Biet dien ap tuc thoi tren cuon day som pha hon dong dien la Tt/4.. Cau 41: Mot tu dien phang khong khi hai ban song song each nhau mot khoang d dugc noi vao nguon dien xoay chieu thi c
Trang 1B 6 trp hien thitc V^t I I L T D H tren Mnh VTV2 t^p 2 - Chu V^n Bicn
A A N B can tai A md M A I = N A B
/ 120
< ,.,;iV;l,„ ^ / /
= » M A N = a
A A M N can tai M vda^ 30" l:o^/3
U L = 120v/3 sin - 60N/3 ^ Z L = ^ = 15V6i
V-Cau 29: Dat dien ap xoay chieu 120 V - 50 Hz vao doan mach noi tiep AB gom
dien tro thuan R, tu dien va cuon cam Khi noi hai dau cuon cam voi m o t
ampe l<e'c6 dien tro rat nho thi so chi cua no la 2 A Neu thay ampe ke bang
von ke CO di^n tro rat Ion thi no chi 100 V, dong thoi dien ap tuc thoi h a i
dau von ke lech pha goc a (cosa = 0,6) so voi di^n ap hai dau dogn mach
AB Tong tro cua cuon cam la : v m , h rMi-J rV- r f i '
A 4 0 Q B 4 0 ^ / 3 Q C 20VS a D 6 0 Q
U
+ Mdc ampe - ke th i Lr bi noi tdt: Z^Q = y = 60
+Mdcv6n-ke,ve gidn do vectd : 'i • • '
UKC = Vl202+]002 2.120.100.cosa = 100 = U^L Z , L = Z R ^ = 60n
V,
i M i l l - - : ]
Cau 3 0 : Dat dien ap xoay chieu u = 41V2 coscot (V) vao hai dau doan mach noi
tiep gom dien tro R, cuon cam c6 do t u cam L, c6 dien tro thuan r va tu die'^
C thi cuong do hieu dung dong qua mach la 0,4 A Biet dien ap hieu dung
tren dien tro, tren cuon cam va tren ty di^n Ian lugt la 25V, 25V va 29V Gi^i
t r j r b S n g ' ^ ^ ^-.f^^^:,: ' r^'
A 5 0 Q B 15Q C 3 7 , 5 n D 3 0 a
300
, , Huong dan
A M N E : N E = V M N ^ - M E ^ = 7625-x^ E B = 29 - yl625-x^
A A E B : A B ^ = A E ^ + E B ^ 1681 = (25 + x)^ + (29 - ^ 6 2 5 ^ ) "
=^r = - ^ = 37,5(n)
!
•4 t
r, L
/
• f^f'H
/ UL
25V M / X
S 4 1 V
B Cau 3 1 : Doan mach xoay chieu noi tiep gom dien tro thuan R, tu dien C va cuon cam thuan L Dat vao hai dau doan mach mot dien ap xoay chieu on djnh thi dien ap hieu dung tren R, L va C Ian lugt la 4 0 V , 120 V va 4 0 V Thay C boi tu dien C thi dien ap hieu dung tren tu la 6 0 V , khi do, dien ap hieu dung tren R la ,v.^ ,, , „,( r.^'
A 6 7 , 1 2 V B 4 5 , 6 4 V C 5 4 , 2 4 V ' D 4 0 , 6 7 V ^
Huong dan
' i n u i ) I ' ? ;
U K = 4 0 ( V )
U L = 1 2 0 ( V )
•rri qfi n-/
= > Z L = 3 R = ^ U ' L = 3 U ' K M V 0£ A
Uc = 40(V) ^ U = > / U ? < + ( U L - U C ) ' = V 4 0 2 + ( 1 2 0 - 4 0 f = 4075 (V)
+K}ii thay ddi C thi U van Id 40V5 (V) yd U ' L = 3U'R
> u 2 = u i + ( U L - u c r
> 8000 = U ' K + (3U'K - 6 0 f lOU'K - 360U'K - 4400 = 0
> U ' K =45,64(V) r - ! 1 ,J ,s) Cau 32: Dat dien ap xoay chieu tan so 300 V - 50 Hz vao hai dau doan mach AB gom hai doan mach A M va MB mSc noi tiep Doan A M gom d''en tro thuan mac noi tiep voi cuon cam thuan, doan MB chi c6 tu dien Biet dien ap hieu dung giua hai dau doan mach MB la 140 V va dong dien trong mach tre pha hon dien ap giua hai dau doan mach AB la cp sao cho coscp = 0,8 Dien ap hieu dung giija hai dau doan mach A M la
A 300 V B.200V C 500 V D 40C V
301
Trang 2B S Ira hicti llnic Vdl !i I r o l l t r e n kenh VTV2, t^p 2 - Chu VSn B i e n
Huong dan
AE = 300cosip = 240(V) / j ^ / ' ^/IK:
BE = SOOsin^p = 30o7l - cos^^ = 180 => E M = EB + B M = 320
A M = VAE^ + EM^ ^240^ + 320^ = 400(V)
Cau 33: M o t mach dien xoay chieu noi tiep gom tu dien c6 dien dung C, dien
tra thuan R va cuon day c6 do t u cam L c6 dien tro thuan r D u n g von keco
dien tro ra't ion Ian luot do hai dau dien tro, hai dau cuon day va hai dau
doan mach thi so chi Ian kigt la 50 V, 30 V2 V va 80 V Biet dien ap tuc thoi
tren cuon day som pha hon dong dien la Tt/4 Dien ap hieu dung tren tu la
A 30 V B 3 0 V 2 V C 60 V D 20 V
Huong dan J j » AAMB Id tarn gidc vuong can tai :^ ,U
E^NE = EB = 30V^ME = MN + NE = 80V = AB , r
V Tii gldc AMNB Id hinh ch a nhat =^ Uc = A M = EB = 30(V)
M R w L, r
302
Cty TnHHMTV OVVII Khang V i ^ t
Cau 34: Vao cung mot thoi diem nao do hai dong dien xoay chieu n = Iocos(cot
+ (p,) va f2= Iocos(cot + 92) CO cung gia trj tuc thai 0,5 ^3 1,,, nhung mot dong
dien dang tang con mot dong dien dang giam Hai dong dien lay lech pha nhau
A.71/3 = ^ B 271/3 C TC D 7I/2 , , , ,
Huang dan
•(cot + cp,) =
-i^ = l 0 C O s ( c D t + ( p , ) =
i'l =-coIosin((ot + (pi)>0 "
12 =!() cos(K)t + cp2)= , n
i'2 =-coIoSin(cot + {p2)<0 1 1 ' 1; r:> Acp = (cot + 92 ) - (ct)t + ) = ^
Cau 35: Dat dien ap xoay chieu on djnh vao hai dau doan mach gom cuon day noi tiep voi tu dien c6 dien dung Ci Khi do dong dien trong mach la ii va cong suat tieu thu ciia mach la Pi Lay mot tu dien khac C = 4Ci mac song song voi tu dien Ci thi dong dien trong mach la i2 va cong suat tieu thu la P2 Biet Pi = 3P2 va ii vuong pha voi i2 Xac djnh goc lech pha 91 va 92 giua dien ap hai dau doan mach voi ii va i2 j
A. 91 = n/6 va 92 = -n/3 , , B. 91 = -71/6 va 92 = 7t/3. j
C 91 = 7i/4 va 92 = -7t/4 D 91 = -7r/4 va 92 = 7r/4 ;
2
P = UIcos9 = — c o s ^ 9 = > 3 = ^
R C2 = C i + C' = 5Ci =>Zc2 =
P2
Z c i
2 cos 9] - => C O S 92
COS 92 cos9i 73
•92 9 , = -7t (P2 = 9 i +
-1 cos 92 73'"
- s m 9 | 7C
•91= cos9[ cos 9]
Cau 36: Tren doan mach xoay chieu khong phan nhanh c6 bon diem theo diing
thu t u A, M , N va B Giua hai diem A va M chi c6 cuon day, ffua hai diem
M va N chi c6 dien tro thuan, giiia 2 diem N va B chi c6 tu dien Dien ap hieu dung giiia hai diem A va N la 60 (V) va dien ap hieu dung giija hai
diem M va B la 40 N/3 (V) Dien ap tuc thoi tren doan A N va tren doan M B
P lech pha nhau 90", dien ap tuc thoi tren doan M B va tren doan N B lech pha
303
Trang 3nhau 30" va cuang do hieu dung trong mnch la N/3 (A) Dien t.6 thuan cua
cuon day la
A 40 Q B 10 Q ''" • C 50 Q. ^tj^ D. 20 Q
Huong dan
A O U K U M B : UK = 40x/3.sin 30" = 20^3 ( V ) ' ''
ZA.OUK+,.UAN : U K „ =60.sin60" = 3 0N/3(V)=^U, = 1 0 7 3 ( V )
r = - ^ = 10(Q)
L, r
U L
M
• O '
,;u.:- v
U L
O
u ,
rig
Uc
I
-60
\40V3
\
L 120V
80V3V
Ur
304
B
MTV DVVH Khang Vi^t
|<Cau 37: Khi dat vao hai dau cuon day mot dien ap xoay chieu 120 V - 50 Hz thi
thay dong dien chay qua cuon day c6 gia tri hieu dung la 2 A va tr6 pha 60"
so vai dien ap hai dau doan mach Khi mac no'i tie'p cuon day tren v6i mot doan mach ctien X roi dat vao hai dau doan mach dien ap xoay chieu nhu tren thi thay dong dien qua mach c6 gia tri hieu dung 1 A va som pha 30" so voi dien ap hai dau mach X Cong suat tieu thu tren toan mach khi ghep them X la •UEti(i).,f«(;» t , v t W ' l
A 120 W B 300 W C 200V2 W
Huovg diin
Khi mac not tie'p : U^j = I.Z,,^ = 1.60 = 60(V)
Ve gidn do vec - W => SAME vuong tai M
D 3OOV3W
A M 1
• cos a = = — r i a = 60
AB 2
•P = U I = 120(W)
M
A B H ^ I
\
120 V
Cau 38: Tren doan mach xoay chieu khong phan nhanh c6 bo'n d i S n theo dung
thu t u A, M , N va B Giira hai diem A va M chi c6 cuon cam thuan, giiJa hai diem M va N chi c6 dien tra thuan, giCra 2 diem N va B chi c6 tu dien Di^n
ap tuc thoi cac doan mach: UAN = 100N/2 cos(1007it) V, UNB = 50 76 cos(100nt
- 2TT/3) V Dien ap.tuc thai tren doan MB la ^M-'
A UMH = 100 V3 cos(1007it - 57T/12)V
B. uMii = 100 N/3 cos(1007rt - 7T/4)V ;
Q UMi! = 50V3 cos(100nt-57T/12) V , | v g S^^j;^: l;>:^::i
D. UMi3 = 50 N/3 cos(1007Tt - TT/2) V
305
Trang 4B6 trp kiSn thiic V4t It L T D H tren kenh VTV2, t^p 2- Chu Van Blgn
Huang dan
M N = 100cos30° =5073 ' ' '
M B = M N V 2 = 5 0 V 6 ( V )
A M N B Id tarn side vuong can taiN :=>{ ^ ^ - n
U M R sam hcfn U M R la —
U M R =50V6.N/2 COS lOOTit +
-3 4
= 100V3cos
NB
lOOnt
U
Cau 39: Dat di^n ap xoay chieu u = \]yi2 coslnit (V) vao hai dau doan mach noi
tiep gom dien tra R, cuon cam thuan L va tu dien C thi dien ap hieu dung
tren R, tren L va tren C Ian luot la 136 V, 136 V va 34 V Neu chi tang tan so
cua nguon 2 Ian thi dien ap hi^u dyng tren dien tro la
A 25 V B.50V C.50^/2V T D 80 V.; ^ ^
3' U = N / U I T ( I V ^ U ^ = ^136^+(136-34)2 ^ ^70^^^
U L = U R = > Z L = R
4 ^ 4 , j r n
Z L = 2 Z L - 2 R = > U ' L = 2 U R
f = 2f:
f i '
64
= > U ' R = 8 0 ( V )
306
cty munnrvDvvnKhang vift
au 40: Doan mach dien xoay chieu tan so fi = 60 Hz chi c6 mpt iu dien Neu
tan so la b thi dung khang ciia tu dien tang them 20% Tan so
A f2 = 72Hz B f2 = 50Hz C £2 = 10 Hz D f2 = 250Hz
Huang dan
^ = = 1 0 0 % + 20% = 1,2 =^ f2 = = 50(Hz) • '
Zci 12 1-2 > { , \
Cau 41: Mot tu dien phang khong khi hai ban song song each nhau mot
khoang d dugc noi vao nguon dien xoay chieu thi cuong do hieu dung qua mach la 5,4 A Dat vao trong tu dien va sat vao mot ban tu mot tarn dien moi day 0,5d c6 hang so dien moi e = 2 thi cuong do hieu dung qua tu la
A 2,7 A
Cn = 9.10^.47id
B.8,1A C 1 0 , 8 A P 7 , 2 A
•„V Humgdan , y,,,,
C i =
-9.10^.471.0,5d
E.S
• = 2C 0
CintC2
9.10^.471.0,5.d
=>Zr = -CO
4
3
=>I = - I o = - 5 , 4 = 7,2(A)
M i f I i ' 1 ! t '
"•au 42: Dong dien xoay chieu chay qua mot doan mach c6 bieu th'vc
i = 2>/2 cos(1007it + (p) (A), t tinh bang giay (s) Vao mot thai diem nao do, ' i = %/2 A va dang giam thi sau do it nha't la bao lau thi i = + ^6 A? / ^^
A 3/200 (s) B 5/600 (s) C 2/300 (s) D 1/100 (s) '
Huong dan
^/2 V6 '
~12 4"^4^6~4
+
200' ' -A 0 0,5A 0,5AV3
Cau 43 (DH 2011): Mot doan mach AB gom hai doan mach A M va MB mac noi
tiep Doan mach A M gom dien tro thuan R i mac noi tiep voi tu dien c6 dien dung C, doan mach MB gom dien tro thuan R2 mac noi tiep voi cuon cam
•thuan CO dp tu cam L Dat dien ap xoay chieu c6 tan so'va gia tri hieu dung , khong doi vao hai dau doan mach AB Khi do doan mach AB tieu thu cong suat bang 120 W va c6 he so cong suat bang 1 Neu noi tat hai dau tu dien thi dien ap giiJa hai dau doan mach A M va MB c6 cijng gia trj hieu dung nhung l^ch pha nhau y , cong suat tieu thu tren doan marh AB trong truong hop nay bang '
A 75 W B 160 W C 90 W D 180 W
Dap an C
' ' 307
Trang 5Bo trp kien thiic V$t IS LTOtl tren henh VTV2 t^p 2 - Chu VSn Bien'
Cau 44: Dat m o t nguon dien xoay cliieu c6 hieu dien the'hieu d u n g U va tan so
f vao hai dau doan mach g o m R, L, C mac noi tie'p, trong do cuon day If
tuong N o i hai dau t i i dien v o i 1 ampe ke thi thay no chi l A , d o n g thoi
d o n g dien tuc thai chay qua ampe ke'cham pha m o t goc — so v o i hieu dien
6 the tuc thai g i i i a hai dau doan mach Neu thay ampe k e b a n g m o t von ke
thi thay no chi 167,3V d o n g thai hieu dien the tuc thai giiJa hai dau von ke
cham pha m o t goc ^ so v o i hieu dien the tuc t h o i giiJa hai dau doan mach
Biet rang ampe ke va von ke deu li t u o n g H i e u dien the hi6u d u n g cua
nguon dien xoay chieu la V > • < > L , u ^
A 100V B 125V C 150V D 175V
=> D a p an C
Cau 45 ( D H 2010): Dat dien ap xoay chieu c6 gia tri hieu d u n g k h o n g doi, tan
so' 50Hz vao hai dau doan mach mac no'i tie'p gom dien tra thuan R, cuon
cam thuan c6 do t u cam L va tu dien c6 dien d u n g C thay do' dugc Dieu
chinh dien d u n g C den gia t r i t = —VLC ——F hoac ——F t h i cong sua't
tieu t h u tren doan mach deu c6 gia trj bang nhau Gia trj ciia L bang
A — H B - H /li,^, C — H tn' - r : D - H
=> D a p an D
Cau 46: M o t doan mach xoay chieu noi tie'p A B g o m dien t r o thuan R, cuon
cam thuan L va t u dien c6 dien d u n g C Dien ap giua hai dau doan AB la
u = Udcoscot (V) t h i dien ap tren L la UL = Uocos((ot + 7i/3) (V) M u o n mach
xay ra cgng h u o n g t h i dien d u n g ciia tu bang
A C V 3 B C 7 2 C 0,5C D 2C
(PL = — m a (pi - 9 = — =>(p = — => tan (p = —i= ^ = tan —
= > R = ( Z L - Z c ) V 3 > 0 , j , ,
U A B = U L ^ Z A B = X / R ' + ( Z L - Z C ) ' = Z L
= ^ 2 (Z L - Z C ) = Z L = ^ Z L = 2 Z C
Muohxdy ra cong hi/dng thi Z'c =Zi =>Z'c=2Zc ,
= 2-^=>c'=o,5c : • ,
coC mC
"au 47: Doan mach A B no'i tie'p gom hai doan mach A M va M B Doan mach
A M la mot cuon day c6 dien tra thuan R = 40 Vs n va d g t u cam L = 0,4/n
H , doan mach M B la mot tu dien c6 dien d u n g C thay doi dugc, C c6 gia tri
h u u han va khac khong Dat vao hai dau doan mach A B mot dien ap:
U A i i = 240cosl00t (V) Dieu c h i n h C de tong dien ap hieu d u n g (UAM + U.MB) dat gia t r i cue dai T i m gia trj cue dai cua tong so'nay ' =
A 2 4 0 V , B.240^/2V C 120V D 120^2 V
Huong dan i ,
SM" dung dinh li ham so sin cho A A N B : ^
120N/2 _ A M _ M B ' , 1 ^
sin a sinP A ' i ' , ' '
A M + M B , nii-j ,.:>
s i n a + sinp :'• ' -''' o
2 s i n " t P c o s " ^ P '^,^8"^''^' sin 60' .0
( U A M + U M B ) - 2 4 0 V 2 C O S ^
= m a x - 2 4 0 V 2 ( V )
Cau 48: Dat m o t nguon dien xoay chieu tan so 50 H z vao hai dau doan mach
R L C mac noi tie'p, trong do dien d u n g C bien doi K h i tu dien c6 dien dung
, Ci = l/(37r) mF thi cuong do hieu d u n g cua dong dien trong mach c6 gia trj
cue dai K h i t u dien c6 dien d u n g C2 = 3/(257t) mF thi hieu dien the'hieu
d u n g a hni dau tu dien c6 gia tri cue dai Dien tro R c6 gia tri la
A 3 0 Q B.4OQ C 5 0 Q D 6 0 Q
, • • • HumgdUn
Z c i = - ^
ZC2 =
coCj
1
= 30Q
250
coC
/ m n x < = > Z L = Z c i = 3 0 Q
-Ucmax <=>Zc2 =
R ' + Z 2 250 R^+30^
" T ~ 30 R = 40Q Cau 49: Dat dien ap xoay chieu c6 gia trj hieu d u n g U va tan so k h o n g doi vao hai dau A va B cua doan mach mac noi tie'p theo t h u t u g o m bie'n tro R, cuon cam thuan c6 do t u cam L va tu dien c6 dien d u n g C thay doi Cac gia
trj R, L, C hfru han va khac khong V o i L = L i t h i dien ap hieu d u n g giira hai
dau bien tro R c6 gia t r i khong doi va khac khong k h i thay doi gia trj R cua
309 j
Trang 6bien tra Vai L = 2Li thi dien ap hieu dung tren doan mach chi chiia R C
bang 100 V Gia trj U bang
A 2 0 0 V ' \ IOOV2V C l O O V D 2 0 G V 2 V
Hu&ngddn
R
U R = I R = U
R 2 + ( Z L- Z c r
• g R = > Z L i = Z ,
L = 2 L I : ^ Z L 2 = 2 Z L I = 2 Z C
I ^
^ U R C = I Z R C = U R 2 + Z ^ = u = U = lOOV
V R ' + ( Z L 2 - Z C ) ' " V R ' + ( 2 Z C - Z C ) '
Cau 5 0 : M o t doan mach A B gom doan A M va M B mac n o i tiep Doan A M gom
dien tro R noi tiep voi tu dien C, con doan M B chi c6 cuon cam L Dat vao
A B mot dien ap xoay chieu chi c6 tan so thay doi dugc thi dien ap tuc thai
tren A M va tren M B luon hion lech pha nhau TC/2 K h i mach cong h u o n g thi
dien ap tren A M c6 gia tri hieu d u n g Ui va tre pha so v o i di^n ap tren AB
i mot goc a i Dieu chinh tan so de dien ap hieu d u n g tren A M la U2 thi dien
ap tuc thai tren A M lai tre pha hon dien ap tren AB mot goc ai
Biet ai + a2 = n/2 va U2 = 0,75Ui Tinh he so cong suat cua mach A M k h i xay
ra cong huong
B.0,8 C l D.0,75
Huong dan '
A 0,6
U ,
COStti = —
-^ U
U2
costto = —^ = S i n a i
^ U ^
2
+
^ u J =
1-U 2 = 0 , 7 5 1-U ]
- i l l = 0,8
u
Cau 5 1 : Dat dien ap xoay chieu u = 100 ^y2 coscot V v a i 00 thay d o i l u IOOTI rad/s den 2007t rad/s vao hai dau doan mach noi tiep gom dien tro R = 300 Q,
cuon cam thuan v o i dp t u cam 1/n H va tu dien c6 dien d u n g 0,l/7t mF Dien
ap hieu d u n g giira hai dau cuon cam c6 gia t r i Ion nhat va nho nhat tuong
l i n g la
A 59,6 V va 33,3 V ^ B l O O V v a S O V
C 50 V v a 100/3 V ' > D 50 V2 V va 50 V
Huang dan
R^ 1/71 300^
2 V I O ~ V T C 2
khong ton tai
UcoL
CO = IOOTI = > U L = lOO.lCO 100
(0 : = 20071 = ^ U L =
^300^ + ( 1 0 0 - 1 0 0 f "3 100.200 80VS
:33,3V
» 59,6 V
^300^+(200-50)^ 3 Cau 52: Dat dien ap xoay chieu u = Uocoscot (Uo khong doi va co thay d o i dugc) vao hai dau doan mach gom dien tra thuan R, cuon cam thuan c6 do t u cam
L va tu dien c6 dien d u n g C mac noi tiep, v o i CR^ < 2L K h i co = 90 rad/s
hoac CO = 120 rad/s thi dien ap hieu d u n g giiia hai dau cuon cam co cung
mot gia t j Dien ap hieu d u n g giCra hai dau cuon cam dat cue dai k h i
A 105 rad/s B 72 V2 rad/s C 150 rad/s D 75 V2 rad/s
Huong dan
1 1
co, ^2 J
COo C0|C02 V2
^/cof+cof
= 72 V271 (rad/s)
Cau 53: Dat dien ap xoay chieu u = UocoslOOTit (V) vao hai dau doan mach mac
ncVi tiep gom dien tro thuan R, tu dien co dien d u n g 0,4/7r (mF) v'a cuon cam thuan CO cam khang Zi thay doi Dieu chinh Z L Ian l u g t bang 15Q, 20Q, 29Q
va 50 Q thi cuong dc) hieu d u n g qua mach Ian lugt bang I i , I2,13 va I4 Trong
so'cac cuong do hieu d u n g tren gia trj Icrn nhat la *
A I i B. I2
Zr=-coC = 25(Q)
C h
Huang dan
D k
V i t r i d i n h Z L O = Z c = 2 5 ( Q ) Gang gan d i n h I cang Idn
=> Z L 2 va Z L 3 g^n hdn Z L O = 25Q hcfn n e n chi can so sanh I2 va I3
Z u , = ^ ' ' ^ :=> 25 ^ ^ Z ' L 2 = > Z L 3 ^ I2 < I3
311
Trang 7Cau 54: Cho mot donn mach xoay chieu gom dien tro thuan R thay doi duoc,
cupn day thuan cam L va tii d i e n C theo thiV t u mac noi tiep voi nhau Dat
vao hai dau donn mach mot liK/n ap xoay chieu co gia trj hieu d u n g 2 0 0 V
va tan so f thay doi dugc Khi f = 5 0 Hz thi cuong do dong dicn hieu diuig
trong mach la 2 A va dien ap hieu dung giCra hai dau RL khong thay doi khi
R thay doi Dien d u n g nho nha't cua tu dien la v ' A
A 25/TC(HF) V , B 50/Tt (HF) C 0,1/7r (|.iF) D 0,2/:: (nF)
Huong dan
U R L = I.ZK,., = U I " " ' ^ g R R^ + zf ^
c^zf = ( Z , - Z c ) ^ =>Zc = 2Z L
Z = sJR^+Zl = — = lOOQ Z[ < lOOQ => Z c = 2 Z L < 200Q
V ^
= > C > ? = ^.10-^F V „ • , J r
lOOn.200 n
C a u 55: Cho doan mach khong phan nhanh dien t r o 1000V2t), cugn day
y J thuan cam c6 do tir cam 2 H , tu dicn c6 dien d u n g 10'' (F) Dat vao hai dau
mach dien dien ap xoay chieu chi co tan so goc o) thay doi Khi dien ap hieu
d u n g hai dau tu C dat gia tri cue dai thi co co gia trj la ,^
A 400 (rad/s) B 707 (rad/s) C 2,5.10"^(rad/s) D 500 (ra'd/s)
Huong dan
(l000^/2f I i
- „ , ^ = 1000(Q)
C 2 VlO-^' 2 ^ ' 0'
U c max <=> Z L = Z , =>(oL = 1000 =>(o = 500 (rad / s) p,\l,a :?.S •
Cau 56: M o t doan mach xoay chieu noi tiep A B gom dien tro thuan R, cugn
cam thuan L va tu dien C K h i noi hai cue cua tu dien v o i mgt ampe ke'co
' dien tro ra't nho thi so chi ciia no la 0,5 A va dong dicn qua ampe ke tre pha
so vcVi dien ap giua hai dau doan AB la 7i/6 Ne'u thay ampe ke bang von ke
CO dien tro rat Ion thi no chi 100 V va dien ap giira hai dau von ke tre pha so
voi dien ap giua hai dau doan mach A B mgt goc n/2 Gia tri cua R la
A 150Q , B.200Q C 250 Q < D 30C Q ; .>\-,
/ V Huang dan j
+Mdc ampe ke th] tu hi noi tdt ;
Z R ''''' '
tan<p = ^ = t a n ^ : ^ Z , ~ ^ ^ ^ ^ ^ , - ^
u = uz = u V ^ ^ 4 ^^"^
312
+Mdc von ke :
Mach cgng hudng => Z L = = R
Uc = 1 0 0 ( V ) = Ui =
73 U K = 1 0 0 V 3 ( V )
U ' - U ? , + ( U L - U C ) '
,73
>R = 3 0 0 ( Q ) i i
Cau 5 7 : M g t doan mach khong phan nhanh gom: dien tro thuan 1 0 0 iX cugn
day thuan cam co do t u cam 12,5 m H va tu dien co dien d u n g 1 pF Dat vao hai dau mach dien mgt dien ap xoay chieu co gia tri hieu d u n g 2 0 0 V va co tan so thay ctoi dugc Gia tri cue dai cua dien ap hieu d u n g tren cugn cam la
A 3 0 0 ( V ) B 2 0 0 ( V ) C 1 0 0 ( V ) D 2 5 0 ( V )
Huong dan vj.v
J-Z \ R^ '12,5.10-"^ 100'
10 ,-6 = 100Q
u C max = u , _ = u ^ = u
L
C
12,5.10 ,-3
• = 200.- 10 L-6
Hi rnfi;j ngtjo ,/J
•J iA\)
- = 250(V) RZ\, " 100.100
Cau 58: Cho doan mach M N theo thi'r tu gom dien tro R mac noi tiep voi cugn thuan cam L ncYi tiep vcVi tu dien co dien dung C thay doi dugc Ggi A
la diem noi L voi C Dat vao 2 dau doan mach dien ap xoay chieu
UMN = 100 V2 cos(1007it + (p) V Thay doi C de dien ap hieu d u n g tren doan
A M cue dai thi bieu thuc dien ap tren do la UMA = 2 0 0 ^ c o s l 0 0 7 i t V Neu thay doi C de dien ap hiei-i d u n g tren t u cue dai thi lap bieu thuc dien ap tren doan M A la
A UMA = 100V6cos(1007it + 7T/6) V B UMA = 200 76 cos(1007:t + 7r/6) V
Hwwi^ dan ^ , f I J , , j „ , ,
= IZviA = + = « Cong hUdng T nmQ mAh <r
U M N =10072COS l O O n t
-UQ = max => U 1 U|.L
A M = 100tan60" =10073(V)
iMA sdm p h a h d n u M N l a
-3 1 -3
Trang 8" M A = 1 0 0 7 6 C O S lOOTCt +
-3 2) (V)
V • ; A
^ 200 / 0, Or
'-—^
100 A'
n \
Cau 59: Dat dien ap xoay chieu vao hai dau doan mach noi tiep pom dien tio
R, cuon cam thuan L va tu dien c6 dien dung C thay doi dirge Khi C thay
doi thi dien ap hieu dung cue dai tren R, L va C Ian lugt la x, y va z Ne'u
z/y= V'S thi z/x bang ' ' :, ,
,,; A 0,5 N/5 ] B 0,75 V2 C 0,75 D 2 >/2 > ^i ,
yy.) ryAii; m.^imii Huong dan > i o i f r J
u
, ( U R m a x va U L^ , , cong huang <=> I ^ , , = - => u ,
Z = U Cmax
R
=> z = = 0 , 5 V 5 U ^ - = 0,5N/5
Cau 60: Dat dien ap u = 125 -Jl coscot (V), co thay doi dugc vao doan mach noi
tiep AMB Doan mach A M gom dien tro R noi tiep tu dien, doan mach MB
chiia cuon day c6 dien tra r Biet dien ap tren doan A M luon vuong pha v6i
dien ap tren doan MB va r = R Voi hai gia trj co = lOOn rad/s va co = 56,257T
rad/s thi mach AB co cung he so cong suat va gia trj do bang
: Huong dan
-Zn Zr
U A M -L U M B =^ tancpAM t a n ^ M B = -1 => ~ — — = -1 =>
D 0,82
L = CR^ ^-^U
c-\
R^
314
l ( R + r r +
1
cojC ( R 4 - r ) 2 + C 0 2 L
-0J2C
=>LC = L=CR L - ^ ^
= R cojC C0|L = R
• cos (pj = • (R + r)
(R + r)^ R./'^i - R ^ 2
2 ( 1—- 1 \
CO2
\ lV«2
= 0,96
•'•)'r''Xifiyi'iV
CO2 Y ™i Cau 61: Cho mach dien noi tiep gom cupn day thuan cam co do tu cam L
! thay doi dugc, tu dien C va dien tro R Dien ap dat vao hai dau doan mach
u = 100 V6 coslOOnt (V) Khi dien ap hieu dung tren cuon day dat gia trj cue
dai ULMnx thi dien ap hieu dung tren doan mach chua RC la 100 (V) Gia trj
ULM.IX la _ w
A 100 (V)
iC 300 (V)
B 150 (V)
D 200 (V)
Huong dan
| U J - U R C
U L = 7100^+3.100^ = 200( V )
{ 'y U
/ l iy-iiQ
;
U,<c
I
ft;
Cau 62: Cho mach dien xoay chieu RLC vol R la bien tro va cuon day co dien
Itra thuan r = 10 Q Khi R = 15 Q hoac R = 39 Q cong suat cua toan mach la
I nhu nhau De cong suat toan mach cue dai thi R bang > t)K MI
| A 27Q B 25Q C 32 Q j D 36 Q
Hwang dan
u2(R + r) (R + r ) ^ + ( Z L - Z c ) - =>
(R^+r) + (R2 + r) =
2 Z L - Z C
( R, + r ) ( R 2 + r ) = ( Z L - Z c r
<=>RQ + r = |ZL - Z C ' i
315
Trang 9.(Ro + r f = ( R , + r ) ( R 2 + r ) = ^ R n +10 = ^ ( 1 5 + 10)(39 + 1 0 ) = ^ Ro = 2 5 Q
B
R
A
M
r, L
1/
1 f ::' \ u,
"1
/ \"
—> M u ' t 1
Cau 63: Hai doan macli noi tiep RLC khac niiau: mach T va mach 2, cona
huong voi dong dien xoay chieu c6 tan sogck Ian lugt la (oo va 2(oi) Biet do
tu cam ciia mach 2 gap ba do t u cam ciia mach 1 Neu mac noi tiep hai doan
mach d o voi nhau thanh mot mach thi no se cong huong voi dong di(<n
xoay chieu c6 tan so goc la
A. coo V3 B l,5co() C. (00 Vl3 D. CStoo Vl3
Hu6iig dan
Diiu kicn cgng hi/dng (o^LC = 1
1
CO2L2C2 = CO2L2
coLi + (0L2 = + -r,^^
0)^ ( L I + L 2 ) = CO? L| + CO2L2 (0^ 4L1 = COQL , + 4coo 3L, => co = 0, SCOQ V T S
Cau 64: Dat dien ap xoay chieu vao hai dau doan mach noi tiep gdm dien t r o
R, cuc)n cam thuan L va tu dien c6 dien dung C thay doi dugc Cac von ke'li
tuong V i va V 2 mac Ian iuc7t vao hai dau R va hai dau C Khi C thay doi de
so'chi V I cue dai thi gia trj nay gap sochi cua V2 Hoi khi so chi V2 cue dai
thi scYchi nay gap may Ian so chi V i li'ic nay?
A 2,24 B 1,24 C 1,75 D 0,5Vs
Huong ddjt
f U v , = U K = U
U
R
R U v 2 - U c - I„,axZc = — Z L 1 51}
U V l - 2 U v 7 ^ R
— > Z L = —
316
CtyTmiii Pirv t> VVH Khang-yi^T—
1 Ucmax <=> Z r = = R>/5
U = R « 0 , 4 9 9 —
J R 2+ ( Z L - Z c f ' ^ _ U
'J • ,'•
V2
^2,24
V I
R R ; 'K r q l
-CaU 65: Mot doan mach xoay chieu mac noi tiep gom cuon day c6 dien tro thuan 40 (Q), c6 cam khang 60 (Q), tu dien ccS dung khang 80 (Q) va mcit bien tro R (0 < R < 00) Dien ap c* hai dau doan mach on dinh 200 V - 50 Hz Khi thay ctoi R thi cong suat toa nhiet tren toan mach dat gia tri cue dai la
A 1000 (W) B 144(W) C 800(W) D 125 (W)
Huong dan "1, r
-P - l 2 ( R + r) =
(R + r ) 2 + ( Z L - Z c ) ' -(R + r ) ^ (R + r) + ( Z L _ I Z C )
]R + r)
2" = max
o R + r = Z L - Zcl => R = -20 < 0 P^,, R = 0
-(R + r) = 2 0 0 ' _-.40 = 800(W)
(R + r ) ' + ( Z L - Z c ) ' ^ ; 40^+20^
rri f!"
.4 76/'•:):!(! c
-20 Q Cau 66: Dat dien ap xoay chieu vao hai dau doan mach noi tiep gom dien tro,
cuon cam thuan va tu dien c6 dung khang Z c thay doi Goi Ucn«x la gia tri cue dai cua dien ap hi$u dung tren tu Dieu chinh Z c Ian lugt bang 50Q, 150Q va lOOQ thi dien ap hieu dung tren tu Ian lugt bang U c i Uc2 va Uc3
^'e'u U C I = U c 2 = a thi
A.Uc^ = Uc,™v B U c » a C Uc3<a D Uc3 =0,5Ucn«
317
Trang 10Bo trtpi klcn thitc V^t If LTDH trSn JkSnh VTV2 t^p 2 - Chu VSn Bun
Huang dan
Uci = » Zco = —^""^-V^ =
> Z c „ = 75(Q) ^ Z c 3 ^ Uc3 ^ Ucnnax
CI < Zc3 < Z c 2 =^ U c 3 > Uc2
Cau 67: Dat dien ap xoay chieu c6 tan so' co thay doi duoc vao hai dau dean
mach RLC noi tiep Khi u) thay doi thi mot gia trj too l a m cho cuong dp hieu
dung trong mach dat gia trj cue dai la Imnx va hai gia tri toi va wi voi toi
-' -' = 300T: (rad/s) thi cuong do hieu dung trong mach dat gia i-rj deu bang
'' Imnv/ V2 Cho L = V(37i) H, tinh R
A R = 30Q B.R = 60Q C.R = 90Q D.R = 100Q
•' Huang dan - , ,; ,^
« = «o Imax = m a x => Cong hi^ang => Zn,in = R
CO = (Oi U (0 = 0)2 I i = I , =
^ Z I = Z 2 = R V 2 = ^ R2 + r
(OiL-(OiC; (R2 + a)2L -co,C = RV2
« l L - - - = R 5
cojC
1
(OjL ^ = - R
co,C
(Oi L = Rco,
^ C ^ •L(COI -CO2) = R(O)I +C02)
=>R = L(coj-ci)2) = 100Q ' '
Cau 68: Dat dien ap u = U coslOOjit (V) vao hai dau doan mach mac noi tiep
theo diing thu tu gom cupn cam thuan c6 cam khang 120 Q, dien tra thuan
R va tu dien c6 dien dung C thay doi Khi C = Co thi dien ap hieu dung tren
doan mach chua RC dat cue dai va gia tri cue dai do bang 2U Dung khang
ciia tu liic nay la ,,
A 160Q B lOOQ C 150Q D.200Q
Huang dan
U R C = I Z R C = U R ' + z g Z ^ + R 2
• u KCmax ~
=>y' =
Z ^ - 2 Z L Z C +
318
| R 2 + ( Z L - Z c f ' " ^ Z ^ - 2 Z L Z C + ( R ' + Z 2 ) 2UR "
Z L + V Z L + 4 R ^ •
V Z ^ + 4 R 2 _ Z L
- 2 Z L ( Z ^ - Z L Z C - R 2 '
Cty TjynH mvDVVnKhang VIft
u 'RCmax 2 U R , 2 U R u = > R = 80(P.)
^ / ^ 2 7 4 R 2 - Z L VI202 ^ 4j,2 _
r-^ Z , + V Z [ + 4 R ^ " _ ^
60(Q)
Cau 69: Mot doan mach xoay chieu gom cuon day c6 dien tra ICO Q., c6 cam
khang 100 Q noi tiep vai hop kin X Tai thoi diem ti dien ap tuc thoi tren cuon day cue dai den thoi diem t2 = ti + 3T/8 (vai T la chu ki dong dien) dien
ap tuc thoi tren hop kin cue dai Hop kin X c6 the la
A cupn cam c6 dien tro thuan B tu dien noi tiep vai dien tro thuan
C tu dien
Z L 1
tancpcd = — = 1=^ Vcd = 7
D cuon cam thuan
Huong dan
1 = In C O S - —
"cd = Uoi cos •27lt 71 + —
T 4
ux =Uo2 cos r27tt
T • + (Px
3 T
U(,jj s6m pha hcin Ux ve thdi gian la —va ve pha la
8
= <=> (pv = ' i| • i ' i f : K
T 8 4 4 4 '
7t , "
=^ 9x = ^ CO the la tu dien , , , | | •
f ( ? i f i ' )
I I / J ' f } ' '
f , Ul i
Cau 70: Cho doan mach AB mac no'i tiep gom tu dien, cuon cam va bien tro R Dien ap xoay chieu giira hai dau doan mach luon on djnh Khi R = 76 Q thi
jl cong sua't tieu thu tren bien tro eo gia trj Ion nhat va bang Po Khi R = R2
• I cong sua't tieu thu ciia mach AB c6 gia trj Ian nha't va bang 2Po Gia tri cua
W R2bang
i A 45,6 Q B 60,8Q C 15,2Q , D 12,4 Q
Huang dan
^ R max
2 ^ / ( Z L - Z c ) ' + r 2 + 2 r
= Pr,
I l 7 y ( ^ L - Z c ) ^ ^ = 76Q
Rrmax
2 Z L - Z C
R 2 = Z L - Z C
= 2Pn
^ ( Z L - Z c ) ' + r 2 + r = 2 l Z L - Z c
R2 + = 76^
r = 2R2-76
=^R2 =60,8Q