🔙 Quay lại trang tải sách pdf ebook Sách Giáo Khoa Vật Lí 11 Ebooks Nhóm Zalo BO GIAO DUC VA DAO TAO « < 1 r NHA XUAT BAN GIAO DUC VIET NAM 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 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 NGUYI N QUY THAO Bien tap lan dau Bien tap tai ban Bien tap kJ thuat: Trinh bay bia va minh hoa SCfa ban in NGUY§N TIEN BINH - PHAM TH! NGOC THANG D 6 THj Bl'CH LIEN TA THANH TUNG TA THANH TUNG 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 115.000 cuon (ST), khd 17 x 24 cm. In tai Cong ty c6 phan In Khoa hoc Ky thuat - HN. So in: 116. SoXB: 01-2010/CXB/568-1485/GD. In xong va nop IL/U chieu thang 2 nam 2010. 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. 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 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 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. Hinh 1.2 H I 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 ? 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. Dien ticli diem la mot vat tfch dien co kfch thu6c rat nho so voi khoang each tai die'm ma ta xet. 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. H I 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. 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. H;n/7 1.3 Can xo^n Cu-I6ng 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. Sac-lo Cu-I6ng (Charles Coulomb, 1736 - 1806), nha bac hoc ngudi Phap CO nhieu edng trinh nghien euu ve tinh dien va tii. 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. ^ ' Neu tang khoang each giiia hai qua cau len ba lan thi \uc tuong tac giufa chung tang hay giam bao nhieu lan ? 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 4 8 16 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. 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. 8 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. 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 : /: = 9.109 N.m^ "c^ (1.2) 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 1). Cdng thiic eua dinh luat Cu-ldng trong trudng hop nay la : i Chat Khong khi (6 dieu kien chuan) Dau hoa Nude nguyen chat Parafin Giay Mica Ebonit e i 1,000594 (coi nhubangi) 2,1 81 2 2 5,7-^7 2,7 F = k m i sr Ddi vdi chan khdng thi e = 1. (1.3) Thuy tinh i Thach anh 1 5 - 10 4,5 J 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 » 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. 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. F = k Ocn vi dien tich la culong (C). "^''1. ^ = 9.10^^^' 1. Dien tich diem la gi ? 2. Phat bieu dinh luat Cu-ldng. CAU HOI VA BAI TAP 3. Lye tuong tac giua cac dien tich khi dat trong mot dien moi se Idn hay nho hon khi dat trong chan khdng ? 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' • • • giua dinh 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 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 1. 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). 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). trinh 2.1 Mo hinh nguyen tCi heli 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. n M l 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. ^ Hay neu mot dinh nghla khac ve vat dan dien va vat each dien. B : Chan khdng din dien hay each dien ? Tai sao ? 12 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. H I 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-VA N DUNG 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 ] 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. H I 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. 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. 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. 13 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 ('^"''^ 2-'^)- electron. 3. Trinh bay hien tuong nhiem dien do hudng {^m + ling va giai thich hien tuong dd bang thuyet Q M i N electron. ^ u o ^ Hinh 2.4 4. 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 ? A. Dien tich d M va W khdng thay doi. Chon cau dung. B. Dien tich d M va A/ mat het. Dua qua cau tich dien Q lai gan qua cau M Q ^len tich d M cdn, d N mat. 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. 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 C. M rdi 0 ve vi tri thang diing. D. M bi day lech ve phia ben kia. xuyen quay rat nhanh. 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 3.1 2. 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 3.2 15 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' lay lam sd do cudng do dien trudng. 16 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. 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. Cucmg do dien tnrcmg dugfC bieu dian bang mot vecta goi la vecta cuong do dien trudng. ^^^'jf-'^^-^'i^^i'- ^BStESfUs^f^-K' q (3.2) A^^^t^'-^^-'^^^ - Veeto eudng dd dien trudng E cd : - 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. ^ 4. 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 Hay chiing minh veeto cUdng dp dien trudng tai diem /W eua mot dien tich diem 0 co phuong va chieu nhu tren Hinh 3.3. ® \ . . .-js Hinh 3.5 - ^ ^ ..Vfc v- > . i 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 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. 1 8 2-VATU 11.(C)-B 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 Hinh 3.10 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. 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. 2. Cudng do dien trudng la gi ? No duoc xac dinh 7. nhu the nao ? Don vi cudng do dien trudng Phat bieu nguyen li chong chat dien trudng. Neu dinh nghia va cac dac diem ciia dudng siic dien. lagi? 3. Veeto cudng do dien trudng la gi ? Neu nhung dac diem eua veeto cudng dp dien trudng tai mot diem. 8. Dien trudng deu la gi ? 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 ? 20 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. B. Dien tich thu q. 12. Hai dien tich diem Q, = +3.10"^ C va C. Khoang each rtu 0 den q. q^= - 4.10-^ 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 = - 9.10"^ 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 GA N 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 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 K c d\ q T F • M 1. Dac diem cua life dien tac dung len mot dien • •1 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 1- ------ - -1 Hinh 4.1 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. 2. Cong cua lUc dien trong dien trUdng deu + + + + + + + + +1 a) Dien tieh q duong di ehuyen theo dudng thang d M F v a «i\X s> MN, lam vdi cac dudng siic dien mdt gdc a, vdi MN - s (Hinh 4.2). Ta ed edng eua lue dien : \ s "^MN ~ ^-^ ~ Fscosa voi H ------- - -1 F - qE va scosa = dthi : ^MN = qEd (4.1) Hinh 4.2 22 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. - 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. H I 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 M6 T OlEN TICH TRONG OlEN TRirdNG 1. Khai niem ve the nang cua mot dien tich trong dien triTdng H I 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 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 I s] 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 "^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 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 1 000 V/m. Hoi cdng cua lye dien cd gia tri nao sau day ? dien trudng. 3. The nang ciia dien tich q trong mot dien trudng A.-1,6.10-16 J. C.-1,6.10-16 J. B.+1,6.10-16 J D.+1,6.10-18 J. 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. 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 1 000 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. 25 •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 trun 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 lucdien tde dung len q khi q di ehuyen titM ravd cue vd dp lan cua q. A •^M q (5.1) 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^=l V 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. 26 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. H I 'M M M» Dien the' cua dat va eua mdt diem d vd cue thudng duge chgn lam mdc (bang 0). 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) : ^MN = ^M-^ N (5.2) 2. Oinh nghia 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^^. d q Mat khac, ta cd the viet: Q ^Mco - ^M N + ^Noo Ket qua. ta thu dugc : A t^MN 9 (5.3) Hinfi 5.2 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. 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 5.3 27 Ne'u di ehuyen mdt dien tfch q tren dudng thang MN thi cdng eua luc dien se la : ^MN = qEd vd\d=MN. 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. AviN •'MN ' 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 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 3 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. 28 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. 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 A.+12V. C. +3 V. Chpn cau dung. B. D. 12 V. •3V. 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 Tha mot electron khong van toe ban dau trong mot dien trudng bat ki. Electron dd se Em CO biet ? electron sinh ra khi nd chuyen ddng tii diem M den diem N. Biet hieu dien the L/^^^g = 50 V. 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 + / ^ I ,yy 1 . ' y^. +^m' -fS'- -t-SU !?• . 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 Hinh 5.5 Trong anh (chijp ngay 7 -12 - 2006) 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. 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 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-TUDIE N 1. Tu dien la gi ? La thiec khac Hmh 6.1 Hinh 6.2 Anh ehup mot so loai tu dien Hmh 6.3 Hmh 6.4 H I Sau khi tich dien cho tu dien, neu ndi hai ban bang mot day dan thi se xay ra hien tugng gi ? 30 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. 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. 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. H I 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 a) Md hinh cau tao b) Anh ehup mdt tu xoay Hinh 6.5 TiJ xoay +AQ Hinh 6.6 32 3. 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 - 250 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 • Q' w 2C 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. C = - U Don vi dien dung la fara (F). 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 - 200 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 T; ong ket DIEN TICH 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 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 : 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 n , = 10. Hieu dien the: 'M» xiic va do hudng ling... 4. 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 N ~ ^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. dien tich diem m r'- 12. Dien dung cua tu dien : C = Don vi dien dung la fara (F). Q u 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. 13. Dien trudng trong tu dien ed du tru nang lugng. 34 3-VATU 11.(C)-B 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 . Cong va cdng suat ciia nguon dien G.S. Om (Georg Simon Ohm) (1789-1854) . Dinh luat Om doi vdi toan maeh . Ghep cac ngudn dien thanh bp 35 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 ? II - Cl/dNG Dp DONG DIEN. DONG DIEN Hinh 7.1 Cac dien tich dich chuyen qua tiet dien thang S cua vat dSn theo phuong vuong goc voi tiet dien nay. 36 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. 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 : / = 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). M J Neu nnot vf du ve mot maeh dien trong dd cd ddng dien khdng doi chay qua. w 5 Do cudng do ddng dien bang dung cu gi ? Mac dung cu dd nhu the nao vao maeh ? 37 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. B E 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. B S 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 ? 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 : 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-NGU6 N DIEN 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. 2. Nguon dien Hay ke ten mot sd nguon dien thudng dung. 38 cac a) Nhd lai nhirng kie'n thiic v^ ngudn dien da hge d THCS de tri Idi C7, C8 va C9. 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. IV - SUAT DIEN DON G 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. 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 ? Hmh 7.3 Nguon dien Hmh 7.4 39 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 ^ A q (7.3) e) Dan vi 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 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. W E 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). V - PIN VA ACQUY 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...). H F 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 Manh Manh dong ton -si 6rj Hinh 7.5 Zn 1® j®i zrfi®!®: Dung dich H2SO4 Hmh 7.6 41 K 1 1 1—'—'—^ 1 ; Zn Cu + JjjL _ • - —- iP'^'f'l^ ;"©H® - "- »^^ - '- - • - Dung dich «P ^ Hinh 7.7 MQ dong Thanh than Mn02 dupe trpn vol than chi trpn vol ho dac V6 kem Hmh 7.8 42 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. 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. 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...). Hinh 7.9 Hmh 7.10 43 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 • va do do duy tn hieu dien the giua hai cue chay qua mdt vat dan ? ciia nd ? 44 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 Du.. hai cue deu a cac vat cach dien. , .' i--i ••- i.^ •>'.-•. = - iia. V.UO ucu ,a v.av. VOL V^OM, uicii. chuyeh qua tiet dien 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 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 -^ u ^^ R I Hinh 8.1 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. C E 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) ? 46 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 : A = Uq = Ult (8.1) RI 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. 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 D6N G 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 p/j= 0 = R/2 = LL bdng nhiet lupng toa ra a vat ddn trong mot dan vi thdi gian. t va hay cho biet ddn I ~ t (8-4) lugng c6 mat trong « cong thdc tren. ES 47 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 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 ng ^ maeh. Cong suat cua nguon dien bang cong suat tieu thu dien n ang cua toan maeh. K,=^j CAU HOI VA BAI TAP 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 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 - 1 000 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 4 190 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 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 +1 - . 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 1 '—1 1 K Hinh 9.2 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 0,1 0,2 0,3 0,4 0,5 /(A) Hinh 9.3 /(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 2,40 50 4-VATLI 11.(C)-B 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 : '=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) (9.5) I^ H I 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^ ? ^ 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 ? 51 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. 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 ? 52 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 : 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. 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. H I 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 : H = )ic h _ IN _ IN r/f (9.9) m Djnh luat 6m doi vdi toan mach : 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+ ^ 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 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. CAU HOI VA BAI TAP m 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 b) Tinh cdng suat mach ngoai va cdng suat doan mach trong mach dien kin. 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 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 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) 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 : A *— R U.^ = ^~l{r + R) 'AB f-•U AB (10.1) b) A 0— R^ hay r + R R AB (10.2) 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 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^ B I 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 di n 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 : ^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. 56 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 : m va r^^ = nr (10.5) 2. Bo nguon song song 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 10.4. 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 '"" = « (10.6) 3. Bo nguon hdn htfp doi xuTng 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 10.5. 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,.- + 1 - +1 - i'^' " B Hinh 10.4 ^ + 1 - >n Hmh 10.5 57 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 Mac hai ngudn dien thanh mach dien kin 1. Dong dien chay qua doan mach chiia ngudn dien CO 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. nhu so dd Hinh 10.6. 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. Mdt acquy cd suat dien ddng va dien trd trong Cho rang dien trd ciia cac den khdng thay ddi theo nhiet dd. Hmh 10.7 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 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 ? "i = 4,5 V r, = 3Q 32-''2 Hinh 10.6 58 ^. = 3V fj = 2 f^. 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 ? I S 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 Hmh 11.1 B I 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. £>i Hmh 11.2 II - BAI TAP VI DU 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. 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. H I 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. 60 b) Tinh cdng suat didn khi dd. HU&ng ddn giai a)Hl 'P va hieu suat H eua ngudn ng 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. 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. 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. 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 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, -R 2 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 va CO dien trd trong khdng dang ke, Cac dien trd R^ = 4 Q ; R2 = 8 Q. 62 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 11.4 3*. 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 X zm c z Hinh 11.5 12 Thi/c hanh : XAC OINH SUAT DIEN O6N G VA OIEN TRd TRONG CUA M 6 T 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 12.1. Hmh 12.1 63 I M +, ?> ' ®—( ^ T "s,r 1. 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. I flo W ^J i Ill-CO sd LI THUYET Hinh 12.2 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 12.2. I M Hmh 12.3 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 ? 64 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). H I 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. 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 DT.830B "fi "- mm. mmm +iicAT.n" ddng dien mdt chieu (DCA), do dien trd {Q.),... 2. 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. Hinh 12.4 5-VATLI 11.(C)-A 65 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 ? B E 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 ? 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. 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 HAN H THI NGHIEM 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 12.1. H i 66 5-VATLI1i.(C)-B 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 12.1. 5. 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 : . 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 : O Hinh 12.5 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 / = 0 = U = 0 t/„ RQ+r (12.3) (12.4) thuc hanh 12,1 ? Tu (12.3) va (12.4), suy ra gid tri suat dien ddng va dien trd trong /• eiia pin dien hod. 67 Phuong an thiir hai Cd the viet he thiie (12.2) dudi dang : ^ = ^{R + R^ + R^ + r) hay voi y=^{x + b) (12.5) y= Y,x = R;b = R^ + R^^r. /o Hmh 12.6 68 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. Ho va ten 1. Ten bai thUc hanh : 2. Bang thUc hanh 12.1 BAO CAO THl/C HANH Ldp .Td x = R(Q) 100 90 80 70 60 50 40 30 . Phuang an thijr nhat Giatri:Ro = (^);R A = (^) /(10-3A) U{V) y=7(A-^) 1 1 i i 1 ! 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) cdtrue tung va true hodnh : / = 0 ^ t/o = (V) RQ+, (A) Tir dd suy ra : "f = (V) ; r = {Q) 69 . PhUdngan thOrhai a) Tfnh cdc gia tri tuong ling ciia v va .v trong Bang thuc hdnh 12.1. 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 Em CO biet ? CACH TiNH SAI SO CUA D6N C H 6 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) 2 000 Gia su M^ la sai sd tuyet ddi cua I^. Khi dd, sai sd ti ddi cua/^ bang 6 = M„ Bang 12.1 Cac thong so kl thuat cua dong ho DT-830B 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 + 2. 2 00 2 000 ~ 0,5 mA nghia la cudng do ddng dien / do duac nlm trong khoang cac gia tri : (26,0 - 0,5) mA < / < (26,0 + 0,5) mA hay / = (26,0 ±0,5) mA Chuc nang '\ DCV DCA Thang do 200 mV 2 000 mV 20 V 200 V 1000 V 200 nA 2 000 |iA 20 mA 200 mA 10A 5 (%) 0,5 0,8 1,0 1,2 2,0 n 2 2 2 2 2 71 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 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. 72 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 : / = 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 + - + ''n > Bd ngudn song song : Neu n ngudn dien ed ciing suat dien ddng c^ va dien trd trong r dugc mdc song song thi : ^ b = ^ 5 /"b = - 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 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 LOA Ban chat ciia ddng dien trong kim loai duge neu ro trong mdt li thuyet tdng qudt ggi la thuyet electron vi ^ 0/00 © : Gf €k er- \© 0 0^0 ^ -^ f : 0 0 , 0 ' 0 f 0 0 0 0^ 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. 74 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. 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 Bang 13.1 Chat Bac Bach kim Dong Nhom Sdt Silic Vonfam Po l^ ' 1,62.10" 10,6.10- 1,69.10- 2,75.10-8 9,68.10-3 0,25.10" 5,25.10-3 a (K-1) 4,1.10-3 3,9.10-3 4,3.10-3 4,4.10-3 6,5.10-3 -70.10-3 4,5.10-3 . i ddi cd hudng cda ede electron tu do dudi tac dung ciia dien trudng. II - SU" PHU THUOC CUA DIEN TR d 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: 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. 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 13.1. 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. H I 400 800 1200 T(K) Su bien thien dien trd suat cua dong theo nhiet do R l Vi sao ngudi ta chpn day bach kim de lam nhiet ke dien trd dung trong cdng nghiep ? 75 Bang 13.2 Nhiet do toi han cua mot so chat sieu dan Ill - DIEN TRd CUA KIM LOAI 6 NHIET DO THAP VA HliN TUONG SiEU DAN 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 Ten vat lieu • Nhom ( Thuy ngan i Chi Thiec Kem NbgSn 1 NbgAl NbgGe j DyBa2Cu307 ' HgBa2Ca2Cu30g 1 7"c(K) 1,19 4,15 7,19 3,72 0,85 18 18,7 23 92,5 134 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 13.2. 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 13.2. 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 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 ? Ti T,>T^ Hmh 13.3 Electron khuech tan tu dau nong qua dau lanh lam dau nong tich dien duong. 76 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 ;) IV - HIEN TUONG NHIET DIEN 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). 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 Von ke Nuoc da 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 tr d chuyen dong cua hat tai dien lam cho dien tr d cua kim loai phu thuoc nhiet do. Den gan 0 K, dien tr d cua kim loai rat nhd. Vat lieu sieu dan cd dien tr d 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 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 '^ D. cac electron hoa tri chuyen dong lu do trong 3. Dien trd ciia kim loai thudng va sieu dan khac mang tinh the. nhau the nao ? 7_ [^pt ^opg ^en 220 V - 100 W khi sang binh 4. Do dau ma trong cap nhiet dien cd suat dien thudng thi nhiet dp ciia day tde den la 2 000°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 ^'^'"'^ ^^^ ' 64.10-3 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 1 000 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 8 900 kg/m^, ciia nhdm la 2 700 kg/m' ,3 78