B bi tp t lun vt l 11

GV: Nguyn Quang Hiu

IN TCH. NH LUT CU-LNG Cu 1: (*)C hai in tch q v q t ti hai im A, B cch nhau mt khong AB = 2d. Mt in tch dng q1 = q t trn ng trung trc ca AB, cch AB mt khong x. a. Xc nh lc in tc dng ln q1? b. p dng bng s: q = 4.10 -6C; d = 3cm; x = 4cm. Cu 2: Cho hai qu cu tch in dng q1 = 9.10 -6C v q2 = 3,6.10 -5C t cch nhau mt on a = 12cm trong chn khng. Ngi ta t thm in tch q0 u v c du nh th no h cn bng? a. Khi q1, q2 gi c nh. b.(*) Khi q1, q2 khng c nh. Cu 3: Hai in tch im bng nhau, t trong chn khng, cch nhau mt khong r1 = 2cm. Lc y gia chng l F1 = 1,6.10 -4N. a. Tm ln ca cc in tch . b. Khong cch r2 gia chng phi bng bao nhiu lc tc dng l F2 = 2,5.10 -4N? Cu 4: Cho hai in tch im q1 = -10 -7C v q2 = 5.10 -8C t ti hai im A, B trong chn khng, cch nhau mt khong AB = 5cm. Xc nh lc in tng hp tc dng ln in tch im q0 = 2.10 -8C t ti C sao cho CA = 3cm v CB = 4cm. Cu 5: Cho hai in tch im q1 v q2 t cch nhau mt khong d = 30cm trong khng kh, lc tc dng gia chng l F. 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 l F? Cu 6: Ba qu cu nh mang in tch q1 = -6.10 -7C, q2 = 2.10 -7C v q3 = 10 -6C t theo th t trn mt ng thng trong nc nguyn cht c hng s in mi = 81 . Khong cch gia cc qu cu l r12 = 40cm, r23 = 60cm. Tnh lc in tng hp tc dng ln tng qu cu? Cu 7: C ba in tch q1 = q2 = q3 = 1,6.10 -6C, t trong chn khng ti ba nh ca tam gic u cnh a = 16cm. Xc nh lc in tng hp tc dng ln mi in tch. Cu 8: Cho ba in tch bng nhau q = 10 -6C t ti ba nh ca mt tam gic u cnh a = 5cm. a. Tnh lc tc dng ln mi in tch. b.(*) Nu ba in tch khng c gi c nh th phi t thm mt in tch th t q0 c du v ln nh th no v t u h bn in tch nm cn bng? Cu 9: Cho hai qu cu tch in dng q1 = q v q2 = 4q t c nh trong khng kh cch nhau mt khong a = 30cm. Phi t in tch th ba q0 nh th no v t u n cn bng? Cu 10: (*)Cho hai qu cu nh ging ht nhau, t cch nhau mt on r = 10cm trong khng kh. u tin hai qu cu tch in tri du, chng ht nhau mt lc F1 = 1,6.10 -2N. Cho hai qu cu tip xc nhau, ri li a ra v tr c th thy chng y nhau vi mt lc F2 = 9.10-3N. Tm in tch ca mi qu cu trc khi tip xc vi nhau. Cu 11: Hai ht bi trong khng kh cch nhau mt on r = 3cm, mi ht mang in tch q = - 9,6.10 -13C. a. Tnh lc tnh in gia hai ht. b. Tnh s electron d trong mi ht bi. Cu 12: Hai vt nh mang in tch t trong khng kh cch nhau on r = 1m, y nhau bng lc F = 1,8N. in tch tng cng ca hai vt l q = 3.10 -5C. Tnh in tch ca mi vt? Cu 13: (*) Ti ba nh tam gic u cnh a = 6cm trong khng kh c t ba in tch q1 = 6.10 -9C, q2 = q3 = - 8.10 -9C. Xc nh lc tc dng ln q0 = 8.10 -9C ti tm tam gic. Cu 14: Hai in tch q1 = - 2.10 -8C, q2 = 1,8.10 -7C t trong chn khng ti A v B, AB = 8cm. Mt in tch q3 t ti C. Hi: a. C u q3 nm cn bng? b. (*) Du v ln ca q3 q1, q2 cng cn bng.

THPT Minh Ph Sc Sn H Ni

1

B bi tp t lun vt l 11

GV: Nguyn Quang Hiu IN TRNG. CNG IN TRNG Cu 1: Mt in tch Q t trong chn khng, gy ra ti im M cch in tch Q mt khong 10cm mt cng in trng 900V/m. Hy xc nh ln in tch Q. Cu 2: Hai in tch im q1 = 2.10 -8C v q2 = - 2.10 -8C t ti hai im A v B cch nhau mt on a = 30cm trong khng kh. a. Xc nh cng in trng ti im M cch u A v B mt on l a. b. Xc nh lc tc dng ln in tch q0 = 2.10 -9C t ti M. Cu 3: Cho hai in tch im q1 = 8.10 -8C v q2 = - 2.10 -8C t ti hai im cch nhau mt on l = 10cm. Xc nh v tr ca im m ti cng in trng bng 0. Cu 4: (*) Mt ht bi tch in m c khi lng m = 10 -8g nm cn bng trong in trng u c hng thng ng xung di v c cng E = 1000 V/m. a. Tnh in tch ht bi. b. Ht bi mt bt mt s in tch bng in tch ca 5.105 lectrn. Mun ht bi vn cn bng th cng in trng phi bng bao nhiu? Cho g = 10m/s2; me = 9,1.10 -31kg. Cu 5: (*) Mt qu cu khi lng m = 0,1g treo trn mt si dy mnh, c t vo trong mt in trng u c phng nm ngang, cng E = 1000 V/m; khi dy treo b lch mt gc 45 0 so vi phng thng ng. Tm in tch ca qu cu? Cu 6: (*) Ti ba nh ca mt tam gic vung ABC (c cnh bn AB = 30cm, AC = 40cm), c t ba in tch dng bng nhau q1 = q2 = q3 = 5.10 -5C. Xc nh cng in trng ti chn H ca ng cao AH h t nh gc vung A xung cnh huyn BC. Cu 7: Hai in tch q1 = 5.10 -9C, q2 = - 5.10 -9C t ti hai im A, B cch nhau 10cm trong chn khng. Hy xc nh vct cng in trng ti im M nm trn ng thng AB v cch A mt khong 5cm, cch B mt khong 15cm. Cu 8: Hai in tch q1 = q2 = 5.10 -16C, t ti hai nh B v C ca mt tam gic u ABC cnh bng 8cm trong khng kh. Hy xc nh vct cng in trng ti nh A ca tam gic ABC. Cu 9: Hai in tch q1 = q2 = 10-5C t ti hai im A v B trong cht in mi c hng s in mi = 2 . Tnh cng in trng ti im M nm trn ng trung trc v cch AB mt khong 4cm. Bit AB = 6cm. Cu 10: (*) Ba im A, B, C trong khng kh to thnh tam gic vung ti A. AB = 3cm, AC = 4cm. t cc in tch q1, q2 ti A v B. Bit q1 = -3,6.10 -9C, vct cng in trng tng hp ti C l E C c phng song song vi AB. Xc nh q2 v cng in trng tng hp EC ti C. Cu 11: (*)Cho hai im A v B cng nm trn mt ng sc ca in trng do mt in tch q > 0 gy ra t trong khng kh. Bit ln cng in trng ti A l 36V/m, ti B l 9V/m. a. Xc nh cng in trng ti M l trung im ca AB. b. Nu ti M t mt in tch im q0 = -10 -2C th ln lc in tc dng ln q0 l bao nhiu? Xc nh phng v chiu ca lc in. Cu 12: Hai in tch im q1 = 4.10 -8C, q2 =4 q1 ln lt t ti hai im c nh A, B cch nhau 50cm 3

trong khng kh. a. Xc nh vct cng in trng ti C. Cho AC = 30cm, BC = 40cm. b. Xc nh v tr im M trn on AB khi t ti M mt in tch im q 3 th cng in trng tng hp ti C bng 0. Tm q3. Cu 13: Cho hai in tch im q1 v q2 t A, B trong khng kh, AB = 100cm. Tm im C ti cng in trng tng hp bng 0 vi: a. q1 = 36.10 -6C; q2 = 4.10 -6C. b. q1 = - 36.10 -6C; q2 = 4.10 -6C. Cu 14: (*)Cho hai in tch q1, q2 t ti A v B, AB = 2cm. Bit q 1 + q2 = 7.10 -8C v im C cc q1 6cm, cch q2 8cm c cng in trng E = 0. Tm q1 v q2. THPT Minh Ph Sc Sn H Ni 2

B bi tp t lun vt l 11

GV: Nguyn Quang Hiu

CNG CA LC IN TRNG. IN TH V HIU IN THCu 1: Mt in tch q = 10 -8C dch chuyn dc theo cc cnh ca tam gic u ABC cnh a = 20cm t trong in trng u c cng E = 3000 V/m. Tnh cng thc hin dch chuyn in tch q theo cch cnh AB, BC v CA, bit rng in trng E c hng song song vi BC. Cu 2: (*) Cho hai in tch q1 = 5.10 -8C v q2 = 3.10 -8C cch nhau mt khong a = 30cm t trong khng kh. Tnh cng cn thit a hai in tch n cch nhau mt khong b = 20cm. Cu 3: Hai bn kim loi song song mang in tch tri du t cch nhau 2cm. Cng in trng gia hai bn l 3000 V/m. St b mt bn mang in dng, ngi ta t mt ht mang in dng c in tch 1,5.10 -6C, khi lng m = 9.10 -31kg. a. Tnh cng ca lc in trng khi ht mang in chuyn ng t bn dng sang bn m. b. Tnh vn tc ca ht mang in kh n p vo bn mang in m. Cu 4: Mt in tch q = 4.10 -8C di chuyn trong mt in trng u c cng E = 100 V/m theo ng gp khc ABC. on AB c chiu di 20cm v hp vi cc ng sc mt gc = 30 0 . on BC di 40cm v hp vi cc ng sc in mt gc =120 0 . Tnh cng ca lc in trng trn c qung ng ABC. Cu 5: Hai bn kim loi phng t nm ngang, song song v cch nhau d = 10cm. Hiu in th gia hai bn U = 100V. Mt lectron c vn tc ban u v0 = 5.106m/s chuyn ng dc theo ng sc v pha bn in tch m. lectron chuyn ng nh th no? Cho bit in trng gia hai bn l in trng u v b qua tc dng ca trng trng. Cu 6: Mt lectron bay vi vn tc v = 1,2.107m/s t mt im c in th V1 = 600V, theo hng ca cc ng sc. Hy xc nh in th V2 ca im m lectron dng li. Cu 7: (*) Gia hai bn kim loi t song song nm ngang, tch in tri du, c mt hiu in th U1 = 1000V. Khong cch gia hai bn l d = 1cm. ng gia khong cch hai bn c mt git thy ngn nh nm l lng. t nhin hiu in th gim xung, ch cn U 2 = 995V. Hi sau bao lu git thy ngn ri xung n bn di? Cu 8: Cho hai im A v B nm trong in trng u c cng E = 8000V/m. Ti im A ngi ta t in tch q = 2.10 -8C. Tm cng in trng EB ti im B, cho bit AB = 10cm v AB hp vi phng ca in trng u mt gc = 60 0 . Cu 9: (*) Hai qu cu nh A v B bng kim loi, ging ht nhau, c khi lng m = 0,1kg, c treo tip xc nhau vo cng mt im O bng hai si dy mnh, cch in, khng gin, di l = 20cm. Ngi ta truyn mt in tch q cho qu cu A th thy hai qu cu y nhau cho n khi hai dy treo hp vi nhau mt gc 1 = 90 0 . a. Xc nh ln in tch q. H thng t trong khng kh. b. Sau ngi ta truyn thm mt in tch q cho qu cu A th thy gc gia hai dy treo gim i cn 2 = 60 0 . Xc inh q v cng in trng ti A v B do qu cu B v A gy ra lc . Cho g = 10m/s2. Cu 10: (*) Mt qu cu kim loi bn knh 4cm tch in dng. di chuyn in tch q = 10 -9C t v cng n M cch mt hnh cu 20cm, ngi ta cn thc hin mt cng A = 5.10 -7J. Tnh in th trn mt qu cu do in tch ca qu cu gy nn. Cu 11: Hiu in th gia hai im M, N trong in trng UMN = 100V. a. Tnh cng ca lc in trng khi mt lectron di chuyn t M n N. b. Tnh cng cn thit di chuyn lectron t M n N. Cu 12: di chuyn q = 10 -4C t rt xa vo im M ca in trng, cn thc hin cng A = 5.10 -5J. Tm in th M (gc in th v cc). Cu 13: Khi bay qua hai im M v N trong in trng, lectron tng tc, ng nng tng thm 250eV (1eV = 1,6.10 -19J). Tnh UMN. Cu 14: lectron chuyn ng khng vn tc u t A n B trong in trng u, UBA = 45,5V. Tm vn tc ca lectron ti im B? THPT Minh Ph Sc Sn H Ni 3