

202 Hmh 31.6 Sd do minh hoa each khic phiic tat can thi b) Tat can thi thudng dugc khde phuc bdng each deo kfnh phan ki cd do tu thfeh hgp dd cd the nhin rd vat d vd cue ma mdt khdng phai didu tie't (ffiinh31.6). U^ Ndu coi nhu kfnh deo sat mdt thi tidu eu cua kfnh duge xde dinh bdi : f=-oc^ PF Hay chdng to rang, he ghep (mat can + thau kinh phan kl) cd dd tu nho hon dd tu ccia mat can. 2. Mat vien va each khac phuc a) Mdt vidn cd do tu nhd hon do tu cua mdt binh thudng. Mdt chum tia sang song song truyen den mdt vidn se cho chum tia Id hdi tu tai mdt diem sau mang ludi (ffiinh 31.7). Cae he qua :, Mat vidn nhin vat d vd cue da phai dieu tie't. Hinh 31.7 So do minh hoa dac diem quang hoc cua mst vidn, Didm C^ xa mdt hon binh thudng. b) Ngudi vidn thi didu tiet mdt (giam tieu eu) ed the nhin thdy dugc eae vat d xa. Tat vidn thi thudng dugc khde phuc bdng each deo kfnh hdi tu dd cd the nhin rd eae vat d gdn mdt nhu mdt binh thudng. Tidu cu eiia thdu kfnh phdi ed gia tri thfeh hgp de dnh do eua diem gdn nha't ma ngudi vidn thi mudn quan sat duge tao ra tai didm cue cdn eua mdt. 3. Mat lao va each khac phuc a) Vdi hdu hd't mgi ngudi, ke tii tudi trung nien, kha nang dieu tiet gidm vi eo mdt ydu di va the thuy tinh trd nen eung hon. Hau qua la diem cue can C ddi xa mdt. Dd la tdt lao thi (mdt lao). Khdng ndn coi mdt lao la mat vidn. Mdt khdng tat, mdt can hay mdt vidn khi Idn tudi ddu cd them tat lao thi. b) De khde phuc tat lao thi, phdi deo kfnh hdi tu tuong tij nhu ngudi vidn thi. 200

203 Dac biet, ngudi cd mdt can khi Idn tudi thudng phdi:. deo kfnh phan ki de nhin xa.. deo kfnh hdi tu de nhin gdn. Ngudi ta thudng thire hien loai ''kinh hai trdng' ed phdn tren phan ki vd phdn dudi hdi tu. Bdi tap vi du 2 Mot nguai can thi lon tu6i ehi con nhin tha'y r5 eae vat trong khoang each mat 50 em ^ 67 em. Tinh dp tu ciia cac kinh phai deo d6 nguoi nay co th6 : - nhin xa vo ciing khong dieu tie't. - doc duoc saeh khi dat gin mdt nha't. each mat 25 cm. Coi kinh deo sat mdt. Gidi - De nhin xa phai eo (ITmh 31.8) : (~) Y '-'"" Cv! - ---^.^A ( 0^""^ ' A ~^ l^1l Hmh 31.8 /l = -O^Cy = -67 cm ==: --m D, = = -1,5 dp - De doc saeh dat gan mat nha't, each mat 25 cm phai deo kinh CO tieu cu/, xac dinh bdi : = => A = 50 cm = 0,50 m /. ^'- D,= 1 =2dp h V - HIEN TU'gfNG LU'U ANH CUA MAT Nam 1829, Pla-td (Plateau) - nha vat If ngudi Bi phdt hien ra la cam nhan do tde ddng ciia dnh sdng len cdc te' bdo mang ludi tiep tue tdn tai khoang - giay ddng hd sau khi chiim sdng tdt. Trong thdi gian giay nay ta vdn edn '"thdy" vat, mac du dnh eua vat khdng cdn duge tao ra d mdng ludi niia. Dd la hien tugng luu dnh ciia mdt. Nhd hien tugng ndy ma mdt nhin thdy ede anh tren man dnh chieu phim (ffiinh 31.9), trdn mdn hinh tivi (ffiinh 31.10),... ehuyen ddng. Hmh 31.9 Hinh

204 Cau tao cua mat gom : mang giac, thuy djch, long den va con nguori, the thuy tinh, dich thuy tinh, mang ludi. Dieu tiet la sir thay doi tieu cu cua mat de tao anh cua vat luon hien ra tai mang ludi. + Khong dieu tiet: f^^^ + Dieu tiet toi da : f- mm - Diem cuc vien la diem tren true ciia mat ma mat nhin ro khi khong dieu tiet. Mat khong tat thi C^ or vo cuc. - Oiem cuc can la diem tren true cua mjt ma mat nhin ro khi dieu tiet toi da. Nang suait phan li la goc trong nho nhat ma mat con phan biet ducrc hai diem. Cac tat cua mdt va each khac phuc : e = 1' (gia tri trung binh) Tat cua mat Dac diem Cach khac phuc Mat can ^max < O^. Deo kinh phan kl. f ^ = - OC^ (kinh sat mat) '4\ Mat vi^n f >0V max. Deo kinh hoi tu. Tieu cit CO gia trj sao cho mat deo kfnh nhin gan nhu mat khong tat Mat lao C, ddi xa mat Deo kinh hoi tu Tae dung cua kinh nhu vdi mat vien Hien tuong luu anh eua mat: Tae dong cua anh sang len mang ludi con ton tai khoang giay sau khi anh sang tat. 202

205 CAU HOI VA BAI TAP 1. Trinh bay cdu tao cua mat ve phuong dien quang hoc. 2. Tnnh bay cac hoat dpng va cac dac diem sau ciia mdt: - Dieu tiet; - Diem cue vi^n ; - Diem cue can ; - Khoang nhin ro. 3. Neu edc dac diem va each khac phuc doi voi: - Mdt can ; - Mat vi n ; - Mdt lao. Co phai nguoi Ion tuoi thi bi vien thi khong? Giai thich, 6. Mdt loai nao co diem cue viin C^ 6 vo cue? A. 1;. B.'!». C. 3. D. T va. 7. Mdt loai naoc6f^3j,> OV? A. 1;. B. (2). C. 3'. D. Khong loai nao. 8. Mdt loai nao phai deo kinh hoi tu? A, :3). B. (2). D. i: va '. 4. Nang suat phan li cua mdt la gi? 5. Trinh bay su luu anh cua mat va cac iing dung. 9. Mdt ciia mot ngudi co diem cue vien C^ each mdt 50 cm. a) Mdt ngudi nay bi tat gi? Cau tao thu gpn ciia mdt ve phuong dien quang hoc duoc bieu dien nhu so do Hinh : 0 : quang tam ciia mdt; y: diem vang tren mang luoi. b) Mudn nhin thay vat 6 vo cue khong dieu tiet. nguoi do phai deo kinh co do tu bao nhieu? (Kinh deo sat mat). c) Diem C(, each mdt 10 cm. Khi deo kinh, mdt nhin thay diem gan nhat cach mat bao nhieu '?' (Kinh deo sat mat). ^ Hmh Quy udc dat: Qj: Mdt binh thudng ve gia : Mat can ; Q>: Mdt vien. 10. Mpt mat binh thuong ve gia, khi dieu tiet toi da thi tang dp tu cua mat them 1 dp. a) Xac dinh diem cue can va cue vien. b) Tinh dp tu ciia thau kinh phdi deo (each mdt 2 cm) de mat nhin thay mpt vat cach mat 25 cm khong dieu tiet. Hay chon dap an diing cho cac bai tap tu so 6. den so

206 Em CO biet? THi NGHIEM DON GIAN VE SU LUU ANH CLJA MAT Co the thuc hien mot tro chai dan gian nhu sau de chung to hien tugng luu anh cua mdt. Dung but den ve len mot mat cua tam bia hinh mot cai long chim. Dung but mau ve len mat kia mpt con chim (Hinh ). Cho tam bia quay nhanh qua lai. Quan sat tam bia. Nhan xet va giai thich hien tugng. Hmh

207 3^ KiNHLUP Trong nhieu truong hgp, con nguai muon quan sat cac vat the, cac chi tiet nho han giai han ma nang sua't phan li cua mit cho phep. Vl du, nguai thg sua dong ho muon quan sat cac bp phan cua chiec dong hd deo tay ; chuyen vien phong thi' nghiem sinh hpc muon quan sat cac te bao, cac hong cau, cac vi trung,... Quang hpc da giup che tao cac dung cu dat dugc yeu cau do. I - TONG QUAT VE CAC DUNG CU QUANG BOTROfCHOMAT Cac dung eu quang ddu cd tde dung tao dnh vdi gdc trdng Idn hon gdc trdng vat nhidu Idn. Dai lugng dac trung cho tac dung nay la sd bdi gidc, dugc dinh nghia nhu sau : G = a UQ tana tan UQ (gdc nhd) trong dd : a la gdc trdng dnh qua kfnh ; a^ Id gdc trdng vat cd gid tri Idn nha't duge xac dinh trong tiing trudng hgp. Bfl Ngudi ta phan cac dung cu quang thdnh hai nhdm : - Cac dung cu quan sat vat nhd gdm kfnh lup, kfnh hidn vi,... - Cdc dung cu quan sat vat d xa gdm kfnh thidn van, dng nhdm,... Hinh 32.1 Kinh liip thdng thudng Kl Sd bdi giac phu thuoc nhdng yeu td nao? II - CONG DUNG VA CAU TAO CUA KINH LUP Kfnh lup la dung cu quang bd trg cho mdt de quan sat cac vat nhd (ffiinh 32.1, 32.2, 32.3 vd 32.4). Hmh 32.2 Kinh liip bo till 205

208 Kfnh lup dugc ca'u tao bdi mdt thdu kinh hdi tu (hay mdt he ghep tuong duong vdi mdt thdu kfnh hdi tu) cd tidu cir nhd (vai xentimet). Hinh 32.3 Kinh liip dung trong vi phsu thuat Hinh 32.4 Kinh liip de ban Hinh 32.5 Mat ngam chirng kinh liip d vd cdc Hinh 32.6 Ill - SU" TAO ANH Bdi KINH LUP Khi quan sat mdt vat nhd qua kfnh lup, mdt nhin anh do cua vat dd qua kfnh. Mudn the, phdi dat vat nhd trong khodng tir quang tam O cua kfnh ddn tidu didm vat chinh F. Ngoai ra, dd mdt cd the nhin thay anh thi dnh phai cd vi trf ndm d trong khoang nhin rd ciia mdt. De thoa man hai didu kien trdn, khi ddng kfnh lup ta phai didu chinh (xd dich kfnh trudc vat hoae nguge lai). Ddng tde quan sat dnh d mdt vi trf xac dinh ggi la ngam chdng a vi trf dd. Khi cdn quan sdt trong mdt khodng thdi gian ddi, ta ndn thuc hidn each ngdm chirng d diem cue vidn de mdt khdng bi mdi. IV - SO Bpl GlAC CUA KINH LUP Xet trudng hgp ngdm chiing d vd cue _ «^ tang ^-^ ~ "o ~ tana 0 Ta cd : tana = AS T Ngodi ra, gdc trdng vat cd gia tri Idn nha't a^ iing vdi vat dat tai didm cue can C^ (ffiinh 32.6). Dodo : tana = AB AB OC^ / AB OCc f 7 206

209 C5 Chu y : Ngudi ta thudng Idy khoang cue can Id OC^ = 25 cm. Khi san xudt kfnh lup, ngudi ta ghi gid tri cua G^ iing vdi khoang cue can nay trdn kfnh. Vf du : Cdc kfnh cd kf hieu 3x, 5x, 8x,... se ed tidu cu tuong img la cm, em, cm,... Chung cd kha nang lam cho gdc 3 5 o trdng dnh qua kfnh Idn hon ba Idn, nam Idn, tam lan,... gdc trdng true tiep vat. Bdi tap vi du Mot nguai co khoang cue can OC^ = 15 cm va die'm C^, a vo cue. Ngudi nay quan sat mpt vat nho qua kfnh liip co tieu cu.5 cm. Mat dat each kfnh 10 cm. a) Phai dat vat trong khoang nao truoc kfnh? b) Tfnh so boi giac eiia kfnh trong trucmg hop nguoi nay ngdm chimg d vo cue. Gidi a) KIwdng dgt vdt Khoang phai dat vat la MN sao cho anh ciia M, N qua kfnh liip lan luot la cac diem C^ d GO va Q. Ta CO : Suy ra : d^ = - O^C^, = - co d^ = f = 5 cm. d^ = - O^f^ = - 5 cm R^ Hay thiet lap cdng thiic ciia so j^^i i^^ ^^l pqgrn chdng d diem cuc can. Tit do : d^= ^ = = 2,50 cm. dn-f -5-5 Khoang phai dat vat la khoang gioi han bdi : 2.50 cm < <:/ < 5 em, b) So hgi gidc Ta CO cong thuc : G^ = ^ Vay : G^^=j = 3. Dung cu quang bo trd cho mat deu tao anh ao co goc trong Idn....., ^ a tan a So DOI giac : G = «-- ^ Cp tan a^ Kinh lup la thau kinh hoi tu co tieu cu nho (vai xentimet). So boi giac cua kinh lup khi ngam chirng d vo citc : G^ = T 207

210 CAU HOI VA BAI TAP 1. Cac dung cu quang bo tro cho mat co tac dung tao anh ra sao? Dinh nghia sd boi giac. 2. Kinh lupco cau tao nhu the nao? 3. Ve duong truyen ciia chum tia sang ung vdi mdt ngdm chung kinh lup d vo cue. Viet cong thuc sd boi giac ciia kinh lup trong trudng hop nay Ve so do tia sang trong trudng hgp mdt ngdm chung kinh liip 6 vo cue de tra Idi cau hoi ciia bai tap 4 va 5 duoi day Yeu to nao ke sau khong dnh hudng den gia tri ciia so boi giac? A. Kich thuoc ciia vat. B. Oac diem ciia mdt. C. Dac diem ciia kinh liip. D. Khong co (cac yeu to A, B, C deu anh hudng). Tiep theo bai tap 4. Cach thuc hien nao sau day van cho phep tiep tue ngdm chung 6 vo cue? A. Ddi vat. B. Ddi thau kinh. C. Ddi mdt. D. Khong each nao. Mpt hgc sinh can thi co cac diem C^, C^ each mdt lan lugt 10 cm va 90 cm. Hgc sinh nay dung kinh lup co do tu +10 dp de quan sat mgt vat nho. Mdt dat sat kinh. a) Vat phai dat trong khoang nao trudc kinh? b) Mgt hgc sinh khac, co mdt khong bi tat, ngdm chiing kinh liip ndi tren d vo cue. Cho OC^ = 25 cm. Tinh so boi gidc. 208

211 <5<5 KINH HIEN VI Kinh hien vi xuat hien lan dau a Ha Lan vao khoang cuoi the ki XVI a clang tho sa. Ngay nay, kinh hien vi co the giup nguai ta quan sat va ehup anh dugc nhung vat the cue nho nhu : cac te bao, cac vi khuan... (Hinh 33.1 va 33.2). I - CONG DUNG VA CAU TAO CUA KINH HIEN VI Kfnh hid'n vi la dung cu quang bd trg cho mdt dd quan sat nhirng vat rdt nhd, bdng cdch tao dnh cd gdc trdng Idn. Sd bdi gidc cua kfnh hien vi Idn hcfn rat nhieu so vdi sd bdi giac cua kfnh lup. Kinh hien vi cd hai bd phan chinh :, Vdt kinh Lj la mdt thdu kfnh hdi tu (thuc ra la mdt he thdu kfnh tac dung nhu thdu kfnh hdi tii) cd tidu cu rat nhd (cd milimet).. Thi kinh L2 la mdt kfnh lup dung dd' quan sat anh cua vat tao bdi vat kfnh. Hai bd phan chfnh nay dugc gdn 0 hai ddu mdt d'ng hinh tru sao cho true chfnh cua chung trung nhau vd khoang each giiia chung OJOT - I khdng ddi (ffiinh 33.5). Ngudi ta ggi F\F-, ^SVadp ddi quang hoc cua kfnh. Ngoai ra cdn cd bd phan tu sang de chidu sdng vat cdn quan sdt. Dd thudng la mdt guong cdu 1dm. Hinh 33.1 Kinh hien vi tho sd d thdi ki dau II - SU" TAO ANN Bdi KINH HIEN VI Vat kfnh cd tac dung tao anh that A,'5j Idn hon vat AB vd d trong khoang 02^2 ^^ quang tam den tidu didn vat cua thi kfnh. Hmh 33.2 Kinh hien vi ngay nay 14. VATL 11(C)-ST-A 209

212 * = * Thi kinh tao dnh do sau cung A^^B', Idn hem vat nhieu Idn va nguge chidu so vdi vat AB. j?^ )r; Mdt dat sau thi kfnh dd quan sdt se nhin thay anh Hinh 33.3 AJB^ *^^^ ^^^ AB tao bdi kinh hien vi. Tieu ban de quan sat qua kinh hien vi Hinh 33.4 Dieu chinh kinh hien vi diing 6c vi cap H] Tai sao phai kep vat gida hai ban thuy tinh mong khi quan sat vat bang kinh hien vi? / B '^^^*^ (") A F, A. 1 Anh sau cung A^fi; phdi dugc tao ra trong khoang nhin rd cda mdt. Do do phdi dieu chinh kinh dd thay ddi khoang each d^ tir vat AB ddn vat kinh Oy Ddi vdi kfnh hien vi, ung vdi khoang C^C^ cua dnh thi khoang Ad^ xd dich vat thudng hd't siic nhd, khoang vai chuc micrdmet. Do dd trong thuc te khi quan sdt vat bdng kfnh hien vi phdi thuc hidn nhu sau : - Vat phdi la vat phang kep giua hai tdm thuy tinh mdng trong sud't. Dd la deu bdn (ffiinh 33.3). Rl - Vat dugc dat cd dinh trdn gid. Ta ddi toan bd d'ng kfnh tir vi trf sdt vat ra xa dan bdng dc vi cdp (Hinh 33.4). Ndu anh sau cdng A^B!, ciia vat can quan sat dugc tao ra d vd cue thi ta cd su ngdm chiing kfnh d vd circ (ffiinh 33.5). F\ 8 I F2 I A\ ^ O2 1 \ N / / - B Hinh 33.5 Dudng truyen c ^hiim tia sang q ua kinh hien vi duac ngsm chung d vd cue 210 B'z ' '',. (o=).-- A 1

213 Bdi tap vi du Vat kfnh eiia mpt kfnh hi6n vi co tieu cu/i = 1 em, thj kfnh eo tieu cu /, = 4 cm. Do dai quang hoc eiia kfnh la 16 em. Mat dat sat thi kfnh. Ngudi quan sat co mat khong bi tat va eo khoang cue can la D = 20 em. Phai dat vat trong khoang nao trade vat kfnh d^ ngudi quan sat co the nhin thay anh cua vat qua kfnh? Gidi Khoang each giira vat kfnh va thi kfnh : I = 0^0^ = 8 + f\ + f\ = 21 cm. Cac vi trf M. N gioi han vi trf vat duoc,\ac dinh nhu sau :. M ^-^ >M; '^ > Ml =C ^21 ^ oo ; (/T = /, =4 cm ; J) 1 = / - ^21 = 17 cm. f/ i = Li^^J dua = mm 'n-./i. N ^^^-T^N; ^ > A'^ =c flit = D = -20 cm : C/TT = "' " = em d22 - fl ^, fli 2 - / - "0-) - cm ; = = "' 3 d^,/ d\, «^ f/p = cm = mm Vat chi c6 thd xe dich trong khoang : M^ = 25 pm. III - SO BOI GlAC CUA KINH HIEN VI Xet trudng hgp ngdm chung d vd cue. Dat : IA" I la so phdng dai dnh bdi vat kinh ; G, la sd bdi gidc cua thi kfnh ngdm chung d vd cue. Ta cd : G^=\k^\G2. '\,,_,_. Cin DUa vao hinh , hay thiet lap ^ he thiic : Hai so lieu nay thudng dugc ghi trdn vanh cua vat kfnh va thi kfnh. G^ = J/CjJGj 211

214 BI Hay thiet lap he thiic : 'V2 Cdng thiic trdn cd thd bien ddi vd viet dudi mdt dang khac : vdi D = OC^. Goo = SD hh im IHai bo phan chinh cua kinh hien vi la : - Vat kinh thau kinh hoi tu co tieu cu rait nho led m ilimet) ; - Thj kinh : kinh lup. Dieu chinh kinh hien vi: dua anh sau cung cua vat h ien ra trong khoang CvCc cua mat. 1 ^ So boi giac khi ngam chirng d vo citc : G^ = IM 6,= SO CAU HOI VA BAI TAP 1. Neu cdng dung va cau tao ciia kinh hien vi. 2. Neu dac diem tieu cy cua vat kinh vd thi kinh A. C. + + (D. B. (D + (D. D. (D + (4) + (5). ciia kinh hien vi. 3. Muon dieu chinh kinh hien vi, ta thuc hien ra 7. Thi kinh cua kinh hien vi tao anh co cac tinh chat ndo? sao? Khoang xe dich khi dieu chinh kinh hien vico gid tri nhu the nao? A. +(4). B. (D +. C. + (D +. D. f2) Ve duong truyen ciia chum tia sdng ung vdi mdt ngam chiing kinh hien vi d vd eye. 8. Khi quan sat mgt vat nho thi anh ciia vat tao bdi kinh hien vi co cac tinh chat nao? 5. Viet cong thiic sd boi giac ciia kinh hien vi khi mdt ngam chiing d vo eye. A (D. C. + (D + (5). ' D. (2) + + (D. 9. Mgt kinh hien vi co cac tieu cy vat kinh va thi Xet cac tinh chat ke sau ciia anh tao bdi thau kinh: kinh la f^ = 1 cm, /j = 4 cm. Do dai quang hgc That; g, Ao ; ciia kinh la 16 cm. Ngudi quan sat co Cling chieu vdi vat; khong bi tat va co khoang eye can OC^ = 20 cm Ngudi nay ngdm chirng d vd cue. Nguoc chieu vdi vat; '"d Lon hon vat. Hay chgn ddp an diing d cac bai tap 6, 7 va 8 dudi day 6. Vat kinh cua kinh hien vi tao anh co cac tinh chat nao? 212 a) Tinh so boi giac ciia anh. b) Nang suat phan li eiia mdt ngudi quan sat la 2'. Tinh khoang each ngdn nhat giua hai diem ciia vat ma mat ngudi quan sat con phan biet duoc anh.

215 34 KINH THIEN VAN Tuy khong phai la nguai che tao ra kfnh thien van ddu tien, nhung Ga-li-le la ngliai ddu tien da su dung kinh thien van de quan sat bau trai va co nhi^u kham pha quan trong : phat hien ra 4 ve tinh cua Moc tinh, vanh dai cua Tho tinh, cac ngpn nui tren Mat Trang,... I - CONG DUNG VA CAU TAO CUA KINH THIEN VAN Kfnh thidn van la dung cu quang bd trg cho mdt, cd tde dung tao anh cd gdc trdng Idn ddi vdi nhung vat d rat xa (cdc thidn the). Kfnh thien van cd hai bd phan chfnh :. Vdt kinh L, la mgt thdu kfnh hdi tu cd tidu cu Idn (cd the den hang chuc met). Hmh 34.1 Kinh thien van co ciia Ga-li-le duac luu giu tai Vien Bao tang thanh pho Flo-rang-xa (Florence). Thi kinh Lj la mdt kfnh lup dd quan sat dnh tao bdi vat kfnh. II - SU" TAO ANH BOI KINH THIEN VAN Vat kfnh tao anh that ciia vat (d vd circ) tai tidu didn anh. Thi kfnh giup mdt quan sat dnh nay. Anh ciia thidn the tao bdi kfnh thien van Id dnh do, nguge chidu vdi vat, cd gdc trdng Idn hon nhieu lan so vdi gdc trdng true tid'p vat. Hinh 34.2 Kinh thien van ciing vdi mai vdm cd dudng hd ds quan sat bau trdi 15. VATL[11(C)-ST-A 213

216 R' Tai sao khi dieu chinh kinh thien van. ta khong phai ddi toan bd kinh nhu vdi kinh hien vi? Khi sir dung kfnh thien van, mdt ngudi quan sat dugc dat sat thi kfnh. Phdi didu chinh kfnh bdng each ddi thi kfnh sao cho dnh sau cung ndm trong khoang nhin rd cua mdt. HI Dd cd thd quan sat trong mdt thdi gian ddi md khdng bi mdi mdt, ta phdi dua dnh sau ciing ra vd cue : ngdm chiing d vd cue (ndu mdt khdng cd tat) (ffiinh 34.3). Hinh 34.3 Dudng truyen cua chiim tia sang qua kinh thien van ngsm chung a vd cue Clui V.' - Gia tri ciia G^ duge ghi tren eae kfnh thien van. - Khi mat ngjm chijng 6 vo cue, kfnh thien van la mot M vo tieu (khong eo tieu diem). III - SO Bpl GlAC CUA KINH THIEN VAN Xet trudng hgp ngdm chiing d vd ctrc (ffiinh 34.3). Ta cd : G a tana a. tana, 0, A^B^ A'Si Vl tana = ^ ^ ; tana^ - * L /2 ^ /l (mdi thidn the cd gdc trdng a^ nhdt dinh). Dodd fl Sd bdi giac cua kfnh thidn van trong didu kidn nay khdng phu thude vi trf dat mdt sau thi kfnh VATLil1(C)-ST-B

217 Bdi tap vi du Vat kfnh cua mot kfnh thien van la mot thau kfnh hoi tu eo tieu cu lon ; thi kfnh la mot tha'u kfnh hoi tu eo tieu cu nho. Mot nguoi, mat khong co tat, dung kfnh thien van nay di quan sat Mat Trang d trang thai khong dieu tiei. Khi dd khoang each giira vat kfnh va thi kfnh la 90 em. Sd bdi giac cua kfnh la 17. Tfnh cac tieu cu ciia vat kfnh va thi kfnh. d.\d\ e,.,^- A,.oT" L L2 /I /> o, " ^ ^1 \ (.. - ', ' ^ '. ' 02/ BL Hmh 34.4 Gidi Neu mat khdng ed tat, quan sat anh d trang thai khdng dieu tiet thi anh nay d vd cue (ngdm chimg d vd cue) (Hfnh 34.4). So do tao anh : Vdi AB' : d\ VdiA,B :rf, AB- -^A.B: L, d, d' Ta suy ra. : d., = I ~ d\ z^ I =f^ +f^ Vay, theo de bai : ->AB' /i+/2 = 90cm (1) Mat khac, so bdi giac cua kinh khi ngdm chimg d vd cue duac tfnh bdi : G = ^ = Tir(l) va (2), ta tim dugc : /j = 85 cm ; /, = 5 cm (2) Chii y : - Kfnh thien van trinh bay d tren thude loai kinh thien vdn lihiic xq, sir dung thau kfnh lam vat kfnh. - Cdn ed loai kinh thien vdn phdn xq, sir dung guong parabol lam vat kfnh. - Ong nhdm la mgt loai kfnh thien van diing de quan sat vat d xa tren mat dat, mat bi6n (Hinh 34.5). Anh cudi eilng qua dng nhdm cung chi6u vdi vat. Hinh 34.5 Ong nhdm Kinh thien van la dung cu quang de quan sat cac thien the. No gom hai bo phan chinh : - Vat kinh : thaiu kinh hoi tu co tieu cu Idn (co the den hang chuc met). - Thj kinh : kinh lup co tieu cu nho (vai xentimet). Phai dieu chinh de anh sau ciing hien ra trong khoang nhin ro cua mat. So boi giac trong trudng hcrp ngam chirng d vo cuc : f. 215

218 CAU HOI VA BAI TAP 1^: 1. Neu cong dung va cau tao ciia kinh thien van. 2. Ve dudng truyen ciia chiim tia sdng qua kinh thien van ngam chung d vo cue, 3. Viet cong thuc ve so boi giac ciia kinh thien van ngdm chung 6 vo cue, 4. Giai thich tai sao tieu cy vat kinh cua kinh thien van phai Ion. Dat f., va ^2 lan lugt la tieu cy ciia vat kinh va thi kinh ciia kinh thien van. Xet cac bieu thiic: m^ f,,f, ^1 fl Hay chon dap an dung 6 cac bai tap 5 va 6 dudi day So boi giac ciia kinh thien van ngdm chung 6 vo eyeco bieu thiic nao? A.. B. d). C. 'S, D, Bieu thiic khac. Khoang each giua vat kinh va thi kinh cua kinh thien van ngdm chiing d vo eye co bieu thiic nao? A.. D. Bieu thiic khac. Vat kinh ciia mpt kinh thien van diing 6 trudng hocco tieu cu f^ = 1,2 m. Thi kinh la mpt thau kinh hoi tu co tieu cy fg = 4 cm. Tinh khoang each giua hai kinh va sd boi giac ciia kinh thien van khi ngam chiing 6 vo eye. Em CO biet? TU KINH THIEN VAN CUA GA-LI-LE OEN KINH THIEN VAN HOP-BON '1* Ga-li-le la nguai dau tien co y tuang dung kinh thien van'^' do Lip-pa-si (Hans Lippershey) a Ha Lan phat minh vao nam (ban dau gpi la "kinh tham tir" : spyglass) vao viec quan sat bdu trai. Chfnh ong da tu che tao ra chiec kinh thien van cd so boi giac khoang 30 va hien dugc luu giu tai Vien bao tang Flo-rang-xa. Dung kinh nay, Ga-li-le da cd nhieu kham pha quan trong ve Thai Duang he. Day la loai kmh thien van khuc xa diing thau kinh hoi tu lam vat kfnh. Hmh 34.6 Kinh thien van l-ec-xd (1) Kfnh nay duoe dat theo ten cila nha thien van MI Hdp-bon. ngudi da phat hien ra quy luat \i chuygn dong ciia cac thien ha mang ten dng. (2) Ta thudng hieiu kfnh visn vong la kfnh diing da quan sat cac vat d xa tren mat dat. cdn kfnh thien van la kfnh diing de quan sat cac thien tht. Hai loai kfnh nay deu cd cung nguyen If cau tao. gdm vat kfnh (la tha'u kfnh hoi tu hay mot guong cdu 1dm) va thi kfnh. 216

219 Cho tai nay, kfnh thien van Idn nhat thuoc loai nay la kfnh cua Oaf thien van l-ec-xo (Mi). Kfnh CO tieu cu 19,8 m va vat kfnh co dudng kfnh be mat la 1,02 m. Che tao cac kfnh thfen van khuc xa Ion rai phuc tap va kho khan. Viec che tao cac thau kfnh CO be mat lan ddi hoi chai lieu thuy tinh phai tinh khiei, lam nguoi phai that cham va cau true ca hoc phai that vung chdc... Du vay, theo thdi gian, thau kfnh lam vat kfnh van bi bien dang (do thuy tinh la chat vo dinh hinh) anh hudng den sytao anh. VI nhung If do neu tren ma vd sau cac kfnh thien van ddu thuoc loai phan xa, trong do vat kfnh la mpt guong - «'*" parabol. Loai kfnh thien van nay dugc Niu-ton phat minh ra va su dung dau tien vao nam 1672, dugc gpi la kfnh visn vong. Hien nay, kfnh thien van phan xa Idn nhai la kfnh thien van Kech cua Dai thien van Mao-na Ki dat tai Ha-oai, co dudng kfnh be Hinh 34.7 mat 10 m. Kinh thien van Niu-tdn Tuy nhien, viec quan sat bau trdi tir cac kinh thien van dat tren mat dat deu bi tra ngai bdi bau khf quyen. Ngoai su can trd do cac hien tugng thdi tiet (mua, bao...) thi su khuc xa cua anh sang khi truydn vao bau khf quyen cung anh hudng den sutao anh. Oe khde phuc nhugc diem nay, vao ngay , CO quan NASA da phdng vao khdng gian kinh thien van l-iap-bon bay quanh Trai Oat. Nhd boat dpng d ngoai bau khf quyen va su dung cac thfei bi hien dai nhai ve quang hpc va vidn thong, kfnh thien van Hdp-bon la cdng cu tinh vi nhat giup con ngudi thu nhan dugc thong tin td nhung vat the rai xa xam cua vu try. Cd the tim dgc them ve kfnh Hdp-bon d dia chf : Hmh 34.8 Anh ehup thien ha Tien Nu (Andromeda) cach Trai Dat nam anh sang qua kinh thien van. Hinh 34.9 Kinh thien van Hdp-bdn 217

220 35 Thac hanh : XAC OINH TIEU Cl/ CUA THAU KINH PHAN Ki Thau kfnh phan kl chf tao ra anh ao cua vat that vdi moi khoang each c/tcr vat den thau kfnh. VI khdng the hung dugc anh ao tren man anh, nen khdng biei chfnh xac vi trf cua anh ao va do dd khdng do dugc khoang each Id 'I tu anh ao de'n thau kfnh. Vay cd each nao xac dinh dugc tieu cu fcua thau kfnh phan kl khdng? I-MUC DICH THI NGHIEM 1. Biet dirgfc phirofng phap xac dinh tieu cir ciia thdu kfnh phan ki bdng cdch ghep no dong tnac vdi mot thdu kfnh hoi tii de tao ra dnh that ciia vat that qua he hai thdu kfnh. 2. Ren luyen ki nang sir dirng gid quang hoc de xac dinh tieu cir ciia thau kfnh phan ki. II-DUNG CU THI NGHIEM Bo thiet bi thf nghiem "Xac dinh tieu cir cua thdu kfnh phan ki" duoc bd trf nhu Hinh 35.la. Hmh 35.1a 218

221 1 Gia quang hoc G, co thude ddi 75 cm. 2. Den chieu D, loai 12 V - 21 W. 3. Ban chdn sdng C, mau den, tren mat co mot 16 tron mang hinh sd 1 dung lam vat AB (Hinh 35.1b). 4. Thau kfnh phan ki L. 5. Thau kinh hoi tu LQ. 6. Ban man anh M. 7. Ngudn dien U (AC - DC : V/3A). 8. Bo hai day ddn co ddu phich cdm. Hinh 35.1b III-COfSdLf THUYET Dat mot vat that AB vuong goc vdd triic chfnh ctia mot thau kfnh phan ki L. Vi thau kfnh phan ki luon tao ra mot dnh do A'B' vdi moi khoang each d tir vat AB den thdu kfnh, nen khdng biet chinh xac vi trf dnh ao A'B'. Do do ta khong do trirc tie'p duoc khoang each \d'\ tir dnh do nay den thau kfnh vd khong xac dinh duoc tieu cir/cua thdu kfnh phan ki L theo cdng thtic : m Hay neu rd : - tfnh chat cua anh ao A'B' tao bdi tha'u kfnh phan ki doi vdi vat that AB. - quy irdc ve dau dai sd ciia cac dai lu'dng d, d', f trong cdng thdc (35.1)'. HI f=^^, (35.1) d + d' De khde phiic kho khan neu tren, ta cd the dp diing phuong phdp sau day : - Dat vat AB tai vi trf (1) trudc thau kfnh hoi tu LQ de thu duoc mot anh that A'B' ro net nhat tren man dnh M (Hinh 35.2a). Sau do, giii cd dinh vi tri ciia thdu kfnh LQ va man dnh M. - Ghep thau kfnh phan ki L dong tnrc vdi thdu kfnh hoi m LQ thanh he thau kfnh (L, LQ). Di chuyen vat AB toi vi tri (2) sao cho anh do A'^B'^ tao ra boi thau kfnh phan ki L dugfc coi la vat that ddi vdi thau kinh hoi tii LQ va thdu kfnh LQ lai tao ra mot dnh that A.!^^ ro net nhat tren man anh M. Khi d6 vi trf cua anh do AJBJ trung vdi vi tri (1) cda vat AB (Hinh 35.2b). a) b) Hmh

222 Nhu vay, ne'u do khoang each d tix vi trf (2) ciia vat AB va khoang cdch \d'\ tit vi tri (1) ciia vat nay den thau kinh phan ki L, ta se xde dinh duoc tieu cu /ciia tha'u kfnh phan ki L theo cong thdc (35.1). IV - GlCri THIEU DUNG CU DO Gid quang hoc G (Hinh 35.3) la mot mang truot bdng hop kim nhom, ddi 75 cm, dat ndm ngang. Tren than gid G co mot thude milimet T, dung xac dinh vi trf ciia vat AB, ciia cdc thdu kfnh L, LQ vd man dnh M gdn tren gid G nhd cdc vft ham. Mot den chieu D (loai 12 V - 21 W) co kfnh tu quang, dung lam ngudn sang va dugfc cap dien bdi ngudn dien U (AC - DC : V/3A). Mudn thay doi vi trf ciia vat AB, ciia cac thau kfnh L. LQ vd cua man dnh M tren gid quang hoc G, ta chi cdn ndi long cac vft ham vd dich chuyen chung trucrt tren gid ndy. u ^3SP Hinh 35.3 V - TIEN HANH THI NGHIEM 1. Cdm phfch lay dien cua den chieu D vao hai 16 cdm cap dien xoay chieu (ghi dau ~ ) ciia ngudn dien U. Van num xoay cua nguon dien nay den vi tri 12 V va bat cdng tde cua nd de den chieu D phdt sdng. 2. Dat vat AB, tha'u kfnh hgi tu LQ vd man dnh M (theo thu tir nay) len gia quang hgc G, vudng goc vdi chifiu ddi cua gid : 220

223 - Vat AB d tai vi tri (1), each den chieu D khodng 10 H- 15 cm. Ghi vi trf (1) cua vat AB vdo Bdng thuc hanh 35.1; - Thau kfnh hgi ttr LQ vd man dnh M a gdn sdt phfa sau vat AB. Didu chinh den D sao cho vdng trdn sdng do nd phdt ra chieu vira kfn mat 16 tron chua vat AB vd truyen qua viing chfnh giiia mat thdu kfnh LQ. CE Dua vao dieu kien tao anh tnat cua thau kfnh hoi tu ddi vdi vat that de phdi hgfp dich chuyen tha'u kinh hgi tu LQ vd man anh M xa dan vat AB cho tdi khi thu dugfc dnh that A'B', Idn han vdt, hien rd net nhdt tren man anh M. I^ Mudn tha'u kfnh hdi tu LQ tao ra anh that A'B' Idn hon vat that AB (Hinh 35.2a), ta can phai chon cac khoang each td vat AB va td man anh M den thau kfnh hdi tu LQ thoa man dieu kien gi so vdi tieu cu cua tha'u kfnh nay? 3. GiG CO dinh vi trf cua thdu kfnh hdi tu LQ vd man dnh M. Dich vat AB rdi xa thdu kfnh hgi tii LQ them 5 cm, den vi trf (2). Dat thdu kfnh phan ki L vao khoang giiia vat AB va thau kfnh hgi tii LQ, ghep thdnh mgt he hai thdu kfnh dong true (L, LQ) tren gid quang hgc G. Dua vao didu kien tao anh do ciia thdu kfnh phan ki ddi vdi vat that de dich chuyen tha'u kinh phan ki L cho tdi khi thu dugc dnh thdta'.,b'^, nhd hem vdtab vd hien rd net nhdt tren mdn dnh M. fe Ghi vao Bang thirc hanh 35.1 gid tri cua : - khoang cdch d tir vi trf (2) cua vat AB den thau kinh phan ki L ; - khoang cdch \d'\ tir vi tri (1) cua vat AB den thdu kfnh phan ki L. tf\ Mudn anh cudi cung ciia vat AB tao bdi he thau kinh (L, LQ) bd tn nhu- Hinh 35.2 la anh that, thi khoang each gida thau kfnh phan kl L va tha'u kfnh hdi tu LQ phai Idn hon hay nho hon tieu cit ctia thau kfnh hoi tu LQ? Giai thi'ch tai sao. 4. Thuc hien nam Idn cdc thao tde 2 va 3 d tren, umg vdi cung vi tri (1) da chgn cua \ at 16. 5, Xac dinh tieu cu/cua tiiau iviiih phan ki L theo cdng thiic (35.1), vdi chu y quy irdc ve ddu dai sd cua cdc dai lugfng d, d' va/. 221

224 BAO CAO THI NGHIEM Hg va ten : Ldp.Td 1.Ten bai thiic hanh 2. Bang thuc hanh 35.1 Vitrl(1)cua vat/a6 : (mm) Lan do t d (mm) \d'\ (mm) f(mm) Af(mm) 1 i i Trung binh 7- (mm) Af= (mm).._ 1 3. Tmh ket qua cua phep do trong Bang thifc hanh Tinh gid tri tieu cir/ciia thau kfnh phan ki L trong mdi Idn do. - Tfnh gia tri trung binh J ciia cdc Idn do. - Tinh sai sd tuyet ddi ctia mdi Ian do. - Tinh sai sd tuyet ddi trung binh A/ cua cdc Idn do. Tfnh sai so ti ddi trung binh 5-4. Viet ket qua cua phep do 171 /=./ ± A/ = vdi 5= + (mm) 222

225 CAU HOI 1. Viet cong thiic thau kinh va noi ro quy uoc ve 4. Hay noi ro cdch xac dinh diing vi tri anh ro net dau ciia cac dai lupng co trong cong thiic nay ciia mot vat hien tren man anh dat d phia sau 2. Trinh bay phuong phap do tieu cu cua thau kinh ^lia met thau kinh hoae cua mot he thau kinh.^ phan ki L da dupc thuc hien trong thi nghiem nay. Ve anh that cua mot vat that AB dat vuong goc vdi true chinh ciia mot he hai thau kinh dong true L, LQ. Cho biet thau kinh phan kl L dat gan vat AB hon so vdi thau kinh hoi tu LQ va anh cuoi ciing tao bdi he thau kinh nay la anh that. Co the xac dinh tieu cu ciia thau kinh hoi tu Lg khi tien hanh thi nghiem ndy dugc khong? Neu biet, em hay noi rd noi dung nay thuoc phan nao ciia bai thi nghiem. 5. Hay cho biet nhung nguyen nhan nao co the gay nen sai sd ngau nhien ciia phep do tieu cu ^^^au kinh phdn kl L trong thi nghiem ndy 6. Co the thuc hien phep do tieu cu f ciia thau kinh phan ki L bang each ghep no dong true vol mot thau kinh hoi tu LQ, nhung vat that dupc ddt gan thau kinh hoi tu hon so voi thau kinh phdn ki dugc khong? Neu biet, em hay trinh bay ro cdc budc tien hanh thi nghiem va ve hinh minh hoa sy tao anh ciia vat. 223

226 T ong ket lyi^t chuong VI! CAC DUNG CU QUANG Bd phan va dung cu Cdu tao Dac diem Cdc ket qua vd cdng thiic (1) (2) (3) (4) 1. Lang kinh Khdi chat trong sud't hinh lang tru tam gidc - Tde dung : -h Tan sdc -t- Ldm lech tia 16 ve ddy - Gdc lech : D = i^-^ /j - A 2. Thau kinh - Khdi chat trong sudt gidi han bdi : + Hai mat cdu -t- Hoae mdt mat cdu vd mgt mat phdng - Hai loai : Hgi tti vd phan ki - Thdu kinh hdi tu : -h/>() -H Anh, vat khdng the cung do + Anh do > vat - Thdu kinh phdn ki: + /<0-1- vat that ludn cd dnh do < vat -Ddtu : D= ~ f - Cdng thdc : + Vttn:^.- = - + So phong dai : i 1 1 j 1 3. Mat Hai bg phan chinh : - The thuy tinh - Mang ludi (vong mac) - Nhin thdy mot vdt: Anh that hien a mang luoi - Dieu net : Thay doi tieu cu : +Cv-./max l+q--/nun - Ndng sudt phdn li : = r - Mat edn : + /; < o\' + Deo kfnh phan ki - Mdt vien : +L..>ov -\- Deo kfnh hgi tu - Mdt Ido : + C^ ddfi xa theo ludi + Deo kfnh hgi tu j 224

227 (1) (2) (3) (4) 4. Kinh lup Thdu kfnh hgi tu cd tieu cu nho (vdi xentimet) - Tao dnh do cua vat CO goc trdng lon - Sd hdi gidc kin ngdm ehitng d vo ci/c : G = 7 5. Kinh hien vi Hai bd phan chfnh : - Vdt kinh : tha'u kfnh hgi tu co/rdt nhd (cd milimet) - Thi kinh : kfnh lup - Anh sau ciing tqo hdi kinh : -I- Ao : lon hon vat nhieu lan -I- Nguge chieu vat - Khodng ddt vdt : A^i = vdi chuc micrdmet -Sdhdi gidc G - i^i ^= I! 6. Kinh thien van Hai bg phan chfnh : - Vdt kinh : thdu kfnh hgi tu co / rdt lon (co the den hang chuc met) Anh do c6 g6c trdng tang nhidu lan ~ Sd bdi gidc G = /r - Thi kinh : kfnh lup 225

228 DAP AN VA DAP SO BAI TAP CHUONGI 1 5. D;6. C;8. ±1.10"^C D;6.A B ; 10. D ; ^^ V/m ; ,6 cm ; ,7.105 V/m D;5. D;6. Bang0;7. 1,6.10"^^ J C;6. C;7. C;8.-f72V; "^^ J D ; 6. C ; 7. a) ^ C ; b) 4.10-^ C ; 8*. a) ^ C ; b) " J ; c) J. c) Hieu dien the giua hai cue ciia m6i pin U^ = 1/2= 1,125 V ; d) Den con lai co cong suat tieu thu la,^/>=0,55w a) R^ = 5 ^ ; b) /^ = /j = 0,2 A; 73 = 0,8 A 2. a) / = 1,5 A ; b).^a - 9 W ;.^/' = 18 W )(1). (1) c).< =18W;l^,g J.^/'!!!=9w ng /(2) W'^^ = J ; 3*. a) X = r - R 1 Q. b) X = /- + R = 1,2 Q ;.^4 (max) = 30 W. CHUONG III B ; 6. D ; 7. R3 = 484 Q ; R, = 48,8 Q ; CHUONG II 8, a) 8, m-3; b) 7,46.10-^ m/s; kg C; 9. D; 10. = 1 Q.m; 11. 2, s D ; 7. B ; 8. B ; 9. D ; 10. C ; 11. B ; 13./ = 3mA;14. AQ = 3C;15.^ = 3J D ; 7. B ; 8. a) vao khoang 10^ V ; b) Vao khoang lo'* V ; c) = 0,35 m ; hat tdi dien B ; 6. B ; 7. /I = J ;.^/^ = 6 W ; A ; 9. B ; 10. 6,25.102^ s-'.m-^ ; 8. b) f = 698 s ; 9. /\ g = J ;.r>^^ = 9,6 W. 11. = 3.10^ m/s A; 5. a) / = 0,6 A; ^ = 9 V ; b), /^ = 5,04 W ; D; 7. D..'/\^ = 5,4 W ; 6. a) Dong dien qua den : / = 0,4158 A, gan bang cudng do dong dien djnh muc,.v = 4,98 W ; b) H = 99,8% ; 7. a) CHUONG IV.^/'' = 0,54 W ; b) Dong dien qua bong den co B ; 6. B ; 7. Kim nam cham nho nam can cuong do / = 0,375 A Ion hon trudc, nen bong bang doc theo hudng mot duong siic tii ciia den sang manh hon. dong dien thdng / = 0,476 A ; ti = 5,714 V ; 5. / = 1,5 A ; B ; 5. B ; 6. a) // dat theo phuong khong L/^g = 0 V ; 6. a) Cdc den sang duoi miic binh song song voi cac dudng sue tir ; b) // ddt thudng, vi hieu dien the tren den la L/J= 2,25 V, song song vdi cac dudng siic tir ; 7. e co nho hon hieu dien the dinh miic ; b) H = 75% ; phuong ndm ngang : ( /7, e ) = a ;t 0 va 180 ; 226

229 cd chieu sao cho chieu quay tcr ij sang B 254. B; 5.C ; 6.0,079 H ; 7.i^-0,3A; 8.0,144 J. thuan vdi chieu thing ddng di len ; cd dp Idn thoa man he thirc : IlBsina = mg. CHUONG VI A ; 4. C ; 5. Cam dng tir ben trong dng B ; 6. A ; 7. D ; 8. ^ 6,4 cm ; 9. 60, nho hon ben trong dng 2; 6. Cam ling tir tai D ; 6. A ; 7. C ; 8. a) Khiic xa, O2 do I, gay ra la 6^ = 10-^ T va do /^ gay ra ^ = 45 ; b) r = 90 ; c) Phan xa toan phan ; la 62 = 62,8.10 '' T ; tuy theo chieu ciia hai dong dien : 6 = 63 ± 6^ ; 7. Diem phai tim nam trong mat phang chira hai dong dien, trong khoang giua hai dong dien, each ddng g ^ < 3QO CHUONG VII thcr nhat 30 cm va dong thir hai 20 cm ; quy D ; 5. C ; 6. A ; 7. a) 36 ; b) n > 1,70. tich nhdng diem ay la dudng thang song song vdi hai ddng dien, each ddng thii nhat 30 cm B ; 5. A; 6. B ; 7. Xem Bang tom tat d trong va ddng thd hai 20 cm bai 29 ; 8. b) ^ 1 cm ; 9. a) Van dung tinh chat C ; 4. D ; 5. C ; 6. Luc dien song song vdi ^^uan nghich ; b) f = ^ ; 10. a) 100 cm ;, con luc Lo-ren-xo vuong goc vdi B ; 25 cm ; ^ 17,54 cm ; b) 15 cm ; 11. a) -20 cm ; 7. a) 1/ = 4, m/s ;b) 7= s; 8*. b)-12 cm ; 0,4 ; 12. Trudng hpp 1 : A ao, Khoang each AC ddi vdi: C2H50H^ la 23 cm,,ha'u kinh hoi tu ; trudng hop :2, : A ao, thau C2H5 la 14,5 cm, OH^ la 8,5 cm, CH20H^ la ^fn^ phan ki, 15,5 cm, CHoMa7,5cmvaCH:ia7,0cm.,,. ^ -> >.,..... or B;2. C;3. a)-10cm,/(=1/2;b)35cm; 4. a) Anh sau cung d vd ci/c ; b) Diing hai tia CHUONG V ^^"9 '^' 9^^ '^'^^'^9 ^^^ ; 5. b) d > 60 cm ; d<20cm D ; 4. A ; 5. a) Mat cua (C) doi dien vdi cue S cua nam cham la mat Bac ; b) Mat cua (C) A ; 7. C ; 8. D ; 9. a) Can thj ; b) -2 dp ; ddi dien v&\ cue S cua nam cham la mat Nam ; c) 12,5 cm ; 10. a) Oiem cue can each mat c) Trong (C) khdng co ddng dien cam dng ; ^ ^' con diem cue vien a vo cue; b) ^ 4,35 dp. d) Trong (C) co ddng dien cam dng xoay chieu A ; 5. C ; 6. a) 5 cm < d < 9 cm ; b) 2, C; 4. lo^t/s; 5.0,1 V; 6*. e^^^^ = B(nR^)co C ; 7. D ; 8. D ; 9. a) 80 ; b) 1,43 p m, B; 6. A; 7.1,24 m;

230 CAC OAI Ll/ONG VA DON VI CHINH SU" DUNG TRONG SACH 1 Dai lircmg Don vi 1 T6n I Kl hieu Ten Kl hieu Dien tfch, dien luong Cudng do dien trudng q.q E culdng vdn tren met C V/m Dien the V von V Hieu dien the Dien dung Cuong do ddng dien Suat dien dong Suat phan dien Dien trd U c IJ? ^p R.r vdn fara ampe vdn vdn 6m V F A V V n Dien trd suat P dm.met Q,m He so nhiet dien trd a mpt tren kenvin K-1 He sd nhiet dien dong Sd Fa-ra-day «T F von tren kenvin culong tren mo! V.K-i C/mol Cam ung dien tu B tesla T Tir thong Suat dien dpng cam irng Suat dien dpng tu cam Dp tu cam Dptu 1 Tieu cu O ^c etc L D f vebe von vdn henry didp met Wb V V H dp m 228

231 MUC LUC Trang Trang PHAN MOT- DIEN HOC DIEN 10* HOC Chifc/ng / - OIEN TICH. DIEN TRJCING,.5 Bai 1. Dien tfch. Dinh luat Cu-16ng 6 Bai 2. Thuytt elejtidii. Dinh luat hao toan dien tich II Bai 3. Dien truong va cudng do dien trudng. Duong sire dien ]5 Bai 4. Cong cua krc dien 22 Bai 5. Dien the. Hieu dien the 26 Bai 6. Tu dien 30 Chitang II - DONG DIEN KHONG OOI.35 Chuang IV - TL/ TRJONG 117 Bai 19. Tu truong 118 Bai 20. Luc tir. Cam irng tir 125 Bai 21. Tir trucmg ciia dong dien chay trong ciic day dan co hinh dang dac biet Bai 22. Luc Lo-ren-xo 134 ChUa/ngV- CAM QNG DIEN TL/ 141 Bai 23. Tir thong. Cam ung dien tir 142 Bai 24. Suai dien dpng cam ung 149 Bai 25. Tucam 153 Bai 7. Dong dien khong doi. Nguon dien.^6 Bai 8. Dien nang. Cong suat dien 46 Bai 9. Dinh luat Om doi vol toan mach...50 Bai 10. Ghep cac nguon dien thanh bo Bai 11. Phuang phap giai mot so bai toiin ve toan mach 59 Bai 12. Thtrc hanh : Xiic dinh suat dien dong va dien tra trong cua mot pin dien hoa 63 ChWctng III - DONG OIEN TRONG CAC MOI TRL/ONG,.73 Bai 13. Dong dien trong kim loai 74 Bai 14. Dong dien trong chat dien phan...79 Bai 15. Dong dien trong chat khf 86 Bai 16. Dong dien trong chan khong 95 Bai 17. Dong dien trong chat ban din Bai 18. Thuc himh : Khao siii dac tfnh chinh luu cua diol hiin dan va dac tfnh khuech dai cua tranzito..108 PHAN HAI - QUANG HINH HOC C/ii^tfngW- KHUC XA ANH SANG Bai 26. Khiic xa anh sang 162 Bai 27. Phan xa toan phan 168 Chu-cfng VII - MAT. CACDUNGCUOUANG 175 Bai 28. Lang kfnh 176 Bai 29. Thau kfnh mong 181 Bai 30. Giai biii toan vi he thau kfnh Bai 31. Mat 196 Bai 32. Kfnh kip 205 Bai 33. Kfnh hmn vi 209 Bai 34. Kfnh thien van 213 Bai 35. Thuc hanh : Xac dinh tieu cu cua thau kfnh phan ki 218 Dap an va dap so bai tap 226

232 WUfl HUAN CHUONG HO CHI MINH VUONG MIEN KIM CUdNG CHAT LUONG Qudc TE \ SACH GIAO KHOA LOP TOAN HOC DAISOVAGlAlTiCHU HiNHHOCII 2. VAT Li HOA HOC SINH HOC NGliVANII (tap mpt, tap hai) 6. LICHSU'11 7. DIA Li TIN HOC CONG NGHE GlAO DUC CONG DAN GIAO DUC QU6C PH6NG -AN NINH NGOAI NGCr TltNGANHII TieNGPHAPH TIENGNGAII -TieNG TRUNG QU6C 11 SACH GIAO KHOA LOP 11 - NANG CAO Ban Khoa hoc Tu nhien : Ban Khoa hoc Xa hdi va Nhan van.toan HOC (BAI SO VA GIAI TICH 11, HINH HOC 11).VATLIII.HOAHQCII.SINH HOC 11.NGCrVAN 11 (tap mpt, tap hai).uchsl/ii.djaliii.ngoai NGU (TIENG ANH 11, TIENG PHAP 11, TIENG NGA 11, TIENG TRUNG QUOC 11) " Gia: d