Tron bo-ly-thuyet-va-bai-tap-vat-ly-11

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CU TRC TI LIU:

CHUONG 1; DIEN TICH - DIEN TRUONG

CHU DE 1. TNG TC IN TCH IM, nhim in CHU DE 2. tong hop luc culong CHU DE 3. in tch chu lc tc dng cn bng CHU DE 4. cng in trng CHU DE 5. cong cua luc dien, hieu dien the CHU DE 6. chuyen dong cua hat mang dien trong dien truong CHU DE 7. T IN CHUONG 2; DONG DIEN KHONG DOI chu de 1. dai cuong dong dien khong doi-nguon dien chu de 2. IN NNG, L JUNLENXO-CNG,CNG SUT NGUN chu de 3. nh lt m cho on mch ch cha R hoc ngun chu de 4. NH LUT M CHO TON MCH chu de 5. inh lut m cho cc loi on mch - hay +kh chu de 6. on tap va kiem tra -DNG IN KHNG I CHUONG 3; DONG DIEN TRONG CAC MOI TRUONG CH 1. DNG IN Trong kim loi CH D 2.Dng in trong CHT IN PHN CH D 3.Dng in trong CHN KHNG V CHT KH CHU DE 4.Dng in trong cc mi trng BN DN CHU DE 5. on tap - kiem tra - chuong 3 CHUONG 4; TU TRUONG CHU DE 1. T TRNG CA CC LOI DNG IN CHU DE 2. LC T - TNG TC T CHU DE 3. LC LO REN X CHU DE 4. ON TAP-K.TRA CHUONG 5; CAM UNG DIEN TU CHU DE 1. Cm ng in t tng qut CHU DE 2. on dy dn chuyn ng trong t trng CHU DE 3. HIEN TUONG TU CAM CHU DE 4. ON TAP - KIEM TRA CHUONG 6; KHUC XA ANH SANG chu de 1. Bai tap tong hop chu de 2. on tap - kiem tra CHUONG 7; MAT- DUNG CU QUANG HOC chu de 1. lang kinh chu de 2. thau kinh mong chu de 3. mat chu de 4. kinh lup, hien vi, thien van chu de 5. on tap kiem tra DE THI - KIEM TRA LP 11


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H v tn hc sinh :..Trng:THPT..................................................... I. TM TT L THUYT: I. kin thc. 1. Lc - c im ca vecto lc + im t ti vt + Phng ca lc tc dng + Chiu ca lc tc dng + ln t l vi ln ca lc tc dng 2. Cn bng lc: l cc lc cng tc dng vo mt vt v khng gy gia tc cho vt - Hai lc cn bng: l hai lc cng tc dng vo mt vt, cng gi cng ln nhng ngc chiu 3. Tng hp lc: - Quy tc tng hp lc: Quy tc hnh bnh hnh Nu vt chu tc dng ca 2 lc 1 2,F F

r r th 1 2F F F= +

r r r

+ 1 2 1 2F F F F F = +r r

+ 1 2 1 2F F F F F = r r

+ 0 2 21 2 1 2( , ) 90F F F F F= = +r r

+ 2 21 2 1 2 1 2( , ) 2 osF F F F F F F c = = + +r r

Nhn xt: 1 2 1 2F F F F F +

Nu vt chu tc dng ca nhiu lc th tin hnh tng hp hai lc ri ly hp lc ca 2 lc tng hp tip vi lc th 3 Lu : chng ta c th tm hp lc bng phng php chiu cc lc thnh phn xung cc trc Ox, Oy trn h trc cc vung gc.

1 2F F F= +ur uur uur

lc ny, biu thc trn vn s dng trn cc trc ta chn Ox, Oy:

1 2

1 2

Ox Ox Ox

Oy Oy Oy

F F F

F F F

= +

= +

uuur uuuur uuuur

uuur uuuur uuuur

ln: 2 21 2Ox OyF F F= +

4. Phn tch lc: - Quy tc phn tch lc: Quy tc hnh bnh hnh Ch : ch phn tch lc theo cc phng m lc c tc dng c th

5. iu kin cn bng ca cht im 1

0n

ii

F=

=rr

II. Bi tp Bi 1: Tm hp lc ca cc lc trong cc trng hp sau (Cc lc c v theo th t chiu quay ca kim ng h)

a. F1 = 10N, F2 = 10N, ( 1 2,F F

) =300

b. F1 = 20N, F2 = 10N, F3 = 10N,( 1 2,F F

) =900, ( 2 3,F F

) =300, ( 1 3,F F

) =2400

B sung kin thc v vct lc

0


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c. F1 = 20N, F2 = 10N, F3 = 10N, F4 = 10N, ( 1 2,F F

) =900, ( 2 3,F F

) =900, ( 4 3,F F

) =900, ( 4 1,F F

) =900

d. F1 = 20N, F2 = 10N, F3 = 10N, F4 = 10N, ( 1 2,F F

) =300, ( 2 3,F F

) =600, ( 4 3,F F

) =900, ( 4 1,F F

) =1800 p s: a. 19,3 N b. 28,7 N c. 10 N d. 24 N Bi 2: Mt cht im chu tc dng ng thi ca 2 lc c ln 20N v 30N, xc nh gc hp bi phng ca 2 lc nu hp lc c gi tr: a. 50N b. 10N c. 40N d. 20N s: a. 00 b. 1800 c. 75,50 d. 138,50 Bi 3: Mt cht im chu tc dng ng thi ca 3 lc: F1 = 20N, F2 = 20N v F3. Bit gc gia cc lc l bng nhau v u bng 120

0. Tm F3 hp lc tc dng ln cht im bng 0? p s: F3 = 20 N Bi 4: Vt m = 5kg c t nm yn trn mt phng nghing gc 300 so vi phng ngang nh hnh v. Xc nh cc lc tc dng ln vt? Bit trng lc c xc nh bng cng thc P = mg, vi g = 10m/s2. p s: P = 50N; N = 25 3 N; Fms = 25 N Bi 5: Vt m = 3kg c gi nm yn trn mt phng nghing gc 450 so vi phng ngang bng mt si dy mnh v nh, b qua ma st. Tm lc cng ca si dy( lc m vt tc dng ln si dy lm cho si dy b cng ra) p s: T = 15 2N

H v tn:..Thpt..

I. kin thc: 1. Vt nhim in_ vt mang in, in tch_ l vt c kh nng ht c cc vt nh.

C 3 hin tng nhim in l nhim in do c xt, nhim in do do tip xc v nhim in do hng ng. 2. Mt vt tch in c kch thc rt nh so vi khong cch ti im ta xt c gi l in tch im. 3. Cc in tch cng du th y nhau, tri (ngc) du th ht nhau. 4. nh lut Cu_Lng (Coulomb): Lc ht hay y gia hai in tch im t trong chn khng c phng trng vi ng thng ni hai in tch im , c ln t l thun vi tch ln ca hai in tch v t l nghch vi bnh phng khong cch gia chng

Cng thc: 2

21.

r

qqkF = Vi k = 9

0

10.9.4

1=

(

2

2.

C

mN )

q1, q2 : hai in tch im (C ) r : Khong cch gia hai in tch (m) 5.Lc tng tc ca cc in tch trong in mi (mi trng ng tnh)

m

m

LC TNG TC IN TCH IM, hin tng nhim in

1


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in mi l mi trng cch in. Cc th nghim chng t rng, lc tng tc gia cc in tch im t trong mt in mi ng cht, chim y khng gian xung quanh in tch, gim i ln khi chng c t trong chn khng:

2

21

.

.

r

qqkF

= : hng s in mi ca mi trng. (chn khng th = 1)

6. Thuyt electron (e) da vo s c tr v di chuyn ca cc e gii thch cc hin tng in v cc tnh cht in ca cc vt. Trong vic vn dng thuyt e gii thch cc hin tng nhim in (do c xt, tip xc, hng ng), ta tha nhn ch c e c th di chuyn t vt ny sang vt kia hoc t im ny n im kia trn vt. 7.cht dn in l cht c nhiu in tch t do,cht cch in(in mi) 8. nh lut bo ton in tch: Trong mt h vt c lp v in, tng i s ca cc in tch l khng i.

PP chung: TH ch c hai (2) in tch im q1 v q2.

- p dng cng thc ca nh lut Cu_Lng : 2

21

.

.

r

qqkF

= (Lu n v ca cc i lng)

- Trong chn khng hay trong khng kh = 1. Trong cc mi trng khc > 1. TH c nhiu in tch im. - Lc tc dng ln mt in tch l hp lc ca cc lc tc dng ln in tch to bi cc in tch cn li. - Xc nh phng, chiu, ln ca tng lc, v cc vect lc. - V vect hp lc. - Xc nh hp lc t hnh v. Khi xc nh tng ca 2 vect cn lu cc trng hp c bit l tam gaic1 vung, cn, u, Nu khng xy ra cc trng hp c bit th c th tnh di ca vec t bng nh l hm s cosin: a2 = b2 + c2 2bc.cosA hay Ftng

2 = F12+F2

2+2F1F2cos II. bi tp t lun: 1. Hai in tch im dng q1 v q2 c cng ln in tch l 8.10

-7 C c t trong khng kh cch nhau 10 cm. a. Hy xc nh lc tng tc gia hai in tch . b. t hai in tch vo trong mi trng c hng s in mi l =2 th lc tng tc gia chng s thay i th no ? lc tng tc gia chng l khng i (bng lc tng tc khi t trong khng kh) th khong cch gia chng khi t trong mi trng c hng s in mi =2 l bao nhiu ? s: 0,576 N, 0,288 N, 7 cm. 2. Hai in tch im nh nhau t trong chn khng cch nhau mt on 4 cm, lc y tnh in gia chng l 10-5 N. a. Tm ln mi in tch. b. Tm khong cch gia chng lc y tnh in gia chng l 2,5. 10-6 N. s: 1,3. 10-9 C, 8 cm. 3. Mi prtn c khi lng m= 1,67.10-27 kg, in tch q= 1,6.10-19C. Hi lc y gia hai prtn ln hn lc hp dn gia chng bao nhiu ln ? s: 1,35. 1036 4. Hai vt nh ging nhau, mi vt tha 1 electron. Tm khi lng mi vt lc tnh in bng lc hp dn. s: 1,86. 10-9 kg.


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5. Hai vt nh t trong khng kh cch nhau mt on 1m, y nhau mt lc F= 1,8 N. in tch tng cng ca hai vt l 3.10-5 C. Tm in tch ca mi vt. s: q1= 2. 10

-5 C, q2 = 10-5 C (hoc ngc li) 6. Hai in tch q1 = 8.10

-8 C, q2 = -8.10-8 C t ti A v B trong khng kh (AB = 6 cm). Xc

nh lc tc dng ln q3 = 8.10-8 C , nu:

a. CA = 4 cm, CB = 2 cm. b. CA = 4 cm, CB = 10 cm. c. CA = CB = 5 cm. s: 0,18 N; 30,24.10-3 N; 27,65.10-3 N. 7. Ngi ta t 3 in tch q1 = 8.10

-9 C, q2 = q3 = -8.10-9 C ti ba nh ca mt tam gic u

cnh 6 cm trong khng kh. Xc nh lc tc dng ln in tch q0 = 6.10-9 C t tm O ca

tam gic. s: 72.10-5 N. 8. Ba in tch im q1 = -10

-6 C, q2 = 5.10-7 C, q3 = 4.10

-7 C ln lt t ti A, B, C trong khng kh, AB = 5 cm. AC = 4 cm. BC = 1 cm. Tnh lc tc dng ln mi in tch. s: 4,05. 10-2 N, 16,2. 10-2 N, 20,25. 10-2 N. 9. Ba in tch im q1 = 4. 10

-8 C, q2 = -4. 10-8 C, q3 = 5. 10

-8 C. t trong khng kh ti ba nh ca mt tam gic u cnh 2 cm. Xc nh vect lc tc dng ln q3 ? s: 45. 10

-3 N.

10 Ba in tch im q1 = q2 = q3 = 1,6. 10-19 C. t trong chn khng ti ba nh ca mt tam

gic u cnh 16 cm. Xc nh vect lc tc dng ln q3 ? s: 15,6. 10-27N.

11. Ba in tch im q1 = 27.10-8 C, q2 = 64.10

-8 C, q3 = -10-7 C t trong khng kh ln lt ti

ba nh ca mt tam gic vung (vung gc ti C). Cho AC = 30 cm, BC = 40 cm.Xc nh vect lc tc dng ln q3. s: 45.10-4 N.

12. Hai in tch q1 = -4.10-8 C, q2 = 4. 10

-8 C t ti hai im A v B cch nhau mt khong 4 cm trong khng kh. Xc nh lc tc dng ln in tch q = 2.10-9 C khi: a. q t ti trung im O ca AB. b. q t ti M sao cho AM = 4 cm, BM = 8 cm. 13. Hai in tch im q1 = q2 = 5.10

-10 C t trong khng kh cch nhau mt on 10 cm. a. Xc nh lc tng tc gia hai in tch? b. em h hai in tch ny t vo mi trng nc ( = 81), hi lc tng tc gia hai in tch s thay i th no ? lc tng tc gia hai in tch khng thay i (nh t trong khng kh) th khong cch gia hai in tch l bao nhiu? 14. Cho hai in tch q1 v q2 t cch nhau mt khong r = 30 cm trong khng kh, lc tc dng gia chng l F0. Nu t chng trong du th lc ny yu i 2,25 ln. Vy cn dch chuyn chng li mt khong bng bao nhiu lc tng tc gia chng vn bng F ? s: 10 cm. III. Bi tp trc nghim: - 1: Cu hi 1: Bn vt kch thc nh A,B, C, D nhim in. Vt A ht vt B nhng y vt C, vt C ht vt D. Bit A nhim in dng. Hi B nhim in g:

A. B m, C m, D dng. B. B m, C dng, D dng C. B m, C dng, D m D. B dng, C m, D dng

Cu hi 2: Theo thuyt electron, khi nim vt nhim in:


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A. Vt nhim in dng l vt ch c cc in tch dng B. Vt nhim in m l vt ch c cc in tch m C. Vt nhim in dng l vt thiu electron, nhim in m l vt d electron D. Vt nhim in dng hay m l do s electron trong nguyn t nhiu hay t

Cu hi 3: a mt qu cu kim loi khng nhim in A li gn qu cu kim loi B nhim in th chng ht nhau. Gii thch no l ng:

A. A nhim in do tip xc. Phn A gn B nhim in cng du vi B, phn kia nhim in tri du. Lc ht ln hn lc y nn A b ht v B B. A nhim in do tip xc. Phn A gn B nhim in tri du vi B lm A b ht v B C. A nhim in do hng ng Phn A gn B nhim in cng du vi B, phn kia nhim in tri du. Lc ht ln hn lc y nn A b ht v B D. A nhim in do hng ng Phn A gn B nhim in tri du vi B, phn kia nhim in cng du. Lc ht ln hn lc y nn A b ht v B

Cu hi 4: C 3 vt dn, A nhim in dng, B v C khng nhim in. B v C nhim in tri du ln bng nhau th:

A. Cho A tip xc vi B, ri cho A tip xc vi C B. Cho A tip xc vi B ri cho C t gn B C. Cho A gn C nhim in hng ng, ri cho C tip xc vi B D. ni C vi D ri t gn A nhim in hng ng, sau ct dy ni.

Cu hi 5: Hai in tch t gn nhau, nu gim khong cch gia chng i 2 ln th lc tng tc gia 2 vt s:

A. tng ln 2 ln B. gim i 2 ln C. tng ln 4 ln D. gim i 4 ln Cu hi 6: a vt A nhim in dng li gn qu cu kim loi B ban u trung ho v in c ni vi t bi mt dy dn. Hi in tch ca B nh no nu ta ct dy ni t sau a A ra xa B:

A. B mt in tch B. B tch in m C. B tch in dng D.B tch in dng hay m tu vo tc a A ra xa

Cu hi 7: Trong 22,4 lt kh Hyr 00C, p sut 1atm th c 12,04. 1023 nguyn t Hyr. Mi nguyn t Hyr gm 2 ht mang in l prtn v electron. Tnh tng ln cc in tch dng v tng ln cc in tch m trong mt cm3 kh Hyr:

A. Q+ = Q- = 3,6C B. Q+ = Q- = 5,6C C.Q+ = Q- = 6,6C D.Q+ = Q- = 8,6C Cu hi 8: Bn qu cu kim loi kch thc ging nhau mang in tch + 2,3C, -264.10-7C, - 5,9 C, + 3,6.10-5C. Cho 4 qu cu ng thi tip xc nhau sau tch chng ra. Tm in tch mi qu cu?

A. +1,5 C B. +2,5 C C. - 1,5 C D. - 2,5 C Cu hi 9: Tnh lc tng tc in, lc hp dn gia electron v ht nhn trong nguyn t Hyr, bit khong cch gia chng l 5.10-9cm, khi lng ht nhn bng 1836 ln khi lng electron

A. F = 7,2.10-8 N, Fh = 34.10

-51N B. F = 9,2.10-8 N, Fh = 36.10

-51N C.F = 9,2.10

-8 N, Fh = 41.10-51N D.F = 10,2.10

-8 N, Fh = 51.10-51N

Cu hi 10: Tnh lc tng tc in gia mt electron v mt prtn khi chng t cch nhau 2.10-9cm:

A. 9.10-7N B. 6,6.10-7N C. 5,76. 10-7N D. 0,85.10-7N Cu 11: Hai in tch im q1 = +3 (C) v q2 = -3 (C),t trong du (= 2) cch nhau mt khong r = 3 (cm). Lc tng tc gia hai in tch l:

A. lc ht vi ln F = 45 (N). B. lc y vi ln F = 45 (N).


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C. lc ht vi ln F = 90 (N). D. lc y vi ln F = 90 (N). Cu 12: ln ca lc tng tc gia hai in tch im trong khng kh

A. t l vi bnh phng khong cch gia hai in tch. B. t l vi khong cch gia hai in tch. C. t l nghch vi bnh phng khong cch gia hai in tch. D. t l nghch vi khong cch gia hai in tch.

Cu 13: Hai qu cu nh c in tch 10-7 (C) v 4.10-7 (C), tng tc vi nhau mt lc 0,1 (N) trong chn khng. Khong cch gia chng l:

A. r = 0,6 (cm). B. r = 0,6 (m). C. r = 6 (m). D. r = 6 (cm). Cu 14: Pht biu no sau y l khng ng?

A. Theo thuyt lectron, mt vt nhim in dng l vt thiu lectron. B. Theo thuyt lectron, mt vt nhim in m l vt tha lectron. C. Theo thuyt lectron, mt vt nhim in dng l vt nhn thm cc ion dng. D. Theo thuyt lectron, mt vt nhim in m l vt nhn thm lectron.

Cu 15: Pht biu no sau y l khng ng? A. Trong vt dn in c rt nhiu in tch t do. B. Trong in mi c rt t in tch t do. C. Xt v ton b th mt vt nhim in do hng ng vn l mt vt trung ho in. D. Xt v ton b th mt vt nhim in do tip xc vn l mt vt trung ho in.

Cu 16: Pht biu no sau y l khng ng? A. a 1 vt nhim in dng li gn 1 qu cu bc (in mi), n b ht v pha vt nhim in dng. B. Khi a 1 vt nhim in m li gn mt qu cu bc (in mi),n b ht v pha vt nhim in m. C. Khi a mt vt nhim in m li gn mt qu cu bc (in mi), n b y ra xa vt nhim in m. D. Khi a mt vt nhim in li gn mt qu cu bc (in mi) th n b ht v pha vt nhim in. Cu 17: Pht biu no sau y l khng ng?

A. lectron l ht mang in tch m: - 1,6.10-19 (C). B. lectron l ht c khi lng 9,1.10-31 (kg). C. Nguyn t c th mt hoc nhn thm lectron tr thnh ion. D. lectron khng th chuyn ng t vt ny sang vt khc.

Cu 18: Hai in tch im nm yn trong chn khng chng tng tc vi nhau mt lc F. Ngi ta thay i cc yu t q1, q2, r thy lc tng tc i chiu nhng ln khng i. Hi cc yu t trn thay i nh th no?

A. q1' = - q1; q2' = 2q2; r' = r/2 B. q1' = q1/2; q2' = - 2q2; r' = 2r C. q1' = - 2q1; q2' = 2q2; r' = 2r D. Cc yu t khng i

Cu 19: th biu din lc tng tc Culng gia hai in tch quan h vi bnh phng khong cch gia hai in tch l ng:

A. hypebol B thng bc nht C. parabol D. elp Cu 20: Hai in tch im nm yn trong chn khng tng tc vi nhau mt lc F. Ngi ta gim mi in tch i mt na, v khong cch cng gim mt na th lc tng tc gia chng s:


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A. khng i B. tng gp i C. gim mt na D. gim bn ln Cu 21: Hai in tch im bng nhau t trong in mi lng = 81 cch nhau 3cm chng y nhau bi lc 2 N. ln cc in tch l:

A. 0,52.10-7C B. 4,03nC C. 1,6nC D. 2,56 pC Cu 22: Hai in tch im bng nhau t trong khng kh cch nhau 12cm, lc tng tc gia chng bng 10N. Cc in tch bng:

A. 2C B. 3C C. 4C D. 5C Cu 23: Hai in tch im t trong khng kh cch nhau 12cm, lc tng tc gia chng bng 10N. t chng vo trong du cch nhau 8cm th lc tng tc gia chng vn bng 10N. Hng s in mi ca du l:

A. 1,51 B. 2,01 C. 3,41 D. 2,25 Cu 24: Cho hai qu cu nh trung ha in cch nhau 40cm. Gi s bng cch no c 4.1012 electron t qu cu ny di chuyn sang qu cu kia. Khi chng ht hay y nhau? Tnh ln lc tng tc

A. Ht nhau F = 23mN B. Ht nhau F = 13mN C. y nhau F = 13mN D. y nhau F = 23mN

Cu 25: Hai qu cu nh in tch 10-7C v 4. 10-7C tc dng nhau mt lc 0,1N trong chn khng. Tnh khong cch gia chng:

A. 3cm B. 4cm C. 5cm D. 6cm Cu 26: Hai in tch im bng nhau t trong chn khng cch nhau mt khong 2cm th lc y gia chng l 1,6.10-4N. Khong cch gia chng bng bao nhiu lc tng tc gia chng l 2,5.10-4N, tm ln cc in tch :

A. 2,67.10-9C; 1,6cm B. 4,35.10-9C; 6cm C. 1,94.10-9C; 1,6cm D. 2,67.10-9C; 2,56cm

Cu 27: Tnh lc tng tc gia hai in tch q1 = q2 = 3C cch nhau mt khong 3cm trong chn khng (F1) v trong du ha c hng s in mi =2 ( F2):

A. F1 = 81N ; F2 = 45N B. F1 = 54N ; F2 = 27N C. F1 = 90N ; F2 = 45N D. F1 = 90N ; F2 = 30N

Cu 28: Hai in tch im cch nhau mt khong 2cm y nhau mt lc 1N. Tng in tch ca hai vt bng 5.10-5C. Tnh in tch ca mi vt:

A. q1 = 2,6.10-5 C; q2 = 2,4.10

-5 C B.q1 = 1,6.10-5 C; q2 = 3,4.10

-5 C C. q1 = 4,6.10

-5 C; q2 = 0,4.10-5 C D. q1 = 3.10

-5 C; q2 = 2.10-5 C

Cu 29: Hai qu cu kim loi nh tch in q1 = 3C v q2 = 1C kch thc ging nhau cho tip xc vi nhau ri t trong chn khng cch nhau 5cm. Tnh lc tng tc tnh in gia chng sau khi tip xc:

A. 12,5N B. 14,4N C. 16,2N D. 18,3N Cu 30: Hai qu cu kim loi nh tch in q1 = 5C v q2 = - 3C kch thc ging nhau cho tip xc vi nhau ri t trong chn khng cch nhau 5cm. Tnh lc tng tc tnh in gia chng sau khi tip xc:

A. 4,1N B. 5,2N C. 3,6N D. 1,7N Cu 31: Hai qu cu kch thc ging nhau cch nhau mt khong 20cm ht nhau mt lc 4mN. Cho hai qu cu tip xc vi nhau ri li t cch nhau vi khong cch c th chng y nhau mt lc 2,25mN. Tnh in tch ban u ca chng:


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A. q1 = 2,17.10-7 C; q2 = 0,63.10

-7 C B. q1 = 2,67.10-7 C; q2 = - 0,67.10

-7 C

C. q1 = - 2,67.10-7 C; q2 = - 0,67.10

-7 C D. q1 = - 2,17.10-7 C; q2 = 0,63.10

-7 C

Cu 32: Hai qu cu kim loi nh tch in cch nhau 2,5m trong khng kh chng tng tc vi nhau bi lc 9mN. Cho hai qu cu tip xc nhau th in tch ca mi qu cu bng - 3C. Tm in tch ca cc qu cu ban u:

A. q1 = - 6,8 C; q2 = 3,8 C B. q1 = 4C; q2 = - 7C

C. q1 = 1,41 C; q2 = - 4,41C D. q1 = 2,3 C; q2 = - 5,3 C

Cu 33: Hai qu cu kim loi nh kch thc ging nhau tch in cch nhau 20cm chng ht nhau mt lc 1,2N. Cho chng tip xc vi nhau tch ra n khong cch c th chng y nhau mt lc bng lc ht. Tm in tch ca mi qu cu lc u:

A. q1 = 0,16 C; q2 = m 5,84 C B. q1 = 0,24 C; q2 = m 3,26 C

C. q1 = 2,34C; q2 = m 4,36 C D. q1 = 0,96 C; q2 = m 5,57 C

Cu 34: Hai in tch im t cch nhau mt khong r trong khng kh th ht nhau mt lc F. a chng vo trong du c hng s in mi = 4, chng cch nhau mt khong r' = r/2 th lc ht gia chng l:

A. F B. F/2 C. 2F D. F/4

Cu 35: Hai cht im mang in tch khi t gn nhau chng y nhau th c th kt lun:

A. chng u l in tch dng B. chng u l in tch m

C. chng tri du nhau D. chng cng du nhau

Cu 36: Hai qu cu kim loi kch thc ging nhau mang in tch ln lt l q1 v q2, cho chng tip xc nhau ri tch ra th mi qu cu mang in tch:

A. q = q1 + q2 B. q = q1 - q2 C. q = (q1 + q2)/2 D. q = (q1 - q2 ) Cu 37: Hai qu cu kim loi kch thc ging nhau mang in tch vi |q1| = |q2|, a chng li gn th chng ht nhau. Nu cho chng tip xc nhau ri tch ra th chng s mang in tch:

A. q = 2 q1 B. q = 0 C. q = q1 D. q = q1/2 Cu 38: Hai qu cu kim loi kch thc ging nhau mang in tch vi |q1| = |q2|, a chng li gn th chng y nhau. Nu cho chng tip xc nhau ri tch ra th chng s mang in tch:

A. q = q1 B. q = q1/2 C. q = 0 D. q = 2q1 Cu 39: Hai in tch im bng nhau t trong chn khng cch nhau mt on 4cm, chng y nhau mt lc 10-5 N. ln mi in tch l:

A. |q| = 1,3.10-9 C B. |q| = 2 .10-9 C C. |q| = 2,5.10-9 C D. |q| = 2.10-8 C

Cu 40: Hai in tch im bng nhau t trong chn khng cch nhau mt on 4cm, chng ht nhau mt lc 10-5 N. lc ht gia chng l 2,5.10-6 N th chng phi t cch nhau:

A. 6cm B. 8cm C. 2,5cm D. 5cm p n

Cu 1 2 3 4 5 6 7 8 9 10 p n

C C D D C B D A C c

Cu 11 12 13 14 15 16 17 18 19 20 p A C D C D C D C A A


Trang 10

n

Cu 21 22 23 24 25 26 27 28 29 30

p n

B C D A D A C C B C

Cu 31 32 33 34 35 36 37 38 39 40 p n

B C D A D C B A A B

H v tn:..Thpt...

I.kin thc: PP Chung: i vi dng bi tp ny, Hs cn vn dng nh lut bo ton in tch: Trong mt h c lp v in, tng i s cc in tch lun lun l mt hng s II. BI TP T LUN: 1. Hai qu cu kim loi nh nh nhau mang cc in tch q1 v q2 t trong khng kh cch nhau 2 cm, y nhau bng mt lc 2,7.10-4 N. Cho hai qu cu tip xc nhau ri li a v v tr c, ch y nhau bng mt lc 3,6.10-4 N. Tnh q1, q2 ? s: 6.10

-9 C , 2. 10-9 C, -6. 10-9 C, -2. 10-9 C. 2. Hai qu cu nh, ging nhau, bng kim loi. Qu cu A mang in tch 4,50 C; qu cu B mang in tch 2,40 C. Cho chng tip xc nhau ri a chng ra cch nhau 1,56 cm. Tnh lc tng tc in gia chng. s: 40,8 N. 3. Hai qu cu nh bng kim loi ging ht nhau, mang in tch nh nhau q t cch nhau mt khong R, chng y nhau mt lc c ln 6,4 N. Sau khi cho chng tip xc nhau ri tch ra mt khong 2R th chng y nhau mt lc bao nhiu ? s: 1,6 N. 4. Hai hn bi bng kim loi ging nhau, hn bi ny c ln in tch bng 5 ln hn bi kia. Cho x dch hai hn bi chm nhau ri t chng li v tr c. ln ca lc tng tc bin i th no nu in tch ca chng : a. cng du. b. tri du. s: Tng 1,8 ln, gim 0,8 ln. 5. Hai hn bi bng kim loi ging nhau c in tch cng du q v 4q cch nhau mt khong r. Sau khi cho hai hn bi tip xc nhau, cho lc tng tc gia chng khng thay i, ta phi t chng cch mt khong r. Tm r ? s: r

= 1,25 r. 6. Hai qu cu kim loi ging nhau, c tch in 3.10-5 C v 2.10-5 C. Cho hai qu cu tip xc nhau ri t cch nhau mt khong 1m. Lc in tc dng ln mi qu cu c ln l bao nhiu? s: 5,625 N. III. BI TP TRC NGHIM:

NH LUT BO TON IN TCH - HP LC TC DNG 2


Trang 11

Cu 1: Hai in tch c ln bng nhau cng du l q t trong khng kh cch nhau mt khong r. t in tch q3 ti trung im ca on thng ni hai in tch trn. Lc tc dng ln q3 l:

A. 8k2

31

r

qq B. k

231

r

qq C.4k2

31

r

qq D. 0

Cu 2: Ti ba nh A, B, C ca mt tam gic u c cnh 15cm t ba in tch qA = + 2C, qB = + 8 C, qC = - 8 C. Tm vct lc tc dng ln qA:

A. F = 6,4N, phng song song vi BC, chiu cng chiu BC B. F = 8,4 N, hng vung gc vi BC C. F = 5,9 N, phng song song vi BC, chiu ngc chiu BC D. F = 6,4 N, hng theo AB

Cu 3: Ti bn nh ca mt hnh vung cnh bng 10cm c bn in tch t c nh trong c hai in tch dng v hai in tch m ln bng nhau u bng 1,5 C, chng c t trong in mi = 81 v c t sao cho lc tc dng ln cc in tch u hng vo tm hnh vung. Hi chng c sp xp nh th no, tnh lc tc dng ln mi in tch:

A. Cc in tch cng du cng mt pha, F = 0,043N B. Cc in tch tri du xen k nhau, F = 0,127N C. Cc in tch tri du xen k nhau, F = 0,023N D. Cc in tch cng du cng mt pha, F = 0,023N

Cu 4: Trong mt phng ta xoy c ba in tch im q1 = +4 C t ti gc O, q2 = - 3 C t ti M trn trc Ox cch O on OM = +5cm, q3 = - 6 C t ti N trn trc Oy cch O on ON = +10cm. Tnh lc in tc dng ln q1:

A. 1,273N B. 0,55N C. 0,483 N D. 2,13N Cu 5: Hai in tch im bng nhau q = 2 C t ti A v B cch nhau mt khong AB = 6cm. Mt in tch q1 = q t trn ng trung trc ca AB cch AB mt khong x = 4cm. Xc nh lc in tc dng ln q1:

A. 14,6N B. 15,3 N C. 17,3 N D. 21,7N Cu 6: Ba in tch im q1 = 2.10

-8 C, q2 = q3 = 10-8 C t ln lt ti 3 nh A, B, C ca tam

gic vung ti A c AB = 3cm, AC = 4cm. Tnh lc in tc dng ln q1: A. 0,3.10-3 N B. 1,3.10-3 N C. 2,3.10-3 N D.

3,3.10-3 N Cu 7: Bn in tch im q1, q2, q3, q4 t trong khng kh ln lt ti cc nh ca mt hnh vung ABCD, bit hp lc in tc dng vo q4 D c phng AD th gia in tch q2 v q3 lin h vi nhau:

A. q2 = q3 2 B. q2 = - 2 2 q3 C. q2 = ( 1 + 2 )q3 D. q2 = ( 1 - 2 )q3 Cu 8: Ba in tch im q1 = 8nC, q2 = q3 = - 8nC t ti ba nh ca tam gic u ABC cnh a = 6cm trong khng kh xc nh lc tc dng ln in tch q0 6nC t tm O ca tam gic:

A. 72.10-5N nm trn AO, chiu ra xa A B. 72.10-5N nm trn AO, chiu li gn A C. 27. 10-5N nm trn AO, chiu ra xa A D. 27. 10-5N nm trn AO, chiu li gn A

Cu 9: C hai in tch q1 = + 2.10-6 (C), q2 = - 2.10

-6 (C), t ti hai im A, B trong chn khng v cch nhau mt khong 6 (cm). Mt in tch q3 = + 2.10

-6 (C), t trn ng trung trc ca AB, cch AB mt khong 4 (cm). ln ca lc in do hai in tch q1 v q2 tc dng ln in tch q3 l:

A. F = 14,40 (N). B. F = 17,28 (N) .C. F = 20,36 (N). D. F = 28,80 (N)


Trang 12

Cu 10: Hai in tch c ln bng nhau tri du l q t trong khng kh cch nhau mt khong r. t in tch q3 ti trung im ca on thng ni hai in tch trn. Lc tc dng ln q3 l:

A. 2k2

31

r

qq B. 2k

2

21

r

qq C. 0 D. 8k

2

31

r

qq

Cu 1 2 3 4 5 6 7 8 9 10 p n

D A C C C C C A B D

H v tn:..Thpt...

I.kin thc cn nh: PP Chung Khi kho st iu kin cn bng ca mt in tch ta thng gp hai trng hp: . Trng hp ch c lc in:

- Xc nh phng, chiu, ln ca tt c cc lc in 1Fr

, 2Fr

, tc dng ln in tch xt.

- Dng iu kin cn bng: 0...21rrr

=++ FF - V hnh v tm kt qu. . Trng hp c thm lc c hc (trng lc, lc cng dy, ) - Xc nh y phng, chiu, ln ca tt c cc lc tc dng ln vt mang in m ta xt. - Tm hp lc ca cc lc c hc v hp lc ca cc lc in.

- Dng iu kin cn bng: 0rrr

=+ FR FRrr

= (hay ln R = F). - Trong SGK VL 11, cng thc ca nh lut CouLomb ch dng tnh ln ca lc tc dng gia hai in tch im. V vy, ta ch a ln (ch khng a du) ca cc in tch vo cng thc. II. Bi tp t lun: 1. Hai in tch im q1 = 10

-8 C, q2 = 4. 10-8 C t ti A v B cch nhau 9 cm trong chn khng.

Phi t in tch q3 = 2. 10-6 C ti u in tch q3 nm cn bng (khng di chuyn) ?

s: Ti C cch A 3 cm, cch B 6 cm. 2. Hai in tch im q1 = q2 = -4. 10

-6C, t ti A v B cch nhau 10 cm trong khng kh. Phi t in tch q3 = 4. 10

-8C ti u q3 nm cn bng? s: CA = CB = 5 cm. 3. Hai in tch q1 = 2. 10

-8 C, q2= -8. 10-8 C t ti A v B trong khng kh, AB = 8 cm.Mt

in tch q3 t ti C. Hi: a. C u q3 cn bng? b. Du v ln ca q3 q1 v q2 cng cn bng? s: CA= 8 cm,CB= 16 cm, q3 = -8. 10-8 C. 4. Hai in tch q1 = - 2. 10

-8 C, q2= 1,8. 10-8 C t ti A v B trong khng kh, AB = 8 cm. Mt

in tch q3 t ti C. Hi: a. C u q3 cn bng? s: CA= 4 cm,CB= 12 cm

in tch chu td lc Culng cn bng

3


Trang 13

b. Du v ln ca q3 q1 v q2 cng cn bng ? s: q3 = 4,5. 10-8 C.

5. Ti ba nh ca mt tam gic u cnh a ngi ta t ba in tch ging nhau q1 = q2 = q3 = 6. 10-7 C. Hi phi t t in tch th t q0 ti u, c gi tr l bao nhiu h thng ng yn cn bng?

s: q0 = Cq 71 10.46,333

6. Cho hai in tch q1 = 6q, q2 = 2

.3 q ln lt t ti A v B cch nhau mt mt khong a (cm).

Phi t mt in tch q0 u v c tr s th no n cn bng? s: Nm trn AB,

cch B: 3

a cm.

7. Hai in tch q1 = 2. 10-8 C t ti A v q2 = -8. 10

-8C t ti B, chng cch nhau mt on AB = 15 cm trong khng kh. Phi t mt in tch q3 ti M cch A bao nhiu n cn bng? s: AM = 10 cm. 8. trng tm ca mt tam gic u ngi ta t mt in tch q1 = C610.3 . Xc nh in tch q cn t mi nh ca tam gic cho c h trng thi cn bng? s: -3. 10-6 C. 9. Hai qu cu nh cng khi lng m= 0,6 kg c treo trong khng kh bng hai si dy nh cng chiu di l= 50 cm vo cng mt im. Khi hai qu cu nhim in ging nhau, chng y nhau v cch nhau mt khong R = 6 cm. a. Tnh in tch ca mi qu cu, ly g= 10m/s2. b. Nhng h thng vo ru tylic (= 27), tnh khong cch R gia hai qu cu, b qua lc y Acsimet. Cho bit khi gc nh th sin tg . s: 12. 10-9 C, 2 cm. 10. Hai qu cu nh ging nhau bng nhm khng nhim in, mi qu cu c khi lng 0,1 kg v c treo vo hai u mt si ch t di 1m ri mc vo cng mt im c nh sao cho hai qu cu va chm vo nhau. Sau khi chm mt vt nhim in vo mt trong hai qu cu th thy chng y nhau v tch ra xa nhau mt khong r = 6 cm. Xc nh in tch ca mi qu cu? s: 0,035. 10-9 C. 11*. Hai qu cu kim loi nh ging nhau mi qu c in tch q khi lng m = 10g treo bi hai dy cng chiu di 30 cm vo cng mt im. Gi cho qu cu I c nh theo phng thng ng, dy treo qu cu II s lch gc = 600 so vi phng thng ng. Cho g= 10m/s2. Tm q ?

s: q = Ck

gml 610

. =

III. Bi tp trc nghim: 1: Cu 1: Hai in tch im q v 4q t cch nhau mt khong r. Cn t in tch th 3 Q c in tch dng hay m v u in tch ny cn bng, khi q v 4q gi c nh:

A. Q > 0, t gia hai in tch cch 4q khong r/4 B. Q < 0, t gia hai in tch cch 4q khong 3r/4 C. Q > 0, t gia hai in tch cch q khong r/3 D. Q ty t gia hai in tch cch q khong r/3

Cu 2: Hai in tch im q v 4q t cch nhau mt khong r. Cn t in tch th 3 Q c in tch dng hay m v u h 3 in tch ny cn bng:


Trang 14

A. Q > 0, t gia hai in tch cch 4q khong r/3 B. Q < 0, t gia hai in tch cch 4q khong 2r/3 C.Q tri du vi q t gia 2 in tch cch q khong r/3 D.Q ty t gia 2 in tch cch q khong r/3

Cu 3: Ti bn nh ca mt hnh vung t 4 in tch im ging nhau q = + 1C v ti tm hnh vung t in tch q0, h nm in tch cn bng. Tm du v ln in tch im q0?

A. q0 = + 0,96 C B. q0 = - 0,76 C C. q0 = + 0,36 C D. q0 = - 0,96 C Cu 4: Mt qu cu khi lng 10g mang in tch q1 = + 0,1C treo vo mt si ch cch in, ngi ta a qu cu 2 mang in tch q2 li gn th qu cu th nht lch khi v tr ban u mt gc 300, khi hai qu cu trn cng mt mt phng nm ngang cch nhau 3cm. Tm du, ln in tch q2 v sc cng ca si dy:

A. q2 = + 0,087 C B. q2 = - 0,087 C C. q2 = + 0,17 C D. q2 = - 0,17 C Cu 5: Ngi ta treo hai qu cu nh khi lng bng nhau m = 0,01g bng hai si dy c di nh nhau l = 50cm( khi lng khng ng k). Cho chng nhim in bng nhau chng y nhau cch nhau 6cm. Tnh in tch mi qu cu:

A. q = 12,7pC B. q = 19,5pC C. q = 15,5nC D.q = 15,5.10-10C Cu 6: Treo hai qu cu nh khi lng bng nhau m bng nhng si dy cng di l( khi lng khng ng k). Cho chng nhim in bng nhau chng y nhau cch nhau khong r = 6cm. Nhng c h thng vo trong ru c = 27, b qua lc y Acsimet, tnh khong cch gia chng khi tng tc trong du:

A. 2cm B. 4cm C. 6cm D. 1,6cm Cu 7: Ngi ta treo hai qu cu nh khi lng bng nhau m = 0,1g bng hai si dy c di nh nhau l ( khi lng khng ng k). Cho chng nhim in bng nhau chng y nhau v cn bng khi mi dy treo hp vi phng thng ng mt gc 150. Tnh lc tng tc in gia hai qu cu:

A. 26.10-5N B. 52.10-5N C. 2,6.10-5N D. 5,2.10-5N Cu 8: Ngi ta treo hai qu cu nh khi lng bng nhau m = 0,1g bng hai si dy c di nh nhau l = 10cm( khi lng khng ng k). Truyn mt in tch Q cho hai qu cu th chng y nhau cn bng khi mi dy treo hp vi phng thng ng mt gc 150, ly g = 10m/s2. Tnh in tch Q:

A. 7,7nC B. 17,7nC C. 21nC D. 27nC Cu 9: Ba in tch bng nhau q dng t ti 3 nh ca tam gic u ABC cnh a. Hi phi t mt in tch q0 nh th no v u lc in tc dng ln cc in tch cn bng nhau:

A. q0 = +q/ 3 , gia AB B. q0 = - q/ 2 , trng tm ca tam gic C. q0 = - q/ 3 , trng tm ca tam gic D. q0 = +q/ 3 , nh A ca tam gic

Cu 10: Hai qu cu nh bng kim loi ging ht nhau tch in dng treo trn hai si dy mnh cng chiu di vo cng mt im. Khi h cn bng th gc hp bi hai dy treo l 2. Sau cho chng tip xc vi nhau ri bung ra, chng cn bng th gc lch by gi l 2 '. So snh v ':

A. > ' B. < ' C. = ' D. c th ln hoc nh hn ' Cu 11: Hai qu cu nh kim loi ging ht nhau mang in tch q1 v q2 t trong chn khng cch nhau 20cm ht nhau mt lc 5.10- 7 N. t vo gia hai qu cu mt tm thy tinh dy d = 5cm c hng s in mi = 4 th lc lc ny tng tc gia hai qu cu l bao nhiu?

A. 1,2.10-7 N B. 2,2.10-7 N C. 3,2.10-7 N D.4 ,2.10-7 N Cu 12: Hai qu cu ging nhau khi lng ring l D tch in nh nhau treo u ca hai si dy di nh nhau t trong du khi lng ring D0, hng s in mi = 4 th gc lch gia hai dy treo l . Khi t ra ngoi khng kh thy gc lch gia chng vn bng . Tnh t s D/ D0


Trang 15

A. 1/2 B. 2/3 C. 5/2 D. 4/3 Cu 13: Bn in tch im q1, q2, q3, q4 t trong khng kh ln lt ti cc nh ABCD ca hnh vung thy hp lc tnh in tc dng ln q4 ti D bng khng. Gia 3 in tch kia quan h vi nhau:

A. q1 = q3; q2 = q1 2 B. q1 = - q3; q2 = ( 1+ 2 )q1 C. q1 = q3; q2 = - 2 2 q1 D. q1 = - q3; q2 = ( 1- 2 )q1

Cu 14: Hai in tch im trong khng kh q1 v q2 = - 4q1 ti A v B, t q3 ti C th hp cc lc in tc dng ln q3 bng khng. Hi im C c v tr u:

A. trn trung trc ca AB B. Bn trong on AB C. Ngoi on AB. D. khng xc nh c v cha bit gi tr ca q3

Cu 15: Hai in tch im trong khng kh q1 v q2 = - 4q1 ti A v B vi AB = l, t q3 ti C th hp cc lc in tc dng ln q3 bng khng. Khong cch t A v B ti C ln lt c gi tr:

A. l/3; 4l/3 B. l/2; 3l/2 C. l; 2l D. khng xc nh c v cha bit gi tr ca q3 Cu 16: Hai qu cu kim loi nh ging nhau khi lng m, tch in cng loi bng nhau c treo bi hai si dy nh di l cch in nh nhau vo cng mt im. Chng y nhau khi cn bng hai qu cu cch nhau mt on r


Trang 16

I. Kin thc cn nh:

1.Khi nim.

- in trng tnh l do cc ht mang in ng yn sinh ra. - Tnh cht c bn ca in trng l n tc dng lc in ln in tch t trong n. - Theo quy c v chiu ca vect cng in trng: Vct cng in trng ti mt im lun cng phng, cng chiu vi vect lc in tc dng ln mt in tch dng t ti im trong in trng. PP Chung . Cng in trng ca mt in tch im Q:

p dng cng thc 2.r

Qk

q

FE

== . q1----------------- 1E

r

q1-------------------

(Cng in trng E1 do q1 gy ra ti v tr cch q1 mt khong r1 : 21

11

.r

qkE

= ,

Lu cng in trng E l mt i lng vect. Trong chn khng, khng kh = 1) n v chun: k = 9.109 (N.m2/c2 ), Q (C), r (m), E (V/m) II. Bi tp t lun: 1. Xc nh vect cng in trng ti im M trong khng kh cch in tch im q = 2.10-8 C mt khong 3 cm. s: 2.105 V/m. 2. Mt in tch im dng Q trong chn khng gy ra mt in trng c cng E = 3. 104 V/m ti im M cch in tch mt khong 30 cm. Tnh ln in tch Q ? s: 3. 10-7 C. 3. Mt in tch im q = 10-7 C t ti im M trong in trng ca mt in tch im Q, chu tc dng ca mt lc F = 3.10-3 N. Cng in trng do in tch im Q gy ra ti M c ln l bao nhiu ? s: 3. 104 V/m. 4 Mt qu cu nh khi lng m= 0,25 g mang in tch q= 2,5. 10-9C c treo bi mt dy v t trong mt in trng u E

r. Er

c phng nm ngang v c ln E= 106 V/m. Tnh gc lch ca dy treo so vi phng thng ng. Ly g= 10 m/s2. s: = 450. III.Bi tp trc nghim: in trng - Dng 1: Xc nh llq E ca in tch im- 1 Cu hi 1: p n no l ng khi ni v quan h v hng gia vct cng in trng v lc in trng : A. E cng phng chiu vi F tc dng ln in tch th t trong in trng

B. E cng phng ngc chiu vi F tc dng ln in tch th t trong in trng

4

IN TRNG - s 1

1Er


Trang 17

C. E cng phng chiu vi F tc dng ln in tch th dng t trong in trng

D. E cng phng chiu vi F tc dng ln in tch th m t trong in trng Cu hi 2: Trong cc quy tc v cc ng sc in sau y, quy tc no l sai:

A. Ti mt im bt k trong in trng c th v c mt ng sc i qua n B. Cc ng sc xut pht t cc in tch m, tn cng ti cc in tch dng C. Cc ng sc khng ct nhau D. Ni no cng in trng ln hn th cc ng sc c v dy hn

Cu hi 3: Mt in tch q c t trong in mi ng tnh, v hn. Ti im M cch q 40cm, in trng c cng 9.105V/m v hng v in tch q, bit hng s in mi ca mi trng l 2,5. Xc nh du v ln ca q:

A. - 40 C B. + 40 C C. - 36 C D. +36 C Cu hi 4: Mt in tch th t ti im c cng in trng 0,16 V/m. Lc tc dng ln in tch bng 2.10-4N. ln ca in tch l:

A. 1,25.10-4C B. 8.10-2C C. 1,25.10-3C D. 8.10-4C Cu hi 5:in tch im q = -3 C t ti im c cng in trng E = 12 000V/m, c phng thng ng chiu t trn xung di. Xc nh phng chiu v ln ca lc tc dng ln in tch q:

A. F c phng thng ng, chiu t trn xung di, F = 0,36N

B. F c phng nm ngang, chiu t tri sang phi, F = 0,48N

C. F c phng thng ng, chiu t di ln trn, F = 0,36N

D. F c phng thng ng, chiu t di ln trn, F = 0,036N Cu hi 6: Mt in tch q = 5nC t ti im A. Xc nh cng in trng ca q ti im B cch A mt khong 10cm:

A. 5000V/m B. 4500V/m C. 9000V/m D. 2500V/m Cu hi 7: Mt in tch q = 10-7C t trong in trng ca mt in tch im Q, chu tc dng lc F = 3mN. Tnh cng in trng ti im t in tch q. Bit rng hai in tch cch nhau mt khong r = 30cm trong chn khng:

A. 2.104 V/m B. 3.104 V/m C. 4.104 V/m D. 5.104 V/m Cu hi 8: in tch im q t ti O trong khng kh, Ox l mt ng sc in. Ly hai im A, B trn Ox, t M l trung im ca AB. Gia EA, EB ,EM c mi lin h:

A. EM = (EA + EB)/2 B. ( )BAM EEE += 21

C.

+=

BAM EEE

112

1 D.

+=

BAM EEE

11

2

11

Cu hi 9: Cng in trng ca mt in tch im ti A bng 36V/m, ti B bng 9V/m. Hi cng in trng ti trung im C ca AB bng bao nhiu, bit hai im A, B nm trn cng mt ng sc:

A. 30V/m B. 25V/m C. 16V/m D. 12 V/m Cu hi 10: Mt in tch q = 10-7C t trong in trng ca mt in tch im Q, chu tc dng lc F = 3mN. Tnh ln ca in tch Q. Bit rng hai in tch cch nhau mt khong r = 30cm trong chn khng: A. 0,5 C B. 0,3 C C. 0,4 C D. 0,2 C

Cu 1 2 3 4 5 6 7 8 9 10 p C B A C D B B D C B


Trang 18

n in trng - Dng 1: Xc nh llq E ca in tch im- 2 Cu hi 1: Mt qu cu nh mang in tch q = 1nC t trong khng kh. Cng in trng ti im cch qu cu 3cm l:

A. 105V/m B. 104 V/m C. 5.103V/m D. 3.104V/m Cu hi 2: Mt qu cu kim loi bn knh 4cm mang in tch q = 5.10-8C. Tnh cng in trng trn mt qu cu:

A. 1,9.105 V/m B. 2,8.105V/m C. 3,6.105V/m D. 3,14.105V/m Cu hi 3: Cho hai qu cu kim loi bn knh bng nhau, tch in cng du tip xc vi nhau. Cc in tch phn b nh th no trn hai qu cu nu mt trong hai qu cu l rng;

A. qu cu c phn b u trong c th tch, qu cu rng ch mt ngoi B. qu cu c v qu cu rng phn b u trong c th tch C. qu cu c v qu cu rng ch phn b mt ngoi D. qu cu c phn b mt ngoi, qu cu rng phn b u trong th tch

Cu hi 4: Mt git thy ngn hnh cu bn knh 1mm tch in q = 3,2.10-13C t trong khng kh. Tnh cng in trng trn b mt git thy ngn :

A. E = 2880V/m B. E = 3200V/m C. 32000V/m D. 28800 V/m Cu hi 5: Mt qu cu kim loi bn knh 4cm mang in tch q = 5.10-8C. Tnh cng in trng ti im M cch tm qu cu 10cm:

A. 36.103V/m B. 45.103V/m C. 67.103V/m D. 47.103V/m Cu hi 6: Mt v cu mng bng kim loi bn knh R c tch in +Q. t bn trong v cu ny mt qu cu kim loi nh hn bn knh r, ng tm O vi v cu v mang in tch +q. Xc nh cng in trng trong qu cu v ti im M vi r < OM < R:

A. EO = EM = k 2OMq B. EO = EM = 0 C. EO = 0; EM = k 2OM

q D. EO = k 2OMq ;

EM = 0 Cu hi 7: Mt qu cu kim loi bn knh R1 = 3cm mang in tch q1 = 5.10

-8C. Qu cu c bao quanh bng mt v cu kim loi t ng tm O c bn knh R2 = 5cm mang in tch q2 = - 6.10-8C. Xc nh cng in trng nhng im cch tm O 2cm, 4cm, 6cm:

A. E1 = E2 = 0; E3 = 3.105 V/m

B. E1 = 1,4.105 V/m; E2 = 2,8.10

5 V/m ; E3 = 2,5.105 V/m

C. E1 = 0; E2 = 2,8.105V/m; E3 = 2,5.10

5V/m D. E1 = 1,4.10

5 V/m; E2 = 2,5.105 V/m; E3 = 3.10

5 V/m Cu hi 8: t mt in tch m, khi lng nh vo mt in trng u ri th nh. in tch s chuyn ng:

A. dc theo chiu ca ng sc in trng. B. ngc chiu ng sc in trng. C. vung gc vi ng sc in trng. D. theo mt qu o bt k.

Cu hi 9: Cng thc xc nh cng in trng gy ra bi in tch im Q < 0, ti mt im trong chn khng cch in tch im mt khong r l: ( ly chiu ca vct khong cch lm chiu dng):

A. 2

910.9r

QE = B.

2910.9

r

QE = C.

r

QE 910.9= D.

r

QE 910.9=

Cu hi 10: Cng in trng gy ra bi in tch Q = 5.10-9 (C), ti mt im trong chn khng cch in tch mt khong 10 (cm) c ln l:


Trang 19

A. E = 0,450 (V/m). B. E = 0,225 (V/m). C. E = 4500 (V/m). D. E = 2250 (V/m). Cu 1 2 3 4 5 6 7 8 9 10 p n

B B C A B C C D A A

Dng 4 chuyn ng ca in tch trong in trng: Bi 1: Mt electron c th khng vn tc u st bn m, trong in trng u gia hai

bn kim loi phng, tch in tri du. Cng in trng gia hai bn l 1000 V/m.

Khong cch gia hai bn l 1cm. Tnh ng nng ca electron khi n p vo bn

dng?

Bi 2: Prtn c t vo in trng u E=1,7.106V/m .

a) Tm gia tc ca prtn? Bit m=1.673.10-27kg.

b) Tm vn tc ca prtn sau khi i c 20cm ?

Bi 3: Electron ang chuyn ng vi vn tc V0 =4.106m/s th i vo in trng u

E=9x102V/m; 0Vr

cng chiu ng sc in trng. M t chuyn ng ca electron

trong cc trng hp sau:

a) Evrr

0 ; b) Evrr

0 ; c) Evrr

0

I. Kin thc cn nh: PP Chung . Cng in trng ca mt in tch im Q:

p dng cng thc 2.r

Qk

q

FE

== . q1----------------- 1E

r

q1-------------------

(Cng in trng E1 do q1 gy ra ti v tr cch q1 mt khong r1 : 21

11

.r

qkE

= ,

Lu cng in trng E l mt i lng vect. Trong chn khng, khng kh = 1) n v chun: k = 9.109 (N.m2/c2 ), Q (C), r (m), E (V/m) . Cng in trng ca mt h in tch im: p dng nguyn l chng cht in trng: + Xc nh phng, chiu, ln ca tng vect cng in trng do tng in tch gy ra. + V vect cng in trng tng hp. + Xc nh ln ca cng in trng tng hp t hnh v.

5

IN TRNG - s 2

1Er


Trang 20

Khi xc nh tng ca hai vect cn lu cc trng hp c bit: , , , tam giac vung, tam gic u, Nu khng xy ra cc trng hp t bit th c th tnh di ca vect bng nh l hm cosin: a2 = b2 + c2 2bc.cosA. II. Bi tp t lun: 1. Cho hai in tch q1 = 4. 10

-10 C, q2 = -4. 10-10 C, t ti A v B trong khng kh bit AB = 2

cm. Xc nh vect cng in trng Er

ti: a. H, l trung im ca AB. b. M, MA = 1 cm, MB = 3 cm. c. N, bit rng NAB l mt tam gic u. s: 72. 103 V/m. 32. 103 V/m. 9. 103 V/m. 2. Gii li bi ton s 4 trn vi q1 = q2 = 4. 10

-10 C. 3. Hai in tch q1 = 8. 10

-8 C, q2 = -8. 10-8 C t ti A v B trong khng kh bit AB = 4 cm.

Tm vect cng in trng ti C trn ng trung trc ca AB v cch AB 2 cm, suy ra lc tc dng ln in tch q = 2. 10-9 C t ti C. s: 12,7. 105 V/m. F = 25,4. 10-4 N. 4. Hai in tch q1 = -10

-8 C, q2 = 10-8 C t ti A v B trong khng kh, AB = 6 cm. Xc nh

vect cng in trng ti M nm trn ng trung trc ca AB cch AB 4 cm. s: 0,432. 105 V/m. 5. Ti ba nh ca mt tam gic vung ti A cnh a= 50 cm, b= 40 cm, c= 30 cm.Ta t ln lt cc in tch q1 = q2 = q3 = 10

-9 C. Xc nh vect cng in trng ti H, H l chn ng cao k t A. s: 246 V/m. 6. Ti hai im A v B cch nhau 5 cm trong chn khng c hai in tch q1 = 16.10

-8 C, q2 = -9.10-8 C. Tm cng in trng tng hp v v vect cng in trng ti im C nm cch A mt khong 4 cm, cch B mt khong 3 cm. s: 12,7. 105 V/m. 7. Hai in tch im q1 = 2. 10

-2 C, q2 = -2. 10-2 C t ti hai im A v B cch nhau mt

on a = 30 cm trong khng kh. Tnh cng in trng ti M cch u A v B mt khong l a. s: 2000 V/m. 8. Trong chn khng, mt in tch im q = 2. 10-8C t ti mt im M trong in trng ca mt in tch im Q = 2. 10-6C chu tc dng ca mt lc in F = 9.10-3N. Tnh cng in trng ti M v khong cch gia hai in tch? s: 45.104V/m, R = 0,2 m. 9. Trong chn khng c hai in tch im q1= 3. 10

-8C v q2= 4.10-8C t theo th t ti hai

nh B v C ca tam gic ABC vung cn ti A vi AB=AC= 0,1 m. Tnh cng in trng ti A. s: 45. 103 V/m. 10. Trong chn khng c hai in tch im q1 = 2. 10

-8C v q2= -32.10-8C t ti hai im A v

B cch nhau mt khong 30 cm. Xc nh v tr im M ti cng in trng bng khng. s: MA = 10 cm, MB = 40 cm. 11*. Bn im A, B, C, D trong khng kh to thnh mt hnh ch nht ABCD cnh AD = a= 3 cm, AB= b= 1 cm.Cc in tch q1, q2, q3 c t ln lt ti A, B, C. Bit q2 = - 12,5. 10

-8C v

cng in trng tng hp D 0rv

=DE . Tnh q1 v q3? s: q1 2,7. 10

-8C, q2 = 6,4. 10-8C.


Trang 21

12. Cho hai in tch im q1 v q2 t A v B trong khng kh, AB = 100 cm. Tm im C m ti cng in trng bng khng vi: a. q1= 36. 10

-6C, q2= 4. 10-6C. b. q1= - 36. 10

-6C, q2= 4. 10-6C.

s: a. CA= 75cm, CB= 25cm. b. CA= 150 cm, CB= 50 cm. 13. Cho hai in tch im q1, q2 t ti A v B, AB= 2 cm. Bit q1 + q2 = 7. 10

-8C v im C cch q1 l 6 cm, cch q2 l 8 cm c cng in trng bng E = 0. Tm q1 v q2 ? s: q1= -9.10

-8C, q2= 16.10-8C.

14. Cho hnh vung ABCD, ti A v C t cc in tch q1 = q3 = q. Hi phi t B mt in tch bao nhiu cng in trng D bng khng? s: q2 = - q.22

III. BI TP TRC NGHIM: in trng - Dng 3: Nguyn l chng cht in trng - 1 Cu hi 1: Hai in tch im q1 = 5nC, q2 = - 5nC cch nhau 10cm. Xc nh vct cng in trng ti im M nm trn ng thng i qua hai in tch v cch u hai in tch:

A. 18 000V/m B. 45 000V/m C. 36 000V/m D. 12 500V/m Cu hi 2: Hai in tch im q1 = 5nC, q2 = - 5nC cch nhau 10cm. Xc nh vct cng in trng ti im M nm trn ng thng i qua hai in tch v cch q1 5cm; cch q2 15cm:

A. 4 500V/m B. 36 000V/m C. 18 000V/m D. 16 000V/m Cu hi 3: Ti ba nh ca tam gic u cnh 10cm c ba in tch bng nhau v bng 10nC. Hy xc nh cng in trng ti trung im ca cnh BC ca tam gic:

A. 2100V/m B. 6800V/m C. 9700V/m D. 12 000V/m Cu hi 4: Ti ba nh ca tam gic u cnh 10cm c ba in tch bng nhau v bng 10nC. Hy xc nh cng in trng ti tm ca tam gic:

A. 0 B. 1200V/m C. 2400V/m D. 3600V/m Cu hi 5: Mt in tch im q = 2,5C t ti im M trong in trng u m in trng c hai thnh phn Ex = +6000V/m, Ey = - 6 3 .10

3 V/m. Vct lc tc dng ln in tch q l: A. F = 0,03N, lp vi trc Oy mt gc 1500 B. F = 0,3N, lp vi trc Oy mt gc 300 C. F = 0,03N, lp vi trc Oy mt gc 1150 D.F = 0,12N, lp vi trc Oy mt gc 1200

Cu hi 6: Ba in tch im cng ln, cng du q t ti ba nh ca mt tam gic u cnh a. Xc nh cng in trng ti im t ca mi in tch do hai in tch kia gy ra:

A. E = k2

22

a

q B.E = 2k 2

3

a

q C. E = k 2

3

a

q D. E = k a

q 3

Cu hi 7: Hai in tch im cng ln q, tri du, t ti 2 nh ca mt tam gic u cnh a. Xc nh cng in trng ti nh cn li ca tam gic do hai in tch kia gy ra:

A. E = k2a

q B. E = k 2

3

a

q C. E = 2k2a

q D. E = 2

1 k2a

q

Cu hi 8: Bn in tch im cng ln cng du q t ti bn nh ca hnh vung cnh a. Xc nh cng in trng gy ra bi bn in tch ti tm ca hnh vung:

A. E = 2k2a

q B. E = 4k 2

2

a

q C. 0 D. E = k 2

3

a

q


Trang 22

Cu hi 9: Bn in tch im cng ln q, hai in tch dng v hai in tch m, t ti bn nh ca hnh vung cnh a, cc in tch cng du k nhau. Xc nh cng in trng gy ra bi bn in tch ti tm ca hnh vung:

A. E = 2k 2

3

a

q B. E = k 2

3

a

q C. E = k 22

3

a

q D. E = 4k 2

2

a

q

Cu hi 10: Hai in tch dng q t ti A v B, AB = a. Xc nh vct cng in trng ti im M trn ng trung trc ca on thng AB cch trung im O ca AB mt on OM = a 3 /6:

A.E = k2a

q , hng theo trung trc ca AB i xa AB B.E = k2

2

a

q , hng theo trung trc ca

AB i vo AB

C. E = k2

3

a

q , hng theo trung trc ca AB i xa AB D. E = k2

3

a

q , hng hng song song

vi AB

Cu 1 2 3 4 5 6 7 8 9 10 p n

C D D A A C B C D C

in trng - Dng 3: Nguyn l chng cht in trng - 2 Cu hi 1: Hai in tch +q v - q t ln lt ti A v B, AB = a. Xc nh vct cng in trng ti im M trn ng trung trc ca on thng AB cch trung im O ca AB mt on OM = a 3 /6:

A.E = k2

2

a

q , hng song song vi AB B.E = k2

2

a

q , hng song song vi AB

C. E = k2

3

a

q , hng theo trung trc ca AB i xa AB D. E = k2

33

a

q , hng song song vi

AB Cu hi 2: Hai in tch t trong khng kh ti M v N. Ti I nm trn ng trung trc ca MN cch MN mt on IH c vct cng in trng tng hp IE nm theo ng trung trc IH v hng ra xa MN th hai in tch c c im: A. q1 > 0; q2 > 0; q1 = q2 B. q1 > 0; q2 < 0; |q1| = |q2| C. q1 < 0; q2 < 0; q1 = q2 D. q1 < 0; q2 >0; |q1| = |q2| Cu hi 3: Hai in tch t trong khng kh ti M v N. Ti I nm trn ng trung trc ca MN cch MN mt on IH c vct cng in trng tng hp IE nm theo ng trung trc IH v hng li gn MN th hai in tch c c im:

A. q1 > 0; q2 > 0; q1 = q2 B. q1 > 0; q2 < 0; |q1| = |q2| C. q1 < 0; q2 < 0; q1 = q2 D. q1 < 0; q2 >0; |q1| = |q2| Cu hi 4: Hai in tch t trong khng kh ti M v N. Ti I nm trn ng trung trc ca MN cch MN mt on IH c vct cng in trng tng hp IE song song vi MN th hai in tch c c im: A. q1 > 0; q2 > 0; q1 = q2 B. q1 > 0; q2 < 0; |q1| = |q2| C. q1 < 0; q2 >0; |q1| = |q2| D. B hoc C Cu hi 5: Hai in tch q1 = +q v q2 = - q t ti A v B trong khng kh, bit AB = 2a. ln cng in trng ti M trn ng trung trc ca AB cch AB mt on h l:


Trang 23

A. 22

2

ha

kq

+ B. ( )222

22

ha

kqa

+ C.

( )23

22

2

ha

kqa

+ D.

22

22

ha

kqa

+

Cu hi 6: Hai in tch q1 = +q v q2 = - q t ti A v B trong khng kh, bit AB = 2a. ti M trn ng trung trc ca AB cch AB mt on h EM c gi tr cc i. Gi tr cc i l:

A. 22a

kq B. 2a

kq C. 2

2

a

kq D. 2

4

a

kq

Cu hi 7: Ba in tch q1, q2, q3 t trong khng kh ln lt ti cc nh A, B, C ca hnh vung ABCD. Bit vct cng in trng tng hp ti D c gi l cnh CD. Quan h gia 3 in tch trn l: A. q1 = q2 = q3 B. q1 = - q2 = q3 C. q2 = - 2 2 q1 D. q3 = - 2 2 q2 Cu hi 8: Hai in tch im q1 = 2.10

-2 (C) v q2 = - 2.10-2 (C) t ti hai im A v B cch

nhau mt on a = 30 (cm) trong khng kh. Cng in trng ti im M cch u A v B mt khong bng a c ln l:

A. EM = 0,2 (V/m). B. EM = 1732 (V/m). C. EM = 3464 (V/m). D. EM = 2000 (V/m). Cu hi 9: Hai in tch q1 = 5.10

-16 (C), q2 = - 5.10-16 (C), t ti hai nh B v C ca mt tam

gic u ABC cnh bng 8 (cm) trong khng kh. Cng in trng ti nh A ca tam gic ABC c ln l:

A. E = 1,2178.10-3 (V/m). B. E = 0,6089.10-3 (V/m). C. E = 0,3515.10-3 (V/m). D. E = 0,7031.10-3 (V/m).

Cu hi 10: Hai in tch im q1 = 0,5 (nC) v q2 = - 0,5 (nC) t ti hai im A, B cch nhau 6 (cm) trong khng kh. Cng in trng ti trung im ca AB c ln l:

A. E = 0 (V/m). B. E = 5000 (V/m). C. E = 10000 (V/m). D. E = 20000 (V/m).

Cu 1 2 3 4 5 6 7 8 9 10 p n

D A C D C A C B D C

in trng - Dng 4: q cn bng trong in trng, E trit tiu - 1 Cu hi 1: Hai in tch im q1 v q2 t ti hai im c nh A v B. Ti im M trn ng thng ni AB v gn A hn B ngi ta thy in trng ti c cng bng khng. Kt lun g v q1 , q2:

A. q1 v q2 cng du, |q1| > |q2| B. q1 v q2 tri du, |q1| > |q2| C. q1 v q2 cng du, |q1| < |q2| D. q1 v q2 tri du, |q1| < |q2|

Cu hi 2: Hai in tch im q1 = - 9C, q2 = 4 C t ln lt ti A, B cch nhau 20cm. Tm v tr im M ti in trng bng khng: A. M nm trn on thng AB, gia AB, cch B 8cm B. M nm trn ng thng AB, ngoi gn B cch B 40cm C. M nm trn ng thng AB, ngoi gn A cch A 40cm D. M l trung im ca AB Cu hi 3: Hai in tch im q1 = - 4 C, q2 = 1 C t ln lt ti A v B cch nhau 8cm. Xc nh v tr im M ti cng in trng bng khng: A. M nm trn AB, cch A 10cm, cch B 18cm B. M nm trn AB, cch A 8cm, cch B 16cm C. M nm trn AB, cch A 18cm, cch B 10cm D. M nm trn AB, cch A 16cm, cch B 8cm Cu hi 4: Hai tm kim loi phng nm ngang nhim in tri du t trong du, in trng gia hai bn l in trng u hng t trn xung di v c cng 20 000V/m. Mt qu


Trang 24

cu bng st bn knh 1cm mang in tch q nm l lng gia khong khng gian gia hai tm kim loi. Bit khi lng ring ca st l 7800kg/m3, ca du l 800kg/m3, ly g = 10m/s2. Tm du v ln ca q:

A. - 12,7 C B. 14,7 C C. - 14,7 C D. 12,7 C Cu hi 5: Mt qu cu khi lng 1g treo u mt si dy mnh cch in. H thng nm trong in trng u c phng nm ngang, cng E = 2kV/m. Khi dy treo hp vi phng thng ng mt gc 600. Tm in tch ca qu cu, ly g = 10m/s2:

A. 5,8 C B. 6,67 C C. 7,26 C D. 8,67C Cu hi 6: Mt qu cu kim loi nh c khi lng 1g c tch in q = 10-5C treo vo u mt si dy mnh v t trong in trng u E. Khi qu cu ng cn bng th dy treo hp vi phng thng ng mt gc 600, ly g = 10m/s2. Tm E:

A. 1730V/m B. 1520V/m C. 1341V/m D. 1124V/m Cu hi 7: Hai qu cu nh mang in tch q1 = - 2nC, q2 = +2nC, c treo u hai si dy cch in di bng nhau trong khng kh ti hai im treo M, N cch nhau 2cm cng mt cao. Khi h cn bng hai dy treo lch khi phng thng ng, mun a cc dy treo v v tr phng thng ng th phi to mt in trng u E c hng no ln bao nhiu: A. Nm ngang hng sang phi, E = 1,5.104V/m B. Nm ngang hng sang tri, E = 3.104V/m C. Nm ngang hng sang phi, E = 4,5.104V/m D. Nm ngang hng sang tri, E = 3,5.104V/m

Cu hi 8: Mt vin bi nh kim loi khi lng 9.10-5kg th tch 10mm3 c t trong du c khi lng ring 800kg/m3. Chng t trong in trng u E = 4,1.105 V/m c hng thng ng t trn xung, thy vin bi nm l lng, ly g = 10m/s2. in tch ca bi l:

A. - 1nC B. 1,5nC C. - 2nC D. 2,5nC Cu hi 9: Hai in tch q1 = q2 = q t trong chn khng ln lt ti hai im A v B cch nhau mt khong l. Ti I ngi ta thy in trng ti bng khng. Hi I c v tr no sau y:

A. AI = BI = l/2 B. AI = l; BI = 2l C. BI = l; AI = 2l D. AI = l/3; BI = 2l/3 Cu hi 10: Hai in tch im q1 = 36 C v q2 = 4 C t trong khng kh ln lt ti hai im A v B cch nhau 100cm. Ti im C in trng tng hp trit tiu, C c v tr no:

A. bn trong on AB, cch A 75cm B. bn trong on AB, cch A 60cm C. bn trong on AB, cch A 30cm D. bn trong on AB, cch A 15cm

Cu 1 2 3 4 5 6 7 8 9 10 p n

C B D C D A C C A A

in trng - Dng 4: q cn bng trong in trng, E trit tiu - 2 Cu hi 1: Ba in tch q1, q2, q3 t trong khng kh ln lt ti cc nh A, B, C ca hnh vung ABCD. Bit in trng tng hp ti D trit tiu. Quan h gia 3 in tch trn l:

A. q1 = q3; q2 = -2 2 q1 B. q1 = - q3; q2 = 2 2 q1

C. q1 = q3; q2 = 2 2 q1 D. q2 = q3 = - 2 2 q1 Cu hi 2: Mt qu cu khi lng 1g treo u mt si dy mnh cch in. H thng nm trong in trng u c phng nm ngang, cng E = 2kV/m. Khi dy treo hp vi phng thng ng mt gc 600. Tm sc cng ca si dy, ly g = 10m/s2:

A. 0,01N B. 0,03N C. 0,15N D. 0,02N Cu hi 3: Hai in tch im q v -q t ln lt ti A v B. in trng tng hp trit tiu ti:

M N

q1 q2


Trang 25

A. Mt im trong khong AB B. Mt im ngoi khong AB, gn A hn C. Mt im ngoi khong AB, gn B hn D. in trng tng hp khng th trit tiu ti bt c im no

Cu hi 4: Hai in tch im q1 v q2 t hai nh A v B ca tam gic u ABC. in trng C bng khng, ta c th kt lun:

A. q1 = - q2 B. q1 = q2 C. q1 q2 D. Phi c thm in tch q3 nm u

Cu hi 5: Hai in tch im q1 = - q2 = 3C t ln lt ti A v B cch nhau 20cm. in trng tng hp ti trung im O ca AB c:

A. ln bng khng B. Hng t O n B, E = 2,7.106V/m C. Hng t O n A, E = 5,4.106V/m D. Hng t O n B, E = 5,4.106V/m

Cu hi 6: Hai in tch im q1 = - 2,5 C v q2 = + 6 C t ln lt ti A v B cch nhau 100cm. in trng tng hp trit tiu ti:

A. trung im ca AB B. im M trn ng thng AB, ngoi on AB, cch B mt on 1,8m C. im M trn ng thng AB, ngoi on AB, cch A mt on 1,8m D. in trng tng hp khng th trit tiu

Cu hi 7: Cc in tch q1 v q2 = q1 t ln lt ti hai nh A v C ca mt hnh vung ABCD. in trng tng hp ti nh D bng khng th phi t ti nh B mt in tch q3 c ln v du bng:

A. - q1 B. - 2 q1 C. -2 2 q1 D. khng th tm c v khng bit chiu di ca cnh hnh vung

Cu hi 8: Ba in tch im bng nhau q > 0 t ti ba nh ca mt tam gic u ABC. in trng tng hp trit tiu ti:

A. mt nh ca tam gic B. tm ca tam gic C. trung im mt cnh ca tam gic D. khng th trit tiu

Cu hi 9: Ba in tch im bng nhau q < 0 t ti ba nh ca mt tam gic u ABC. in trng tng hp trit tiu ti:

A. mt nh ca tam gic B. tm ca tam gic C. trung im mt cnh ca tam gic D. khng th trit tiu

Cu hi 10: Ba in tch im q1, q2 = - 12,5.10-8C, q3 t ln lt ti A, B, C ca hnh ch nht

ABCD cnh AD = a = 3cm, AB = b = 4cm. in trng tng hp ti nh D bng khng. Tnh q1 v q3:

A. q1 = 2,7.10-8C; q3 = 6,4.10

-8C B. q1 = - 2,7.10-8C; q3 = -

6,4.10-8C C. q1 = 5,7.10

-8C; q3 = 3,4.10-8C D. q1 = - 5,7.10

-8C; q3 = - 3,4.10-8C

Cu 1 2 3 4 5 6 7 8 9 10 p n

A D D D D C C B B A

CNG CA LC IN - IN TH - HIU IN TH. 6


Trang 26

I. Kin thc: 1. Khi mt in tch dng q dch chuyn trong in trng u c cng E (t M n N) th cng m lc in tc dng ln q c biu thc: A = q.E.d

Vi: d l khong cch t im u im cui (theo phng ca Er

). V th d c th dng (d> 0) v cng c th m (d< 0) C th nh hnh v: khi in tch q di chuyn t M N th d = MH.

V cng chiu vi Er

nn trong trng hp trn d>0. Er

Fr

Nu A > 0 th lc in sinh cng dng, A< 0 th lc in sinh cng m. 2. Cng A ch ph thuc vo v tr im u v im cui ca ng i trong in trng m khng ph thuc vo hnh dng ng i. Tnh cht ny cng ng cho in trng bt k (khng u). Tuy nhin, cng thc tnh cng s khc. in trng l mt trng th. 3. Th nng ca in tch q ti mt im M trong in trng t l vi ln ca in tch q: WM = AM = q.VM. AM l cng ca in trng trong s dch chuyn ca in tch q t im M n v cc. (mc tnh th nng.) 4. in th ti im M trong in trng l i lng c trng cho kh nng ca in trng trong vic to ra th nng ca in tch q t ti M. 5. Hiu in th UMN gia hai im M v N l i lng c trng cho kh nng sinh cng ca in trng trong s di chuyn ca in tch q t M n N. 6. n v o in th, hiu in th l Vn (V) II. Bi tp t lun: Dng 1: Tnh A ca lc in trng -U, V * Hng dn gii bi tp: - Cng m ta cp y l cng ca lc in hay cng ca in trng. Cng ny c th c gi tr dng hay m. - C th p dng nh l ng nng cho chuyn ng ca in tch. Nu ngoi lc in cn c cc lc khc tc dng ln in tch th cng tng cng ca tt c cc lc tc dng ln in tch bng tng ng nng ca vt mang in tch. - Nu vt mang in chuyn ng u th cng tng cng bng khng. Cng ca lc in v cng ca cc lc khc s c ln bng nhau nhng tri du. - Nu ch c lc in tc dng ln in tch th cng ca lc in bng tng ng nng ca vt mang in tch. Vi m l khi lng ca vt mang in tch q. - Trong cng thc A= q.E.d ch p dng c cho trng hp in tch di chuyn trong in trng u. - Cng ca lc in tc dng ln mt in tch khng ph thuc vo hnh dng ng i ca in tch m ch ph thuc vo v tr ca im u v im cui ca ng i trong in

q

A

q

WV MMM

==

q

AVVU MNNMMN ==

2

.

2

..

22MN

MNMN

vmvmUqA ==


Trang 27

1Er 2E

r

trng. Do , vi mt ng cong kn th im u v im cui trng nhau, nn cng ca lc in trong trng hp ny bng khng. Cng ca lc in: A = qEd = q.U Cng ca lc ngoi A = A. nh l ng nng:

Biu thc hiu in th: q

AU MNMN =

H thc lin h gia cng in trng hiu in th trong in trng u: d

UE =

* Bi tp vn dng: 1. Ba im A, B, C to thnh mt tam gic vung ti C. AC = 4 cm, BC = 3 cm v nm trong

mt in trng u. Vect cng in trng Er

song song vi AC, hng t A C v c ln E = 5000V/m. Tnh:

Er

a. UAC, UCB, UAB. b. Cng ca in trng khi mt electron (e) di chuyn t A n B ? s: 200v, 0v, 200v. - 3,2. 10-17 J.

2. Tam gic ABC vung ti A c t trong in trng u Er

, = ABC = 600, AB E

r. Bit BC = 6 cm, UBC= 120V.

a. Tm UAC, UBA v cng in trng E? Er

b. t thm C in tch im q = 9. 10-10 C. Tm cng in trng tng hp ti A. s: UAC = 0V, UBA = 120V, E = 4000 V/m, E = 5000 V/m. 3. Mt in tch im q = -4. 10-8C di chuyn dc theo chu vi ca mt tam gic MNP, vung ti

P, trong in trng u, c cng 200 v/m. Cnh MN = 10 cm, MN Er

.NP = 8 cm. Mi trng l khng kh. Tnh cng ca lc in trong cc dch chuyn sau ca q: a. t M N. b. T N P. c. T P M. d. Theo ng kn MNPM. s: AMN= -8. 10

-7J. ANP= 5,12. 10-7J, APM = 2,88. 10

-7J. AMNPM = 0J. 4. Mt in trng u c cng E = 2500 V/m. Hai im A , B cch nhau 10 cm khi tnh dc theo ng sc. Tnh cng ca lc in trng thc hin mt in tch q khi n di chuyn t A B ngc chiu ng sc. Gii bi ton khi: a. q = - 10-6C. b. q = 10-6C s: 25. 105J, -25. 105J. 5. Cho 3 bn kim loi phng A, B, C c tch in v t song song nh hnh. Cho d1 = 5 cm, d2= 8 cm. Coi in trng gia cc bn l u v c chiu nh hnh v. Cng in trng tng ng l E1 =4.10

4V/m , E2 = 5. 10

4V/m. Tnh in th ca bn B v bn C nu ly gc in th l in th bn A. d1 d2 s: VB = -2000V. VC = 2000V.

6. Ba im A, B, C nm trong in trng u sao cho Er

// CA. Cho AB AC v AB = 6 cm. AC = 8 cm. a. Tnh cng in trng E, UAB v UBC. Bit UCD = 100V (D l trung im ca AC) b. Tnh cng ca lc in trng khi electron di chuyn t B C, t B D.

MNMNMN vvmUqA22

2

1.

2

1. ==


Trang 28

1Er 2E

r

s: 2500V/m,UAB= 0v, UBC = - 200v, ABC = 3,2. 10-17J. ABD= 1,6. 10

-17J. 7. in tch q = 10-8 C di chuyn dc theo cnh ca mt tam gic u ABC cnh a = 10 cm trong in trng u c cng l 300 V/m.

Er

// BC. Tnh cng ca lc in trng khi q dch chuyn trn mi cnh ca tam gic. s: AAB = - 1,5. 10

-7 J, ABC = 3. 10-7 J. ACA = -1,5. 10

-7 J. 8. in tch q = 10-8 C di chuyn dc theo cnh ca mt tam gic u

MBC, mi cnh 20 cm t trong in trng u Er

c hng song song vi BC v c cng l 3000 V/m. Tnh cng thc hin dch chuyn in tch q theo cc cnh MB, BC v CM ca tam gic. s: AMB = -3J, ABC = 6 J, AMB = -3 J. 9. Gia hai im B v C cch nhau mt on 0,2 m c mt in trng u vi ng sc hng t B C. Hiu in th UBC = 12V. Tm: a. Cng in trng gia B c C. b. Cng ca lc in khi mt in tch q = 2. 10-6 C i t B C. s: 60 V/m. 24 J. 10. Cho 3 bn kim loi phng tch in A, B, C t song song nh hnh. in trng gia cc bn l in trng u v c chiu nh hnh v.Hai bn A v B cch nhau mt on d1 = 5 cm, Hai bn B v C cch nhau mt on d2 = 8 cm. Cng in trng tng ng l E1 =400 V/m , E2 = 600 V/m. Chn gc in th ca bn A. Tnh in th ca bn B v ca bn C. d1 d2 s: VB = - 20V, VC = 28 V. 11. Mt electron di chuyn c mt on 1 cm, dc theo mt ng sc in, di tc dng ca mt lc in trong mt in trng u c cng 1000 V/m. Hy xc nh cng ca lc in ? s: 1,6. 10-18 J. 12. Khi bay t im M n im N trong in trng, electron tng tc, ng nng tng thm 250eV.(bit rng 1 eV = 1,6. 10-19J). Tm UMN? s: - 250 V. III. BI TP TRC NGHIM: 1 Cu hi 1: Mt in trng u cng 4000V/m, c phng song song vi cnh huyn BC ca mt tam gic vung ABC c chiu t B n C, bit AB = 6cm, AC = 8cm. Tnh hiu in th gia hai im BC:

A. 400V B. 300V C. 200V D. 100V

Cu hi 2: Mt in tch q chuyn ng t im M n Q, n N, n P trong in trng u nh hnh v. p n no l sai khi ni v mi quan h gia cng ca lc in trng dch chuyn in tch trn cc on ng: A. AMQ = - AQN B. AMN = ANP C. AQP = AQN D. AMQ = AMP

Cu hi 3: Hai tm kim loi phng song song cch nhau 2cm nhim in tri du. Mun lm cho in tch q = 5.10-10C di chuyn t tm ny sang tm kia cn tn mt cng A = 2.10-9J. Xc nh cng in trng bn trong hai tm kim loi, bit in trng bn trong l in trng u c ng sc vung gc vi cc tm, khng i theo thi gian:

Er

Er

M Q

N

P


Trang 29

A. 100V/m B. 200V/m C. 300V/m D. 400V/m Cu hi 4: Hiu in th gia hai im M, N l UMN = 2V. Mt in tch q = -1C di chuyn t M n N th cng ca lc in trng l:

A. -2J B. 2J C. - 0,5J D. 0,5J Cu hi 5: Mt ht bi khi lng 3,6.10-15kg mang in tch q = 4,8.10-18C nm l lng gia hai tm kim loi phng song song nm ngang cch nhau 2cm v nhim in tri du . Ly g = 10m/s2, tnh hiu in th gia hai tm kim loi:

A. 25V. B. 50V C. 75V D. 100V Cu hi 6: Mt qu cu kim loi khi lng 4,5.10-3kg treo vo u mt si dy di 1m, qu cu nm gia hai tm kim loi phng song song thng ng cch nhau 4cm, t hiu in th gia hai tm l 750V, th qu cu lch 1cm ra khi v tr ban u, ly g = 10m/s2. Tnh in tch ca qu cu:

A. 24nC B. - 24nC C. 48nC D. - 36nC Cu hi 7: Gi thit rng mt tia st c in tch q = 25C c phng t m my dng xung mt t, khi hiu in th gia m my v mt t U = 1,4.108V. Tnh nng lng ca tia st :

A. 35.108J B. 45.108 J C. 55.108 J D. 65.108 J Cu hi 8: Mt in tch im q = + 10C chuyn ng t nh B n nh C ca tam gic u ABC, nm trong in trng u c cng 5000V/m c ng sc in trng song song vi cnh BC c chiu t C n B. Bit cnh tam gic bng 10cm, tm cng ca lc in trng khi di chuyn in tch trn theo on thng B n C:

A. 2,5.10-4J B. - 2,5.10-4J C. - 5.10-4J D. 5.10-4J Cu hi 9: Mt in tch im q = + 10C chuyn ng t nh B n nh C ca tam gic u ABC, nm trong in trng u c cng 5000V/m c ng sc in trng song song vi cnh BC c chiu t C n B. Bit cnh tam gic bng 10cm, tm cng ca lc in trng khi di chuyn in tch trn theo on gp khc BAC:

A. - 10.10-4J B. - 2,5.10-4J C. - 5.10-4J D. 10.10-4J Cu hi 10: Mt trong ca mng t bo trong c th sng mang in tch m, mt ngoi mang in tch dng. Hiu in th gia hai mt ny bng 0,07V. Mng t bo dy 8nm. Cng in trng trong mng t bo ny l:

A. 8,75.106V/m B. 7,75.106V/m C. 6,75.106V/m D. 5,75.106V/m Cu hi 11: Hai tm kim loi phng nm ngang song song cch nhau 5cm. Hiu in th gia hai tm l 50V. Tnh cng in trng v cho bit c im in trng, dng ng sc in trng gia hai tm kim loi: A. in trng bin i, ng sc l ng cong, E = 1200V/m B. in trng bin i tng dn, ng sc l ng trn, E = 800V/m C. in trng u, ng sc l ng thng, E = 1200V/m D. in trng u, ng sc l ng thng, E = 1000V/m Cu hi 12: Hai tm kim loi phng nm ngang song song cch nhau 5cm. Hiu in th gia hai tm l 50V. Mt electron khng vn tc ban u chuyn ng t tm tch in m v tm tch in dng. Hi khi n tm tch in dng th electron nhn c mt nng lng bng bao nhiu:


Trang 30

A. 8.10-18J B. 7.10-18J C. 6.10-18J D. 5.10-18J Cu hi 13: Cng ca lc in trng lm di chuyn mt in tch gia hai im c hiu in th U = 2000V l 1J. Tnh ln in tch :

A. 2mC B. 4.10-2C C. 5mC D. 5.10-4C Cu hi 14: Gia hai im A v B c hiu in th bng bao nhiu nu mt in tch q = 1C thu c nng lng 2.10-4J khi i t A n B:

A. 100V B. 200V C. 300V D. 500V Cu hi 15: Cho ba bn kim loi phng tch in 1, 2, 3 t song song ln lt nhau cch nhau nhng khong d12 = 5cm, d23 = 8cm, bn 1 v 3 tch in dng, bn 2 tch in m. E12 = 4.104V/m, E23 = 5.10

4V/m, tnh in th V2, V3 ca cc bn 2 v 3 nu ly gc in th bn 1: A. V2 = 2000V; V3 = 4000V B. V2 = - 2000V; V3 = 4000V C. V2 = - 2000V; V3 = 2000V D. V2 = 2000V; V3 = - 2000V

Cu hi 16: Mt qu cu kim loi bn knh 10cm. Tnh in th gy bi qu cu ti im A cch tm qu cu 40cm v ti im B trn mt qu cu, bit in tch ca qu cu l.10-9C:

A. VA = 12,5V; VB = 90V B. VA = 18,2V; VB = 36V C. VA = 22,5V; VB = 76V D.VA = 22,5V; VB = 90V

Cu hi 17: Mt qu cu kim loi bn knh 10cm. Tnh in th gy bi qu cu ti im A cch tm qu cu 40cm v ti im B trn mt qu cu, bit in tch ca qu cu l - 5.10-8C:

A. VA = - 4500V; VB = 1125V B. VA = - 1125V; VB = - 4500V C. VA = 1125,5V; VB = 2376V D. VA = 922V; VB = - 5490V

Cu hi 18: Mt git thy ngn hnh cu bn knh 1mm tch in q = 3,2.10-13C t trong khng kh. Tnh cng in trng v in th ca git thy ngn trn b mt git thy ngn:

A. 2880V/m; 2,88V B. 3200V/m; 2,88V C. 3200V/m; 3,2V D. 2880; 3,45V

Cu hi 19: Mt ht bi kim loi tch in m khi lng 10-10kg l lng trong khong gia hai bn t in phng nm ngang bn tch in dng trn, bn tch in m di. Hiu in th gia hai bn bng 1000V, khong cch gia hai bn l 4,8mm, ly g = 10m/s2. Tnh s electron d ht bi:

A. 20 000 ht B. 25000 ht C. 30 000 ht D. 40 000 ht

Cu hi 20: Mt in trng u E = 300V/m. Tnh cng ca lc in trng trn di chuyn in tch q = 10nC trn qu o ABC vi ABC l tam gic u cnh a = 10cm nh hnh v: A. 4,5.10-7J B. 3. 10-7J C. - 1.5. 10-7J D. 1.5. 10-7J

Cu hi 21: Xt 3 im A, B, C 3 nh ca tam gic vung nh hnh v, = 600, BC = 6cm, UBC = 120V. Cc hiu in th UAC ,UBA c gi tr ln lt: A. 0; 120V B. - 120V; 0 C. 60 3 V; 60V D. - 60 3 V; 60V

Cu hi 22: Mt ht bi khi lng 1g mang in tch - 1C nm yn cn bng trong in trng gia hai bn kim loi phng nm ngang tch in tri du c ln bng nhau. Khong cch gia hai bn l 2cm, ly g = 10m/s2. Tnh hiu in th gia hai bn kim loi phng trn:

A

B C

E


Trang 31

A. 20V B. 200V C. 2000V D. 20 000V Cu hi 23: Mt prtn mang in tch + 1,6.10-19C chuyn ng dc theo phng ca ng sc mt in trng u. Khi n i c qung ng 2,5cm th lc in thc hin mt cng l + 1,6.10-20J. Tnh cng in trng u ny:

A. 1V/m B. 2V/m C. 3V/m D. 4V/m Cu hi 24: Gi thit rng mt tia st c in tch q = 25C c phng t m my dng xung mt t, khi hiu in th gia m my v mt t U = 1,4.108V. Nng lng ca tia st ny c th lm bao nhiu kilgam nc 1000C bc thnh hi 1000C, bit nhit ha hi ca nc bng 2,3.106J/kg

A. 1120kg B. 1521kg C. 2172kg D. 2247kg Cu hi 25: Mt in trng u cng 4000V/m, c phng song song vi cnh huyn BC ca mt tam gic vung ABC c chiu t B n C, bit AB = 6cm, AC = 8cm. Tnh hiu in th gia hai im AC:

A. 256V B. 180V C. 128V D. 56V Cu hi 26: Mt in trng u cng 4000V/m, c phng song song vi cnh huyn BC ca mt tam gic vung ABC c chiu t B n C, bit AB = 6cm, AC = 8cm. Tnh hiu in th gia hai im BA: A. 144V B. 120V C. 72V D. 44V Cu hi 27: Cng ca lc in trng lm di chuyn mt in tch gia hai im c hiu in th U = 2000 (V) l A = 1 (J). ln ca in tch l

A. q = 2.10-4 (C). B. q = 2.10-4 (C). C. q = 5.10-4 (C). D. q = 5.10-4 (C). Cu hi 28: Hai tm kim loi song song, cch nhau 2 (cm) v c nhim in tri du nhau. Mun lm cho in tch q = 5.10-10 (C) di chuyn t tm ny n tm kia cn tn mt cng A = 2.10-9 (J). Coi in trng bn trong khong gia hai tm kim loi l in trng u v c cc ng sc in vung gc vi cc tm. Cng in trng bn trong tm kim loi l:

A. E = 2 (V/m). B. E = 40 (V/m). C. E = 200 (V/m). D. E = 400 (V/m). Cu hi 29: Hai tm kim loi phng nm ngang song song cch nhau 5cm. Hiu in th gia hai tm l 50V. Mt electron khng vn tc ban u chuyn ng t tm tch in m v tm tch in dng. Hi khi n tm tch in dng th electron c vn tc bng bao nhiu:

A. 4,2.106m/s B. 3,2.106m/s C. 2,2.106m/s D.1,2.106m/s Cu hi 30: Cho hai bn kim loi phng t song song tch in tri du, th mt lectron khng vn tc ban u vo in trng gia hai bn kim loi trn. B qua tc dng ca trng trng. Qu o ca lectron l:

A. ng thng song song vi cc ng sc in. B. ng thng vung gc vi cc ng sc in. C. mt phn ca ng hypebol. D. mt phn ca ng parabol.

Cu 21 22 23 24 25 26 27 28 29 30

Cu 1 2 3 4 5 6 7 8 9 10 p n

A D B B C B A C C A

Cu 11 12 13 14 15 16 17 18 19 20 p n

D A D B C D B A C D


Trang 32

p n

A B D B A A B D A B

I. Kin thc cn nh: Khi ht mang in c th t do khng vn tc u trong mt in trng u th di tc dng ca lc in , ht mang in chuyn ng theo mt ng thng song song vi ng sc in. Nu in tch dng (q >0) th ht mang in (q) s chuyn ng cng chiu in trng. Nu in tch m (q


Trang 33

a. Gia tc ca e. b. Vn tc ca e khi n chuyn ng c 2. 10-7 s trong in trng. s: 3,52. 1014 m/s2. 8,1. 107 m/s. 6. Mt protn bay theo phng ca ng sc in. Lc protn im A th vn tc ca n l 2,5. 104 m/s. Khi bay n B vn tc ca protn bng 0. in th ti A bng 500 V, Hi in th ti B ? cho bit protn c khi lng 1,67. 10-27 kg, c in tch 1,6. 10-19 C. s: 503,3 V. III. BI TP TRC NGHIM. A, U, V - : Chuyn ng ca q trong in trng - 1: Cu hi 1: Mt electrn chuyn ng dc theo hng ng sc ca mt in trng u c cng 100V/m vi vn tc ban u l 300 km/s . Hi n chuyn ng c qung ng di bao nhiu th vn tc ca n bng khng:

A. 2,56cm B. 25,6cm C. 2,56mm D. 2,56m Cu hi 2: Trong n hnh ca my thu hnh, cc electrn c tng tc bi hiu in th 25 000V. Hi khi p vo mn hnh th vn tc ca n bng bao nhiu, b qua vn tc ban u ca n:

A. 6,4.107m/s B. 7,4.107m/s C. 8,4.107m/s D. 9,4.107m/s Cu hi 3: Mt prtn bay theo phng ca mt ng sc in trng. Lc im A n c vn tc 2,5.104m/s, khi n im B vn tc ca n bng khng. Bit n c khi lng 1,67.10-27kg v c in tch 1,6.10-19C. in th ti A l 500V, tm in th ti B:

A. 406,7V B. 500V C. 503,3V D. 533V Cu hi 4: Hai tm kim loi phng nm ngang song song cch nhau 5cm. Hiu in th gia hai tm l 50V. Mt electron khng vn tc ban u chuyn ng t tm tch in m v tm tch in dng. Hi khi n tm tch in dng th electron c vn tc bao nhiu:

A. 4,2.106m/s B. 3,2.106m/s C. 2,2.106m/s D. 1,2.106m/s Cu hi 5: Trong Vt l ht nhn ngi ta hay dng n v nng lng l eV. eV l nng lng m mt electrn thu c khi n i qua on ng c hiu in th 1V. Tnh eV ra Jun, v vn tc ca electrn c nng lng 0,1MeV:

A. 1eV = 1,6.1019J B. 1eV = 22,4.1024 J; C. 1eV = 9,1.10-31J D. 1eV = 1,6.10-19J

Cu hi 6: Hai bn kim loi phng nm ngang song song cch nhau 10cm c hiu in th gia hai bn l 100V. Mt electrn c vn tc ban u 5.106m/s chuyn ng dc theo ng sc v bn m. Tnh gia tc ca n. Bit in trng gia hai bn l in trng u v b qua tc dng ca trng lc:

A. -17,6.1013m/s2 B. 15.9.1013m/s2 C. - 27,6.1013m/s2 D. + 15,2.1013m/s2

Cu hi 7: Mt ht bi kim loi tch in m khi lng 10-10kg l lng trong khong gia hai bn t in phng nm ngang bn tch in dng trn, bn tch in m di. Hiu in th gia hai bn bng 1000V, khong cch gia hai bn l 4,8mm, ly g = 10m/s2. Chiu tia t ngoi lm ht bi mt mt s electrn v ri xung vi gia tc 6m/s2. Tnh s ht electrn m ht bi mt:

A. 18 000 ht B. 20000 ht C. 24 000 ht D. 28 000 ht Cu hi 8: Mt electrn chuyn ng dc theo mt ng sc ca in trng u c cng 364V/m. Electrn xut pht t im M vi vn tc 3,2.106m/s i c qung ng di bao nhiu th vn tc ca n bng khng:

A. 6cm B. 8cm C. 9cm D. 11cm


Trang 34

Cu hi 9: Mt electrn chuyn ng dc theo mt ng sc ca in trng u c cng 364V/m. Electrn xut pht t im M vi vn tc 3,2.106m/s. Thi gian k t lc xut pht n khi n quay tr v im M l:

A. 0,1s B. 0,2 s C. 2 s D. 3 s Cu hi 10: Hai bn kim loi phng nm ngang song song cch nhau 10cm c hiu in th gia hai bn l 100V. Mt electrn c vn tc ban u 5.106m/s chuyn ng dc theo ng sc v bn m. Tnh on ng n i c cho n khi dng li. Bit in trng gia hai bn l in trng u v b qua tc dng ca trng lc:

A. 7,1cm B. 12,2cm C. 5,1cm D. 15,2cm Cu 1 2 3 4 5 6 7 8 9 10 p n

C D C A D A D B A A

A, U, V -: Chuyn ng ca q trong in trng - 2: Cu hi 1: Mt electrn c phng i t O vi vn tc ban u v0 vung gc vi cc ng sc ca mt in trng u cng E. Khi n im B cch O mt on h theo phng ca ng sc vn tc ca n c biu thc: A. Ehe B. Ehev +20 C. Ehev

20 D.

hm

Eev 220 +

Cu hi 2: Mt electrn c phng i t O vi vn tc ban u v0 dc theo ng sc ca mt in trng u cng E cng hng in trng. Qung ng xa nht m n di chuyn c trong in trng cho ti khi vn tc ca n bng khng c biu thc:

A. Ee

mv

2

20 B.

20

2

mv

Ee C.

2

20Emve D. 2

0

2

Emve

Cu hi 3:Electron chuyn ng khng vn tc ban u t A n B trong mt in trng u vi UAB = 45,5V. Ti B vn tc ca n l: A. 106m/s2 B. 1,5./s2 C. 4.106m /s2 D. 8.106m/s2 Cu hi 4:Khi bay t M n N trong in trng u, electron tng tc ng nng tng thm 250eV. Hiu in th UMN bng: A. -250V B. 250V C. - 125V D. 125V Cu hi 5: Mt t in phng c cc bn nm ngang cch nhau khong d, chiu di cc bn l l. Gia hai bn c hiu in th U. Mt electron bay vo in trng ca t t im O gia cch u hai bn vi vn tc 0v song song vi cc bn. ln gia tc ca n trong in trng l:

A. d

Ue B.

md

Ue C.

20mdv

Ule D.

20dv

Ule

Cu hi 6: Mt t in phng c cc bn nm ngang cch nhau khong d, chiu di cc bn l l. Gia hai bn c hiu in th U. Mt electron bay vo in trng ca t t im O gia cch u hai bn vi vn tc 0v song song vi cc bn. lch ca n theo phng vung gc vi cc bn khi ra khi in trng c biu thc:

A. d

Ue B.

md

Ue C.

20mdv

Ule D.

20

2

2mdv

Ule

Cu hi 7: : Mt t in phng c cc bn nm ngang cch nhau khong d, chiu di cc bn l l. Gia hai bn c hiu in th U. Mt electron bay vo in trng ca t t im O gia


Trang 35

cch u hai bn vi vn tc 0v song song vi cc bn. Gc lch gia hng vn tc ca n

khi va ra khi in trng v so vi 0v c tan c tnh bi biu thc:

A. d

Ue B.

md

Ue C.

20mdv

Ule D.

20

2

2mdv

Ule

Cu hi 8: Mt electron bay vo in trng ca mt t in phng theo phng song song cng hng vi cc ng sc in trng vi vn tc ban u l 8.106m/s. Hiu in th t phi c gi tr nh nht l bao nhiu electron khng ti c bn i din A. 182V B.91V C. 45,5V D.50V Cu hi 9: Khi mt electron chuyn ng ngc hng vi vect cng in trng th:

A. th nng ca n tng, in th ca n gim B. th nng gim, in th tng C. th nng v in th u gim D. th nng v in th u tng

Cu hi 10: Mt electron c tng tc t trng thi ng yn nh hiu in th U = 200V. Vn tc cui m n t c l: A. 2000m/s B. 8,4.106m/s C. 2.105m/s D. 2,1.106m/s Cu 1 2 3 4 5 6 7 8 9 10 p n

D A C A B D C A B B

A, U, V -: Chuyn ng ca q trong in trng - 3: Cu hi 1: Mt prtn v mt mt electron ln lt c tng tc t trng thi ng yn trong cc in trng u c cng in trng bng nhau v i c nhng qung ng bng nhau th:

A. C hai c cng ng nng, electron c gia tc ln hn B. C hai c cng ng nng, electron c gia tc nh hn C. prtn c ng nng ln hn. electron c gia tc ln hn D. electron c ng nng ln hn. Electron c gia tc nh hn

Cu hi 2: Mt electron th cho chuyn ng khng vn tc ban u trong in trng u gia hai mt ng th V1 = +10V, V2 = -5V. N s chuyn ng :

A. V pha mt ng th V1 B. V pha mt ng th V2 C. Ty cng in trng m n c th v V1 hay V2. D. n ng yn

Cu hi 3: Mt electrn c phng i t O vi vn tc ban u v0 dc theo ng sc ca mt in trng u cng E ngc hng in trng. Khi n im B cch O mt on h vn tc ca n c biu thc:

A. Ehe B. Ehev +20 C. Ehev 20 D. hm

Eev 220 +

Cu hi 4: Trong Vt l ht nhn ngi ta hay dng n v nng lng l eV. eV l nng lng m mt electrn thu c khi n i qua on ng c hiu in th 1V. Tnh vn tc ca electrn c nng lng 0,1MeV:

A. v = 0,87.108m/s B. v = 2,14.108m/s C. v = 2,87.108m/s D. v = 1,87.108m/s Cu hi 5: Hiu in th gia hai im bn ngoi v bn trong ca mt mng t bo l - 90mV, b dy ca mng t bo l 10nm, th in trng( gi s l u) gia mng t bo c cng l:

A. 9.106 V/m B. 9.1010 V/m C. 1010 V/m D. 106 V/m Cu hi 6: Khi st nh xung mt t th c mt lng in tch - 30C di chuyn t m my xung mt t. Bit hiu in th gia mt t v m my l 2.107V. Nng lng m tia st ny truyn t m my xung mt t bng:

A. 1,5.10-7J B. 0,67.107J C. 6.109J D. 6.108J


Trang 36

Cu hi 7: Chn mt p n sai : A. Khi mt in tch chuyn ng trn mt mt ng th th cng ca lc in bng khng B. Lc in tc dng ln mt in tch q trong mt mt ng th c phng tip tuyn vi mt ng th C. Vct cng in trng ti mi im trong mt ng th c phng vung gc vi mt ng th D. Khi mt in tch di chuyn t mt mt ng th ny sang mt mt ng th khc th cng ca lc in chc chn khc khng Cu hi 8: Khi electron chuyn ng t bn tch in dng v pha bn m trong khong khng gian gia hai bn kim loi phng tch in tri du ln bng nhau th:

A. Lc in thc hin cng dng, th nng lc in tng B. Lc in thc hin cng dng, th nng lc in gim C. Lc in thc hin cng m, th nng lc in tng D. Lc in thc hin cng m, th nng lc in gim

Cu hi 9: Hai im A v B nm trn cng mt mt ng th. Mt in tch q chuyn ng t A n B th: A. lc in thc hin cng dng nu q > 0, thc hin cng m nu q < 0

B. lc in thc hin cng dng hay m ty vo du ca q v gi tr in th ca A(B) C. phi bit chiu ca lc in mi xc nh c du ca cng lc in trng D. lc in khng thc hin cng

Cu hi 10: Mt in tch +1C chuyn ng t bn tch in dng sang bn tch in m t song song i din nhau th lc in thc hin mt cng bng 200J. Hiu in th gia hai bn c ln bng:

A. 5.10-3V. B. 200V C. 1,6.10-19V D. 2000V Cu 1 2 3 4 5 6 7 8 9 10 p n

A A D D A C B C D B

IV.Bi tp nng cao (CC HAY , CC KH, CC HC SINH GII)

1. Mt qu cu khi lng 10 g, c treo vo mt si ch cch in. Qu cu mang in

tch

q1= 0,1 C . a qu cu th 2 mang in tch q2 li gn th qu cu th nht lch khi v tr lc

u, dy treo hp vi ng thng ng mt gc =300. Khi 2 qu cu nm trn cng mt

mt phng nm ngang v cch nhau 3 cm. Tm ln ca q2 v lc cng ca dy treo?

g=10m/s2

HD: F=P.tan ; P=T.cos ; S: D ln ca q2=0,058 C ; T=0,115 N

2.Hai in tch im q1=-9.10-5C v q2=4.10

-5C nm c nh ti hai im AB cch nhau 20 cm

trong chn khng.

1) Tnh cng in trng ti im M nm trn ng trung trc ca AB cch A 20 cm

2) Tm v tr ti CT bng khng . Hi phi t mt in tch q0 u n nm cn

bng? S: Cch q2 40 cm


Trang 37

3. Mt e di chuyn mt on 0,6 cm t im M n im N dc theo mt ng sc in ca 1

in trng u th lc in sinh cng 9,6.10-18J

1) Tnh cng m lc in sinh ra khi e di chuyn tip 0,4 cm t im N n im P theo phng

v chiu ni trn?

2) Tnh vn tc ca e khi n ti P. Bit vn tc ca e ti M bng khng

HD: Ta dng cng thc: AMN =q.E. '' NM v AMN>0; q0 nn '' NM


Trang 38

1) Bit UCD=100 V. Tnh E, UAB; UBC ( S: 5000V/m; UBC=-200 V; UAB=0)

2) Tnh cng ca lc in khi mt e di chuyn :

a) T C n D b) T C n B c) T B n A

HD: Dng cc cng thc: AMN=q.UMN; E= UMN/ '' NM ; UMN=VM-VN

8. Mt ht bi mang in c khi lng m=10-11g nm cn bng gia 2 bn ca 1 t in phng.

Khong cch gia 2 bn l d=0,5 cm. Chiu nh sng t ngoi vo ht bi. Do mt mt phn

in tch,ht bi s mt cn bng. thit lp li cn bng ngi ta phi tng hiu in th gia

2 bn ln mt lng U =34V. Tnh in lng mt i bit ban u ht gia 2 bn l 306,3V

HD: Lc u: m.g=F=q.U/d (1); Sau (q- q ).(U+ U )/d = m.g (2). T (1) v (2) ta c q

9. Gia 2 bn ca t in t nm ngang cch nhau d=40 cm c mt in trng u E=60V/m.

Mt ht bi c khi lng m=3g v in tch q=8.10-5C bt u chuyn ng t trng thi ngh

t bn tch in dng v pha tm tch in m. B qua nh hng ca trng trng. Xc nh

vn tc ca ht ti im chnh gia ca t in S: 0,8 m/s

HD: Tnh a theo L 2 sau dng cng thc ca chuyn ng bin i u

10. Cho 3 bn kim loi phng A,B,C t song song vi nhau,tch in u cch nhau cc khong

d1=2,5 cm; d2=4 cm.Bit CT gia cc bn l u c ln E1=8.104V/m; E2=10

5V/m c

chiu nh hnh v. Ni bn A vi t.

Tnh in th ca bn B v C

HD: VA-VB=E1.d1 VB; VC-VB=E2.d2 VC=2000 V

11. Mt qu cu tch in khi lng m=0,1 g nm cn bng gia 2 bn t in phng t thng

ng cch nhau d=1cm. Hiu in th gia 2 bn l U. Gc lch ca dy treo so vi phng

thng ng l 100. in tch ca qu cu l 1,3.10-9C. Tm U (cho g=10m/s2) S: 1000

V

12. Hai qu cu ging nhau bng kim loi tch in tri du t cch nhau 20 cm chng ht nhau

bng 1 lc F1=4.10-3N. Cho 2 qu cu tip xc vi nhau sau li tch chng ra v tr c. Khi

2 qu cu y nhau bi 1 lc F2=2,25.10-3N. Xc nh in tch ca mi qu cu trc khi cho

chng tip xc nhau.

13. Ti cc nh A,B,C ca 1 hnh vung ABCD cnh a=1,5 cm ln lt t c nh q1,q2,q3

E1

E2

A B C


Trang 39

1) Bit q2=4.10-6C v CT tng hp ti D bng khng. Tnh q1, q3 (S: q1=q3=-1,4.10

-6C)

2) Tm CT tng hp ti tm O ca hnh vung (3,2.108 V/m)

KIM TRA 15 T in - Dng 1: in dung, nng lng in trng H V TN:TRNG........................... Cu hi 1: Mt t in c in dung l bao nhiu th tch ly mt nng lng 0,0015J di mt hiu in th 6V:

A. 83,3F B. 1833 F C. 833nF D. 833pF Cu hi 2: Nng lng ca t in tn ti:

A. trong khong khng gian gia hai bn t B. hai mt ca bn tch in dng C. hai mt ca bn tch in m D. cc in tch tn ti trn hai bn t

Cu hi 3: Mt t in in dung 12pF mc vo ngun in mt chiu c hiu in th 4V. Tng hiu in th ny ln bng 12V th in dung ca t in ny s c gi tr:

A.36pF B. 4pF C. 12pF D. cn ph thuc vo in tch ca t Cu hi 4: Mt t in c in dung 20 F mc vo hiu in th ca ngun mt chiu th in tch ca t bng 80C. Bit hai bn t cch nhau 0,8cm. in trng gia hai bn t c ln:

A. 10-4V/m B. 0,16V/m C. 500V/m D. 5V/m Cu hi 5: Khi t t in c in dung 2 F di hiu in th 5000V th cng thc hin tch in cho t in bng:

A. 2,5J B. 5J C. 25J D. 50J Cu hi 6: Vi mt t in xc nh c in dung C khng i, tng nng lng in trng tch tr trong t in ln gp 4 ln ta c th lm cch no sau y:

A. tng in tch ca t ln 8 ln, gim hiu in th i 2 ln B. tng hiu in th 8 ln v gim in tch t i 2 ln C. tng hiu in th ln 2 ln D. tng in tch ca t ln 4 ln

Cu hi 7: Pht biu no sau y l khng ng? A. T in l h hai vt dn t gn nhau nhng khng tip xc vi nhau. Mi vt gi l mt bn t. B. T in phng l t in c hai bn t l hai tm kim loi c kch thc ln t i din vi nhau. C. in dung ca t in l i lng c trng cho kh nng tch in ca t in v c o bng thng s gia in tch ca t v hiu in th gia hai bn t. D. Hiu in th gii hn l hiu in th ln nht t vo hai bn t

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