nh chnh sch B quyt n luyn thi i hc theo ch mn Vt L Dao ng c
nh chnh sch B quyt n luyn thi i hc theo ch mn Vt L in xoay
chiuTrang inSa li
6V d 4: Mt dng in xoay chiu c cng tc thi: i = 4cos100(t (A) i
qua mt in tr R = 5 (.
1) Tnh nhit lng to ra in tr R trong thi gian 7 pht.2) Nhng R vo
mt bnh cha m = 1,2 kg nc. Hi sau thi gian 10 (pht) nhit nc trong
bnh tng bao nhiu . Bit hiu sut ca qu trnh un nc l H = 90% v nhit
dung ring ca nc l c = 4,2 (kJ/kg.C0).
Hng dn
1) p dng cng thc: .
2) Ta c:
V d 4: Mt dng in xoay chiu c cng tc thi: i = 4cos100(t (A) i qua
mt in tr R = 5 (.
1) Tnh nhit lng to ra in tr R trong thi gian 7 pht.2) Nhng R vo
mt bnh cha m = 1,2 kg nc. Hi sau thi gian 10 (pht) nhit nc trong
bnh tng bao nhiu . Bit hiu sut ca qu trnh un nc l H = 90% v nhit
dung ring ca nc l c = 4,2 (kJ/kg.C0).
Hng dn
1) p dng cng thc: .
2) Ta c:
14V d 2: in p hai u on mch c biu thc u = 200cos(100t + 5(/6) (u
o bng vn, t o bng giy). Trong khong thi gian t 0 n 0,01 s in p tc
thi c gi tr bng 100 V vo nhng thi im
A. 3/200 s v 5/600 s.B. 1/400 s v 2/400 s.C. 1/500 s v 3/500
s.D. 1/200 v 7/600 s.
V d 2: in p hai u on mch c biu thc u = 200cos(100t + 5(/6) (u o
bng vn, t o bng giy). Trong khong thi gian t 0 n 0,02 s in p tc thi
c gi tr bng 100 V vo nhng thi im
A. 3/200 s v 5/600 s.B. 1/400 s v 2/400 s.C. 1/500 s v 3/500
s.D. 1/200 v 7/600 s.
26V d 1: Dng in xoay chiu chy trong dy dn c biu i = 2cos(100(t -
(/6) (A) (t o bng giy). Tnh in lng chuyn qua tit din thng ca dy dn
trong 1/300 (s) k t lc t = 0.A. 6,666 mC. B. 5,513 mC. C. 6,366 mC.
D. 6,092 mC.Hng dn
Cch 1:
V d 1: Dng in xoay chiu chy trong dy dn c biu i = 2cos(100(t -
(/6) (A) (t o bng giy). Tnh in lng chuyn qua tit din thng ca dy dn
trong 1/300 (s) k t lc t = 0.A. 6,666 mC. B. 5,513 mC. C. 6,366 mC.
D. 6,092 mC.Hng dn
Cch 1:
28V d 6: Cho dng in xoay chiu c gi tr hiu dng 2 A chy qua bnh in
phn cha dung dch H2SO4 vi cc in cc tr. Tnh th tch kh iu kin tiu
chun thot ra trong thi gian 16 pht mi in cc.A. 0,168 lt. B. 0,0235
lt. C. 0,047 lt. D. 0,056 lt.V d 6: Cho dng in xoay chiu c gi tr
hiu dng 2 A chy qua bnh in phn cha dung dch H2SO4 vi cc in cc tr.
Tnh th tch kh iu kin tiu chun thot ra trong thi gian 5 pht mi in
cc.A. 0,168 lt. B. 0,0235 lt. C. 0,047 lt. D. 0,056 lt.
58V d 9: t in p xoay chiu vo hai u on mch AB theo th t gm cun dy
thun cm L c cm khng 100 , in tr R = 100 v t in C c dung khng 200 mc
ni tip, M l im gia L v R, N l im gia ca R v C. Kt qu no sau y khng
ng?A. in p hai u on AN sm pha hn in p hai u on mch AB l 2/3
B. Cng dng in tr pha /3 so vi in p hai u on mch AB.
C. in p hai u on AN sm pha hn in p hai u on mch AB l 2/3.D. in p
hai u on mch AB sm pha hn in p hai u t in l /6.
Hng dn
EMBED Equation.DSMT4
V d 9: t in p xoay chiu vo hai u on mch AB theo th t gm cun dy
thun cm L c cm khng 100 , in tr R = 100 v t in C c dung khng 200 mc
ni tip, M l im gia L v R, N l im gia ca R v C. Kt qu no sau y khng
ng?A. in p hai u on AN sm pha hn in p hai u on mch AB l 2/3
B. Cng dng in tr pha /3 so vi in p hai u on mch AB.
C. in p hai u on AN sm pha hn in p hai u on mch AB l 2/3.D. in p
hai u on mch AB sm pha hn in p hai u t in l /6.
Hng dn
EMBED Equation.DSMT4
80Bi 79: oan mach AB mc ni tip theo th t gm in tr R = 50 ( cun
dy c in tr r, c t cm L v t in C = 0,2/( mF, M la im ni gia C va cun
dy. Mt in ap xoay chiu n inh c mc vao AM, khi o dong in trong mach
i1 = 2cos(100(t - (/3) (A). in ap nay mc vao AB thi dong in qua
mach i2 = cos(100(t + (/6) (A). t cam cua cun dy bng:Bi 79: oan
mach AB mc ni tip theo th t gm in tr R = 50 ( cun dy c in tr r, c t
cm L v t in C = 0,02/( mF, M la im ni gia C va cun dy. Mt in ap
xoay chiu n inh c mc vao AM, khi o dong in trong mach i1 =
2cos(100(t - (/3) (A). in ap nay mc vao AB thi dong in qua mach i2
= cos(100(t + (/6) (A). t cam cua cun dy bng:
88V d 3: Mt on mch cha hai trong ba phn t: t in, in tr thun, cun
cm thun mc ni tip. Bit in p gia hai u on mch v cng dng in qua n ln
lt c biu thc: u = 60cos(100(t - (/2) (V), i = 2sin(100(t + (/6)
(A). Hi trong on mch c cc phn t no? Tnh dung khng, cm khng hoc in
tr tng ng vi mi phn t . Tnh cng sut tiu th ca on mch.
A. R = 15 (; ZL = 15 ( v P = 30 (W).
B. R = 15 (; ZC = 15 ( v P = 30 (W).
C. R = 15 (; ZC = 15 ( v P = 30 (W).D. R = 15 (; ZL = 15 ( v P =
30 (W).
Hng dn
Vit li biu thc: i = 2sin(100(t + (/6) (A) = 2cos(100(t - (/3)
(A).
(
V d 3: Mt on mch cha hai trong ba phn t: t in, in tr thun, cun
cm thun mc ni tip. Bit in p gia hai u on mch v cng dng in qua n ln
lt c biu thc: u = 60cos(100(t - (/2) (V), i = 2sin(100(t + (/6)
(A). Hi trong on mch c cc phn t no? Tnh dung khng, cm khng hoc in
tr tng ng vi mi phn t . Tnh cng sut tiu th ca on mch.
A. R = 15 (; ZL = 15 ( v P = 30 (W).
B. R = 15 (; ZC = 15 ( v P = 30 (W).
C. R = 15 (; ZC = 15 ( v P = 30 (W).D. R = 15 (; ZL = 15 ( v P =
30 (W).
Hng dn
Vit li biu thc: i = 2sin(100(t + (/6) (A) = 2cos(100(t - (/3)
(A).
(
102V d 7: Mt on mch xoay chiu ni tip AB gm in tr thun R, cun cm
thun L v t in c in dung C. in p hai u on AB l u = U0cos(t (V) th in
p trn L l uL = U0cos((t + (/3) (V). Mun mch xy ra cng hng th in
dung ca t bngV d 7: Mt on mch xoay chiu ni tip AB gm in tr thun R,
cun cm thun L v t in c in dung C. in p hai u on AB l u = U0cos(t
(V) th in p trn L l uL = U0cos((t + (/3) (V). Mun mch xy ra cng hng
th in dung ca t bng
112Bi 8: Mt on mch xoay chiu ni tip AB gm in tr thun R, cun cm
thun L v t in c in dung C. in p hai u on AB l u = U0cos(t (V) th in
p trn C l uC = U0cos((t - 2(/3) (V). Mun mch xy ra cng hng th in
dung ca t bngBi 8: Mt on mch xoay chiu ni tip AB gm in tr thun R,
cun cm thun L v t in c in dung C. in p hai u on AB l u = 2U0cos(t
(V) th in p trn C l uC = U0cos((t - 2(/3) (V). Mun mch xy ra cng
hng th in dung ca t bng
112Bi 9: Mt mch in xoay chiu gm mt t in C ni tip vi mt cun dy. t
vo hai u on mch mt in p u = Ucos(t (V) th in p hai u t in C l uL =
Ucos((t + 3(/4) (V). T s gia dung khng v cm khng bngBi 9: Mt mch in
xoay chiu gm mt t in C ni tip vi mt cun dy. t vo hai u on mch mt in
p u = Ucos(t (V) th in p hai u t in C l uC = Ucos((t + 3(/4) (V). T
s gia dung khng v cm khng bng
161V d 19: (GIN R-C-rL) t in p xoay chiu u =120cos(t (V) vo hai
u on mch AB gm hai on mch AM v MB mc ni tip th cng hiu dng qua mch
l 0,5 A. on AM gm in tr thun R mc ni tip vi t in C, on MB gm cun
cm. Bit in p gia hai u on mch MB v in p gia hai u on mch AB lch pha
nhau (/2. in p hiu dng trn R bng mt na in p hiu dng trn on AM. Cng
sut tiu th ca mch lV d 19: (GIN R-C-rL) t in p xoay chiu u
=120cos(t (V) vo hai u on mch AB gm hai on mch AM v MB mc ni tip th
cng hiu dng qua mch l 0,5 A. on AM gm in tr thun R mc ni tip vi t
in C, on MB gm cun cm. Bit in p gia hai u on mch AM v in p gia hai
u on mch AB lch pha nhau (/2. in p hiu dng trn R bng mt na in p hiu
dng trn on AM. Cng sut tiu th ca mch l
203V uX t cc i tr hn uLr v thi gian l T/4 (tc l v pha l 2(/2)
nn: . Ta thy: nn X c th l in tr mc ni tip vi t ( Chn B.V uX t cc i
tr hn uLr v thi gian l T/4 (tc l v pha l (/2) nn: . Ta thy: nn X c
th l in tr mc ni tip vi t ( Chn B.
289V d 12: on mch AB ni tip gm hai on mch AM v MB. on mch AM l
mt cun dy c in tr thun R = 40 ( v t cm L = 0,4/( H, on mch MB l mt
t in c in dung C thay i c, C c gi tr hu hn v khc khng. t vo AB mt
in p: uAB = 120cos100(t (V). iu chnh C tng in p hiu dng (UAM + UMB)
t gi tr cc i. Tm gi tr cc i ca tng s ny.A. 240 V.B. 120V.C. 120
V.D. 120 V.Hng dn
Xt (AEM:
p dng nh l hm s sin cho (AMB:
EMBED Equation.DSMT4
EMBED Equation.DSMT4
EMBED Equation.DSMT4 Khi : ( Chn B.V d 12: on mch AB ni tip gm
hai on mch AM v MB. on mch AM l mt cun dy c in tr thun R = 40 ( v t
cm L = 0,4/( H, on mch MB l mt t in c in dung C thay i c, C c gi tr
hu hn v khc khng. t vo AB mt in p: uAB = 120cos100(t (V). iu chnh C
tng in p hiu dng (UAM + UMB) t gi tr cc i. Tm gi tr cc i ca tng s
ny.A. 240 V.
B. 120V.
C. 120 V.D. 120 V.Hng dn
Xt (AEM:
p dng nh l hm s sin cho (AMB:
EMBED Equation.DSMT4
EMBED Equation.DSMT4
EMBED Equation.DSMT4 Khi : ( Chn A.
307Ch : Chng ta nh li cc cng thc gii nhanh sau y:
( Khi R thay i hai gi tr L1 v L2 m c cng P th Pmax khi: .Ch :
Chng ta nh li cc cng thc gii nhanh sau y:
( Khi R thay i hai gi tr R1 v R2 m c cng P th Pmax khi: .
308*c cng UC th UCmax khi: .*c cng UC th UCmax khi: .
322Bi 49 p n BBi 49 p n D.
328By gi nu cho thm iu kin: th ta c h: By gi nu cho thm iu kin:
th ta c h:
329Ch : iu kin c th tr hnh di dng iu kin vung pha.Ch : iu kin c
th tr hnh di dng iu kin vung pha.
347Bi 16 p n B, Bi 30 p n ABi 16 p n D, Bi 30 p n B
362V d 20: Mch RLC mc vo my pht in xoay chiu. Khi tc quay ca
roto l n (vng/pht) th cng sut l P h s cng sut 0,5. Khi tc quay ca
roto l 2n (vng/pht) th cng sut l 4P. Khi tc quay ca roto l n
(vng/pht) th cng sut bng bao nhiu?A. 16P/7. B. P. C. 9P. D.
24P/13.
Hng dn
* (1)
*
(2). T (1), (2) suy ra: .*
V d 20: Mch RLC mc vo my pht in xoay chiu. Khi tc quay ca roto l
n (vng/pht) th cng sut l P h s cng sut 0,5. Khi tc quay ca roto l
2n (vng/pht) th cng sut l 4P. Khi tc quay ca roto l n (vng/pht) th
cng sut bng bao nhiu?A. 16P/7. B. P. C. 8P/3. D. 24P/13.
Hng dn
* (1)
*
(2). T (1), (2) suy ra: .*
389V d 21: Trong mt gi thc hnh mt hc sinh mun mt qut in loi 180
V 220 W hot ng bnh thng di mt in p xoay chiu c gi tr hiu dng 220 V,
nn mc ni tip vi qut mt bin tr. Ban u hc sinh bin tr c gi tr 70 ( th
o thy cng hiu dng trong mch l 0,75 A v cng sut ca qut in t 92,8%.
Mun qut hot ng bnh thng th phi iu chnh bin tr nh th no?A. Gim i 20
(.B. Tng thm 12 (.C. Gim i 12 (.D. Tng thm 20 (.Hng dn
*Lc u, ng c hot ng di nh mc, cng sut tiu th ca n:
T phng trnh vc t: chiu ln trc honh v trc tung ta c:
EMBED Equation.DSMT4 kt hp vi , suy ra: ( ( 0,5424 rad hay .*Khi
ng c hot ng bnh thng:
T phng trnh vc t: chiu ln trc honh v trc tung ta c:
EMBED Equation.DSMT4
Gim i 70 58 = 12 ( ( Chn C.V d 21: Trong mt gi thc hnh mt hc
sinh mun mt qut in loi 180 V 120 W hot ng bnh thng di mt in p xoay
chiu c gi tr hiu dng 220 V, nn mc ni tip vi qut mt bin tr. Ban u hc
sinh bin tr c gi tr 70 ( th o thy cng hiu dng trong mch l 0,75 A v
cng sut ca qut in t 92,8%. Mun qut hot ng bnh thng th phi iu chnh
bin tr nh th no?A. Gim i 20 (.B. Tng thm 12 (.C. Gim i 12 (.D. Tng
thm 20 (.Hng dn
*Lc u, ng c hot ng di nh mc, cng sut tiu th ca n:
T phng trnh vc t: chiu ln trc honh v trc tung ta c:
EMBED Equation.DSMT4 kt hp vi , suy ra: ( ( 0,5424 rad hay .*Khi
ng c hot ng bnh thng:
T phng trnh vc t: chiu ln trc honh v trc tung ta c:
EMBED Equation.DSMT4
Gim i 70 58 = 12 ( ( Chn C.
404V d 19: Mt my bin p c li i xng gm bn nhnh nhng ch c hai nhnh
c qun hai cun dy. Khi mc mt cun dy vo in p xoay chiu th cc ng sc t
do n sinh ra khng b thot ra ngoi v c chia u cho hai nhnh cn li. Khi
mc cun 1 (c 1000 vng) vo in p hiu dng 60 V th cun 2 khi h c in p
hiu dng l 40 V. S vng dy ca cun 2 l
V d 20: Mt my bin p c li i xng gm 5 nhnh nhng ch c hai nhnh c
qun hai cun dy. Khi mc mt cun dy vo in p xoay chiu th cc ng sc t do
n sinh ra khng b thot ra ngoi v c chia u cho hai nhnh cn li. Khi mc
cun 1 vo in p hiu dng 120 V th cun 2 khi h c in p hiu dng U2. Khi
mc cun 2 vi in p hiu dng 3U2 th in p hiu dng cun 1 khi h lV d 19:
Mt my bin p c li i xng gm bn nhnh nhng ch c hai nhnh c qun hai cun
dy. Khi mc mt cun dy vo in p xoay chiu th cc ng sc t do n sinh ra
khng b thot ra ngoi v c chia u cho cc nhnh cn li. Khi mc cun 1 (c
1000 vng) vo in p hiu dng 60 V th cun 2 khi h c in p hiu dng l 40
V. S vng dy ca cun 2 l
V d 20: Mt my bin p c li i xng gm 5 nhnh nhng ch c hai nhnh c
qun hai cun dy. Khi mc mt cun dy vo in p xoay chiu th cc ng sc t do
n sinh ra khng b thot ra ngoi v c chia u cho cc nhnh cn li. Khi mc
cun 1 vo in p hiu dng 120 V th cun 2 khi h c in p hiu dng U2. Khi
mc cun 2 vi in p hiu dng 3U2 th in p hiu dng cun 1 khi h l
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