DNG 3: NH LUT ễM I VI TON MCH I NH LUT ễM I VI TON MCH 1.nh lut Ohm cho mch in kớn cú cha ngun in v in tr -Biu thc: E I= RN + r I E,r Trong ú: E :l sut in ng ca ngun in r:in tr ca ngun v RN :l in tr tng ng ca mch ngoi R *H qu: -hiu in th mch ngoi: U N = I R = E I r E, rRN E r Ngun in cú in tr cng nh thỡ dũng on mch cng ln v cng nguy hi +nu pin b on mch thỡ mau ht pin +nu acquy b on mch thỡ acquy s b hng - Hin tng on mch: Xy RN = v ú: Imax = E,r 2.nh lut Ohm cho mch in cú cha ngun in,mỏy thu v in tr R: I= Trong ú: E , E :l sut in ng ca ngun in v sut phn in ca Rmỏy thu r,r:in tr ca ngun v ca mỏy thu , R:in tr mch ngoi Hiu sut ngun in: H = E E' R+r +r' U RN A coự ớch = N ( 100% ) = A toaứn phan E RN + r *BI TP: Bi 1: Mt pin cú s ghi trờn v l 1,5V v cú in tr l 0,5 Mc mt búng ốn cú in tr R = 2,5 vo hai cc ca pin ny tr thnh mch kớn Tớnh cng dũng in qua ốn ú v hiu in th qua hai u ca nú S:I=0,5A,U=1,25V Bi 2: Mc mt in tr 14 vo hai cc ca mt ngun in cú in tr l thỡ hiu in th gia hai cc ca ngun l 8,4V a/Tớnh cng dũng in chy mch v sut in ng ca ngun in b/Tớnh cụng sut mch ngoi v cụng sut ca ngun in ú c/Tớnh hiu sut ca ngun in S:a/0,6A, 9V b/ Pngdien =5, 4W , Pmngoai =5, 04W c/93,3% Bi 3: Ngun in cú sut in ng l 3V v cú in tr Mc song song hai búng ốn nh cú cựng in tr l vo hai cc ca ngun in ny a Tớnh cụng sut tiờu th ca mi búng ốn b Nu thỏo b mt búng ốn thỡ búng ốn cũn li sỏng mnh hn hay yu hn so vi trc ú? S:a/ P1 = P2 = 0,54W b/trng hp sau sỏng hn E,r Bi 4: Cú mch in nh hỡnh v Ngun in R cú sut in in E = 7,5V, cú in tr r = 1.ốn cú ghi b 6V 3W.Tớnh giỏ tr ca bin tr Rb ốn sỏng bỡnh thng.S: Rb = Bi 5: Cho mch in nh hỡnh v Ngun in cú sut in ng 7,8V,v in R1 C R2 tr r = 0,4 Cỏc in tr mch ngoi R1 = R2 = R3 = 3, R4 = A B a Tớnh cng dũng in chy qua cỏc in tr v R3 D R4 hiu in th hai u mi in tr b Tớnh hiu in th gia hai im C v D E,r c Tớnh hiu in th hai u ngun in v hiu sut ca ngun in E,r S:a/ I1 = I = 1,17 A, I = I = 0, 78 A, U1 = U = 3, 51V , U = 2,34V , U = 4, 68V R b/ U CD = 1,17V , c/U = 7,02V,H = 90% Bi 6: Cú mch in nh hỡnh v Ngun in cú sut in in ng 24V v cú in tr r = Trờn cỏc búng ốn cú ghi: 1( 12V- E 6W), , r 2(12V 12W),in tr R = a Cỏc búng ốn sỏng nh th no? Tớnh cng dũng in qua cỏc búng ốn b Tớnh cụng sut tiờu th ca mch in v hiu sut ca ngun in R I =1,3 A, I = 0,67 A ốn chỏy b/44W,92% S: Bi 7: Cú mch in nh hỡnh v Ngun in cú sut in in E = 18V v cú in tr r = Trờn cỏc búng ốn cú ghi: 1( 12V- 12W), 2(12V 7,2W), bin tr R cú giỏ tr bin thiờn t n 100 a iu chnh R = 20 Tớnh cng dũng in chy qua cỏc búng ốn , r sỏnh sỏng ca hai búng ốn v in tr.E So b iu chỡnh R bng bao nhiờu ốn sỏng bỡnh thng S:a/ A I d1 = 0, 75 A, I d = 0,375 A, ốn sỏng hn b/ R=5 Bi 8: R1*: Cú R mch in nh hỡnh v Ngun in cú sut in Eng , r2 E = 12V,in tr r = R l bin tr a iu chnh R cụng sut mch ngoi l 11W Tớnh giỏ tr V R tng ng.Tớnh cụng sut ca ngun trng hp ny b Phi iu chnh R cú giỏ tr bao nhiờu cụng sut ta nhit trờn R l ln nht R S:a/R=11,P = 12W b/ R=1,P = 36W E E,r Bi 9: * Cho mch in cú s nh hỡnh v:Trong ú ngun in cú sut in ng = 12V v in tr r =1,1 , tr mch R =0,1 x R R1 tr X phi cú giỏ tr l bao nhiờu cụng sut a in tiờu th mch ngoi l ln nht? b in tr X phi cú giỏ tr l bao nhiờu cụng sut tiờuR th in tr ny l ln nht? Tỡm cụng sut ln nht ú ẹS: a/ Rx=1 b/Rx=1,2,Pmax = 30W DNG 4: NH LUT ễM I VI CC LOI ON MCH 1/ l Ohm cho mch kớn cha ngun v mỏy thu mc ni tip: I = E EP R + r + rP 2/ nh lut Ohm tng quỏt: + UAC = rI E hay UCA = E rI : hiu in th gia hai cc ca ngun in + UCB = EP + (R + rP)I: hiu in gia hai u mỏy thu v in tr R UAB = (R + r + rP) + EP E vy I = U AB + E EP R + r + rP Lu ý: Trong mch in, nu dũng in cú chiu i vo cc dng thỡ E úng vai trũ l mỏy thu in Ngc li, nu dũng in cú chiu i t cc dng thỡ E úng vai trũ l ngun in 3/Mc cỏc ngun in thnh b Mc ni tip: + Eb = E1 + E2 + + En + rb = r1 + r2 + + rn Nu cú n ngun ging nhau, mi ngun (E ,r): Eb = n E v rb = n.r Mc xung i: Eb = E1 E2 nu E1 > E2 Eb = E2 E1 nu E2 > E1 v rb = r1 + r2 Mc song song: Cú n ngun ging nhau, mi ngun cú (E, r) Eb = E v rb = r/n Mc hn hp i xng: - B ngun cú N ngun ging nhau, c mc thnh n hng (dóy) song song, mi hng cú m ngun ni tip - Tng s ngun in N = m.n - Sut in ng tng ng: Eb = m.E v in tr tng ng: rb = m r n Bi 1: Cho b ngun c mc nh hỡnh v: cỏc ngun in ging nhau, mi ngun cú E = V v in tr r = 0,2 Tỡm Sut in ng b ngun v in tr tng ng ca b ngun? S: Eb = 24 V , r = Bi 2: Cho on mch nh hỡnh v, E1 = V, r1 = 1,2 ; E2 = V, r2 = 0,4 ; in tr R = 28,4 Hiu in th gia hai u on mch UAB = V Cng dũng in mch cú chiu v ln l bao nhiờu? S: chiu t A sang B, I = 0,4 A Bi 3: Cho mch in nh hỡnh v: E1 = V, r1 = 1,2 , E2 = V, r2 = 0,4 ; R = 28,4 , hiu in th gia hai u on mch o c l UAB = V a/ Cho bit mch in ny cha ngun in no v cha mỏy thu no? Vỡ sao? b/ Tớnh cng dũng in chy qua on mch v cho bit chiu ca nú c/ Tớnh hiu in th UAC v UCB? Bi 4: Cho mch in nh hỡnh v: E1 = V, r1 = 0,5 , E2 = V, r2 = 0,5 ; R1 = , R2 = , R3 = a/ Tỡm in tr tng ng ca mch in v hiu in th UAB b/ Tớnh cng dũng in qua in tr R3 Bi 5: Cú pin nh nhau, mi pin cú sut in ng E = V v in tr r = 0,5 Bit R1 = 12 , ampe k v khúa K cú in tr khụng ỏng k Khi K m, ampe k ch IA = 24/27 A Tớnh s ch ca Ampe k K úng S: IA = 1,26A Bi 6: Cho mch in nh hỡnh v: E1 = E3 = V, E2 = V, r1 = r2 = r3 = , R1 = R2 = R3 = , R4 = 10 Tớnh: a/ Sut in ng v in tr ca b ngun b/ Hiu in th gia hai im M v N S: a/9V , b/ UMN= -1V Bi 7: Cho mch in nh hỡnh v: ú: R1 = 3,5 , R2 = R3 = , R4 = , E1 = 2,4 V, r1 = 0,1 E2 = 3V, r2 = 0,2 a/ Tớnh sut in ng v in tr ca ngun b/ Tớnh in tr tng ng ca mch ngoi c/ Tớnh cng dũng in qua mch chớnh d/ Tớnh hiu in th UAB v UAC S: a/5,4V , b/5,1 c/1A d/UAB=1,5V,UAC=-2V Bi 8: ốn cú in tr R4 ghi: (3V 6W), cỏc in tr: R1 = 12 , R2 = , R3 = Ngun E = V, r1 = 1,5 , E = 20 V, r2 = , in tr Ampe k RA a/ Tỡm in tr tng ng ca mch ngoi b/ Tỡm s ch ca Ampe k c/ Tỡm cụng sut ta nhit trờn R3 v UMN d/ Thay R2 bng R5 thỡ thy ốn sỏng bỡnh thng Tỡm R5 v hiu sut b ngun lỳc ny S: RD = 1,5, RN = 7,5, I A = 1,6 A, P3 = 1, 92W ,U MN = 16V , R5 = 3, H ( 0 ) = 68, 75 0 TRC NGHIM: Cõu Cho mt mch in gm mt pin 1,5 V cú in tr 0,5 ni vi mch ngoi l mt in tr 2,5 Cng dũng in mch l A A B 3/5 A C A D 0,5 A Cõu 2: Mt ngun in cú in tr 0,5 c mc vi in tr thnh mch kớn Khi ú hiu in th gia hai cc ca ngun in l 18 V Sut in ng ca ngun in v cng dũng in mch l bao nhiờu? A.U = 1,98V, I=3,6A B.U = 198V, I=36A C U = 18,9V, I=6,3A D U = 19,8V, I=3,6A Cõu 3: Cho mch in nh hỡnh v Mi pin cú sut in ng E = 1,5 V, in tr r = in tr mch ngoi R = 3,5 Cng dũng in mch ngoi l bao nhiờu? A 1A B 2A C 0,1A D 0,2 A Cõu 4:Mt ngun in cú in tr 0,4 c mc vi mt in tr 4,8 thnh mch kớn thỡ hiu in th mch ngoi bng 28V Tỡm sut in ng ca ngun in ny? A E =303,32V B E =3,0332V C E =30,332V D E =30,32V Cõu 5:Mt mch kớn gm ngun in 18V; 1,5 c mc vi mch ngoi cú hai in tr R1 = v R2 = mc song song Cng dũng in mch bng bao nhiờu? A 4,61A B 46,1 A C 0,46 A D 61,4 A Cõu Ghộp pin ging ni tip mi pin cú sut in ng V v in tr Sut in ng v in tr ca b pin l A V v B V v 1/3 C V v 1/3 D V v Cõu Hai búng ốn cú in tr mc song song v ni vo mt ngun cú in tr thỡ cng dũng in mch l 12/7 A Khi thỏo mt ốn thỡ cng dũng in mch l A 6/5 A B 5/6 A C A D A Cõu Cho in tr ging cựng giỏ tr , hai in tr mc song song v cm ú ni tip vi in tr cũn li on mch ny c ni vi ngun cú in tr thỡ hiu in th hai u ngun l 12 V Cng dũng in mch v sut in ng ca mch ú l A A v 12 V B 0,5 A v 12 V C 0,5 A v 14 V D A v 14 V Cõu Mt búng ốn ghi V- W c mc vo mt ngun in cú in tr l thỡ sỏng bỡnh thng Sut in ng ca ngun in l A V B V C 12 V D 36 V Cõu 10 Ghộp song song mt b pin ging loi V - thỡ thu c b ngun cú sut in ng v in tr l A V - B V - C V - 1/3 D V -