Bổ trợ kiến thức luyện thi đại học môn vật lý phần dòng điện xoay chiều p2

B 6 trp hien

thitc

V^t I I L T D H

tren

Mnh VTV2.

t^p 2 - Chu V^n

Bicn

,

,

Huong dan
7625-x^

A M N E :N E = V M N ^ - M E ^ =
/
< ,.,;iV;l,„
/

^

^

A A E B : A B ^ = A E ^ + EB^

L *

7

.

N

'

/

!

l:o^/3

30"

- 60N/3 ^ Z L = ^

1681 = (25 + x)^ + (29 - ^ 6 2 5 ^ ) "

=^r = - ^ = 37,5(n)

V-

U L = 120v/3 sin

yl625-x^

• f^f'H

=»MAN = a
A A M N can tai M vda^

= 29 -

/

X = 15
A A N B can tai A md M A I = NAB

EB

120

M /

25V

/

UL
X

•4 t
= 15V6i

r, L

Ur

S.41V

—'B

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
B

von ke CO di^n tro rat Ion thi no chi 100 V, dong thoi dien ap tuc thoi h a i

Cau 3 1 : Doan mach xoay chieu noi tiep gom dien tro thuan R, tu dien C va

dau von ke lech pha goc a (cosa = 0,6) so voi di^n ap hai dau dogn mach

cuon cam thuan L. Dat vao hai dau doan mach mot dien ap xoay chieu on

AB. Tong tro cua cuon cam la
A.40Q.

:

B.40^/3Q.

C. 20VS a

. v m , h .rMi-J rV- r f i '

djnh thi dien ap hieu dung tren R, L va C Ian lugt la 4 0 V , 120 V va 4 0 V .

D.60Q.

Thay C boi tu dien C thi dien ap hieu dung tren tu la 6 0 V , khi do, dien ap
,v.^ ,,

hieu dung tren R la
U

+ Mdc ampe - ke th i Lr bi noi tdt: Z^Q = y = 60
+Mdcv6n-ke,ve

gidn do vectd :

...

B. 45,64 V .

•rri
qfi
'in u
i ) In-/.
' ? ; .

'i • • '

„,( r.^'

C. 54,24 V .

Z , L = Z R ^ = 60n

'

D. 4 0 , 6 7 V .

^

Huong dan

UK=40(V)

UKC = Vl202+]002--2.120.100.cosa = 100 = U^L
.

A. 6 7 , 1 2 V .

,

.V 0£ .A

M

= > Z L = 3 R = ^ U ' L = 3U'K
UL=120(V)

Uc = 40(V) ^ U = > / U ? < + ( U L - U C ) ' = V 4 0 2 + ( 1 2 0 - 4 0 f = 4075 (V)

V,

+K}ii thay ddi C thi U van Id 40V5 (V) yd U ' L = 3U'R

>u2=ui+(UL-ucr
> 8000 = U ' K + (3U'K - 6 0 f
> U ' K =45,64(V)
i.

Mill--:].

A.50Q.
300

' ^

B. 15Q.

r-

!

1 ,J

,s)

Cau 32: Dat dien ap xoay chieu tan so 300 V - 50 Hz vao hai dau doan mach AB

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 tu 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
trjrbSng

lOU'K - 360U'K - 4400 = 0

.....

^

C.37,5n.

^-.f^^^:,: '

r^'

D.30a

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

B S Ira hicti

Vdl !i I r o l l

llnic

t r e n kenh

VTV2,

Huong

30o7l -

/ j ^ / ' .

OVVII

Khang

Vi^t

+ (p,) va f2= Iocos(cot + 92) C O cung gia t r j tuc thai 0,5 ^3 1,,, n h u n g m o t d o n g

^/IK:

dien dang tang c o n m o t d o n g dien dang g i a m . H a i d o n g dien .lay lech pha

cos^^ = 180 => E M = EB + B M = 320

nhau
A.71/3.

^240^ + 320^ = 400(V)

A M = VAE^ + EM^

TnHHMTV

Cau 34: Vao cung m o t t h o i d i e m nao d o hai d o n g dien xoay chieu n = Iocos(cot

dan

A E = 300cosip = 240(V)
BE = SOOsin^p =

Cty

t^p 2 - Chu VSn B i e n

=

^ B. 271/3.

C. TC.
Huang

i^ = l 0 C O s ( c D t + ( p , ) =

=!()

cos(K)t +

•(cot + cp,) = - "

cp2)=

,

n

i'2 =-coIoSin(cot + {p2)<0
r:> Acp = (cot +

92 ) - (ct)t

,,,,

dan

i ' l =-coIosin((ot + ( p i ) > 0
12

D. 7I/2.

+

11'

) =

1;

^

Cau 35: Dat dien ap xoay chieu on d j n h vao hai dau doan mach g o m cuon day
noi tiep v o i t u dien c6 dien d u n g C i . K h i d o dong dien t r o n g mach la i i va
'R

cong suat tieu t h u ciia mach la Pi. Lay mot t u dien khac C = 4 C i mac song

E

Cau 33: M o t mach d i e n xoay chieu noi tiep g o m t u d i e n c6 dien d u n g C, dien
t r a thuan R va cuon day c6 do t u cam L c6 dien t r o thuan r. D u n g v o n keco
dien t r o ra't i o n Ian l u o t d o hai dau dien tro, h a i dau cuon d a y va h a i dau
doan mach thi so chi Ian k i g t la 50 V, 30 V2 V va 80 V. Biet dien ap tuc thoi
tren cuon day som pha h o n d o n g dien la Tt/4. D i e n ap hieu d u n g tren t u la
A . 30 V

B.30V2V.

C. 60 V.

E^NE
V

Id tarn gidc vuong can tai

= EB = 30V^ME

Tii gldc AMNB

dien ap hai dau doan mach v o i ii va i2.
A . 91 = n/6 va 92 = -n/3.

= MN + NE = 80V = AB

J j»
:^

,U
., r

,

,

C. 91 = 7i/4 va 92 = -7t/4.

j
B. 91 = -71/6 va 92 = 7t/3.

j

D . 91 = -7r/4 va 92 = 7r/4.

;

Huong dan

D . 20 V .

Huong dan
AAMB

song v o i t u dien Ci thi d o n g dien trong mach la i2 va cong suat tieu t h u la
P2. Biet Pi = 3P2 va i i v u o n g pha v o i i2. Xac d j n h goc lech pha 91 va 92 giua

2

P = UIcos9 = — c o s ^ 9 = > 3 = ^
R
P2
C2 = C i + C' = 5Ci =>Zc2 =

Id hinh ch a nhat =^ Uc = A M = EB = 3 0 ( V )

Zci.

2
cos 9]
- => C O S 92
COS 92 cos9i

-i^y'-'

73

7t

•92 . 9 , = -

(P2 = 9 i + M

R

w L, r

92

-sm9|

73'" cos9[

cos 9]

1

cos

7C

•91=--

Cau 36: Tren doan mach xoay chieu k h o n g phan nhanh c6 bon d i e m theo d i i n g
t h u t u A , M , N va B. Giua hai diem A va M chi c6 cuon day, ffua hai d i e m
M va N chi c6 d i e n t r o thuan, giiia 2 diem N va B chi c6 t u dien. D i e n ap
hieu d u n g g i i i a hai d i e m A va N la 60 (V) va dien ap hieu d u n g giija hai

d i e m M va B la 40 N/3 (V). D i e n 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
302

303


Ctyrmin

nhau 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.
Huong dan

A O U K U M B : U K = 40x/3.sin 30" = 20^3 ( V )
ZA.OUK+,.UAN : U K „ .

^tj^

D. 20 Q.

|thay dong dien chay qua cuon day c6 gia tri hieu dung la 2 A va tr6 pha 60"

'

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

=60.sin60" =30N/3(V)=^U,. = 1 0 7 3 ( V )

them X la

•UEti(i).,f«(;» t , v t W . ' l

A. 120 W.

B. 300 W.

C. 200V2 W.

-

UL

D. 3 O O V 3 W .

Huovg diin

I

M

Khi mac not tie'p : U^j = I.Z,,^ = 1.60 = 60(V)

. . . -

Ve gidn do vec - W => SAME vuong tai M
60

O'

Vi^t

doan mach ctien X roi dat vao hai dau doan mach dien ap xoay chieu nhu

L, r

•

Khang

so vai dien ap hai dau doan mach. Khi mac no'i tie'p cuon day tren v6i mot

r = - ^ = 10(Q)

UL

MTV DVVH

AM
UR

O

• cos a =

1

r i . a = 60
AB
2
ABH^I
•P = U I = 120(W)

I

u,

= —

\

M
\40V3

rig

\

Uc
,;u.:- v..

Ur

JV

M

N

UR

120 V
Cau 38: Tren doan mach xoay chieu khong phan nhanh c6 bo'n diSn theo dung

L

120V

thu t u A, M , N va B. Giira hai diem A va M chi c6 cuon cam thuan, giiJa hai
80V3V

diem M va N chi c6 dien tra thuan, giCra 2 diem N va B chi c6 tu dien. Di^n

Ur

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. u M i i

= 100 N/3 cos(1007rt - 7T/4)V. ;

Q. UMi! = 50V3 cos(100nt-57T/12) V. , | v g
B

304

D.

UMi3

S^^j;^:..l;>:^::i

= 50 N/3 cos(1007Tt - TT/2) V.
305


B6

trp kiSn

V4t It L T D H

thiic

tren

kenh

VTV2,

t^p 2-

Chu

cty munnrvDvvnKhang

Van Blgn

Huang dan
M N = 100cos30° =5073

'

'

'

M B = M N V 2 =50V6(V)
AMNB

Id tarn side vuong can taiN :=>{ ^
^
n
U M R sam hcfn U NMBR la —

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.
B.8,1A.
C.10,8A.P.7,2A.
•„V Humgdan
,
y,,,,.
>

+ - = 100V3cos lOOnt

U M R =50V6.N/2 COS lOOTit

3

U

4

Ci=Cn =

9.10^.47id

• = 2C0

9.10^.471.0,5d
E.S

QA

CintC2

4

9.10^.471.0,5.d

=>Zr =

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^^^
UL=UR=>ZL=R
R

4

^4

uf

.

,jr .

ZL=2ZL-2R=>U'L=2UR
f = 2f:
^ 2 8

^ 8

306

4

=>I = - . I o = - . 5 , 4 = 7,2(A)

Mif

I

i '

1!

t '

3
"•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 AM 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

64
=>U'R=80(V)

fi '

n

-CO

truong hop nay bang
A. 75 W.
B. 160 W.
Dap an C

C. 90 W.

'
D. 180 W.
'

'

307


Bo trp kien

thiic

V$t IS LTOtl

tren henh

VTV2. t^p 2 - Chu

VSn

Bien'

"au 47: Doan mach A B no'i tie'p g o m hai doan mach A M va M B . Doan mach

Cau 44: Dat m o t n g u o n dien xoay cliieu c6 hieu dien the'hieu d u n g U va tan so

A M la m o t cuon day c6 dien t r a thuan R = 40 Vs n va d g t u cam L = 0,4/n

f vao hai d a u d o a n mach g o m R, L, C mac noi tie'p, t r o n g d o cuon day If

H , doan mach M B la m o t tu dien c6 dien d u n g C thay d o i dugc, C c6 gia t r i

t u o n g . 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

h u u han va khac k h o n g . Dat vao hai dau doan mach A B m o t d i e n ap:

d o n g dien tuc t h a i chay qua ampe ke'cham pha m o t goc — so v o i hieu dien

UAii

= 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.

6
the tuc t h a i g i i i a hai d a u doan mach. N e u thay ampe k e b a n g m o t von ke

A.240V.

B.240^/2V.

,

Huong

t h i thay no chi 167,3V d o n g thai hieu dien the tuc thai giiJa hai dau v o n ke
c h a m pha m o t goc ^ so v o i hieu dien the tuc t h o i giiJa h a i d a u doan mach.

SM" dung

Biet rang ampe ke va v o n ke deu l i t u o n g . H i e u d i e n the hi6u d u n g cua

120N/2 _ A M _ M B

n g u o n dien xoay chieu la

sin 60'.0

A. 100V.

V

> •

B. 125V.

<..>L, .u

.

C. 150V.

C. 120V.

^

sin a

'

,

A. . ' i ' , ' . '
,

s i n a + sinp

=> D a p an C

^

^.

sinP

AM + MB

D . 175V.

--1

D . 1 2 0 ^ 2 V.
i ,

dan

dinh li ham so sin cho A A N B :

'=

nii-j ,.:>
:'• '

-''' .o

Cau 45 ( D H 2010): Dat dien ap xoay chieu c6 gia t r i hieu d u n g k h o n g d o i , tan
so' 50Hz vao hai d a u doan mach mac no'i tie'p g o m dien t r a t h u a n R, cuon

2sin"tPcos"^P

'^,^8"^''^'

cam t h u a n c6 do t u cam L va t u dien c6 dien d u n g C thay d o ' dugc. Dieu
chinh dien d u n g C den gia t r i t = —VLC ——F
2
471

hoac ——F
In

t h i cong sua't
(UAM+UMB)-240V2COS^

tieu t h u tren d o a n mach deu c6 gia trj bang nhau. Gia trj ciia L bang
A. — H .

B. - H .

C. — H .

/li,^,

= max-240V2(V)

tn' - r : D . - H .

=> D a p an D

C a u 48: D a t m o t n g u o n dien xoay chieu tan so 50 H z vao hai d a u d o a n mach

Cau 46: M o t d o a n mach xoay chieu noi tie'p A B g o m d i e n t r o t h u a n R, cuon

R L C mac n o i tie'p, t r o n g do dien d u n g C bien d o i . K h i tu d i e n c6 dien d u n g

cam t h u a n L va t u dien c6 dien d u n g C. D i e n ap giua hai dau doan A B la

, Ci = l/(37r) m F t h i c u o n g do hieu d u n g cua d o n g dien t r o n g mach c6 gia trj

u = Udcoscot (V) t h i dien ap tren L la UL = Uocos((ot + 7i/3) (V). M u o n mach

cue d a i . K h i t u d i e n c6 dien d u n g C2 = 3/(257t) m F t h i hieu dien t h e ' h i e u

xay ra cgng h u o n g t h i dien d u n g ciia t u bang
A.CV3.

d u n g a hni dau tu dien c6 gia t r i cue dai. Dien t r o R c6 gia t r i la

C. 0,5C.

B. C 7 2 .

D . 2C.

A.30Q.
,

Zi - Z r
7t
(PL = — m a (pi - 9 = — =>(p = — => tan (p = —i=
^ = tan —
2
3
6
R
6
=>R = (ZL - Z c ) V 3 >0
,j, , . .
71

,

7t

71

UAB=UL^ZAB=X/R'+(ZL-ZC)'

1

=ZL

coC

ra cong hi/dng thi Z'c

= 2-^=>c'=o,5c
mC

:.

=

coC

D.60Q.

HumgdUn

Z c i = - ^ = 30Q
coCj

=^2(ZL-ZC) = ZL=^ZL=2ZC
Muohxdy

• • •

ZC2

C.50Q.

B.4OQ.

250

/mnx<=>ZL=Zci=30Q

R'+Z2

Ucmax <=>Zc2 =

-

250

R^+30^

"T~

30

R = 40Q

Cau 49: Dat d i e n ap xoay chieu c6 gia trj hieu d u n g U va tan so k h o n g d o i vao
=Zi

=>Z'c=2Zc

,

.

hai d a u A va B cua doan mach mac noi tie'p theo t h u t u g o m bie'n t r o R,

.

•

. , ..

cuon cam t h u a n c6 do t u cam L va t u dien c6 dien d u n g C thay d o i . Cac gia
trj R, L, C hfru han va khac k h o n g . V o i L = L i t h i dien ap hieu d u n g giira hai
d a u bien tro R c6 gia t r i k h o n g doi va khac k h o n g k h i thay d o i gia trj R cua
309 j


bien tra. V a i L = 2 L i thi dien ap hieu dung tren doan mach chi chiia R C
bang 100 V. G i a trj U bang
A.200V.

'

\. I O O V 2 V .

D.20GV2V.

ClOOV.
Hu&ngddn

U R = IR =

R

U

I

cuon cam t h u a n v o i d p t u cam 1/n H va tu dien c6 dien d u n g 0,l/7t m F . D i e n
l i n g la

•gR=>ZLi =Z,

A . 59,6 V va 33,3 V .

.

C. 50 V v a 100/3 V .

L = 2LI:^ZL2=2ZLI=2ZC

= U

den 2007t rad/s vao hai dau doan mach n o i tiep g o m d i e n t r o R = 300 Q,
ap hieu d u n g giira hai dau cuon cam c6 gia t r i Ion nhat va n h o nhat t u o n g

R2+(ZL-Zcr

^ U R C = I Z R C

Cau 5 1 : Dat d i e n ap xoay chieu u = 100 ^y2 coscot V v a i 00 thay d o i l u IOOTI rad/s

R^2 +

Z^

V R ' + ( Z L 2 - Z C ) '

=u
"

R^

= U = lOOV
V R ' + ( 2 Z C - Z C ) '

2

'
300^

1/71
VIO~VTC

Cau 5 0 : M o t doan mach A B g o m doan A M va M B mac n o i tiep. D o a n A M g o m

^

tren A M va tren M B l u o n h i o n lech pha nhau TC/2. K h i mach cong h u o n g thi

khong ton tai.

(0 : = 2 0 0 7 1 = ^ U L =

dien ap tren A M c6 gia t r i hieu d u n g U i va tre pha so v o i d i ^ n ap tren AB
ai.

va 50 V .

2

UcoL

A B m o t dien ap xoay chieu chi c6 tan so thay d o i d u g c t h i dien ap tuc thai

ap tuc thai tren A M lai tre pha hon dien ap tren A B m o t goc

V2 V

lOO.lCO

100

^300^ + ( 1 0 0 - 1 0 0 f

"3

100.200

80VS

^300^+(200-50)^

3

CO = IOOTI = > U L =

dien tro R n o i tiep v o i t u d i e n C, con doan M B chi c6 cuon cam L. Dat vao

i m o t goc a i . D i e u chinh tan so de dien ap hieu d u n g tren A M la U2 t h i dien

B.lOOVvaSOV.

>
D . 50
Huang dan

:33,3V

» 59,6 V

Cau 52: D a t dien ap xoay chieu u = Uocoscot (Uo k h o n g d o i va co thay d o i dugc)
vao hai dau doan mach g o m dien t r a thuan R, cuon cam t h u a n c6 d o t u cam

Biet a i + a2 = n/2 va U2 = 0,75Ui. T i n h he so cong suat cua mach A M k h i xay

L va tu d i e n c6 dien d u n g C mac noi tiep, v o i CR^ < 2L. K h i co = 90 rad/s

ra cong h u o n g .

hoac CO = 120 rad/s t h i dien ap hieu d u n g g i i i a hai d a u cuon cam co cung

A . 0,6.

B.0,8.

C.l.

D.0,75.

Huong dan

m o t gia t . j . D i e n ap hieu d u n g giCra hai dau cuon cam dat cue d a i k h i
A . 105 rad/s.

'

B. 72 V2 rad/s.
Huong

U,
COStti

^

=—-

U
U2
.

costto = — ^ = S i n a i
^
U
^

2

+

^u J

= 1-

U2=0,75U]

1

- . i l l = 0,8

u

co,

1

COo

C0|C02 V2

C. 150 rad/s.

D . 75 V2 rad/s.

dan

= 72 V271 (rad/s)

^/cof+cof

^2 J

Cau 53: Dat dien ap xoay chieu u = UocoslOOTit (V) vao hai dau doan mach mac
ncVi tiep g o m dien t r o thuan R, tu dien co dien d u n g 0,4/7r (mF) v'a cuon cam
t h u a n CO cam k h a n g Z i . thay d o i . Dieu chinh Z L Ian l u g t bang 15Q, 20Q, 29Q
va 50 Q t h i c u o n g dc) hieu d u n g qua mach Ian l u g t bang I i , I2,13 va I4. T r o n g
so'cac c u o n g d o hieu d u n g tren gia t r j Icrn nhat la
C. h.

B. I2.

A. I i .

Huang
Zr=-

coC

*
D. k

dan

= 25(Q)

Vi t r i dinh ZLO = Zc =25(Q)
Gang g a n d i n h I cang I d n
= > Z L 2 va Z L 3 g^n h d n Z L O = 25Q hcfn n e n chi can so s a n h I2 va I3.
Zu, =

^ ' ' ^ :=> 25 ^

^

Z'L2 =

> Z L 3 ^ I2 < I3
311


Cau 54: Cho m o t donn mach xoay chieu g o m dien t r o thuan R thay d o i duoc,

Mach cgng hudng => Z L =

cupn day thuan cam L va tii d i e n C theo thiV t u mac noi tiep v o i 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. K h i f = 5 0 H z t h i c u o n g d o d o n g d i c n hieu d i u i g

Uc =100(V) = Ui. =

R thay d o i . Dien d u n g nho nha't cua tu dien la

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

c^zf

R^ + zf

.

""'^

= — = lOOQ
^

V
=>C>

?

^

hai dau mach dien mgt dien ap xoay chieu co gia t r i 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.300(V).

V „

•

,J

...r

R^

Z\

n

y J thuan cam c6 d o tir cam 2 H , tu d i c n c6 dien d u n g 10'' (F). Dat vao hai dau
m a c h dien dien ap xoay chieu chi co tan so goc o) thay d o i . K h i dien ap hieu
d u n g hai dau tu C dat gia tri cue dai t h i co co gia trj la
B. 707 (rad/s).

,^

C. 2,5.10"^(rad/s). D . 500 (ra'd/s).

Huong dan
-„

C

2

,

B. 2 0 0 ( V ) .

(l000^/2f

VlO-^'

I

^ = 1000(Q)

2

^ '

U c max <=> Z L = Z , =>(oL = 1000 =>(o = 500 (rad / s)

C. 1 0 0 ( V ) .

Huong dan
'12,5.10-"^
10

100'

,-6

u

C max

D. 2 5 0 ( V ) .
........J-

vj.v.

= 100Q
Hi rnfi;j ngtjo ,/J

12,5.10,-3

L

C a u 55: C h o doan mach k h o n g phan nhanh dien t r o 1000V2t), cugn day

A . 400 (rad/s).

,73
ii

day thuan cam co do t u cam 1 2 , 5 m H va t u dien co dien d u n g 1 pF. Dat vao

. gR

Z[ < lOOQ => Z c = 2 Z L < 200Q

= ^.10-^F

lOOn.200

>R = 3 0 0 ( Q )

Cau 5 7 : M g t doan mach khong phan nhanh g o m : dien t r o thuan 1 0 0 iX cugn

= ( Z , - Z c ) ^ =>Zc = 2 Z L

Z = sJR^+Zl

U ' - U ? , + ( U L - U C ) '

v . ' A.

R

U K =100V3(V)

73

+Mdc von ke :

t r o n g mach la 2 A va dien ap hieu d u n g giCra hai dau R L k h o n g thay d o i khi

=

L-6

= u , _ = u . ^ = u.. C • = 200.- 10
R Z \, " 100.100

•J

- = 250(V)

iA\)

Cau 58: Cho doan mach M N theo thi'r t u gom dien tro R mac noi tiep v
thuan cam L ncYi tiep vcVi tu dien co dien d u n g C thay d o i dugc.
la diem noi L v o i C. Dat vao 2 dau doan mach dien ap xoa

i

UMN = 100 V2 cos(1007it + (p) V. Thay d o i C de dien ap hieu d u n g tren doan

0'

thay d o i C de dien ap hiei-i d u n g tren t u cue dai t h i lap bieu thuc dien ap

p,\l,a :?.S •

A M cue dai thi bieu thuc dien ap tren d o la UMA = 2 0 0 ^ c o s l 0 0 7 i t V . N e u
tren doan M A la

Cau 56: M o t doan mach xoay chieu noi tiep A B g o m dien t r o thuan R, cugn

A . UMA = 100V6cos(1007it + 7T/6) V.

B. UMA = 200 76 cos(1007:t + 7r/6) V .

cam thuan L va t u dien C. K h i noi hai cue cua tu dien v o i m g t ampe ke'co

C. UMA = 10076 cos(1007rt + 7t/3) V.

D . UMA = 200 76 cos(1007:t + 7t/3) V.

' dien t r o ra't nho thi so chi ciia no la 0,5 A va d o n g dicn qua ampe ke tre pha

Hwwi^ dan

so vcVi dien ap giua hai dau doan A B la 7i/6. Ne'u thay ampe ke bang von ke

= IZviA =

+

=

^

« Cong hUdng

,

f

I

J,.,j.„

,,

T nmQ mAh
CO dien t r o rat Ion thi no chi 100 V va dien ap giira hai dau von ke tre pha so
v o i dien ap giua hai dau doan mach A B m g t goc n/2. Gia t r i cua R la
A. 150Q. ,
/

B.200Q.

C. 250 Q.

V

Huang dan
Z
tan

+Mdc ampe ke th] tu hi noi tdt ;

. < D . 30C Q. ;. .>\-,
j

u = uz = u V ^ ^ . 4 ^^"^
A-

312

.1, : , J

U M N =10072COS l O O n t - -

R
''''' '
= tan^:^Z,~.^^^^^,-^

A M = 100tan60" =10073(V)
UQ =

max => U 1 U | . L

iMA s d m p h a h d n u M N

la--

vS

313


" M A

= 1 0 0 7 6 C O S lOOTCt
.V.

• ;

3

A

+ - (V)

(R + r)

C O S ( p i = C 0 S ( P 2 <=> •

2)

l(R+rr +
1

^ 200

/

0,.

cojC
L=CR
L-^^

=>LC =

Or

A'

'-—^

(R + r)^
\

M

C02L

-

0J2C

=R

^-^•Wfi^ *

C02

(R + r)

• cos (pj = •

n

(R4-r)2 +

cojC

C0|L = R

100

(R + r)

R./'^i

-R^2

CO2

Y ™i

2

(

1—-

1

"1-

= 0,96

\

CO2

\

•'•)'r''Xifiyi'iV.

lV«2

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

N

u = 100 V6 .coslOOnt (V). Khi dien ap hieu dung tren cuon day dat gia trj cue
Cau 59: Dat dien ap xoay chieu vao hai dau doan mach noi tiep pom dien tio

dai ULMnx thi dien ap hieu dung tren doan mach chua RC la 100 (V). Gia trj

R, cuon cam thuan L va tu dien c6 dien dung C thay doi dirge. Khi C thay

ULM.IX la

doi thi dien ap hieu dung cue dai tren R, L va C Ian lugt la x, y va z. Ne'u

A. 100 (V).

B. 150 (V).

z/y= V'S thi z/x bang

i C . 300 (V).

D. 200 (V).

] B. 0,75 V2 .

,,; A. 0,5 N/5 .
yy.) ryAii;

'

m.^imii

C. 0,75.

Huong dan

u

, ( U R m a x va U L ^ , , cong huang <=> I ^ , , = -

' :,

,

_ w

D. 2 >/2 . > .^i ,

{

Huong dan

'y

U Cmax

iy-iiQ

/ l

> ioifrJ
|UJ-URC

u,

=>

;

U L = 7100^+3.100^ = 200( V )
Z =

U

I

R
U,
=> z =

R

= 0 , 5 V 5 U ^ - = 0,5N/5

Cau 62: Cho mach dien xoay chieu RLC vol R la bien tro va cuon day co dien

X

Cau 60: Dat dien ap u = 125 -Jl coscot (V), co thay doi dugc vao doan mach noi

I t r a thuan r = 10 Q. Khi R = 15 Q hoac R = 39 Q cong suat cua toan mach la

tiep AMB. Doan mach A M gom dien tro R noi tiep tu dien, doan mach MB

I nhu nhau. De cong suat toan mach cue dai thi R bang

chiia cuon day c6 dien tra r. Biet dien ap tren doan A M luon vuong pha v6i

| A . 27Q.

B. 25Q.

rad/s thi mach AB co cung he so cong suat va gia trj do bang
B.0,85.
:

C.0,91.

(R + r ) ^ + ( Z L - Z c )

Huong dan
-Zn

Zr
U A M -L U M B =^ tancpAM t a n ^ M B = -1 => ~ — — = -1 =>

L = CR^

c-\

> t)K MI
D. 36 Q.

- =>

(R^+r) + (R2 + r) =
(R,+r)(R2+r) = ( Z L - Z c r

.^-^U
2ZL-ZC

R^
314

u2(R + r)

D. 0,82.

C. 32 Q. j
Hwang dan

dien ap tren doan MB va r = R. Voi hai gia trj co = lOOn rad/s va co = 56,257T

A. 0,96.

ft;

<=>RQ + r = |ZL - Z C

'

i

315


CtyTmiii

Pirv t> VVH

Khang-yi^T—

.(Ro + r f = ( R , + r ) ( R 2 + r ) = ^ R n +10 = ^ ( 1 5 + 10)(39 + 1 0 ) = ^ Ro = 2 5 Q

B

1

1/
::'

1 f

R

r, L

= R>/5

Ucmax <=> Z r =

=R«0,499 —
JR2+(ZL-Zcf
'
^_

u,.

\
/ \"

—>

M

M

1

u'

t

Cau 63: H a i doan macli n o i tiep R L C khac niiau: mach T va mach 2, cona
h u o n g v o i d o n g dien xoay chieu c6 tan s o g c k Ian l u g t la (oo va 2(oi). Biet do
tu cam ciia mach 2 gap ba do t u cam ciia mach 1. N e u mac noi tiep hai doan
mach d o v o i nhau thanh m o t mach t h i no se cong h u o n g v o i d o n g di(D . C S t o o Vl3

C. (00 V l 3 .
Hu6iig

Diiu kicn cgng hi/dng

2

CO2L2C2

(o^LC = 1

coLi + (0L2 =

1

wCj

K h i thay ctoi R thi cong suat toa nhiet tren toan mach dat gia t r i cue dai la
A . 1000 (W).

B. 1 4 4 ( W ) .

C. 8 0 0 ( W ) .

Huong dan
P - l 2 ( R + r) =

ZL-

(R + r ) 2 + ( Z L - Z c ) '

Zcl => R = - 2 0 < 0

"1, . . .

D. 125 (W).
.

r-

-(R + r ) ^ .
(R + r ) +

P^,,

(ZL_IZC)

2" = max

]R + r)

R=0
200'

2
= CO2L2

(0C2

; - ..'K r q - . - l . -

bien t r o R (0 < R < 00). Dien ap c* hai dau doan mach o n d i n h 200 V - 50 H z .

o R +r=

+

R

thuan 40 (Q), c6 cam khang 60 (Q), tu dien ccS d u n g khang 80 (Q) va mcit

dan
1

^2,24

CaU 65: M o t doan mach xoay chieu mac noi tiep g o m cuon d a y c6 dien t r o

xoay chieu c6 tan so goc la
B. l,5co().

= 0,5V5^

. W ^

U vV2
7 =
U
- '-'Cmax
R

U V2
U VI

"1

A

A . coo V3 .

'J • ,'•

U

_-.40 = 800(W)
-(R + r) = .
(R + r ) ' + ( Z L - Z c ) ' ^
; . 40^+20^
-r,^^

0)^ ( L I + L 2 ) = CO? L| + CO2L2
(0^ .4L1 = COQL , + 4coo .3L, => co = 0, SCOQ V T S

Cau 64: D a t d i e n ap xoay chieu vao hai dau doan mach noi tiep g d m dien t r o
R, cuc)n cam thuan L va tu dien c6 dien d u n g C thay doi dugc. Cac v o n ke'li

rri f!"

t u o n g V i va V 2 mac Ian iuc7t vao hai dau R va hai dau C. K h i C thay doi de

.4 76/'•:):!(!

so'chi V I cue dai thi gia trj nay gap s o c h i cua V2. Hoi k h i so chi V2 cue dai

c

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
fUv,

R
UVl-2Uv7 . ^
— > Z L

316

R

= —

-20 Q

= U K = U

U
U v 2 - U c - I„,axZc = — Z L
R

1 51}

Cau 66: Dat dien ap xoay chieu vao hai dau doan mach noi tiep g o m dien tro,
cuon cam t h u a n va tu dien c6 dung khang Z c thay d o i . Goi Ucn«x la gia t r i
cue dai cua d i e n ap hi$u d u n g tren t u . D i e u chinh Z c Ian l u g t bang 50Q,
150Q va lOOQ t h i dien ap hieu dung tren t u Ian l u g t bang U c i . U c 2 va Uc3.
^'e'u U C I = U c 2 = a thi
A . U c ^ = Uc,™v.
B. U c . » a .

C. Uc3
D . Uc3 =0,5Ucn«..
317


Bo trtpi klcn thitc

Bun

V^t If LTDH trSn JkSnh VTV2. t^p 2 - Chu VSn

Cty TjynH mvDVVnKhang

Huang dan
Uci =

2UR

u 'RCmax

,

2UR

^/^274R2 - ZL

r-^

CI < Zc3 < Z c 2 =^ Uc3 > Uc2

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

60(Q)

Huong dan
1 = In C O S - —

Ii = I , =

CO = (Oi U (0 = 0)2

Z , + VZ[+4R^"_^

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.
D. cuon cam thuan.
C. tu dien.

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.

71
+—
T 4
r27tt

• + (Px
ux =Uo2 cos

ZL 1
tancpcd = — = 1=^ Vcd = 7

"cd = Uoi cos

r

^ Z I = Z 2 = R V 2 = ^ . R2 + (OiL-

« l L - - - =R 5
cojC

L
^

(Oi

1

C

(OiC;

= Rco,
^

(R2 + a)2L -

co,C

= RV2

•L(COI -CO2) = R(O)I +C02)

.
'

'

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

R'+zg

• uKCmax ~

'"^Z^-2ZLZC+(R'+Z2)

<=>

4

7t

(pv =

4

,

'

i| • i ' i f :

'

ifi')

f

}

'

f

,

'C=

•

2

i

Ul

i

"

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
= Pr,

2^/(ZL-Zc)'+r2+2r

I l 7 y ( ^ L - Z c ) ^ ^ = 76Q
ZL + VZL+4R^

' '

K.

4

"

-2ZL(Z^-ZLZC-R2'

. .

=^ 9x =

^ CO the la tu dien.
, , , || •
Cau 70: Cho doan mach AB mac no'i tiep gom tu dien, cuon cam va bien tro R.

^ R max

VZ^+4R2_ZL

318

=

8

?

Z^+R2

2UR

Z^-2ZLZC +

(

U(,jj s6m pha hcin Ux ve thdi gian la —va ve pha la
8
II/.J
27t 3 T 371
71
371

T

|R2+(ZL-Zcf

f

3T

co,C

URC=I.ZRC=U.

•27lt

T

^ = -R

=>R = L(coj-ci)2) = 100Q

=>y' =

. u = > R = 80(P.)

VI202 ^ 4j,2 _

» Zco = —^""^-V^ =

A.
2

> Z c „ = 75(Q) ^ Zc3 ^ Uc3 ^ Ucnnax

(OjL

VIft

^ ( Z L - Z c ) ' + r 2 + r = 2lZL-Zc

Rrmax

= 2Pn
2ZL-ZC

R2=ZL-ZC
R2 +

= 76^

r = 2R2-76

=^R2 =60,8Q


Cty TNHHMIV

Cau 71: Dat dien ap xoay chiou 220 V - 50 H z vao hai dau doan mach n o i tiep

Huang

g o m dien tro 50 f2, cuon cam thuan c6 cam khang 100 Q va tu dien c6 d u n g

khang Zc thay d o i . Dieu chinh Zc ian i u g t bang 50 Q, 100 Q, 180 Q va 200 Q
thi dien ap hieu d u n g tren t u Ian l u g t bang U c i , Ucz, U c i va Uc4. T r o n g so
cac dien ap hieu d u n g noi tren gia t i i ion nha't la
A. Uci.

(,,,:; n

B. Uc2.

C.Va.

P=

u2(R

Zro =

,

,5b::;ipvfi^'>-,

,
, = 1 2 5 " k : ) ^ 0,008R2+Zf
Zcl, = 1 8 0 ' ' =0,0056

•"

^'«> .A:-;
.muh

Zc4 = 2 0 0 ' ' =0,005
Gang gan di'nh

.1,;,'

(R + r ) ^ + ( Z L - Z c )

«Ro

=?> ( R „ + r )

+r= ZL-ZC

= ( R i + r)(R2 + r)

R„ + 1 0 = 7(15 + 1 0 ) ( 3 9 + 1 0 )

;

-f'

\

u-<\7 r ; V , , , i v f - o y q A a v i h tf:Q/:c^? xnl,

=> Ro = 2 5 Q

"'"'^

<^

au 74: Dat dien ap u = uV2cos(ot (V) vao hai dau doan mach mac n o i tiep

500 (V). K h i Zc = 0,4Zci t h i d o n g d i ^ n tre pha 7r/4 so v o i dien ap h a i dau

.I55llM=.z-

n ^ m ngoai ( Z ' c 2 ; Z c 2 )

(R,+r)(R2+r) = (ZL-Zcr

Zc = Zci t h i d i e n ap hieu d u n g tren tu dat cue dai va gia t n cue dai d o bang

ne n chi can so s a n h \JQ2 v a Uc^.

=>

dan

theo d u n g t h u t u g o m cuon cam va tu dien c6 d u n g k h a n g Zc thay d o i . K h i

cang 16n => va Z(23 gan T^QQ hdn

Zj|,=SilM=,,25-'

Vl§t

( R i + r ) + (R2 + r) =

+ r)

2Z,

Ze2 = 100"^ =0,01

aliang

D . U c . r.'

d,t

Z^'l = 5 0 " ' = 0 , 0 2

uvvn

J5-"

=0,006

doan mach. Gia trj U bang
A. 100N/5'(V).

,

B. 5 0 V 5 ( V ) .

Uc3 be h d n

C. lOO(V).

Huong

l a u 72: D o a n mach noi tiep A B g o m tu dien c6 dien d u n g l/(6Tt) niF, cuon cam

'~7

tan(p2=

i

dan

7

^"^ "

=tan^^Zc2=ZL-R

CO d o t u cam L = 0,3/7i H c6 dien t r a r = 10 Q va 1 bie'n t r o R. Dat vao dien ap
xoay chieu co tan so f thay d o i . K h i f = 50 H z , thay d o i R t h i dien ap hieu

D . 50 (V).

U

U r = I.Zr =

U

.Zr =

d u n g tren tu cue dai la Ui. K h i R = 30 Q, thay d o i f t h i dien ap hieu d u n g

-,--2.ZL.

1

- +1

tren tu cue dai la U2. T i s6'Ui/U2 bang
A. 1,58.

B. 3,15.

C. 0,79.
Huong

"TT'

D . 6,29.

dan

.

=

= max

^

U.60

^Q^^^^

^/(0 +10)2+(30-60)^
(R +

r)2

=> 7 7 ^ = 1,58

x/T4
U C 2 = L J L „ , , , = U . (R
. „ + r ) Z \4 =u.

4,5
^
~ 1

r^-

CI

:

^au 73: Cho mach dien xoay chieu RLC v o l R la bien t r o v a cuon day c6 dien
t r a t h u a n r = 10 Q. K h i R = 15 Q hoac R = 39 Q cong sua't ciia toan mach la
n h u nhau. D e c o n g sua't toan mach cue dai thi R bang
20

B.25Q.

C. 32 Q.

R

= 100V5

= ^ = 2,5Zc2 = 2 , 5 ( Z L - R ) = ^ Z L = 2 R
ZL

Ur

1800
I /-M II I

U^R^ + Z^

Zci

"

= 10VT4Q
L
L
C
.

A.27Q.

-——^-2,5Zc2

u Cmax

J(R + r ) 2 + ( Z L - Z c f
i.t.ii^D

Zci

' UZc

"

U c i = IZQ =

^'^'

D . 36 Q.

U C . . , . = H S . 5 0 0
R

^

VR^ 4R'
R

= 5 0 0 = > U = 100^/5(V)

u 75: M o t doan mach R-L-C mac noi tiep. Dat vao hai dau doan mach m o t
dien ap xoay chieu c6 gia t r i hieu d u n g U , tan so'thay doi duac. Tai tan so
80 H z dien ap hai dau cuon day thuan cam cue dai, tai tan so 50 H z dien ap
hai ban tu cue dai. De cong sua't trong mach cue dai ta can dieu c h i n h tan so'
den gia trj
A.loVSHz.

B.20VTOHZ.

C.loViOHz.

D.lOHz.
321


B6 tr^hicn

thJrc V^t liLTDH

tren kenh VTV2. tpp 2 - Cliu V^n Blen

Huang
L

R2

ULmax <=^Zc = - ^

cojL.

dan

cosy = - ^

= Z,

=>

1
CO1CO2

=

2

L va tu dien cc) d i i ' n d u n g C mac ncVi tiep, vc'>i CR^ < 2L. K h i (o = coi hoar co =
= ^

=

C02=

2OVTO

t r o R, cuon day cam thuan L = 2/7i H va tii dien c6 dien d u n g C thay doj

2coi t h i dien ap hieu d u n g giua hai ban tu dien co ciang m o t gia tri. K h i

CO = 50 rad/s thi dien ap hieu d u n g giua hai ban tu dien dat cue dai. T i n h co:.
A . 25 V2 rad/s.

B. 10/lO

rad/s.

doan mach. K h i C = Ci/2,5 thi dien ap hieu d u n g gifia hai tu cue dai. Tinh
tan so goc cua d o n g dien.
A.

2OO7:

rad/s.

B.

rad/s.

SOTT

•'•f^.

C.

IOOT: rad/s.

i •• Huang dan

+C = C, =^ tan(p, =

^ ^' =

D . lOjtrad/s.

\""r" '

' \

4 ^ K =Z L -Zci

;y.

C. 100/3 rad/s.

«o = ^ ( « i

+ « 2 ) ^ ' - S ' ^ ' =2,5(of =>o), =:10x/iO( rad/s)

cuon cam thuan ccS dc) t u cam 1/n H . Ne'u dat mc)t t r o n g cac dien ap xoay
chieu sau day vao hai dau doan mach trC'n thi c u o n g dc) hieu d u n g trong

r^,;.j

mach kVn nha't iVng vcM dien ap nao?
C. u = U«cos(957rt) V.

^'

+ Uc = max <=> Z(22 = — ; ^

n 71

^»^' .

|

D . u = Uocos(707tt) V.

,

" •

;

'

=> — = 2

2 1(1^"'

• (o^LC, = 2 ^ co^ --^

B. u = Ui)Cos(857tt) V.
Huang dan

^/->Z(2i =

'''''' .

Cau 79: Doan mach ncVi tiep g o m dien tro, tii dien co dien d u n g 0,l/7i mV va

A . u = U()Cos(1057it)V.

2,5

D . 12,5^/lO rad/s.

Hmhtg dciu

dupe. K h i C = C: = OAlu mF thi d o n g dien tre pha K/4 S O v o i d i e n ap hai dau
"

7

vao hai dau doan mach g o m dien tro thuan R, cuon cam thuan co do tu cam

Cau 76: Dat dien ap xoay cliieu vao hai dau doan mach A B no'i tiep g o m dien

'

=0,14

Cau 78: Dat dien ap xoay cliieu u = Uocostot (Uo k h o n g doi va co thay d o i duc)c)

1

C0,|, = VC0,C02 => f,|,

^

^

.7

LC

U c m a x ^ Z L =(02L = Z ,
TT

=-,

= 2 rr> CO = 1007c(rad/s)

Gang gan v i t r i cong h i f d n g I cang Ic'in

chi can so s a n h CO3 = 95:1 rad/s

va CO4 = 10571 rad/s.

^" .'^^

:,,„:,..•,

..rg-

Cau 77: Dat dien ap xoay chieu vao hai dau doan mach A B n o i tiep g o m dien
tra R, cuon day cam thuan L va tu dien co dien d u n g C thay d o i d u g c . Khi
'

C = Ci t h i d o n g dien som pha n/4 so v o i dien ap giica hai dau doan machK h i C = Ci/6,25 t h i dien ap hieu d u n g giua hai tu cue dai. T i n t i he so cong
sua't mach A B k h i do.
A . 0,14.

:?

,

•!

••;•••;/•

B.0,71.

C.0,8.

D . 0,9.

|

HuOltg dmi

';''

+C = Ci =^tan(pi = ^ i - ^ ^ = t a n y =:>Zc, = Z L + R

' , . 6 ^ 0 ^

COQ = C 0 3 0 ) ' 3 r=> (IOOTT)^ = 9 5 7 1 ( 0 ' 3 --^ { 0 ' 3

* 105,371 > CO4 = > I3 < I4

' -i r'ii'

Cau 80: M o t doan mach A B g o m doan A M va M B mac noi tiep. D o a n A M g o m
tu dien C noi tiep vcVi dien t r o R, con doan M B chi co cuon cam L . Dat vao
A B m o t dien ap xoay ciiieu chi co tan so'goc (o thay d o i d u g c thi dien ap tuc
t h o i tren A M va tren M B l u o n l u o n lech pha nhau 7r/2. K h i mach cong
h u o n g t h i dien ap tren A M va M B co cung gia trj hieu d u n g . K h i o) = coi thi
dien ap tren A M ccS gia trj hieu d u n g U i va tre pha so vc>i dien ap tren A B
m o t goc a i . K h i co = (02 thi dien ap hieu d u n g tren A M la U2 va dien ap tiic
thai tren A M lai tre pha h o n dien ap tren A B m o t goc a2. Bie't a i + a2 = TC/2 va

+C = - - r - = > Z c 2 = 6 , 2 5 Z c i - 6 , 2 5 ( Z L + R )
6, 2n

U i = 0,75U2. T i n h he so cong sua't cua mach l i n g v o i coi va C02.
,

,-,7

*\'tr., fi-V

A . 0,75 va
C. 0,75 va

0,75.
0,45.

B. 0,45 va 0,75

,
. . •

D . 0,96 va 0,96.
Huang divi

;;

322

+ U c = max <^ Zc2 =

=> 6 , 2 5 ( Z L + R) =

^ Z^

^

Khi cong hMng

U ^ M = U ^ B = > U R = U,

'
323


la 92,0%. Biet dien tro suat ciia dong nho hon dien tro suat ciia nhom 1,47

TraSng hap Mt k i :

.Ur

cogR = — {•MY>r

rr,
''••'f-

'

=>(p = 2
^ a ---9^0
u " =?
=> cos(p = ssin2a
inza
,

AM

Ian. Neu dung day dan bang dong cung kich thuoc voi day d i n bang nhom
noi tren de thay day nhom truyen tai dien thi h i | u suat truyen tai di^n se la

MB

T H I : cos
iii;

Cau 82: Hieu suat ciia qua trinh truyen tai dien nang tren day dan b3ng nhom

U

sinp = iii-

; •

r_

A. 92,5%.

n')ih !:n
B. 93,3%.

D. 97,5%.

C. 94,6%. ,J
Huattgddn

U
.,U.

T H 2: ccos
osaj = - j j - = sina.

^ ^ U i ^ ^ ^ U ^ ^ =1
U y +V U

jcosa, = 0 , 6 =>cos(p, =0,96

-.uOiuV

^0^6 -

0,75

U^cos^(p

it)

'

cosa2 = 0,8 => cos(p2 = 0,96

;

• • ^/ ^

/;

-

'

\''

'

PR,

I-H1 =

PR:

1-H, =

l-Hi_Ri

1-0,92

1-H,

1-H,

R,

= 1,47 =:>H2 =^0,946

U^cos^cp
Cau 83: Mot may bien ap c6 loi do'i xung gom n nhanh nhung chi c6 hai nhanh
dugc qua'n hai cuon day. Khi mac mot cupn day vao dien ap xoay chieu thi
cac duong sue t u do no sinh ra khong bi thoat ra ngoai va dugc chia deu
cho hai nhanh con lai. Khi mac cuon 1 vao dien ap hieu dung U thi a cuon 2
khi de ho c6 dien ap hieu dung U2. Khi muc cuon 2 vai dien ap hieu dung
U2 thi dien ap hieu dung a cuon 1 khi dg ho la
A. U(n + l)-2.

B. U ( n - l ) - 2 .

D. U ( n - l )

C. Un-2.

Huang dan
02 =

Cau 81: Mot mach xoay chieu RLC noi tiep chi c6 tan so f dong dien thay doi
dirge. Khi f = 12,5 Hz va f = 50 Hz thi cong sua't tieu thu cua mach nhu nhau.
Thay doi f sao cho cong suat toan mach Ion nhat th' trong thai gian 1 s c6
bao nhieu Ian cuong dp dong dien qua mach bang 0?
A. 50.
B. 15.
C. 25.

Pi = P2 ^ I , = I2 ^ R2 + co,L

=>f = 7W = 25(Hz)

(24

'ft a A

f

C O TT
L

M

1

»2Cj

2
1

= max =>(o = — =^0) =(0,0)2 M ^ n % J J o ( ( i

wC

(n-1)

(n-l)Ni

El
(n-1)

U2U'2 _

N2

N,02
N2O',

1
(n-1)'

(n-l)N2

U2.U'2

U.U2

1

(n-1)"

u

U ' , =•
' (n-1)"

n,,f,v,v..,

AB gom R, cuon cani thuan L va C mac noi tiep. Khi roto cua may quay deu
voi toe do Ian lugt ni vong/phiit va n2 vong/phiit thi cuong do dong dien

^

R2 + coL -

U2 _ N2O2 _

Cau 84: No'i hai cue ciia may phat dien xoay chieu mot pha voi mot doan mach
D. 75.

Huong dan
2

O2 =

O,

hieu dung va tong tro cua mach trong doan m^ich AB Jan luct la Ii, Zi va
I2, Z2. Biet I2 = 411 va Z2 = Zi. De tong tro ciia doan mach AB c6 gia t n nho
nhat thi roto ciia may phai quay deu voi toe do bang 480 vong/phiit. Gia tn

ciia ni va n2 Ian lugt la
A. 300 vong/phiit va 768 vong/phiit.

V

B. 120 vong/phiit va 1920 vong/phut.

=> Tron^^ 1 chu k i dong dien = 0 hai Idn

C. 360 vong/ phiit va 640 y^ng/phut.#^

=> Trong 1 s dong dien = Ola 25.2 = 50 idn

D. 240 vong/phiit va 960 vong/phut.

325


Bo trp kien

thiic

V$t li LTBH

tren

henh

VTV2.

t^p 2 - Chu van

Huang
f=
E =

Bien

Q^U 87: D i e n ap h i ^ u d u n g giua hai cue cua mot t r a m phat di§n can tang len

dan
= 4 o ) | => n2 = 4 n i

.CO = 27lf

60
N2TrfO,

l2=4Ii

a)2L-

V2^

1

cojC

•cof =0,25

<^^"^ AWcm^ => COn =

Zmin

1
1

-coiL

A . 9,5286 Ian.

1

a% =

phat d i e n xoay chieu m o t pha g o m 10 cap cue (dien t r a t r o n g k h o n g dang
ke). K h i roto ciia m a y phat dien quay v o i toe d p 2,5 v6ng/s t h i c u o n g do
d o n g dien hieu d u n g t r o n g mach la ^Jl A . Thay d o i toe d o quay cua roto
cho deh k h i t r o n g mach co cong h u d n g . Toe d o quay eua roto va c u o n g do
d o n g d i e n hieu d u n g k h i d o la
A . 2,5 >/2 vong/s va 2 A .

B. 25 V 2 v6ng/s va 2 A .

C. 25 N/2 v6ng/s va V2 A .

= 200Q

^I =

= — A P

= a%UI = — U I

20,
P.iou i h u = ( l - a % ) U I = ^ U I
21
I
I
a%UI
= U'.P ticii thu = U
^ ' .• f—
n
v/TOO
vn
>U'*9,5286U
P tieu thu ~ Ptiou _ thu

1

UI

21100

•/,„•:•':,• y^^.-':

Cau 88: D o a n mach no'i tiep A B g o m dien t r o R = 100 Q, : u o n day thuan cam c6

quay cua roto va c u o n g d o d o n g dien hieu d u n g k h i d o la

E-:200(V)
(ZL-zcr

A. 2,5 N/2 v6ng/s va 2 A .

BAO/S

C. 25 N/2 v6ng/s va ^

D . 2,5 7 2 v6ng/s val^ll

A.
Huong

f

vong/s va 8 / A .

'

A.

dan

= 25V2Hz = fV2 ^ n ' = n V 2 = 2 , 5 7 2 ( V / s)
f = np = 25Hz => CO = 27if = 507t

E ' E V 2 = 2OOV2 ( V ) => r = | - = 2 V 2 A

nhanh d u o c quah hai cupn day. K h i mac m o t cuon day vao d i e n ap xoay

hieu d u n g 60 V t h i 6 cuon 2

=>! =

C. 600 v o n g .

WMWJ^dan
40

N,

60

3.1000

,

D . 400 v o n g .
,

. .

1

,,s•
E,
'

,

El = 2 0 0 ( V )

> ^ . ( Z , - Z C )

72
Dat

k h i de h o c6 d i e n ap hieu d u n g la 40 V. So

= 200Q=>Ii=

^ _ N27ifOo

chia d e u cho hai n h a n h con lai. K h i mac cuon 1 (c6 1000 vong) vao dien ap
\g day cua cuon 2 la

"

E;

chieu t h i cac d u o n g sue t u d o no sinh ra k h o n g b j thoat ra ngoai va d u g c

B. 200 v o n g .

1

Z , =(oL = 1 0 0 Q ; Z r =

Cau 86: Moc may bien ap c6 161 d o i x u n g g o m bon n h a n h n h u n g chi c6 hai

U,

1 + 5%

cho den k h i c u o n g do d o n g dien hieu d i j n g t r o n g mach dat cue d a i . Toe do

V2

4-1

u

d o n g d i e n hieu d u n g t r o n g mach la \f2 A. Thay d o i toe d o quay ciia roto

'

N27ifO,0

N2O
O'2,

5%

dan

ke). K h i . o t o ciia m a y phat dien quay v o l toe d o 2,5 v6ng/s t h i c u o n g do

'

f = n p = 25Hz=>to = 27if = 5071

Oi

AU

D . 9,505 Ian.

phat d i e n xoay chieu m o t pha g o m 10 cap ct,rc (dien t r o t r o n g k h o n g dang

D . 2,5 -Jl v6ng/s va 2 V? A . "
Huaitg dan

A. 2 0 0 0 v o n g .

C. 10 Ian.

L = 2/71 H n o i tiep va ti.i dic-n c6 dien d u n g C = 0,1/TC niF. N o i A B v o i may
*'

1
27if'L = 27:f'C
E'

B. 8,709 Ian.
Huong

LC

L = 2/71 H no'i tiep va tu d i e n c6 dien d u n g C = 0,1/;: mF. N o i A B v o i may

Cong hiidng'.

chua tang dien ap, do giam dien the tren d u o n g day tai dien bang 5% dien
voi d i e n ap dat len d u o n g day.

LC

Cau 85: D o a n mach n o i tiep A B g o m dien t r o R = 100 Q, cuon day t h u a n cam c6

coC

voi dieu k i e n cong suat t r u y e n den tai tieu t h u k h o n g doi? Bie't rang k h i
ap hieu d u n g tren tai. Coi c u o n g do d o n g dien trong mach l u o n cung pha

.

=> (0, = 0,5cO() => n j = 0,5n() = 240 =i> n2 = 4 n , = 960

Z| = (oL = 1OOQ; Z c =

bao nhieu Ian de g i a m cong suat hao p h i tren d u o n g day tai dien 100 Ian,

n = xnj

„^,,,,

^

, ,

,;, ^

XZL-^C

3

276

^.

i

2x
2

j
1

,;

xE

h

• = max

(

877

2^
x ,

A ; n = xn] =

x
576,

x
, .

(v/s)

• N 2 = 2000
327


Cau 89: M o t may phat dien xoay chieu mot pha c6 d i e n t r o t r o n g k h o n g dang

Huang

ke, mac vao doan mach n o i tiep RLC. K h i toe d o quay ciia roto bang n i hoac
n2 t h i c u a n g d o hieu d u n g t r o n g mach c6 cCing gia t r i . K h i toe d o quay cug
roto la n(i t h i c u o n g do hieu d u n g t r o n g mach cue d a i . C h o n he t h i i c d u n g .
A. n() = (nin2)"-\• •

'

-

B. no^ = a5(ni2 + n22).

•

C. nir2 = 0,5(nr2 + n2-2).

„^

Huong

' "

E =

NOn

^/2^V2

1

2 +

2
n2j

A. D i e m C each d a u A m o t doan
A. 25 k m .

2 ; CO

"

B. 50 k m .

C. 75 k m .
Huong

sib;

^ B.220.

C. 250.
Huang
P-

Pcos^

D. 85 k m .

dan

D e h d d a u B : 2 x - f R = — = 75Q=:>R = 7 5 - 2 x
I

D o a n m a c h dKu B : 2x
AC =

N e u dat ..ae m a y tai nha may dien thi cung cap d u d i e n nang cho

cp

P-

,

,

D . 200.

•2x +

dm

P^R

16U^ cos^ cp
P^R
64U^ cos^ (p

100

R.(200-2x)

U

500

R + (200-2x)

1

7

Q

A B = 25km

(75-2x)(200-2x)

500

275 - 4x

7

X

= 25Q
100-x

•—

= 192P,

B

P = 200Po

100-

= 198R

X

C a u 93: M o t m a y bien ap eo loi d o i x u n g g o m ba n h a n h n h u n g chi c6 hai

" 1 : D i e n nang d u g c t r u y e n t u may tang ap dat tai A toi m a y ha ap dat tai

n h a n h duoe qua'n hai cuon day. K h i mac m o t cuon day vao d i e n ap xoay

B bang day d o n g tie't dien t r o n d u o n g k i n h 1 cm v o l t o n g chieu dai 200 k m .

chieu t h i cac d u o n g sue t u d o no sinh ra k h o n g bj thoat ra ngoai va dugc

C u o n g d o d o n g dien tren day tai la 50 A , cae eong suat hao p h i tren d i r o n g

chia deu cho hai n h a n h con l a i . K h i mac cuon 1 vao dien ap hieu d u n g 60 V

day tai bang 5% cong suat tieu t h u 6 B. Bo qua m o i hao p h i t r o n g cac may

thi 6 cuon 2 k h i cte h o eo dien ap hieu d u n g U2. K h i mac cuon 2 v o i dien ap

bien ap, coi he so cong suat cua cac mach so cap va thtr cap deu bang 1,

hieu d u n g U2 t h i dien ap hieu d u n g 6 cuon 1 k h i de h a la

dien t r o suat cua d o n g la 1,6.10 « Q m . Dien ap hieu d u n g 6 may t h u cap cua
may tang-ap c? A la
A. 43 k V .

528

= 41000(V)

n g u o n la 0,168 A . K h i dau B h o t h i c u o n g do d o n g d i e n qua n g u o n la 0,16
,

d u d i e n nang Ian l u o t cho 192 may hoat d o n g va 198 m a y hoat dong.

P,t = P - A P =

0,05

k h o n g d a n g ke. K h i l a m dc:)an mach dau B t h i c u o n g d o d c n g dien qua

.J. Ian lu'ot m a y tang ap c6 ti scY v o n g day N2/N1 = 4 va N2/N1 = 8 t h i ncxi tieu

A. 280.

0,05

t o n g cong cua d u o n g day la 200 Q. D o day each dien k h o n g tot nen tgi m o t

Cau 90: D i e n nang t r u y e n tai t u nha may phat dien den n o i tieu t h u . N e u d i i n g

thu

50.41

d i e m C, n g u o i ta d u n g n g u o n dien eo suat dien d o n g 12 V, d i e n t r o t r o n g

1

V

\

I,R

d i e m C nao d o tren d u o n g day c6 hien t u o n g ro d i e n . De phat hien v i t r i

C
f

A P = i f R = 0,05PB = 0 , 0 5 U , I | ^ U j =

U = U j + I j R = 41.10-^50.41 = 4 3 0 5 0 ( V ) * 4 3 ( k V )

V2

Z

^ rL

1

71(0,5.0,01)

7r(0,5df

dan

CO

l l

S

200.Kr 2 ~ 4 1 ( Q )

-8

Cau 92: M o t d u o n g day tai dien g i i i a hai d i e m A, B each nhau 100 k m . D i e n tro

-co

NOn

V2

= 1,6.10

Dien dp diXa ten diCdng day d A :

...,ll,!r,i1 =

1

D . nu = 0,5(ni + n2).

f = n p =>(o = 2ni = 2npn
En

1
R = p— = p

diin

,

,
P..

!2 JvV.

.V:

{.
C. 40 kV.

A. 15 V.

B. 60 V.
Huong

x
D . 20 k V .

C. 30 V.

HD:

-1

^ ^

2

2

D . 40 V. ' ' ' '

dan
U'2

=15V
329


•xiry'rrwnTivrv-a-rrTr-Tanmg-r,^

l a u 94: M o t thiet bj dien diroc dat d u o i dien ap xoay ciiieu u = 200':oslOOnt (V),
t t i n h bang giay (s). Thiet bj ciii boat d o n g ilA. 0,0126 s.

B. 0,0063 s.
J

C. 0,63 s.

d o n g d i e n 6 1 cuon co gia trj bang ii = 3 72 A va dang tang t h i d o n g d i e n 6
cuon 2 va 3 t u o n g u n g bang
A . 1,55 A va 3 A .

D . 1,26 s.

C.

Humigiidn

H D : tx = 4 - a rccos ^
= 4 —*— a rccos —
* 0,0126 (s)
CO
U(,
lOOn
200

1,55

A va -5,80

t,, =f.tT=o,63(s)

'

.

A.

'

I620V2

— = UIC03
3

B.-5,80 A va \55 A .
D . 3 A va - 6

m^i

mm

1

„ " i

ir • — arccos-^-;^

.....^

^

„

12 - 6cos

„ «i

-arccos^

^0

^

,,

^0

,

.

,.
.

„

.
,

.

.

,

Zau 95: M o t may phat dien xoay chieii mot pha c6 mot cap cue, macn ngoai duoe
noi v o i m o t maeh RLC noi tiep gom cuon thuan cam c6 do t u cam L = 0,4/TrH,
tu d i e n C va dien t r o R. K h i may phat dien quay v o i toe d p 750 v o n g / p h u t
thi d o n g dien hieu d u n g qua mach la V2 A ; k h i may phat d i e n quay v o i toe
dp 1500 v o n g / p h u t t h i trong mach co cpng h u o n g va d o n g d i e n hieu d u n g
qua mach la 4 A . Gia trj eua dien t r o thuan R va tu dien C Ian l i r p t la

;

A. R = 25

-

= 1/(2571) mF.

B. R = 30 Q; C = 1/TC mF.

C. R = 15 Q; C = 2/71 mF.

D . R = 305 Q; C = 0,4/7t mF.
Huoitg

= 2001.0,9=^ I = 372 ( A )

*-5,80A

f noi tir A deh B la 100 Q. M a y B co so v o n g day eiia cuon so cap gap 10 so
: v o n g day eua cuon t h i i cap. Mach t h u cap cua may B tieu thu eong sua't
lOOKW va c u o n g d p hieu d u n g 6 maeh t h u cap la 100 A . Gia s u ton hao cua
cac may bie'n the 6 A va B la khong dang ke. He so eong sua't tren cac maeh

deu bang 1. Dien ap hieu d u n g 6 hai dau maeh t h u ca'p eua may \a
B. 10000 V.

C. 9000 V.

D . 12000 V.

= V2
:

" ' *

^'
I2

Ni

I,
'

' Ni

= 1 0 0 . 1 = 10(A)
10
^3

[Pi = P2 => U , I i = P2 => U,.10 = 100.10^

^
U , = 10^ ( V )

day c) A .• A U = I i R = U -

lendi/dng

U = 11000(V)
'

"

n ' = 2n => Cong hudng
2ZL = = >

R

^5

f CO cuon so cap noi vcVi dau ra cua may tang the A . D i e n t r o tong --c^ng cua day

Dien dp dm

=>E = N/2^R^+(10-ZC) ( V )

r = — =

27:

*1,55A

au 97: C u o n so cap eua may tang the A dutic ncYi vcVi nguon va B la may ha the

MdyB:

V2

2E

27t^

cot + 3 ;

A.llOOOV.

N27cfOo

^ 2

^

cot =

dan

Z L = roL = 1 0 Q ; Z c = — = — * — ^ I = ,
^
=
o)C
257iC
JR2+(ZL-ZC)'
=

2

ri> Z r - 40Q
^

10.100 = U - lO"*
,

,

,

au 98: M o t day dan d u o n g k i n h 0,5 m m d u n g l a m eau chi dien xoay chieu.
>

2.10 = ^

•

•

13 = 6cos cot--

f = - ^ = 12,5=>(o = 27:f = 257t
60

E

> '.li'r;

.

i i = 6cos((i)t) = 372 va dang tang

1

A.

C = — ^

257T.80

2.V2VR2+(10-Zcf
^
^
5^
^
= 4 r ^ R = 30Q

Day c h i u dupe c u o n g dp d o n g dien hieu d u n g toi da la 3 A . Bie't nhiet

^

l u p n g to.i ra mdi t r u o n g x u n g quanh t i le thuan v o i d i e n tieh mat ngoai eua

=-.lO^^F
7C

day. Ne'u day eo d u o n g k i n h 2 m m t h i day m o i ehju dupe c u o n g d p d o n g

dien hieu d u n g toi da la
^

A . 32 A .

R

Zau 96: D o n g co k h o n g d o n g bp 3 pha mac h i n h sao, k h i d o n g eo hoat d o n g

B. 1 2 A .
,. - ^

d i e n 6 cac cuon day 1, 2 va 3 Ian l u p t la 0, 27r/3 va -27r/3. Vao t h o i d i e m

Tidj

Q =

k7ld2i =

24 A .

D. 8 A.

Huong dan

Q = k7rd,URiI?t = p ^ I ? t

b i n h t h u o n g a d i e n ap 200 V thi eong sua't tieu thu cua d o n g co bang
1620 72 VV va he so eong sua't la 0,9 eho m o i pha. Pha ban dciu eua d o n g

,

R2l2t = p A - l 2 t
nd2

ill
41?

, , ,;
I9=ll

d2

Ui;

1,5

1,5

= 3

= 24A

10,5;
331


Cty Tisnii nirv nx'vii
Cau 99: Neu toe d o quay cua roto tang them 1 v6ng/s thi tan so ciia d o n g dien d o

II = 4 0 0 ( 0 , 5 ) 2 ^ + 400(0,1)2 : ! = 0 , 4 2 5 V

may phat ra tang t u 60 H z den 70 H z va suat dien dong hieu d u n g d o may
phat ra thay d o i 40 V so voi ban dau. H o i neu tiep tuc tang toe do cua roto

Cau 102: M o t may bien ap l i t u o n g luc m o i san xuat c6 ! i so d i e n ap hieu d u n g

them 1 v6ng/s nua thi suat dien dong hieu d u n g do may phat ra la bao nhieu?

giOa cuon so cap va t h u cap bang 2. Sau m o t t h o i gian s u d u n g d o l o p each

A . 320 V .

d i e n kern nen c6 x v o n g day cuon t h u cap bj noi tat, v i vay t i so d i e n ap hieu

B. 240 V.

C. 280 V .
Hu&iig

f, = n p = 60Hz
f = np:

D.400 V.

dan

d u n g giua cuon so cap va t h u cap b3ng 2,5. De xac d j n h x n g u o i ta quan
them vao cuon t h u cap 135 v o n g day t h i thay t i so d i e n ap hieu d u n g cuon

fn = 6

1

f2 = ( n + l ) p = 7 0 H z J ' ^ | p = 10

so cap va t h u cap bang 1,6. So v o n g day bj noi tat la

f3 = ( n + 2 ) p = 80Hz

A. X = 50 v o n g .

N2nf
V2"

V2

0

_N27i(f2-fi)Oo

t.2

- c.)

^

^ N27rf3

-

10.N27tOo

^/2

sl2

= 40

V2

C a u 100: Can truyen tai cong suat dien va dien ap nhat d j n h t u nha rnay den noi
tieu thu bang day dan c6 d u o n g k i n h day la d. Thay the day t r u y e n tai dien
b^ng m o t day khac cung chat lieu n h u n g c6 d u o n g k i n h 2d t h i hieu suat tai
dien la 9 1 % . H o i k h i thay the day truyen tai bang loai day cijng chat lieu
nhu-ng CO d u a n g k i n h 3d thi hieu sua't truyen tai dien k l i i d o la bao nhieu?
A . 96%.

B.94%.
y

R=pl=p
S
H =

C.92%.
Huaiig

'
,
n{0,5df

P-AP

1

H,

U^cos^cp

' 0001T,
R

=1-.
= 91% x 4
U^cos> 4

H , = l -

R

D . 95%.

dan

P

R

U^cos^cp 9

x9

^ 9 H 2 - 4 H i = 5 = ^ H 2 =0,96
dien ap hieu d u n g k h o n g d o i U i = 400 V . T h u cap g o m 2 c u o n N2 = 50 vong,
N 3 = 100 v o n g . Giira 2 dau N2 d a u v o i m o t dien t r o R = 40 Q, giOa 2 d a u N i
d a u v o i m o t d i e n t r o R' = 10 Q. Coi d o n g dien va d i e n ap l u o n cung pha.
C u o n g d o d o n g d i e n hieu d u n g chgy t r o n g cuon so cap la
B. 0,450 A .

C. 0,425 A .

Huong
Psc=Ptc=^UiIl=U2l2+U3l3

U2_N2
U2

U3
R

t

N, =

U2

1_

R'

u

N "

N , - x = - ^- N ,
2,5
+ 135 = - - N ,
1,6""'

N2-x

f

D . x = 40 v o n g .
;jlJ

'!

Nj

=10x

N2

=5x

• 5X
•

r-f

'1

)

- i l l ' n'*if"i 1 f ' f . u r ! ' . ( I >

fl"; • - I ' X j C / i

.'"1

J(i

1
+ 135 =
lOx r:i>
'
1
,
6

- X

X

= 60

may ha the'H t u o n g c6 t i so v o n g day bang 2. Dien ap hieu d u n g giua hai cue

cua m o t t r a m phat dien can tang len bao nhieu Ian de g i a m cong suat hao p h i
tren d u o n g day tai dien 100 Ian, v o i dieu kien cong suat truyen den tai tieu
thu k h o n g doi? Biet rang khi chua tang dien ap, do giam dien the tren d u o n g
day tcii dien bang 15% dien ap hieu d u n g tren tai tieu t h u . Coi c u o n g do dong
D . 9,3 Ian.
dien
t r oIan.
n g mach l u o nB. cimg
pha v o i dien C.
ap 8,7
datIan.
len d u o n g day.
A
. 10,0
7,5 Ian.
Huong
tren di/dng day:

dan
, ,

A U = 0,15U2 = 0 , 0 7 5 U i = 0 , 0 7 5 ( U - A U ) = : > A U = ^ U
+C6ng suat hao phi

tre n diidng

day:

AP = I^R = A U I = — U I

+ Cong suat nhan diCdc cuoi dUdng day : P j _ thu
D . 0,015 A .
phi

giam 100 Idn (AF' =

AP

dm
40
""^ 43

3
~ 43
^^^^^-UI)

thicUcfng

do dong dien giam 10 Idn (f = 0, l.I) va cong suat nhan dUdc cuoi
= 0,05
0,1

!l

au 103: T r o n g qua t r i n h truyen tai dien nang d i xa, 6 cuoi d u o n g day d u n g

I- De cong suat hao

dan

C. X = 80 v o n g .
.f! r

N2 =-'-Ni

+Do giam the

C a u 101: M o t may bien ap ly t u o n g , cuon so cap N i = 1000 v o n g d u g c n o i vao

A . 0,150 A .

B. X = 60 v o n g .

Huang dan

10.N271O
^-320(V)

72

332

HhangVlft

day luc nay la:

P',i,„_„u, = U T - A P ' = U ' . 0 , 1 I -

I''tieu tnii=''tioii thu

. -U ' . 0 , 1 I -

3 -UI = ^ U I
43
4300

3

-UI
4300

dudng

+.1-

• U'*9,3U

.,8

333


Cau 104: C u o n so cap cua mot may bie'n ap co Ni = 1000 v o n g va r u o n t h u c^'p

C a u 107: M a c h RLC mSc vao may phat dien xoay chieu. K h i toe do quay cua

ccS N2 = 2000 v o n g . H i e i i dien tiic'iiieu d u n g cua cuon so cap la tJi = 110 V vj,

roto la n (vong/phut) t h i cong sua't la P he so cong sua't 0,5^2 . K h i toe do

. cuon t i i u cap de ha la U2 = 216 V. T i so giua dien tro thiuan R va cam khar,

quay cua roto la 2n (vong/phut) t h i cong sua't la 4 P . hoi K h i toe do quay cua

Zi cua cuon so cap la
B.0,15.

,,};A.0,19.

C. 0,1.

x r i n j i : y.'

Huong
=

• no^

roto Ih n 42

dan

= 108(V)

216.-

2000

D.

;,!;iV/V/

1,2.

Z,

U, ,

108

^1.1

U K =^20,88(V)

-

J

D. 4P.

c. 9 P .

Huong

•Mil) uMr, •„!

dan

V2

R

coscp =

f = n p = > fo = 2Ki

=108^

'

B_p73;-;i!e

A. 3 P .

r:.i ,,,,,,,

E =
[

(vong/phut) thi cong sua't bang bao nhieu?

.(Z,.-Zc)'=R'

R'+(ZL-zcr

N2Trfcl)o

~V2

E^R

p = rR =

^. .•'f-;*';''

C a u 105: Cho mach dien xoay chieu R, L, C mac no'i tiep theo t h u tir do (cu6n

R^ + ( Z L - Z c f

2Z, -•

cam thuan). D i e n d u n g C co the tiiay d o i dugc. D i e u c h i n h C de d i e n ap 0
R2

hai dau C la ion nha't. K h i dcS dien ap hieu d u n g 6 hai dau dien t r o R 1^
1 0 0 V2

V . K h i d i e n ap tuc thai 6 hai dau doan mach la 100^y2 V t h i dien ap

tiVc t h o i giua hai dau doan mach chiia dien t r a va cuon cam la

F ^ ^ a

-WOjZv.

R ' + ( Z U - Z C ) '

P

R^

T i n h t r i hieu d u n g cua dien ap 6 hai dau doan mach A B .
A . 5 0 V.

B. 6 1 5 V.

C. 2 0 0 V.

f-iooVe'

2

1

UKLV2J

U

1

1

(hai day iai d i c M i bj noi tat boi mot vat c o dien tro co gia trj xac d j n h

= 1

r

• U = 200V

R). De

tieu t h u , sau d o d u n g nguon dien k h o n g d o i 1 2 V , d i e n t r o t r o n g k h o n g
d a n g ke, noi vao hai dau cua hai day tai d i e n tai M . K h i hai dau day tai N
de h o t h i c u o n g d o d o n g dien qua nguon la 0 , 4 0 A , con k h i hai dau day tai

V thi san ra cong sua't co hpc 178 W . Biet he so

C u o n g d o d o n g hieu d u n g chay qua d o n g co la
B. 5 , 3 7 5 A.

,,,

C I A .

Huong dan
UIcoscp = P ' + I ^ R =^ 220.1.0,9 = 178 + 1^20

D. 17,3

N d u g c noi tat b o i m o t doan day co dien tro k h o n g dang ke t h i c u o n g do
d o n g dien qua n g u o n la 0 , 4 2 A . Khoang each M Q la
A. 135 k m .

B. 1 6 7 k m .

C. 4 5 k m .

D. 90 km.

'

=> Dap an C

A.

\

u.,

, , M . j y rv^UK

"I

I = 8 , 9 ( A ) => P(„ = I 2 R = 5,375^32 = 1584,2W > 178W

334

42)

le t h u a n v o i chieu dai cua day). Do su co, d u o n g da / bi ro d i e n tai d i e m Q

cong sua't cua d o n g co la 0,9 va cong sua't hao p h i nho h o n cong sua't co hpc

I = 1(A)

y

day CO d i e n t r o tong cong 8 0 Q (coi day tai dien la d o n g cha't, r o dien tro ti

•><.

C a u 106: M o t d o n g co dien xoay chieu co dien t r a day cuon la 20 Q, mach dien

A.

72Z,

+

j =4

Zc

dien nang d u g c truyen tai den noi tieu thu N , each M 1 8 0 k m . Biet d i r o n g

IOOI2

A . 0,25

R 2 + ( Z , - Z C ) '

xac d j n h v j t r i Q , trirdc tien n g u o i ta ngat d u o n g day k h o i may phat va tai

1

CO dien r.p hieu d u n g 220

!>••
^

-= 2
R2

I

rioo72f
UV2 J

=^ZC=2R;ZL=R

D. 300 V. ^

luV2
1

1

IURLV2, + I

-

Cau 108 ( D H 2012): T i r m o t t r a m phat dien xoay chieu m o t pha dat tai v j t r i M ,

u KL
C max < ^ U R L

2Z,

+

= R2

'
i'K

'
>•)

1
'I

1

'

,
'

1,
'

* '

I

»

'AM
( (

jiiy

!4>i

(J,)^;'.

/ \

I

*

',

iifi
<

(1 - / I 1 1 1 , ' '

ill

,

. ,

^

,

I,

.

^
,

t

A

!

• ,
331