Bổ trợ kiến thức luyện thi đại học môn vật lý phần dòng điện xoay chiều p1

A.

^

^

M

.B

X

u ,R O

M

Up

3

u ,CO:

= 60*

A

Huong

•E

dan

O

K h i mac n o i tiep cuon day v o i doan mach X: U^^ = IZ^^ = 3.50 = 150 ( V ) .
,

-n

Ti

Ve gian d o vec t o : s^x =

.^•(ttU'jII'f'rHiO i\\

U

=j. 250^ = 150^ +

B

It

=

Ucd L U x

U = U

u

2
6
3
U x = 2 0 0 ( V ) =4>Px = U x I c o s 9 x = 3 0 0 ( W )

C h o n B.

V i du 12: H a i c u o n d a y c6 d i e n t r o t h u a n v a d o t u c a m I a n l u g t la R i , L i v a R2,

V i du 10: M o t cuon day c6 d i e n t r o thuan R = 100 N/S Q va d o t u cam L = 3/^

L2 d u o c m a c n o i t i e p n h a u v a m a c v a o m o t d i e n a p x o a y c h i e u c6 g i a t r j

(H). Mac n o i tiep v o i cuon day m o t doan mach X c6 t o n g t r o Zx r o i mac vao

h i e u d u n g U . G o i U i v a U2 la d i e n a p h i e u d u n g t u o n g tVng gii>a h a i d a u

hieu dien t h e x o a y chieu c6 hieu dien t h e h i e u d u n g la 120 V, tan so 50 Hz

c u o n ( R i , L i ) v a (R2, L2). D i e u k i e n d e U = U i + U2 la

t h i thay d o n g d i e n qua mach nhanh pha 30" so v o i hieu dien the hai dau

A . Li/Ri = L2/R2.

B. Li/R2 = L2/Ri.

doan mach X va c6 gia trj h i e u . d u n g 0,3 A . Cong suat tieu t h y tren doan
mach X la bao nhieu?
A. 30W.

•

,

•At

„j..

C.9V3W.

B.27W.

Huang dan
Z,rf =

• -

W.

•

R

dan

U = U , + U j => (Pi = (P2 => tancpi = tancp.

R,

Li

L,

Ri

R,

• Chon A .

v o i n h a u . Doan mach A M g o m dien tro R i mac noi tiep v o i tu dien c6 dien

=^U,^ =IZcd = 6 0 7 3 ( V )
=

D . L1.L2 = 2R1.R2.

V i dv 13: M o t doan mach A B g o m hai doan mach nho A M va M B mac n o i tiep

+ Zl = 200^/3 (n)

tanked = - r

Huong

:r

D . 18x/3

C. L1.L2 = R1.R2.

d u n g C i . Doan mach M B g o m dien t r o R2 mac noi tiep v o i t u dien c6 dien

X

M

d u n g C2. K h i dat vao hai dau A , B m o t dien ap xoay chieu c6 gia t r i hieu

M

^

d u n g U t h i dien ap hieu d u n g gii>a hai dau doan mach A M la U i , con dien
ap hieu d u n g g i u a hai dau doan mach M B la U2. N e u U = U i + U2 t h i he thuc

Ve gian d o vec to cho doan A M truoc, roi ve

60V3/

A"

tiep doan M B tre pha h o n d o n g dien la 30".
Ta nhan thay A A M B v u o n g tai M nen:

lien he nao sau day la dung?
A.CiRi=C2R2.

120 V

B . C i R 2 = C2Ri.

D. CiC2RiR2= 1.

C.CiC2=RiR2.

Huong dan

Ux = M B = ^120^ - (60>y3)' = 6 0 ( V )
Px = U x l c o s i p , = 60.0,3.cos30" = 9^/3(W) =^ Chon C.

U = U | + UT =>(P| =

Binh luan: Sau khi fun dime MB sc tun dime ;^6c a roi gdc (p va P = UJcoscp.
V i du 11: C u o n day c6 dien t r o thuan R va do t u
cam

L

mac

vao

dien

ap

xoay

chieu

u

=
A*

250N/2 coslOOTct (V) thi d o n g dien qua cuon day
CO gia t r i hieu d u n g la 5 A va lech pha so v o i

d u n g qua mach la 3 A va dien ap giira hai dau
cuon day v u o n g pha v o l dien ap gii>a hai dau X.
Cong suat tieu t h u tren doan mach X la
A . 200W.
C. 2OOV2 W .
120

. B. 3 0 0 W .
.

D . 300N/3

W.

/
^

':30^^'""

-

Khi lien quan den gid tri tue thai cm u va i thi truac tien phdi vie't hieu thuc ciia

30'

cuon day v o i doan mach X t h i c u o n g do hieu

.

a. Tinh gin tri tux thai dim vao bicu thi'rc

M

dien ap hai dau doan mach la 7t/6. Mac noi tiep

R , C , = R 2^2
,C

Chon A .
G i a tri tu'c thoi

M

coC,

=> tancpi = tanq)2

cac dai luang da truac.

>B

^

V i du 1: Bieu thuc cua dien ap giua hai dau doan mach la u = U()cos(1007it +
n/4) (V). Biet d i e n ap nay som pha n/3 d o i v o i c u o n g do d o n g dien trong
mach va c6 gia t r i hi^u d u n g la 2 A . C u o n g do d o n g d i ^ n t r o n g mach k h i
t = 1/300 (s) la
A . 2 V2 ( A ) .

B. 1 ( A ) .

C. V3 ( A ) . ,

D.

2 (A).
121


Huang
i = 2V2,cos

1007tt + -

u = U()Cos

4.

dan

Giti tri ti'tc thai lien qiian dm xu hitang tang giiim

^ po'i v a i bai loan d a n g nay thong t h u o n g lam nhu- sau:

lOOTlt--

12

*

QOOTI

i = IQCOS

4

cos

(1/300)

3

300

71 ^

*

= 2(A)=^ChonD.

12

0,4/7i

( H ) , va m o t t u dien co dien d u n g

l/(87t) (mF). D o n g dien t r o n g mach co bieu thuc: i = I(icos(1007rt - 2n/3) ( A ) .
1 Tai t h o i d i e m ban dau dien ap g i i i a hai d a u doan mach co gia t r i -40 V2
i;,;Tinhl0.

; , j

A . V6 ( A ) .

• '

B. Jh5

(A).

•3

C.

Huang

V2

> i j,

(A).

(V).

>;'^-?'l
D.

Vs

(A) .

loCOS

80

'KI

71

=7i^(A)=>ChonB.

'

hai dau doan mach no'i tie'p g o m tu dien co dien d u n g C = 0,2/n (mF) va
dien t r o thuan R = 50 Q. H o i sau t h o i d i e m ban dau (t = 0) m o t khoang t h o i
gian ngan nhat bang bao nhieu t h : dien tich tren tu dien bang 0?
B. 750 ((.is).

C. 2,5 (ms).

Huong dan

i

,

,
j

• = 50Q
wC

(V),

>'', ••<•''

7t

• VKI,

= -

4

= 50V2 cos 0)t + •

•

(V)

cot- — = - —=> wt = —. Thay gia t r i nay vao U K I , ta duoc:
2

4
4
•'Rl.

= 50 N/2 cos cot + — = 50V2 cos

r

=0

,4

,

i»

'i

Chon A.

4J

V i d y 2: D a t vao hai dau doan mach g o m cuon day co dien t r o thuan R va cam

hieu d u n g giua hai dau day va giCra hai ban tu dien Ian l u o t la Ud = 50 (V)
va Uc = 70 ( V ) . K h i dien ap tufc t h o i giua hai ban t u d i e n co gia t r i uc = 35 >/2
A, -25 V6 ( V ) .

= -1

B. -50

V2 (V).

(D =

4
7t/4 ma uc tre h o n i la n/l nen uc tre pha h a n u la 7r/4.

D o do:

lOOjtt

COS

4
lOOTit - " - =
4 2

1
2

t = 12,5.10"^^ (s) => Chon D .
^ '

C. 50 (V).

.

D . 50 ^/2 ( V ) .

Huang dan
tan(p,^L=-Tr
R

=

,,

^ = ' ^ K L = ?

571

2J

lOOTit - ^ - ^ = - | + 2 7 i r ^ t = 22,5.10"'^ (s)
122

-'

>/2

(V) va d a n g g i a m thi dien ap tuc thai giiJa hai dau cupn day co gia t r i la

R
D o u tre pha h o n i la

Uc = 0:

=1

R

D . 50

khang Z L = R^/3 mac no'i tiep v o i tu dien C m o t dien ap xoay chieu, dien ap

D . 12,5 (ms).

1

= UQ(2

C. 50 (V).

Theo bai ra uc = 70 V va dang tang nen nam nua d u o i V T L G

V i d u 3: D a t dien ap xoay chieu u = U()cos(1007ct — n/2) (V) (t do bang giay) vao

UQ

V2 ( V ) .

Ne'u bieu thuc d o n g dien la i = I(, coscot

v3

-Zc

B. -50

Huong dan

cos(1007it-;t)

U(o) = Io-y=cos(1007C.O-7r) = - 4 o V 2 ( V ) = > I „

tancp =

va Uc = 70 (V). K h i dien ap tiVc thoi giira hai ban tu d i ^ n co gia t r i uc = 70 (V)

80

(p =

80

Zc =

khang Zi. = R mac noi tiep vcVi tu dien C m o t d i ^ n ap xoay chieu, d i ^ n ap

U e =70V2cos c o t - - l ( V )

1 0 0 n t - y ^ + (p = 1,-

A . 25 ().is).

d o a n mach g o m cuon day co d i e n t r o thuan R va cam

hieu d u n g giua hai dau day va gifra hai ban tu dien Ian l u p t la Ud = 50 (V)

lOOnt-3 .

U = IgZCOS

JJV ; ; i

Thay gia trj cua cot vao bieu thuc can t i n h .

A. 0.

R
1 =

*

V i d y 1=

tan tpiu. =
tan

i«

va dang tang t h i dien ap tiVc t h o i g i i i a hai dau cuon day co gia t r i la

,

= 80(Q)
wC

'

Di.ra vao V T L G va xu h u o n g tang g i a m de xac d j n h (cot + cp) (tang t h i n a m

dan
3"

Z, =(oL = 4 0 ( 0 ) , Z e =

'

nua d u a l V T L G , con giam t h i 6 n i i a tren);

V i d u 2: C l i o m o t mach dien k h o n g phan nhanh g o m dien t r o thuan 40/^/3 Q,
cuon day t l i u a n cam co do t u cam

Viet b i e u thuc cac d a i l i r o n g co lien quan;

UQ =:70>/2COS c o t - ^
' = ly COSCOt

ui^L

-

->COt

2,
50\/2

COS

©t + —

3

= 50 72 cos

(5n
6

= +— :

2

cot =

—

3

+ — = -25N/6(V)
3)

;;=:> Chon A .
123


c.

Cty TtWit nrv

Cgni^ cac ^in tri ti't'c thai (ton^ Iiap aic dao dong dicu hoa)

Ta can phan biet gia trj cue dal (Uo, lo l u o n d u a n g ) , gia tri hi^u d u n g ( U , I

=

U„ = J u , ^ | + U , i 2 + 2 U „ , U „ 2 C o s ( c p 2 - c p , ) = W-

+ ( U L - U c ) ' ; u = u,, + u^ + uc

2c
V i d u 1 : M a c h dien xoay chieu k h o n g phan nhanh g o m dien t r a thuan R, cu6n

U=-Iil = 60V2(V)
V2

+ 3.60^ + 2.60.60^3 cos^ = 120(V)

r^ChonB.

cam t h u a n co cam k h a n g Zi, va tu dien c6 d u n g khang Zc = 3 Z i . Vao mot

V i d u 4: Cho doan mach xoay chieu AB g o m hai doan mach A N va N B mac noi

thoi d i e m k h i hi^u dien the t i e n dien t r o va tren tu di?n c6 gia t r i tuc thoi

tiep. Dat vao hai d a u doan mach A B m o t dien ap xoay chieu o n d j n h U A U =

t u o n g u n g la 40 V va 30 V t h i h i ^ u dien thegiCra hai d a u mach dien la

200N/2 cos(1007tt + 7t/3) ( V ) , k h i d o dien ap tuc t h o i giCra hai d a u doan mach

A . 55 V.

N B la U N B = 50N/2 sin(1007it + 57x/6) ( V ) . Bieu thuc d i ^ n ap tuc t h o i giua hai

B. 60 V.

- ^•'-'.•^ C. 50 V.

^'"'•

D . 25 V.

dau d o a n mach A N la
Thay u,^ = 4 0 ( V ) ,

= 30(V) va u, = - u ^ — = - 1 0 ( V ) vao he thiVc:

u = U R + U | + U c => u = 40 + (-10) + 30 = 60(V) => Chon B.

f^o-,

cam t h u a n co cam khang Zi va tu dien c6 d u n g k h a n g Zc = 3 Z L . Vao mot

A . 20 V.

B. 60 V.

C. 50 V.

B. U A N = 150 V2 cos(1207xt + 7i/3) ( V ) .
D . U A N = 250N/2 cos(1007:t + 7t/3) ( V ) .

Huang dan
Uf^B =50^2 sin 1007Ct +

AB -

D . lOOV.

>

Hucmgdan
U L

uc

=30

i

.ivu

=-3UL

o

=-90

A . 100>/2V.

heat la: UAB = Uoicosicot + cpi) (V), unc = Uo2cos(cot + (pi) (V) thi bic'u tlii'ec dicn lip
trcn doan AC la UAC - UAU + UBC.

tan(p =

UQI'^'"^!

doan mach do. Bieu thuc dien ap tuc thoi tren cac doan mach A B , B C Ian
UBC

= 6 0 c o s ( ] O O K t + 27t/3) ( V ) . Dien

ap hieu d u n g giira hai d i e m A , C la
B. 60N/2V.

D.200V2V.

Hiiongdan
.

-

v

=coscot(Ai coscp,

l

.

-

'

+A2Cos(p2

V
•

•

:

+ . . . ) - s i n c o t ( A i sincp, + A j sintpj + - )

u = cosl007tt 40074. cos - + 400 cos — + 500 cos T:
4
2

= -100cosl007tt(V) = 100cos(1007ct + 7 t ) ( V ) => Chon B.

COS92

= 60cos(100Kt + n/6) ( V ) ,

C.200V.

-sinlOOnt 40074. sin - + 400 sin — + 500 sin n
4
2

V i d u 3: Cho doan mach xoay chieu k h o n g phan nhanh. A , B , C la ba d i e m tren

A . 128 V .

.U...,.
U2 + U 3

+ U ( ) 2 ^'"'P2

•(13 rrf

UAii

Cdchl:
u = u, +

•2U„,Uo2COs((p2-(p,)''^*'^'"'

U()| cos(pi + U()2

l u o t la:

B.IOOV.

nf.>; . u * i

khong phan nhanh va bic'u thi'ec dicn ap tuc thai trcn cdc doan mach AB, BC livi

Cdch 1:

n/2)

(V), U 3 = 500cos(100nt + n) (V). Xac d i n h dien ap cue d a i giOa h a i d i e m A, D .

Chti y: NcU A, B, C tlwo di'ini^ ihi't tir la ba diciu trcn doan mach dicn xoay ch ICII

02

3j

V i d u 5: Cho doan mach xoay chieu k h o n g phan nhanh. A , B, C va D la 4 d i e m

I-;

I

1007tt+- ( V ) =^ChonC.

va C D Ian l u o t la: u i = 400 V2 cos(1007tt + n/4) (V), U2 = 400cos(1007it U K = 4 0 - ( - 9 0 ) - 3 0 = 100(V)

=> Chon D.

• • fit

= 15072cos

U N15

tren doan mach do. Bieu thuc dien ap tuc t h o i tren cac d o a n mach A B , BC

u = 40
U - Ui - Ur

= 50V2 cos 1007tt + - ( V )
3

6

,,
+ to-

-> 'J

C. U A N = 150N/2 cos(1007it + 71/3) ( V ) .

t h o i d i e m dien ap hai dau doan mach va tren cuon cam co gia t r j tuc thoi
t u o n g i r n g la 40 V va 30 V t h i dien ap tren R la

t i ^-^^^

A . U A N = 150 72 sin(1007it + 7i/3) ( V ) .

V i d u 2: M a c h dien xoay chieu k h o n g phan nhanh g o m d i ^ n t r o thuan R, cuon

124

KhangVlft

Huong dan

l u o n d u o n g ) va gia trj tuc thoi (u, i c6 the am, d u o n g , bSng 0):
U5 = u,^K + ( U , „ - U o c f ;

D VVH

Cdch 2: u = 4 0 0 7 2 Z - + 4 0 0 Z - - + SOOZjt = -100

^ .{nlutii

'ith iftrf o mdl

=^u = -100cosl007rt(V) = 100cos(100;tt + 7 t ) ( V ) . '

nif- ;

3^,;.
' U ', ^

•^^

=>ChonB.
V i d u 6: Dat d i ? n ap u = Uocos(1007it + 77i/12) (V) vao hai d a u d o a n mach A M B
t h i bieu thuc d i e n ap g i i i a hai dau cac doan mach A M va M B Ian l u o t la

C . 120 V .

D. 155 V .

3.,

U A M = 100cos(1007it + 7t/4) (V) va U M B = Uoicos(1007tt + 37t/4) ( V ) . Gia t r j Uo va
Uoi Ian l u g t la
125


try KIS„ th^c V^t II LTBtl

tren kcnh

VTV2. t^p 2 - c„u l u n B u „

A . IOOV2 V v a l O O V .

B. ^00^/3 V v a 2 0 0 V.

C. TOO V va 100 V2 V.

:

u =UK

D. 200 V v a l O O V s V,

Huang

.

j d u n g v o i t.

D e t i n h cac bien d p con lai t h i ta c6 the chon cac t dac biet.

U() cos

771)

U

12

> Chon D.

+ Ujo cos

U„=200(V)

. 4 ^ 4

/ 7C 7t

U

^4,

+ U]() cos

n

U

37t)
4

,

• Ujo =100,73 ( V )

1/: N(?M si'c di/n^v^ f^fl«/i f/zflo may tinli ton^ hap dao dong thi c6 the dim
,. phuang phdp thu tumig doi nhanh.
•"'> •

. • .1.1

U

T
H a i t h o i d i e m v u o n g pha t2 - t [ = (2k +1) — =>
y

H a i d ^ i lug-ng x, y v u o n g p h a

V ymax

IX-

-&i.o:>n

d a u d i ^ n t r o R la UK thi
B. UOR = uucsincp + URCOScp.

C. (ui,c)2 + (uK/tan(p)2 = (UOK)^.

D . (UR)^ + (ui.c/tancp)^ = (UOR)2.

tancp = UoLC
U,OR

^ +

IULV2J

i'

=1

=>ChonD.

'„ , •

.

' -

N2,
'-

tancp

=1

'

'orif oiiV' SI f\,

= UgR
.V

• • ' ^ ' ;^

,

V i d u 3: D o a n mach xoay chieu A B noi tiep gom dien t r o t h u a n R, t u d i e n C va
cuon cam t h u a n L. Goi ui., uc, UR Ian l u p t la d i e n ap tuc t h a i tren L, C va R.
Tai t h a i d i e m t i Ccic gia t n tuc t h a i u i (ti) = - 2 0 V2 V, uc(ti) = 10 N/2 V, UR(ti) =

2

+

.Uc^/2J

=1

hai d a u dien t r o v a cuon cam deu la -100N/6 V. T i n h g i a t r j h i | u d y n g cu3

0 V. T a i t h o i d i e m t2 cac gia trj tuc thai ui.(t2) = -10 72
UR(t2) = 15 72
A. 50 V.

:

t = ti

V, uc(t2) =

5-j2V,

V . T i n h bien dp dien ap dat vao hai d a u mach AB?
,

.,

C. 30 72 V.

B. 20 V.

Z::;^0mi4^: .,,..v •„,..
UK=O

-

Huangdan

. '

- v -

^''r^r:'-^'-':-

.

D . 20

72

V.

M,.-*""-::

;;^|uoL=2o72(v)

U L = -UoL = -2072(V);uc = Uoc = 1 0 7 2 ( V ) [ U o c -1072(V)

d i e n ap 6 h a i d a u d o a n mach A B .
C. 300

V . ,

\U[:jT)

D.200 V.

=

^=^UL-20073(V)

2

t = t o =>

U,OR

/

+

U[

\2

= !=>

ri572^

I

2

UOR,

+

r-io72] = l = > U o R =1076(V)
[2072 J

Uo = V U o R + ( U o L - U o 2 ) ' = 2 0 7 2 ( y )
=>chonD.

26

UQLC = UoK tancp
\2

dien ap tiVc t h a i a hai dau doan mach la 100^2 V t h i dien ap tiic t h o i giiJ'''

^'^[-J^j

dan

."L =-UoL,Uc =+Uoc
,2

u i e n xoay chieu K, L, C mac no'i tiep theo t h u t u d o (cupn

[ U L ^ J

Huong

" U L = U ( ) L A 1 C =-U()c

cam thuan). K h i d o d i e n ap hieu d u n g 6 hai d a u d i e n t r o R la 200 V. Khi

UR72J

, „

Chu y: Vi UR vuong pha voi 111. va uc ncn a mot thai diem nao do UR = 0 thi

= 1.

(IUR72J

B. 615 V.

•.'•'^

A. UOR = ULccoscp + URsincp.

U,OLC J

.2"
+ X2 = A^

C h a n g h?n UK v u o n g pha v o i IJL y a uc nen: <

A. 500 V.

=1

tuc t h a i 6 hai d a u doan mach chua L C la ULC v a d i e n ap tuc t h o i gi&a hai

.6

2

ff

v-iiu iiicicn

UcV2

^2

tuc t h a i q u a mach va bien d o dien ap tren R l a UOR. O t h o i d i e m t, d i e n ap

: i :!U

d. Dm vao dau hieii vuong pha detinh cac dai hnmg

.

\2

"i'-' ' •

'T'-

, .

C/iii

*

100(>y2+2x/6)

-IOOV3I

=> Uc = 200(1 + 2 V 3 ) ( V ) => U = 7 U R + ( U L - U c f = 615(V)
=>ChonB.

, ,v/}'(£\ •.•MK)rteo:> SVOSf

= 100 cos

= 100(>/2 + 2^/6)(V)

tuc t h a i gii>a hai d a u doan mach lech pha la cp so v a i c u a n g d p d o n g d i e n

a./:Chon t = - - ( s ) t h i
^7t

= 1=>

=>UC

Vl^t

V i d y 2: D o a n mach x o a y c h i e u theo d u n g t h u t u R, L, C mac n o l tiep. D i e n ap

(s) t h i
400
n 7n
= 100 cos
4 "^12;

,.,f:l

>200cos

=>100>/2 = - 1 0 0 V 6 - 1 0 0 V 6 + U C

uc'
UrV2

URN/2

^,

+ Ui„ cos I lOOnt + ~

Uo cosf lOOnt + ^12 1 = lOOcosf lOOnt +

Chon t =

+ U L +UC

datt

P h i r o n g t r i n h u = UAM + UMB hay

'

Cty TISIIH MTV D VVH Khang

{ •

••^'"''^
127


Ba trp hicn thiic V^t li L TON tren kenli VTV2. tap 2 - Cliu V^n Bl&n
V i d u 4: D a t d i e n a p 5 0 V2

V - 50 H z v a o h a i d a u d o a n m a c h A B g o m h a i d o a n

A M v a M B m a c no'i tie'p. D i e n a p t r e n d o a n A M v a d o a n M B l e c h p h a n h a u
71/2. V a o t h o i d i e m to, d i e n a p t r e n A M b a n g 64 V t h i d i e n a p t r e n M B l a 3 6 V .
D i e n a p h i e u d u n g t r e n d o a n A M C O t h e la
A. 40>/^V.

^

B.50V.
Huang
" A M

n

I
" A M

U

" M B

" M B

U Q A M

* f^^jUoAM

J

OAM

= 1

d u

=80(V)=^UAM

UOAM;

=4072(V)

V

50/^/3 Q . V a o t h o i d i e m to, d i e n a p t r e n A N b a n g 80\/3

B . 150 V .

Y

= ^

-z

j

=^ ^ A N

ZAN =

^ " 7J

^

••MB
J

V'QZMB

= 1 =>
}

B.50V3V.

Z,

-7c

r

R

C.40V2V.

Huang

- Z c f

+ (ZL

f

36

^

2

^

64

^

V '-'(1MB J

i =

IQ COS

" A N

-Zr

-1

R

>/3

" ^ " A N - L U M B

+^1=

= 60(V)=>U^M

UoMB

=SO(V)

-I 0 0

=

— I n

= 80>/3

rV

= l=^Io =^y3(A)

100

= V 3 . ^ ^ ^ = 50V7

= -^;Z,3 =;

L cos

cotCOS

7t

= 6 0 = > IQ s i n

IT
Wt + —

3;

cot + —

3

=30^/2(V)

•Chon D.

ditMi

^

a p g i u a h a i d a u d o a n m a c h M B c 6 the la
A . U A M = 50cos(cot - 571/12) ( V ) . ^

B. U A M = 50cos(a)t - 7i/4) ( V ) .

C. U A M = 200cos((ot - 7i/4) ( V ) .

D . U A M = 200cos(a)t - 57t/12) ( V ) .

= ^ ( Q )

Hii&ngddn

= - ' ' = ^ " A M

^ " M B =

30

+

^OAM

V L'uMB )

lo = -73

U

0MB

+

= 50(V)
=

V '-'oMB

. '-'oAM J

U,l\

40N/3 1

" M B

" A M

.r»(5< •

Z,, - Z c

M B„ = 100

= 0,8^/3

= 0,6^3

C

a p g i u a h a i d a u m a c h A M la 30 V . B i e u t h u c c u a d i e n

=>ChonC.

(V)

d u n g

d ? t u c a m L . Bie't L = r R C . V a o t h o i d i e m to, d i e n a p g i i r a h a i d a u c u o n c a m
b a n g 40N/3 V t h i

—(")

60

37

100,
" M B

n

UoMB

hai d o a n A M v a M B m a c n o i tie'p. D o a n A M g c i m t u d i e n c 6 d i e n

V '-'oAM J

(Dt + —

= 1

UoAM+UdMB=100-

cot

= IOOIQ C O S

'Ml!

u OAM

1
•^PMB

.

V '-'oAM 7

• • A M -L " M B

= 1

I

= rRC:
Cdch 2:

(
^AM

= - 1

^
=^ Uo = IflZ = I O V / R ^

dan

D. 3 0 V 2 V .

n o i tie'p v o i d i e n t r o R v a d o a n M B c h i c6 c u o n c^m c 6 d i e n t r a t h u a n r v a c6

100

(

lOOIoJ

"

u OAM

thi dien ap tren

100(")

=

'''MB = - J ' - Z M S =

\

" A N

' '"

khang

_,^anorif>c:c.

I

f

V 'OZAN

+

7u

-1

L = rRC

D . lOOTsV.

•''
=

n o i tie'p vcVi ctien t r o R v a d o a n M B c h i CCT cuc)n c a m c 6 d i e n trtV t h u a n r v a c6

V i d u 7: D a t d i e n a p u = 100cos((i)t + 7T/12) ( V ) v a o h a i d a u d o a n m a c h A B g o m

•••

tancpMB = HQ f t :.>t

AM,

Hu&ngdan

Cdchl:

^ ,

d i ^ n a p t r e n A M l a 36 V . D i e n a p h i e u d u n g t r e n d o a n A M cc) t h e la

50\/3 Q,

dung

, ,,

d 9 t u ' c a m L . Bie't L = r R C . V a o t h o i d i e m to, d i e n a p t r e n M B b a n g 64 V t h i

doan

.

C. 50 > y 7 V .

• '

3

,

:,l:^..^u.t-.:

khang

voi

dien

_

hai docin A M v a M B m a c n o i tie'p. D o a n A M g o m t u d i e n c6 d i e n d u n g C

/v

m a c h A B g o m ba

doan

,

— = - 1 => tancp^i tancpf^^; = - 1 => u^, 1 u,^^R

—

• Chon A.

d o a n M N chi d i e n t r a R = 50 Q v a d o a n N B c h i c6 t u

tancp^N =

1 -:

=1

V^OMB

M N v a N B m a c n o i tie'p. D o a n A M c h i c6 c u o n c a m v o i c a m

A. lOOV.

•

= 30^/7 ( V )

the tra hinh ditvi bie'u tlii'ir L = rRC

/:/•(,'«

A . 50 V .

5: D a t d i e n a p u = Uocoscot v a o h a i d a u

M B l a 60 V . T i n h Uo.

2

36

UQ

1U„MB=60(V)
Vi

64

=

y i d u 6: D a t d i e n a p u = 100cos(o)t + 7:/12) ( V ) v a o h a i d a u d o a n m c i c h A B g S m

J Hi

UoMB -

+

D. 50>/2V.

dan

u. 0 M B

C/jM t/-" D/C'H

=>rR = - = Z | Z c ^

C. 3 0 V 2 V .

^

1.

j,.

. U„ = l„Z = 1„ > ^ + ( Z , - Z , . f

30N/3(V)

I
J

U0MB

A,

I
"mV

B

50* ,

[ i f g i a n d o v e c t o ta tha'y, U A M t r e p h a h o n
lAi!

UL

la 7t/3 n e n
M

129


Bo trp hie'n thiic
U AM

V^t li LTDH

Cty mnn

tren k&nh VTV2. t^p 2 - Chu VHn BI6n

(V)

= 5 0 COS cot +

Huong

Chon B.

12
3

V i d u 8: M o t doan mach A B g o m doan A M va M B mac noi tie'p. D o a n A M g6n^
d i e n t r o R n o i tie'p v o i t u dien C, con doan M B chi c6 cuon c a m L . D a t vao

D VVH lUiang

Vift

dan
MB

• AAMB vuong tai M

nrv

tana =

r
n
= Vs => a = 60".

AM
V i R = r nen p = a = > cp = a + p - 9 0 " = 30" => coscp = 0,866 => Chon C.

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 thoj

V i d u 10: M o t doan mach A B g o m doan A M va M B mac n o i tie'p. D o a n A M

tren A M va tren M B l u o n l u o n lech pha nhau 7t/2. K h i mach coug h u o n g thi

g o m t u dien C no'i tie'p v o i dien t r o R, con doan M B chi c6 cuon cam c6 d p

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

tir cam L va dien t r o thuan r = R. Dat vao A B m o t dien ap xoay chieu chi c6

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

tan so goc co thay d o i d u g c t h i dien ap tuc t h o i tren A M va tren M B l u o n

ap tvVc t h o i tren A M lai tre h o n dien ap tren A B m o t goc ai. Bie't a i + aa = 7t/2

luon lech pha nhau nil. K h i co = coi t h i dien ap tren A M co gia t r j hieu d u n g

va U i = 0,75U2. T i n h he so cong sua't ciia mach A M k h i xay ra cong h u o n g .

U i va tre pha so v o i dien ap tren A B m o t goc a i . K h i co = C02 t h i dien ap hieu

A . 0,6.

B. 0,8.

C.l.

D . 0,75.
Huong

cosai =

HI

\

u

%.
=• =

cosa,

u

sinai

/

+

I

uJ

r

u

^'7a^- ,U
\

/

\

= r^ = L/C sity ra u ^ ^

•=>tanP-^M.

cosp = •

'.

MB J

MB
AM

C. 0,75 va 0,45.

Huong

= 0,6

• (|) = 2 a - 9 0

/

= tan a => a = P => cp = 2a - 90

AM

= t a n a => P = a

=> coscp = sin 2a

u

TH2:cosa2 =

MB

MB

THl:cosa, = H I

"MB •

D . 0,96 va 0,96.

dan

•^tanP = A M =

cosp = •
MB J

M

AM

B. 0,45 va 0,75.

sinp = AM

/

sinp = -

m o t goc ai. Bie't a i + a2 = 7i/2 va U i = U2 Vs . T i n h he so cong sua't ciia mach
u n g v o i COI va C02.

0,75

= 11

/

Chu y: Tu dieu kien

d u n g tren A M la U2 va dien ap tuc thoi tren A M lai tre h o n d i e n ap tren A B

A . 0,87 va 0,87.

u
\

B

dan

2

^ u)

R

A

2

= sin a

I

U)

+

r_

^/3

I u)

• cos(p = sin 2a

MB

V i d u 9: D o a n mach xoay chieu A B g o m

M

h a i doan mach A M noi tie'p M B . D o a n
m a c h A M g o m dien t r o R n o i tie'p v a i
t u dien c6 dien d u n g C, doan mach M B
CO cuon cam c6 d o t u cam L va dien t r a
r. Bie't R^ = r^ = L/C va dien ap hieu

/

d u n g giij-a h a i d a u M B I o n gap V3
d i e n ap h a i d a u A M .
A . 0,887

V-l-.

/

so' cong sua't

•"• ciia A B la
,

/

0,

/

B. 0,755.

•

C. 0,866.

D . 0,975.

Khi L thay doi deUum, thi 0,^^. 1 0 (URC va U la hai cqnh cm tain giac vuong dm
Uumx la cqnh huyen, UR la dumig cao thuoc cqnh huyen):


&itfp kidit thvtc vai i(ii-hti tten k&nh VTV2. t^p2-chu

K/n' C thay dot dcUcmx tin 0,^,

f r

U

UV2

f

= .1;

1

1

K h i t o n g 2 so k h o n g d o i , tich 2 so Ion nha't k h i 2 so bang nhay.

^

R+

1

>

2|Z| - Zcl

(R + r) +

V i d u 11: Cho mach dien xoay chieu R, L, C m3c rioi fi#p theb t'HiVfe rfo (cuon
cam thuan). D i e n d u n g C c6 the thay d o i duoc. D i e u c h i n h C de dien ap 6

.., \|,

K h i tich 2 s o k h o n g d o i , tong nho nha't k h i 2 so bang nhau.

1 0 (UKI. va U la hai cqnh cua tamgidc viian^ con

Uomn la cqnh Inn/en, UK lii dicaiii^ cao thuoc cqnh hiii/cn):
UKL

(a + b),„i„ = 2 7 i : b
a + b *^^u " = " xay ra k h i a = b

a + b > 2. VaTb

= 1;

UV2

UKCV2

van bleu

*

da'u " = " xay ra k h i R = |Z,

- Z^.

> 2|ZL - Zcl dau " = " xav.ra k h i R + r = IZL - Z ^

Tarn thitc hqc 2: y = f(x)

= qx^ + bx + c (a ^0)

hai dau C la ion nha't. K h i do dien ap hieu d u n g 6 hai dau dien tro R la
100 V2

V. K h i dien ap tuc thoi 6 hai dau d o a n mach la 100N/2 V t h i dien ap

\

tu'c t h a i g i u a hai dau doan mach chi'ia dien t r o va cuon cam la -100-76 V.
C. 200 V.

B. 615 V.

/

\

T f h h gia t r j hieu d u n g cua dien ap 6 hai dau doan mach A B .
A. 50 v.-

y

D . 3 0 0 V.

^

:,. ^•

a >0

ymin

'KL

uC

=1

UV2
max

1

•'fit?:.'';; '.i'iiv--:.

X

Hucmgddn

(-^oo^/6
Urn

f looVz

0

\

V2

-b
-A _
a > 0 t h i tgi^di^h^P^r^^ql xo. = — x6^^mm —
•) rvw>. • 4a

1

1

u RL

Kl.

100^2

4ac

-

g?il,r:

Dao ham khao sat ham so

BAi TOAN LIEN QUAN DEN C^C TR|

Ham

y

f(a)

De t i m gia trj Ion nhat va nho nhat cua m o t dai l u g n g (Z, I , UK, U I , Uc, U M N ,

L a p bang bien thien t i m eye t r j .

P . . . ) k h i CO m o t yeu to bien thien thong t h i r o n g lam theo cac buck sau:

Neu h a m so d o n g bien hoac.nghieh bien tren m o t doan [a, b] t h i max va mir

Zi., Z t , w).

the d u n g gian do vec to phoi hop v d i d j n h l i ham so sin.
M o t bai toan c6 the giai theo nhieu each n h u n g t h u o n g chi c6 mot each hay
va ngcin gon. V i vay, nen tranh tinh trang "Diiiii^ dao mo trail dccat tict ga".

Bat dmn; thi'iT Cosi

^.;Hi»^i

u-j

,

...

N e l l a, b la hai so dirarig t h i \;> •AiisW sit^ .•i^ni^i K\U ,\v:iky;is\ i\\

UIA

* ,

f(a) rih6|i|hat.

hogc tam thuc bac 2 ( t i m (o, Zi, de Ui n..iv, t i m co, Zc de Ucmnx) hoac dao ham
doi v o i bai toan t i m Ui ni..v k h i L thay d o i hoac t i m Ucn,.ix k h i C thay d o i thi c6

i,

f(b) Ian nha't.

Pni..v)

khao sat h a m so de t i m max, m i n ( t i m Zu de UKI n.ix, t i m Zc de UKCI.I.IX). Rieng

v A t .,,

V D : T r o n g doan [a,b]:

•'

Buo'c 2: De t i m max, m i n ta t h u o n g d u n g : 6at dang thifc Cosi ( t i m R de

• R

la hai gia t r i ciia h a m tai hai dau m u t do.

Budc 1: Bieu dien dai hrgng can t i m cue trj la mot h a m cua bien so thay d o i (R,

*

m

s o y = f(x) c6 eye t r i k h i f'(x) = 0

Giai p h u o n g t r i n h f'{x) = 0

gidi

•)£^-HC:.;

6:) r r n : i;;'

^
-A
4ac-b" ,, .

-b
a < 0 t h i ym,,x = — =
krji xo =
4a
4a
2a

U = 200(V) ii>ClionC.

Phuoitg phdp

b'

4a

1. R thay d o i .
.f.

R thay den lien quan dm cue tri P

p = rR =

U^R

' ''''' R ^ + ( Z L - Z c f

U^
{ Z L ^ c f

u^

"2|ZL-ZC

Pmax

2ZL-ZC

RO=|ZL-ZC

13:


oa ttffRieh

tHiTc v^mt^Tunrren

Kcnn

vi vj, t^p j - una van men

D a n g d o thj c u a P theo R:

0,4f^ ± 1 9 0 f - 5 0 0 0 = 0 => f = 2 5 ( H z ) = > C h o n A.
Binh

R,lt,

(z, y.cf
(7'

Kl

luan:

pl-idp thu

Dc

trnnh

gidi

yhieong

trinh

bac hai phi'ec tap ta c6 the dung

phieang

nhu'sau:

':,Mf\

Z L =COL = 10
i = 2 5 ( H z ) => M = 5 0 7 r ( r a d / s ) =:

1
Zc =

coC

•= 200

=> Z , - Z c
'

=190(Q)

=> Z L - Z c
^
^

= 109(0)

Z | = coL = 16
f = 4 0 ( H z ) => to = 8 0 ; t ( r a d / s )

-

1
Z c =

De t i m hai gia trj Ri, R2 c6 cung P t h i t u P = —

= 125

coC

•ZL=COL = 20

R'+(ZL-2C)
R,R,=(Z,-Ze)'=R(^

f = 5 0 ( H z ) => CO = ] 0 0 7 i ( r a d / s ) :

1

Zc=

= 100

(OC

- — R + ( Z L - Z ^ - ) - = 0 , theo d j n h h' Viet:

1>V"
^ | Z L - Z C |=
'
^'

80(Q)

^iV

'

Z L =COL = 32

R,+R,=
f = 80 ( H z ) ^(£,

= 1607i(rad / s ) :

|ZL - Z r = 30,5(Q)

1
(oC

'• ""

V i d y 3: M o t doan m a c h x o a y c h i e u mac no'i tie'p g o m tu C = 50/7i (jiF); cuon

Tir do thj ta n h a n thay:
2Rn

cam t h u a n c6 d o t u cam 0,8/7i (H) va bien t r a R. Dat vao h a i d a u doan mach
dien ap u = 200cosl007Tt (V) (t d o bang giay). De cong suat tieu t h u cua

V i d u 1: (DH-2008) Doan mach dien xoay chieu g o m bien t r o R, cuon day

mach cue dai thi gia t r i ciia bien t r a va cong suat cue d a i la

t h u a n cam c6 do t u cam L va t u dien c6 di§n d u n g C mac noi tie'p. Biet dien

A. 120 Q va 250 W.

B. 120 Q v a 250/3 W .

ap hieu d u n g g i i i a hai dau doan mach la U , cam Ichang Zi., d u n g k h a n g Zc

C. 280 Q va 250/3 W.

D. 280 Q v a 250 W .

(voi Zc ^ ZL) va tan so d o n g dien t r o n g mach k h o n g d o i . Thay d o i R den gia
trj Ro t h i cong suat tieu t h u cua doan mach dat gia trj cue dai P,n, k h i do .
A . Ro = Zi. + Zc.

B. Pm = U2/R().
Huong

p = rR =

dan

U^R

R

P^

=•
2|ZL-ZC

1^0

= Z[_

- Z(;

1
coC

250

= 200(Q)

2Ro

V i d u 2: Cho mach dien noi tie'p g o m cuon cam t h u a n do t u cam 0,2/n (H), tu

V i d y 4: D o a n mach d i ^ n xoay chieu g o m bien t r a R, cuon day t h u a n cam va t u
dien c6 dien d u n g IOO/TI (JIF) no'i tie'p. Dat vao hai d a u mach d i ^ n ap xoay
chieu 100 V - 50 H z . Thay d o i gia trj bien t r a t h i cong suat dat gia t r i cue dai
A . 71(H).

B . 1/7I(H).

mach d i ^ n ap xoay chieu on d j n h c6 tan so f (f < 100 H z ) . Thay d o i R den gia
trj 190 Q t h i cong suat tieu t h u tren toan mach dat gia trj cue dai. Gia t r i f la
C. 50 Hz.
Huong
Pmax «

134

R = |ZL - Z c l «

|ZL - Z c l = 190

D. 80 H z .

2c =

1
coC

= 100(Q)3>P„

2Z,

-Zr

D . 1,5/71 ( H ) .

dan
•50 =

100^
2|ZL-100

•L=-(H)

Chon C.
d y 5: Cho m g t d o a n mach n o i tie'p gom m o t cupn day t h u a n cam, t u di§n c6

dan
« 2nf.-

C.2/7I(H).

Hwang

dien CO dien d u n g 0,l/7t (mF) va bien t r a R. D i e n ap dat vao hai d a u doan

B.40HZ.

3

• Chon B.
(W)

bang 50 W . D o t u cam cua cuon day c6 gia t r j :

=>ChonD.

A. 25 H z .

i H

R O = | Z L - Z C | = 120(Q)

Z L =coL = 8 0 ( a )

Zc =

, ;j ,
'!

Huaitgddn

D. Ro = |ZL - Zc|.

C. Pm = Zi,VZc.

_

0,2

1

= 190

dien d u n g k h o n g d o i va m o t bien t r a R. Dat vao h a i d a u d o a n mach m p t
dien ap xoay chieu on d j n h . Thay doi R thay k h i R = 24 Q cong suat tieu t h y
135


Bo trp kicn

tliiic

V^t li LTOtl

VTV2. tap 2 - Chu VSn

tren k^nh

Bi€n

cue dai t r o n g ctoan mach la 200 W . K h i R = 18 Q thi macli tieu thu cong sua'j
bc^ng
,•
A. 2 8 8 W .

B. 168W.

C. 192 W .
Huong

Ro

= Z, - Z ,
2

= 24(Q)

- => 2.24

2R {)

k h o n g d o i . Dieu chinh t r i so dien tro R de cong suat tieu thu cua doan mach
dat cue dai. K h i do he so cong suat cua doan mcich bang

dan

A . 0,85.

i''

&jr.m r r

9600.18
y = 1 9 2 ( W ) zoChonC.
18^+24"

ta n (p =

V i d u 6: Cho mach dien xoay chieu gom RLC mac noi tie'p. T r o n g do, L = 0,2/?!
mac vao mang dien xoay chieu c6 tan so f = 50 (Hz). K h i dieu chinh bien tro
A . ban dau tang dan sau dcS giam dan. B. tang dan.
C. ban dau g i a m dan sau do tang dan.
Jift-ij

im

1 nj-

Huong dan

./)

'jtyi

,

Zi - Z r

.

(p =

.
.

• ,r

D. l/^/2.

i * '-A

Ro

,,>,!;,;.;;.,

_ 1

R2+(ZL-Zcr

;

• Chon D.

J2

7t

— ^ = ±1 =>(p = ± Rn
4
U

1=

A)

U

VR^(Z,,-Z,)^"ROV5

de dien t r o tang dan thi cong suat tren mach se:

unijh

"

Luc nay d o n g dien lech pha so voi dien ap la TI/4. •

(H), C = I/TT (mF), R la m o t bie'n tro v o i gia tri ban dau R = 20 Q. M a c h difoc

li.thi'i

B. 0,5. .

• COS

(ZL-Zcf

R^

144W.

doan mach RLC khong phan nhanh. Bie't do tu cam va dien d u n g d u g c giu

= 2 0 0 ^ U = 40V6(V)

U^R

P

D.

V i d u 8: (DH-20(>8) Dat dien ap u = Uocosait (Uo va io k h o n g doi) vao hai dau

D. giam dan.

Huang dan

rrt aiioh jf>l'..1

^imtii

(fb m

(Kuril

=

0 + (UL -

Uc)'

=> U K „ = |UL -

Uc

72

V i d u 9: Cho iri^ch dien xoay chieu noi tie'p g o m bien t r o R, cuon day thuan

61 Z L =coL = 2 0 ( Q ) ;

cam CO cam khang 200 Q va tu dien c6 d u n g khang 100 Q. Dien ap dat vao

1

hai dau d o t i n m a c h u = 100 N/2 coslOOnt ( V ) . Xac d j n h gia tri ciia bien tro de

Zc =

coC

= 10(Q)

cong suat tieu t h u tren doan mach la 40 W .

f^nx « R o = | Z | , - Z e | =

10(Q)

A . 100 Q hoac 150 Q.

C. 200 Q h o l e 150 Q.

Luc dau R = 20 (Q), roi tang dan tiVi
cang ngay cang xa gia t r i cue dai nen P

...|....:.,^1

giam dan => C h g n D.

"* '"

V i d u 7: Cho m o t doan mach RLC c6 R thay d o i . Dat vao'hai dau doan macin
m o t dien ap xoay chieu c6 gia tri hieu d u n g U k h o n g doi va dieu chinh R =
.Ro de cong suat tieu thu trcMi nicich dat cue dai. K h i do dien ap hieu dung
•p tren hai dau ciia R l a 45 V . T i n h dien ap hieu d u n g giua hai dau R k h i dieu
' chinh R = 2Ru.
A . 56,92 V .

B. 5 2 , 9 6 V .

C. 6 2 , 5 9 V .

D . 69,52 V .

Huong dan
"

K h i R = Ro: P,,,, « R „ = | Z , - Z e i = ^ | U , , - U e | = U R „ = 4 5 ( V )
U = Juf^o + ( U , - U c f
Khi

R = 2RQ^JZL-ZC

nen: 45^2 = U ' ^ +

4

= 45V2 ( V ) (Gia t r i nay k h o n g thay doi!)

U^R

,t u 0.t •

D . 200 Q. hoac 50,Q.

i i c,iO ;Vi'

fjumig dan

•40--

R2+(ZL-Zcr

\/ Cfc&

R, =200(Q)

lOO^R
R^

+100^

R2 = 5 0 ( Q )

> Chon p .

V i d u 10: (DH-2009) Dat dien ap xoay chieu c6 g i a t r i hieu d u n g k h o n g doi vao
hai dau doan mach gom bien tro R mac noi tie'p voi t u dien. D u n g khang cua
tu dien la 100 Q. K h i dieu chinh R t h i tai hai gia t r j R i va R2 cong sua't tieu
thu cua dogn mach nhir nhau. Bie't dien ap hieu d u n g giira hai dau tu dien
k h i R = R I bang hai Ian dien ap hieu d u n g giua hai d a u tu ^ien k h i R = RzCac gia t r i R i va

R2

la

'A. R i = 5 0 Q , R 2 = 100Q.

C. R i = 50Q,:R2 = 2 0 0 Q .

."y

>

g f i V i P/>

rhn-''-' lif'n U't*^ s.':^''.

;B. R i = 40 Q, R2 = 250 Q.

/;

• D . R i = 25 Q, R2 = 100 Q.
Huang dan

R

ma

2
U'R

P = I^R =

ff^:

B. 100 Q hoac 50 Q.

=,.Ui+(U'L-,U'cr
P = I^R =

=18VT0 *

56,92 ( V )

4 ^

. R 2 - - ! i - R + Z ^ = 0 => R1R2 = Z ^ = 10000

U c i = 2Uc2 => I , = 2I2

Z2 = 2Z, :=> R2 +

= 4(R? + Z ^ ) ^ R2 _ 4R? ^ 30000

• Chon A.
136

,137


=>

fRi=50(Q)
R2 =200(Q)

„,:.,.

=> Chon C.

V i du 11: Mot mach dien gom tu dien C, mot cuon cam thuan L va mot bien tro
R dugc mac no'i tiep.
Dat vao hai dau mach dien mot di^n ap u = 100 V2 coslOOrtt ( V ) . Khi de bien
tro 6 gia trj Ri hoac R2 thi cong sua't tieu thu tren doan mach la nhu nhau.
Neu Ri + R2 = 100 Q thi gia trj cong sua't do bang
A. SOW.

B. 200W.

y{ du 14: Mot mach dien AB gom mot tii dien C, mot cuon cam L thuan cam

khang va mot bien tro R dugc mac noi tiep. Dat vao hai dau mach dien mot
hieu dien the xoay chieu u = 120 V2 cosl207rt (V). Bie't rang ung voi hai gia
tri cua bien tro: Ri = 18 Q va R2 = 32 Q thi cong sua't tieu thu tren AB la nhu
jihau. Cong sua't cua doan mach AB khong the nhan gia tri
A, P = 72W.
B. P = 288W.
C. P = 144W.
D. P = 576W.
Huong dan

,1

C. 400W.

D. lOOW.

Tir R 1 R 2 = ( Z L - Z c )

= Ro va P^ax =

Huong dan
^2

p = rR =

•

R'+(ZL-ZC)'

•P = -

R1+R2

.1..:..:,-::.,

2

R + (Z| - Zc f = 0 => Ri + R2 = —

P

cam

R,R2=(Zi -Zc)'=R,i
';y. r^firin. o r i - )

2R„

Ri +R2 =

3#|i' r'

CO

do t u cam 0,5/7c (H) va tu dien c6 dien dung 0,l/7t (mF). Dien ap dat

vao hai dau doan mach u = UA/2 coslOOTtt ( V ) . Khi thay doi R, ta thay c6 hai
gia trj khac nhau ciia bien tro la Ri va R2 thi cong sua't tieu thu ciia mach
deu la P. Chon ke't luan dung.
A. R1R2 = 5000 Q2.

B. R, + R2 = 2U7P.

C.P
gom cuon cam thuan mac noi tiep vdi mot bien tro R. Ung voi hai gia trj
Ri = 20 Q va R2 = 80 Q thi cong sua't tieu thu trong doan mach deu bang
400W. Gia trj ciia U la
'

• = B.200V.

.,

C.IOOV.

Z L =CoL

= 50(Q),Zc = — = 100(Q)
coC

R, + R , =

bien tro R, cuon cam thuan va tu dien. Thay doi R thi mach tieu thu cung
mot cong sua't ung voi hai gia trj ciia bien tro la Ri = 90 Q va R2 = 160 CI.
so'cong sua't ciia mach AB ung voi Ri va R2 Ian lugt la
.. i , ;
cosipi =
RiR2=(ZL-Zcf
COS(P2 =

138

Vv,

C.0,8va0,6.

^;;v;<:) ,

100

^J^f^:

R,

R,

7R^+(ZL-ZC)'

VR'+RIR:

.P<

100

•Chon D.

mach tieu thu cong sua't deu bang 80 W. Khi thay doi R thi cong sua't tieu
thu tren mach dat cue dai bang
, A. 250 W.

D. 0,75 va 0,6. K

V2

W.

C. 100 W.

Huong dan
va P„

Ri + R , =

P(Rl+R2)

Chon B.
max

2 V R ^

80(45 + 80)
2V45.8O

250

2Rn

D . 250/3 W .
'1

RiR2=(ZL-Zcf=Rg

= 0,6
= 0,8

B. 80
'

3
Ri

P

J

Huang dan
VR?+(Z,^-ZC)'

2Z, - Z r

xX^,

thuan cam. Thay doi R ta tha'y voi hai gia trj Ri = 45 Q hoac R2 = 80 Q thi

V i du 13: Dat dien ap xoay chieu vao hai dau mot doan mach AB no'i tiep gom

;.,

; ^. ;

Vi du 16: Mach dien xoay chieu gom mot bien tro R mac no'i tiep voi cupn day

R, +R2 = . ^ = > U = 7P(R, +R2) = 200(V)=>ChonB.

B. 0,6 va 0,8.

,

a

Huong dan,

A. 0,6 va 0,75.

.

^j^,;'

Huong dan

R1R2 = ( Z L - Z C f = 2500(Q2 ) => P„

D.IOOV2 V.

y

D. P
V i du 12: (CD-2010) Dat dien ap u = UV2coscot (V) vao hai dau doan mach

A. 400V.

r>i.

Vi du 15: Cho mach dien xoay chieu noi tiep gom bien tro R, cuon day thuan

Chu y: Khi c6 hai i^id trj Ri va R2 dc cd ciing P thi c6 the gidi nhanh khi dm vao:

P„

suy ra:

= 300(W) => P < 300(W) =^ Chon D.

^max

= 100(W) =>ChonD. .'1

va

2R,

suy ra:

til,

' if '
t

(W) =^ChonD.

139


ety

y i d v 17: M(?t maoh dien xoay chieu g o m tu dien C, mot cuon cam thuan L vji
doan mach cue dai la 300 W. K h i de bien t r o 6 gia trj 18 Q hoac 32 Q thi

tan(p3 =

cong suat ticu thu tren doan mgch l^Vnhu nhau ya gia trj d o bang
. w,!,.,J

;n
--i.p

B. 1 4 4 W .
.

ro,1>J;' , C . 2 4 0 W .
Huong dan

R,R2=(ZL-Zcf=R,^
Tif

P

Z L - Z c | = #;R7=12(f2):

^

2Ro

. i = 1Ocos 100Tit + - ( A ) z ^ C l i o n C .
4

/

2 8 8 ( W ) ^ Chon A.-'"^:

Hhaiig

R,

Vlft

4

u0

U '0 _

l03 =

;-..;.t/;.i ^

^2

R, + R , = ^

- ^ZoHlVMi
.
R,+R2

D. 150W.

UVVII

Hu&itg dan

m o t bion tro R d u o c mMc noi tiep. K h i R = 24 Q thi cong suat tieu thu tren

A,288W.

TNtiH MTV

- = 10(A)

Ri+(ZL-ZcK
.vvrDc-

• fl--i

R,R2=(ZL-ZC)'=R,^

^

I) Khi CO hai gid tri Ri vii R2 dcPi = P2 = P thi:

V i d u 18: Doan m a c h xoay c h i e u RLC noi t i e p v o i R la bien t r o . K h i Ri = 40 U
hoac R2 = 1 0 U t h i cong suat tieu thu cua doan mach n h u nhau. K h i R = R,,

ZL " Zc Z L -

thi c o n g suat tieu t h u cua doan mach dat gia t r i Ion n h a t , va c u a n g d o dong
d i g n q u a m a c h i = 2cos(1007it + K/12) (A). Dien ap h a i d a u doan mach c6 the
CO b i e u t h u c

R,

ZQ

R.

= 1 ^ tafi' cp, tart(p2 = 1 => (pi +
2) Ddo Iqi: NeU cp, + (P2 = ^ tin _Pi = Pz = P = ^^^^

^ h i,n Q £e .yv •

A. u =50^/2 cos(100Kt + 7rt/12) (V).

B. u = 50 V2 cos(100Trt - 5TI/12) (V).

C. u = 40 V2 cos(1007it - 7i/6) (V).

D . u = 40cos(1007tt + K / 3 ) (V).

lech pha giua dien ap hai dau doan mach va d o n g dien qua mach u n g vcVi

dan

cac gia tri Ri = 270 Q va R2 = 480 Q cua R la cpi va (p2. Biet (pi + 92 = n/2. Dien

Humg

V i d u 20: Cho mach dien c6 2 pfian tit mSc noi tiep Va tu C va bieri t r o R. Do

ap hieu d u n g giua hai dau doan mach la 150 V . Goi Pi va P2 la c o n g suat cua

TCr R1R2 = ( Z L - Z c ) ' = , R ^ =>Rp = V R ; R 7 = 2 0 ( Q )

mach u n g v o i Ri va R2. T i n h Pi va P2.
A. P I = 40 W ; P2 = 40 W .

"

OsJ^E - J'. .^1 \ ,!f\.. :4asf> •i•;'
B. Pi = 50 W ; P2 = 40 W .

Z = ^Ro + ( Z L -Zcf

= 20V2Q =^ U ( , = loZ = 4 0 V 2

c:,

^^ i>

K h i (p = + - =0 u = 40>/2cos lOOjit + — + - ( V )
4
I
12 , 4 / '
^ChonC.

tiuoltgddn

... ,>|

Khi {p = - - = > u -40^/2cosf^OOnt+ — - - ] ( V )
12
4

Chu 1/; Dcfio sthili cong snii't ton nhict ta c6

"

V i d u 19: M a c h dien xoay chieu g o m ba phan t u , dien t r o t h u a n R, cuon cain
thuan L va tu dien C mac noi tiep. Dien tro R thay d o i dugc. Dat vao hai
dau dogn mach dien ap xoay chieu u = 120 V2 coslOOjit ( V ) . D i e u c h i n h R

do thi P thco R. Dm vao do tlii ta I

R cdng gifn Rn thi cong sunt cdng Ian, cdng
xa

Ro

thi

cong

i^uat

cdng

k h i R - Ri = 18 Q t h i cong sua't tren mach la Pi, k h i R = R2 = 8 Q t h i cong sua*
P2, biet P I = P2 va Zc > Z L . K h i R = Ih thi cong suat tieu thu tren mach dat cu^
dai. Bieu thuc c u d n g d o d o n g d i ^ n qiia mach k h i R = R 3 la
A . i = 10 x/2 cos(1007tt + 7t/4) (A)..

B. i = 10 72 cos(1007rt - 7r/4) ( A ) .

C. i = 10cos(1007tt + 7i/4) ( A ) .

D . i = 10cos(1007rt-7i/4)(A).
/•

.

:

P, = P2 = P thi

Ro = |Z|, - Z,-\ V R J R ,

R3G(R,;R2)=>P3>r^
R3 ^ [ R , ; R 2 ] : : : ^ 1 ^ < P

,,,, „ .

„,„a

1^»'_ = 30(W)
270.480

^ ' ' ^ ' ^ ^ ^ ^ = i " " ^ ^ ' = ^ = ^ ' = R,.R2

thcdhng

; , v;

D . PI = 3 0 W ; P 2 = 3 0 W .

C. Pi = 40 W; P2 = 50 W .

140

,. .

be

ori' - J i r t t l o v -gn''"
>H nsn vf'b

muhmln

. r;

Bd trp kiSn

thitc

V^t It LTDH

tren

hSnh

VTV2,

t^p 2 - Chu VSn

Cty

Blen

Tisntl

V i d u 2 1 : M o t mach dien xoay chieu gom tu dien C, m o t cuon cam thuan L vo
m o t bien tro R d u g c mSc noi tiep. K h i R thay doi thi cong suat loa nhiet cuc
d?ii la

Pirax.

' R max

Pu =•

K h i de bien t r o a gia tri Ian l u g t la 18 Q, 32 Q va 20 Q thi con^

R+

•:'_^(Az^cf
-

suat tieu t h u tren doan mach Ian l u g t la Pi, P2 va P:^. Ne'u Pi = P2 = P thi
A.

P3

> P.

D.

C. Ps < P.

B. P 3 = Pinnx.

P3

MTVDVVHKhang

^ 2 r ' 2 > / ^ Z , - Z c ) ^ + 2 r [R„,^

u2(R + r )

= P.

Vift

- 2RoR+2r

=

+(z,-Zcf

2>

u

(xet r < | Z , - Z ^ l )

Huang dan
Vi R3 e ( R , ; R 2 ) = > P 3 > P = > C h o n A .
ChtUj:

•
•

•

,
•

vci P4 ta co thP'dung plurang pluip "giang day" nine sau: Tir P3 kc

1) Dc so sdnh

dirang soug song vai true hoanh ncu P4 tren day tin P4 > P.) va nc'ii duvi day tin
P4

< Pi.

* max

— <

P =
(R + r ) +

(Z,-Zcr2|Z,-Zc
RQ

N e u hai gia trj R i , R2 c6 cung P thi t u P = —
V

,

^7

2

ZL

+r=

1 ) Dc tun cong suat Ion nbat trong socac cong suat da cho, ta chi can so sank hai gia

tri gan dinh nhat bang pliuvng pluip "ginng day".

~

ZL

ry

-Zc
- Z,

u2(R + r)
3——

(R + r )

2

+ ( Z L - Z C )

V i d u 22: M o t mach di?n xoay chieu g o m tu dien C, m o t cugn cam thuan L va
m o t bien t r a R d u g c mac noi tiep. K h i R Ian l u g t bang 18 Q, 20 Q, 22 Q, 26,5

.(R + r ) 2 - ^ ( R + r ) + ( Z L - Z c ) ' = 0

Q, 27 Q, va 32 Q thi cong suat tieu thu tren doan mach Ian l u g t la Pi, P2, ? \
( R , + r ) ( R 2 + r) = ( Z L - Z c f = ( R ( , + r)

P 4 , Ps va Vh. N e u Pi = P(> thi trong cac gia trj cong suat noi tren gia trj Ion
^,,

Theo d i n h l i Viet:

nhat la

A.P4. , .•^T\n'^

^Huong

, .J
V i t r i d i n h : /?„ =

=

(Ri+r) + (R2+r) =

D. Ps.
dan

24(Q)

1' •

D a n g do t h i cua P theo R:

^^

T u do t h i ta nhan thay:

V i R cang gan Ro thi P cang Ion nen

2R,

chi can so sanh cong suat l i n g v o l R 3

2
U^r

R = 0=>P =

va R4 nam gan Ro nhat va hai phia

^,

r2+(ZL-Zcr

do'i v o i Ro.
R = Rn=^P,
0 —' 1 max

De so sanh P3 va P4 ta d u n g p h u a n g
phap "giang day", t u P 3 ke d u o n g

2(Ro + r)

1

R =

song song v a i true hoanh va nhan

CO

P„,:„ = 0

thay P4 nam d u o i day nen P 4 < P3
=>ChgnB.
= R 3 R '3 => 24^ = 22.R '3 =^ R4 « [ R 3 ; R '3 ] =i> P3 > P4 ^^""^^^^W^***^

^

Chit y: Kid cugn day c6 dien tra thuan th) cong suat tieu thu tren R va cd r.
U^r
U^r

P,=I^r =

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

U^r

r2+(ZL-Zcr

r'+(ZL-Zcr

T r o n g trucrng h g p

thi do thi P theo R c6 dang n h u

h i n h ben. T u do t h i ta nhan thay:
R = 0 = > P „ ax

U^r
2 /T
^ V
r^+(ZL-Zc)

U^R
{R + r ) ' + ( Z L - Z c ) '

r>|ZL-Zc|

R = =o=>Pmin=0

a"

P
(/{, + r)(W, + r ) ^ ( / , - Z , ) ' = K + r)'


Bo trp kie'n thiic

Vat li L roll

trcn hcnii

VTV2^Lpp^ 2-

Chu Van Btett

V i d u 23: M o t mach xoay chieu mac noi tiep g o m bien t r o R, cuon day c6 do tir
cam L CO dien t r d thuan r va tu dien c6 dien d u n g C. Dieu chinh bien t r o de
R = r thi d u n g luc cong sua't tieu thu ciia mach cue dai. T i so'giua dien ap
hieu d u n g tren doan mach cuon day-tu dien va dien ap hieu d u n g tren toan
mach luc nay la

•

v

, !

B. 1 / V 2 .

A . 0 , 2 3 VTO .

•

C.

-^^

tiuwigdan

P = l 2 ( R + r) = -

=

(R +

rr+(Z,-Zcr

72/4.

D . 0,5

tni

M

• " (R,+r) +

-I

(260 +10) + (470 +10)

(R2+r)

y i d u 26: M o t doan mach xoay chieu mac noi tie'p gom. cuon day c6 dien t r a
thuan 40 (Q), c6 cam khang 60

M )

tu dien c6 d u n g khang 80 (Q) va m o t

bien t r o R (0 < R < « ) . Dien ap 6 hai dau doan mach on d j n h 200 V - 50 H z .
K h i thay doi R thi cong sua't toa nhiet tren toan mach dat gia t r i cue dai la
A. 1000 (W).

{Z,-Zc)
(R + r)

B. 1 4 4 ( W ) .

C. 800 (W).

D . 125 (W).

Huong dan

'

(R + r ) 2 + ( z , - Z c ) '
U,LG = I Z „ x =

UJr^ +(Z[ - Z c )
, ^
/
'

r-

. =

= 0'25UVTO

"

^ Chon A .

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

Ne'u ap d u n g

;

P,„^^.^

,

,.

/

<=> R + r = |ZL - Z ^ l => R = -20 < 0 : k h o n g thoa m a n .
1 0 ? : ( 0 + r)

-.H.-'^....,,

200^ 40

V i d u 2 4 : Cho mach dien xoay chieu RLC v o i R la bie'n tro va cuon day c6 dien
trcV thuan r = 1 0 Q. K h i R = 1 5 Q hoac R = 3 9 (.1 cong sua't cua toan mach la
n h u nhau. De cong sua't toan mach cue dai thi R bang
A.27Q.

B. 2 5 Q .

Vi du 27: M o t doan mach mac noi tiep gom cuon day c6 dien tro thuan 40 (Q),

C. 32 Q .

Huatigdan

D. 36 Q .

'

'

do t u cam L = 0,7/7t (H), tu dien c6 dien d u n g 0,l/7i (mF) va m o t bien tro R.

'

Dien ap 0 hai dau doan mach on d i n h 120 V - 50 H z . K h i R = Ro t h i cong sua't

( R , + r ) ( R 2 + r ) = ( Z L - Z c f = ( R o + >-)'

toa nhiet tren bien tra dat gia trj cue dai la Pm. Gia t r i Ro va Pm Ian l u g t la

cin'M oh-finGQ

Ro +10 = 7(15 + 10)(39 + 10) 3 ^ Ro = 25(Q) => Chon B.

V i d u 25: Cho mach dien noi tiep g o m tu dien, cuon day c6 dien t r a 10Q va

A. 30 (Q) va 240 (W).

B. 50 (Q) va 240 (W).

C. 50 (Q) va 80 (W).

D . 30 (Q) va 80 (W).
'

bien t r o R. D o lech pha giua dien ap hai dau doan mach va d o n g dien qua
mach Ling v o i cac gia trj R: = 260Q va R2 = 470Q cua R la cpi va (p2.

j

tyl

P = I^R^

Bie't (pi + (p2 = K/2. Cho dien ap hieu d u n g giua hai dau doan m.ach la 150V.

« .

Huong dan
2=

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

^ \

>^

R + i ^ L - - ? c ) _ l i ! + 2r

'

'

"

Goi P I va P2 la cong sua't cua mach u i i g voi R i va R2. T i n h Pi va P2.
A. Pi = 40 VV;

P2

= 40 VV.

C. Pi = 40 W ;

P2

= 50 W .

*

' '

Huovg
Ne'u hai gia tri R i ,

R2

de Pi =

P2 = P

B. Pi = 50 W ;

P2

= 40 W .

D. Pi = 30 W;

P2

= 30 W .

;

5!"

Pmax=

dan

2^(ZL-ZC)

thi tu P =

^

+

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

Z] - Zc Z i - Zr-

=>—1=

Ri+r

144

,

,

2

'

.

i

^'^-- = 2 ( R o + R . , „ „ )
/•

-ir-o

=50(Q)

•

'f

-

rt

^ = 1 :=> t a n t p i tancp, = 1 = > ( P i + 9 2 = —

R2 + r

^ 0 = Z c o n lai

2

=0=>
( R , + r ) + (R2 + r) =

R =7(ZL-Zcf+

-80(W)

^flc/z nha nhanh: Cong sua't trcn bicn tra cue dai khi bien tra = tong tra plian con lai:

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

.(R + r ) 2 - ^ ( R + r) + ( Z L - Z c f

+r^+2r

.

,

27(ZL-Zc)' + r2+2r

P .

^ , f^TO.i

l>< 'i •

.00'

'
^^.v

^* d u 28: Cho doan mach xoay chieu noi tiep g o m bien t r a R, cuon day c6 dien

i

t r o thuan 30 Q c6 cam khang 50 7 3

S j
,i.

•

. .

Q va tu dien c6 d u n g k h a n g 20 N/3 fi.

145


Bo tr^ hien thiic

V^t li LTBtl

tren kenh

VTV2.

t^p 2 - Chu Van

Cty Train MTV own

Btin

Dieu chinh R de cong suat tren R c6 gia Ian nha't thi h§ so cong suat cijg
toan mach khi do la
A.2/V7.

PRn^ax «

,

;

B. 0,573.

C.0,5V2.

Huong dan

RO = Z.on 1„ = ^^^Z^

=

D.3/^/7.:'

60(Q)

A. 45,6 Q.

60 + 30

7(Ro+rf+(ZL-ZC)^

^(60 + 3 0 ) 2 + ( 5 0 7 3 - 2 0 V 3 f

;>

Huang dan
^ R max <=>• .R i

ZL-ZC

P m a x « > R 2 = | Z L - Z c | - r = 10(Q)

.A =^ChonC.

Pmax<»R2+r=

i '

Huong dan

^ r^ + ( Z L -Zcf=

7(?

N2

Z L - Z C nen r^ + ( R 2 + r)'' = 76^

PRmax ^ R 2 + r

R, + r

Pmax

76+ r

R] + r

D. 12,4 Q.

(2).

2

Tu (1) va (2) giai ra: r = 45,6 Q va R2 = 15,2Q.

'

'

Chu y; Khi PR,m,x thi R = Zed,, im, neu ve gidn do vec ta ta se dm vao tarn gidc can
tr<;n gidn do.
Tarn gidc AMB can tai M nen:

r = 30(Q)

= Zcon 1,. - ^ / r ' + ( Z L - Z c f = 50(Q)

C. 15,2 Q.

PR max « R1 = Z,6n lai = ^r^+iZf^-Zcf

29: Cho mach dien RLC mac noi tiep, L c6 dien tra thuan r, con R la bien
tro. Dat vao hai dau doan mach dien ap xoay chieu on dinh. Dieu chinh Ian
lu(?t bien tra R c6 gia tri Ri = 50 Q va R2 = 10 Q thi Ian lugt cong suat tieu thu
tren bien tro cue dai va tren doan mach cue dai. Tinh r.
A.50Q.
B.40Q.
C.30Q.
D.20Q.^

i

B. 6a8 Q.

1

COS(p =

Vi

VIft

V i du 31: Cho doan mach AB mac noi tiep gom tu di§n, cuon cam va bien tra
R. Dien ap xoay chieu gifra hai dau doan mach luon on dinh. Khi R = 76 Q
thi cong suat tieu thu tren bien tra c6 gia tri Ian nha't va bang Po. Khi R = R2
cong suat tieu thu cua mach AB c6 gia trj Ion nha't va bang 2Po. Gia tn ciia
R2 bang

73

Rn+r

Khang

9conlai

0,5U

=40(Q)

'
ta tinh duvc cdc gia tri cong suat cue

Binh luan: Sau khi tint ditgc r va | Z L

dai tren R, toan mach va tren r:
R = Rl=>PRmax-

2(Ri+r)

RRmax

P

U2
R = R2:^Pn

P

2(R2+r)

+r

Rj + r
V i du 32: Cho doan mach xoay chieu noi tie'p gom bien tra R, cuon day c6 dien

rmax

tro thuan r va tu dien C. Dieu chinh R de cong suat tren R Ian nha't. Khi do

max

dien ap giiia hai dau doan mach Ian gap 1,5 Ian dien ap gii>a hai dau dien

P

U^r

R = 0:

max

R2

tro. He so cong suat cua mach khi do la

r'+(ZL-Zc)'
V i du 30: Cho mach dien RLC mac noi tiep, L c6 dien tra thuan r = 30 Q, con R la

A. 0,67.

B.0,75.

cue dai

PRmax

thi R I bang
A.50Q.

Til- cong thuc
Chon D.

va tren doan mach cue dai

Pmnx.

Neu

PRnux/Pmnx

= 0,5 va R2 = 20 ^

^ '^-^1^;

• '^t- ^'

Huong dan

bien tra. Dat vao hai dau doan mach dien ap xoay chieu on dinh. Dieu chinh
Ian lugt bien tro R c6 gia tri R i va R2 thi Ian lugt cong suat tieu thu tren bien trO

C. 0,5.

COS(p' :-

0,5U

0,5.1,5Uu

-77—=^ - r f

„

= 0,75

Chon B.

^

,'

• '

'

• V i du 33: Dat dien ap u = U >/2 coslOOnt (V) vao doan mach xoay chieu noi tiep
B.40Q.

=

Ri + r

C.30Q.
Huang dan
thay so vao 0,5 =

D.70a

gom bien tro R, cuon day c6 cam khang Z L = 400, dien tro thuan r = 20Q va
tu dien CO dung khang Zc = 60 Q. Dieu chinh R de cong suat tren R Ion nha't.

20 + 30
Ri + 30

.Ri=70(Q)

Khi do dien ap giua hai dau doan mach chua cuon day va tu dien la 150 V.
TinhU.
A. 150 V.

B.261V.

C.277V.

D. lOOV.


to'trfiklen

thu'c

V$tllLTDIt

tten kenh

VTV2,

t^p 2 - C l i u

Huotig

V^n

Bien

dan

Up,

= IZ|„ = U

tan(p,Lc =
COS(p =

^

U = 2UR COS (p = 2.150COS —

;.

R thai/ doi lien qiian den cur tri I, UK, UL, UC, URI,

'

I, U L , Uc luon nghich bien theo R
1=

URC, UI.C

CI

u l.m>ix

u

I,

|Z,,-Zc|

* = * i m i n

uz,

=o;u;.L

u

Cm

ax

pf:-

lai!)

Z , = 2Ze (Zr m (fi = 2 / « » Z c a /rti/)

100Q, Zc = 200^2, R In
.

A . R = 0 va Ui n,.. = 200

V.

Q va ULmnx = 200

V.

C . R = 0 va Ui.m,,v = 100

V.^j. ' . /

Q va UL„>ax = 100

V.

j,^ ^i^^

, B. R = 100
' '

D . R = 100

dan
U,,

^z,,-z,f

-^cl
z,1, -z,

-i^7i%--100(V)

nz,,-zci

=> Chon C.

,. -

-

V i du 2: ( D H - 2 0 I 0 ) Dat dien ap xoay chieu co gia t r j hieu d u n g 200 V va tan so
k h o n g d o i vao hai dau A va B cua doan mach mac noi tiep theo thiV tir g o m
bien tro R, cuon cam thuan co do tu cam L va t i i dien co dien d u n g C thay

lR = -=>u„„,, =u

doi. Goi N la d i e m noi giua cuon cam thuan va tu dien. Cac gia t r j R, L, C
hCfu han va khac k h o n g . V o i C = Ci thi dien ap hieu d u n g giua hai dau bien

R^

*

( Z c ra (fi = 2 /rtM Z r a

u = 100 72 coslOOTit ( V ) . D i e u chinh R de Ui,,„.x k h i do

uz,.

U R luon dong bien theo R

L(z,-zj;

= UVR »

Huong

=o;Ue,„i„ =0

UK=IR=-

2 c = 2Z,

bien tro (0 < R < x). Biet dien ap giua hai dau doan mach co bieu thiVc

1,11^,11^

7R-+(ZL-Ze)'

^
yR-+(Z|-Z^.)

^

V i du 1: Mach dien xoay chieu RLC mac no! tiep, co Zi =

j.ct

u, =iz,,

R = 0

R =

UKC = IZKC- = U

~ 277 ( V ) ==> Choii C.

, '^'+Z|,
_ ^
VR"+(Z,,-Ze)

U R I luon nghich bien theo R k h i Zc < 2 Z L

tro R CO gia trj k h o n g ctoi va khac k h o n g k h i thay d o i gia t r i R cua bien tro.

va luon dong bien k h i Zc > 2 Z L

Voi C = 0,5Ci t h i dien ap hieu d u n g giua A va N bang
A. 200 V.

R^+Z?.

B. 100

V2 V.
Huong

^R^+(Z,-ZJ^
R = 0=>U,,i, = U

UR = I R = - P = — — = « R « z , ,
Z,

C. 100 V,

D . 200

dan
=z,
. i:v

^2

-Zc

R = 00 => U K , = U

C = -±^Z,.=2Z,,

=2Z,

V2 V.

=>UK,,=IZ„

_

•(&'^-i.\io;

: ... .

.„ .

URC luon nghich bien theo R k h i Z L < 2Zc
va luon dong bien k h i Z L > 2Zc
R-+Z^-

URC=1ZRC = U

'R
R = 0 => UKC = U

+(ZL-Zcr

= U

\z,<2Z,

u

z,.

Cac truong hgp de thi hay khai thac
Up = IR =

= UVR <=> Ze = Z , 0««c/i cpn^ hu&ng!)
>^^+(Z,-Zef

R^ + Zf

I

= u J i ^ - ^ f r - ^ ^ = u = 2oo(v)
^R-+(Z,-2Z,.)-

, ^^,.f,.

;

V i du 3 : (DH-2010) Dat dien ap u = U V2 coscot vao hai dau doan mach A B gom
hai doan mach A N va N B mac noi tiep. Doan A N g o m bien t r o R mac noi
tiep v o i cuon cam thuan co do tir cam L, doan N B chi co tu dien vtii dien

R = «! => U^c = U

*

+ zr

R-+(Z,,-Ze)-

=> Chon A.

R

ZL-ZC

R-

d u n g C. Dat coi = 0,5(LC)^'^ De dien ap higu d u n g giua hai dau doan mach

II

A N k h o n g p h u thuoc R tiii tan so goc co bang

A. 0,5o)i/V2.

B. (01V2. \. W1/V2.

D . 2(01.
149


v^i

f t ^jrmr^TCWt

nKMMn-rTV^,

jr — « ntt

t^p

Huong

van

OiCfT'

tan so' f thay d o i d u g c . K h i f = 50 H z t h i c u o n g do d o n g d i e n hieu d u n g

dan

trong mach la 2 A va d i f n ap h i e u d u n g giu-a hai d a u RL k h o n g thay d o i k h i
p thay d o i . D i e n d u n g n h o nhat cua tu di?n la
A. 25/7t C^iF).
B. 50/71 (^iF).
C. 0,l/7i (|aF).

=>

Huang

= 2coL = > CI) = — ? = V 2 = CO, v 2 => Chon B

coc

2VLC

'

;' .

'

= I.ZRT

V i du 4: Dat d i e n ap xoay chieu c 6 bieu thirc u = U >/2 coscot (V) (trong d o U va
CO k h o n g doi) vao iiai dau A B ciia m o t doan mach g o m doan mach A M noi
tiep v o i doan mach M B . Doan mach A M c6 cuon cam t h u a n c6 d o t u cam L
va bien t r o R mac noi tiep, doan mach M B chi c6 tu d i e n c6 d i e n d u n g C.
Bie't rang co = (2LC)~^''''. K h i thay d o i bien tro den cac gia t r i R i = 50 Q , R2 =

100 Q va R 3 = 150 Q t h i dien ap hieu d u n g giua hai d i e m A M c6 gia t r i Ian
l u g t la U i , U2, U3. Ket luan nao sau day la dung?
A. U l < U 2 < U 3 .

M l ;

B.Ul>U2>U3.
C. U l = U 3 > U 2 .
Huong dan
R- + Z f

ZC=2Z,=^U„L=IZK,, = U

D. U l = U 2 = U 3 .
,.,

= UgR=>ChonD.

;i

= (Z, - Z c = >

Zc = 2 Z ,

R2+(ZL-ZC)

u

ZL<100Q

Z . 7 F 7 z [ = y = 100Q

1

2ZL < 200Q n> C >

^Zc^

dan

, . R «

^ ^ ^ ^

=u.

D . 0,2/7t (^iF).

^

'

50

.10-*' (F) ^ Chon B.

10071.200

Vi d v 7: (DH-2010) D a t d i e n ap xoay chieu co gia t r j hieu d u n g va tan so k h o n g
doi vao hai d a u d o a n mach g o m bien t r o R mac noi tiep v o i t u d i e n co d i ^ n

d u n g C. G g i d i e n ap hieu d u n g g i i i a hai dau t u dien, g i i i a hai d a u bien tro
va he s o c o n g sua't ciia doan mach k h i bien t r o co gia t r i R i Ian l u g t la U c i ,
URI va coscpi; k h i bien t r o co gia trj R2 t h i cac gia t r i t u o n g u n g n o i tren la
Uc2, UR2 va coscp2. Bie't U c i = 2Uc2, UR2 = 2 U R I . Gia t r j cua coscpi va coscp2 la:

V i d\ 5: Xet mach d i e n A B g o m cac phan t u mac noi tiep theo t h u t u la cupn
day thuan cam c6 d o t u cam L, dien t r o thuan R, tu d i e n c6 d i e n d u n g C.

A. coscpi = 1/N/3 , coscp2 = 2/V5 .
C. coscpi = 1/75

Gt)i M la d i e m noi giua L va R, N la diem noi giua R va C. Dat vao A , B m o t
dien ap xoay chieu c6 gia trj hieu d u n g U k h o n g d o i va tan so'goc co thay
doi duc7c. K h i Ian l u o t cho co cac gia trj c o i , C02, co3 t h i Ian l u o t dien ap hieu
d u n g giOa hai dau M N , giua hai dau A N , giua hai dau M B deu bang U . K h i
do, he thuc d u n g la:
A.

C03 =

C02/>y2

• • , B .

= coi/2.

C. C03 = C02/2 = coi/V2 .

<

CO, xay ra ccing h u o n g d i e n nen coi =

'^ci

N/2

C02

= 2coi.

, COSCP2 = 2/75 .-- ' '
D . coscpi = 0,5/72 , coscp2 = 1/72 .
Huang dan
i . , '
' i •ifi 7,, J<1 ; i

u

= IZ,

+z^" = 2

nn=2Uo^ii=2i?^Z2=2Zi
R.

^^.

dan
.—
vLC

= 2Z[,2 =>

^
=

r =

2-

JifTz^

R2=4Ri

Ri

Zr-2Ri

1

"
=> Chon C.

COSCP2

^

4i
VLC

2- L, C va CO thay doi lien quan den cpng huong.

S u y r a 0)3 =2co2 =c)|V2 =:> C h o n D . ' ^
Vi du 6: Cho mot doan mach xoay chieu g o m dien t r o thuan R thay d o i dugc,
cuon day thuan cam L va tu dien C theo thii t u mac n o i tiep v o i nhau. Dat
vao hai d a u doan mach mcit dien ap xoay chieu co gia t r i hieu d u n g 200 V

-^...^r

Ri

coscpi =

(!), l a m cho U[^(j = U nen Z, 3 = IZ^^ =>o)3 =

50

Z

=

1/73.

D . C03 = 2co2 = coi 72 .
Huong

lam cho U,^L =

C03 =

I = ^

B. coscpi = \lsl5 , coscp2 =

• •

ZL = Z c <=> « L =
Dieu kien cgng h u o n g :

1
coC

IZL=IZC<=>I"L = I

R
A

C

L,r

M

N

B

1
coC
151

thufc

V^t

HLTDH

trcn

kcnh

VTV2,

u

t^ip

2 -

Chu

Viin

Bicn

U

(R + r ) 2 + ( Z ,

- Z ^ f

R + r
U

R + r

=r

p

r =

I -

o

(

u

Khi L, C va lo thai/ doi thi P,,,,,,, = —

u

R +r

U

p

Cty

R + r

^-

R + r
U

U

„

R +r

R +r

y

U

0,1/Tt

Khang

Vi^t

Z, = Z^-.

khi

chieu giua A va B co gia t r i hieu d u n g va tan so !u6n khong d o i . Ban dau
R^+Zf

L = L I , cho R thay d o i k h i R = Ri thi cong suat tieu thu cua mach A B Ion nhat

R^ + Zi
|Z,,-Z,.| = 0

V i du 1 : Doan mach noi tiep g o m cuon day co dien t r o thuan 1 0 Q, c6 do tu
cam

l i VVtl

cam L thay dcii duoc, mot tu dien C va mot bie'n tro R. Bie't dien ap xoay

la

(Pi)ni,ix

= 92 W . Sau d o co d i n h R = Ri, cho

suat tieu thu cua mach A B Ion nhat la
A. 2 7 6 W .

Gia t r i cua

D . 92 W .

"( ,

Khi

C va

L,

(0

thay d o i t h i

,

P,,,,,,

:• ; ^

,

.

= —^

bang

'

K h i R thay d o i thi P,,,,,I =
2R|

thi cong

L = L2

(P2)max

C. 184 W.
Huong dan

H , tu dien co dien d u n g C thay doi va mot ampe ke'co dien tro

rat nho. Dat vao hai dau doan mach m o t dien ap 5 0 V - 5 0 H z . Thay d o i C

thay d o i , k h i

L

(P2)m,ix.

B. 4 6 W .

R+r

R + r

MTV

V i du 3: Cho doan mach dien khong phan nhanh g o m mot cuon cam co do t u
z,

U

V

TJytlll

,

' ' ^ ' v
.

' max2 = 2Pniaxi

,

,

.

= 184(W) ^ Chon C.

thi so chi cua ampe ke'la cue dai va bang 1 A . Gia trj cua R va C la
, A . R = 50 Q

va

C =

Hn

mF.

B. R = 5 0 Q

C. R = 40 Q

va

C =

l/n

mF.

D.

•

R = 40

va

C

O va

= l / n mF.

V i du 4: M o t cuon day mac noi tiep v o l tu dien co dien d u n g thay d o i d u g c roi

mF.

mac vao nguon dien xoay chieu co bieu thuc u = Uocoscot (V). Thay d o i dien

C = I/TT

d u n g cua tu dien de cong suat toa nhiet tren cuon day dat cue dai t h i k h i do

Hu'6n
u

1 =

• = max o

dien ap hieu d u n g giua hai ban tu la 2Uo. Dien ap hieu d u n g giua hai ctau

())L-- - = 0

cuon day luc nay la

+ r)^ + (oL ~

(R

C =

A, 3 U o v ^ .

10

•••1

lOO^K^.M

-3

n

-(F)

U^r

T2

l\ r r

=

C. 1,5U()N/2.

D . 4U()V2.

-y = max

^
^
r:> Z L = Zc

^
Z = r

' U
I,,,,^ = — =

Uo

r

rv2

r ^+(7,-7-)
^+(ZL-Zcr

.Chon D.

= l ( A ) = > R + r = 5 0 = > R = 40(Q)

V i du 2: Cho mach dien noi tiep g o m cuon day thuan cam co d o tu' cam L tiia\
doi du-OQ t u dien co dien d u n g l/(6Tr) (mF) va dien tro 20 Q. Dien ap dat vno
hai dau doan mach u = UocoslOOjit (V). Xac d j n h d o tir cam ciia cuon day dt'

U c = l Z c - • ; - ^ . Z c = 2 U o - > Z c =2V2.r.;.. ,. , v „Opl^,^,.a,
rV2=>ClionC.

Uo /TTTT

Ucd=IZea=;;j^V'
V i du 5: Mach

ditMi

Uo / T T T T _ 3 U „
.8,

- - ^

'

,.v:

>^-'
rv.

xoay chieu ncYi tiep gom dien tro thuan R, o n g day thuan

dien ap hieu d u n g giua hai dau d j a n mach chua RC dat gia t r i cue dai.

cam CO cam khang Zi = 2R va tu dien co dien d u n g C thay d o i dugc. K h i

A . 0,6/K ( H ) .

thay d o i C den gia t r i Co thi cong suat tieu thu tren mach dat cue dai la

B . 0,8/71 ( H ) .

C. 0,4/Tr ( H ) .

D , 0,3/71 ( H ) .

Huong dan
U
KC

\

R" + Z^- = mnx <=> Z , -Zr

R^+(Z,-Ze)^

, 1
• coL =
WC

,0,6
=> L =
( H ) =>Chon A.

^

71

=0

Pm.,x = 100 VV. K h i thay d o i C den gia trj bang 2G) thi cong sua't tieu thu tren
mach la :
A. 25 W .

khi

B. SOW.

R^ = \Zy - Z ^ .

1 - A"

C. 60W.|

Huong dan

A'
P.iiax

Chu \j: Khi R thai/ do} thi P,„_,^, =

152

B. 3Uo.

'

i, '-.i

,

Huong dan

J-'

U

'

(

D . SOW.
...

cong hudng Zco = Z L = 2 R

\^:'MnMKU.r:

• •
152


tS trff kI6n thitc V$t li ITUtI m» Kerm-viVJ.

C = 2Co

Z r = - Z r o = R =^ P =

t^p u - unu van aieir

R2+(ZL-Zcf

2R

= 50(W)

:=>ChonD.

d u 6: (DH-2009) Dat dien ap xoay chieu c6 gia t r i hieu d u n g 120 V , tan so
50Hz vao hai dau doan mach mac n o i tiep g o m dien t r o t h u a n 30 Q, cuon
cam t h u a n c6 d o t u cam 0,4/7t ( H ) va t u dien c6 d i e n d u n g thay d o i dugc.
Dieu chinh dien d u n g cua t u dien thi dien ap hieu d u n g giOa hai dau cuon
cam dat gia t r i cue dai bang
A . 150 V.

,

B. 160 V .

C. 1 0 0 V ; A ' h G

Huong
U,

D . 250 V .

7R'+(ZL-ZC)'

mach no'i tiep g o m dien t r o thuan 200 Q., cuon cam t h u a n c6 d o t u cam
25/(36TI) H va t u dien c6 dien d u n g 10 VTI (F). C u o n g d o h i ^ u d u n g d o n g
dien qua mach la 0,5 A . Gia t r i ciia CO la
p^, 15071 rad/s.

j , B. 507i rad/s.
:

U

ti'^'-

200^ + c o L -

dan

. Z L =160(V) ^ C h o n B .
VR^+0

= I . Z , =•

y i dV 9: Dat d i e n ap u = 100 N/2 coswt (V), c6 co thay d o i d u g c vao hai d a u doan

d u 7: Dat d i e n ap 150 V - 50 Hz vao hai dau doan mach mac no'i tiep g o m
cuon day c6 d i e n t r o thuan R , c6 d o t u cam L va t u d i e n c6 d i e n d u n g C.
Thay d o i C d e d i e n ap gii>a hai dau cuon day dat gia t r j cue dai t h i gia t r j d o
B. lOOV.

C. I O O V 2 V .

Huong
U,,=I.Z,,=

D. 150N/2V.

r + ( Z L - z c r

• = 0,5=>(oL = ^
coC
coC

l0/(247i) mF. D e hieu dien the hieu d u n g giua hai dau doan mach chua L C
A. 60 H z .

B. 50 H z .

ULC=IZLC=-

-—TT^

1 ^

= 60(Hz)

U L = 200 =:> U c = 2 0 0 ( V ) =5 Chon A.

' ''

'

' ';'

tan so f2 = 120 Hz, he so cong suat la 0,5 N/2 . 6 tan so b = 90 Hz, h ^ so cong
!'
B. 0,486.

C. 0,625.

Huong dan

d o g i a m d a n d i e n d u n g t h i goc lech pha giua d i e n ap tren cuon day va dien
A . 7i/2 va k h o n g thay d o i .

I'l i)(

B. 7r/4 va sau d o tang dan.

\,

Jin

Huong
= coL = 5 0 ( Q )

dan

r

tancp =

ZL-Z,

= 1

i ^ = -l=>(p = —
4

,

'

,j

j ;)

vnivi ..i

,

f = f2 = 120 (Hz) = 2fi =>

,
^
ma
coscp,
=0,5V2
hay
Z'c =0,5a

R

R

C. 7r/4 va sau d o g i a m dan.
D . 71/2 va sau d o tang d a n .

D . 0,781.

,,,„,vj u';^;vn>uh wm

f = fj = 6 0 ( H z ) = > c o s ( p , = 1 = > Z L = Z c = a

ap toan mach luc d a u la

54

Chon A.

'

chieu CO tan so thay d o i dugc. 6 tan so fi = 60 Hz, he s o c o n g suat bang 1. 6

mot dien ap xoay chieu o n d j n h c6 tan so 50 H z . L i i e d a u C = 0,l/7c (mF) sau

(Pj,£) - (p = — => Chon D.

= Zc

ZL

2nJ-

suat cua mach bang

=100(Q)

= min = 0 «

ZL - Zcl

^

D . 40 H z . / ? ...

dan

>2+(ZL-ZC)

A. 0,874.

Zci=-

C. 55 H z .
Huong

tiep v o i m o t t u d i e n c6 dien d u n g C thay d o i . Dat vao hai d a u doan mach

]

•{O = 1207r(rad/s) =:>ChonD.

I6n 247t
Vi d u 11: Mae vao doan mach R L C k h o n g phan nhanh m o t n g u o n dien xoay

d u 8: M o t cuon day c6 dien t r o thuan 50 Q, c6 d o t u cam 0,5/7r ( H ) , mac noi

ZL

.,,p,,.„o^

dat gia t r i cue tieu thi tan so bang

UK = U = 150(V)

>0
U ? d = U f , + u2L=2502

D . 12071 rad/s.

di^n xoay chieu R L C mac theo t h u t u d o c6 R = 50 Q , L = l/(67t) H va C =

dan

= max o Z L = Z(2 = >

..

Vi d u 10: D a t hieu d i e n the xoay chieu c6 f thay d o i vao hai dau doan mach

f =

UVR

'•

C. IOO71 rad/s.

Hudngdan

b3ng 250 V . Luc nay, d i e n ap hieu d u n g tren tu bang
A.200 V .

..

Z ' l =2a

= 0,572:

R2+(Z'L-Z'cf

. 7 - , ' ! v ( ..
>R = l , 5 a

VR2+(2a-0,5a)2

^

Z"L=l,5a
f = f 3 = 9 0 ( H z ) = l,5f,

• COS(p3 =

Z"c =

R
7R'+(Z"L-Z'C)'

2a

1,5a
c
1,5a
1

* 0,874 =>ChonA.
2a
155


Bo

trf> kien

thiic

V^t

II LTDtl

trcn

henh

VTV2.

t^p

2 - Chu

Van

Bien^

V i d u 12: Goi ii, LIK, U I va I R Ian l i i o t la dien ap

Cach 2: D u n g gian d o vec to

tiic tiiai giua hai dau macii, liai dan diC'ii tra
R, hai dau cuon cam thuan L va hai dau tu '

"'

dien C cua doan mach xoay chieu noi tiep.
Ban dau mach c6 tinh cam khang, sau do

i ' - ' ^ -

'

^ g i a m dan tan s o ' d o n g dien qua macii thi dai
; :x|i l u g n g giam theo la do lech pha giu'a
A . u va uc.

B. u i . v a u i ^

C.

D.

UI

va u .

j b n m nr"h

UK

ir»|-

: , "j ^

>

'

Huong dan

^'c

vr,o;

N

Sau do f giam thi cam khang giam dan nen U quay vc phia T nghia la do
Ta c6: sin a =

Chon A.

V i d u 13: M o t mach dien xoay chieu gom RLC ghep no'i tiep. Ta dat vao hai

U

pha h o n d i e n ap u . N e u chi tang dien d u n g C t u tir t h i h ^ so cong suat cua

C. g i a m nhe roi tang ngay.
.>
n

R

'

'

B. tang.

j-

D . giam.

')7fVn£

K i l l t Ant; ('111)/(^-=

f;i:nii n r n

(/.(^'--/.[)"

'

Kiiiiil

V

He

U

sin p

sina

U

R2

„„o _^

;

,,

I

, T

=> U 1 UR,_^-

^

,

..,

uJR^ + z
»6b ifirt

R

uz,

UZ,

7R'+(ZI - Z e f

^(R-+Z^.)-2ZeZL+z'L

A,,'f

^

xj

L.,

+ Z^^ = Z C Z L ^

ZL

''

•B

b^+c^

,j,«,^^^,_,„

U R - U c ( U L - U c ) » h 2 =b'c'

1
o

'

qua:

=U,.(UL-Uc)ob2

- = max

i j y W l n

= - y - ^

1

1

1

ij,

=ab'
1

U?
[Ul

U

;.'nvh

Z^N = Z^N-ZNE

u[=U^+U^^U|c^a2=

3. L, C thay d o i l i e n q u a n den d i e n ap h i e u d u n g .
(7. Kill L tliiiif doi fun dieii kieii Ui.iii,n
',i,«?^'t>*'
^
A M:
Cdch 1: V i

"I..

...

sin a

C h o n B.

, u , , = IZ,, =

„

!- = m a x » P = 90

AN^ = MN.NB o
«

->cos(p taiig

JR-+(Ze-ZO^,,QJ.§,;-•;•^-

Z AN

•=>U| =

sin a

Khi do:

'

AN

U

Huong dan

Cl)S(p = — 7 =

•

sinp

"("-S

A . k h o n g thay d o i .

A M _ Z,,M

A p d u n g d j n h ly h a m stYsin cho tam giac A N B :

dau doan mach m o t dien ap u = UusinlOOTit (V). H i e n tai d o n g dien i sum
mach ban dau se

U,'RC

Uc

'^•'vl it/'i :(.';

Luc dau mach co tinh cam khang nen U nam tren I .
lech pha giua u va uc g i a m

O

>

—

va uc.
•

I

M

W

^

1

"c^

•

'

'

V i d u 1 : Cho mach d i e n noi tiep g o m cuon day thuan cam c6 d o t u cam L thay
d o i duoc, t u d i e n ccS d u n g khang 60 Q va d i e n t r a t h u a n 20 Q. D i e n ap dat

2

,

.

<=> ax + b\ c = mm <=> x =

h
2n<=>

vao hai dau doan mach u = 20 Vs coslOOTit (V). K h i cam khang bang Zi. t h i

i
Z|

dien ap hieu d u n g tren cuon day dat gia trj cue d a i

R-+Z^.

Ui-irax.

Gia t r j Zi. va U:

m.nx

Ian l u o t la
Thay bieu t l i i i c Z i vao U ,

— tinh ra: U| ,
>^+(Z,,-Z,.)^

156

R

A . 200/3 Q va 200 (V).
C. 200 Q va 200 (V).

B. 200/3 Q va 100 (V).
^

D . 200 Q va 200 (V).

,
;

.
,
157


B6 trp klen

thiic

V$t I I L T D I 1 tren

kcnh

VTV2.

t^p 2 - Chu VHn Bl&n

V i du 4: (DH-2009) D a t dien ap u = Uncoscot vao hai d a u doan mach mac n o i

j'/r.;;)

Huong dan

T r u d c k h i lam bai nay, chung ta phai nhuan n h u y e n p h u o n g phap da noj

tie'p g o m d i e n t r o t h u a n R, tu d i e n va cugn cam t h u a n c6 d o t u cam L thay

tren. Va luc nay ta k h o n g nen lap lai cac buoc tuan t u m a nen ap d u n g

d o i dugc. Bie't d u n g khang cua tu dien bang R>/3 . D i e u c h i n h L de dien ap

t r i n h giai nhanh nhir sau:

hieu d u n g giOa hai dau cugn cam dat cue dai, k h i d o

u

A . d i e n ap g i i i a hai d a u d i ^ n t r o l§ch pha n/6 so v o l d i e n ap giOa hai dau
L max

doan mach.

R

;X ; ' T ' ' ^ ' • ^ 4 ' ' n-,?:;

B. dien ap giOa hai dau tu dien lech pha n/6 so v o i d i e n ap gii>a hai dau
ION/TON/ZO^

'-'Lmax

Thay so vao ta dugc:

z, =

+60^

20

20^ + 60

200

60

3

d o a n mach.

= 100(V)
> Chon B.

...j.^. M/,,,,,.. .•

D . d i e n ap giOa hai dau cugn cam lech pha n/6 so v o i d i e n ap g i u a hai dau

doan mach.

l^idndovectode'tiinnhniilike'tqiid.

5:.j,j;!:p.i/:,i',,rj'

Huang dan

tan a = — ^ = —!^ = - =
UK
R
V3

u = UV2 coslOOiit vao hai dau doan mach

^
e a c h 2: U , . . . «

t u cam L thay d o i dugc. D i e u chinh L de

bang 100 V va d i e n ap hieu d u n g 6 hai

UL

max <=>

1

t

0 1

iJ^^^•,

r

Hu&itgdan

=> Chon A.

•-•fei''•s(y'':,.Ji-pt

J-^)'^-^'-'

1(l^y.>4..\J:.~,-.;,ijl:',[i

,
''i j '

,

d o i dugc, t u dien C va dien t r a R. Dien ap dat vao hai d a u d o a n mach u =
100N/6 coslOOnt (V). K h i dien ap hieu d u n g tren cugn day dat gia trj cue dai
Ui,M.ix t h i d i e n ap hieu d u n g tren tu la 200 (V). Gia t r j UIMM
•

•*

^ L m a x <=> U

dugc:
=5 Chon C.
158

B. 1 5 0 ( V ) .

1

"
URC' 3P

•yvJ-UUi::

:

C.300(V).

D . 200 (V).

:k:H&i

B. 50 Q.

C. 150 Q.

l i i : . : D . 200 Q.

; / C r ' ' ' K ' ^ ' . ' . H u o n g
dan
f Pmnx » cong hucing => Z i 1 = Zc

R 2 + Zr

ZL2 = Z L I

+ 50 nen:

Zc
^.Zr-^ 50 = ^ " " l " " . ^ ^ =^^c = 200(Q) =^ Chon D.
Zc
va cugn cam t h u a n , d a n g xay ra cgng h u o n g . Neu chi tang d g t u cam cu£
cugn t h u a n cam m o t l u g n g ra't nho t h i

d u n g he thuc l u g n g t r o n g tam giac v u o n g b^ = a.b' ta
3.100^ = U,. ( U L - 2 0 0 ) => U L = 300(V)
V - • >'^':-^l-:;-''K;''^;:;.:..i/.

A . 100 il.

V i du 6: C h o n phat bleu SAL Mach d i e n n o i tie'p g o m d i e n t r o thuan, t u dien

la

Hwang dan

= U , ( U L - Uc)

V3

mach d a n g dat gia trj cue dai ma tang cam khang t h e m 50 Q t h i dien ap tren

K h i L thay d o i :

' '

V i dy 3: Cho mach d i ^ n no'i tie'p g o m cugn day thuan cam c6 d o tir cam L thay

A . lOO(V).

Z^-

hai d a u cugn cam d a t cue d a i . T i n h d u n g k h a n g cua t u .

^:':•'••;•!';•-•••

U - =100(100-36) =>U = 80(V)

=- L = _L
R

day t h u a n cam L c6 the thay d o i gia t r j dugc. K h i cong sua't Lieu t h u tren
D . 48 V .

ap d u n g he thuc l u g n g t r o n g t a m giac v u o n g b^ = a.b' ta

dugc: U - = U | , ( U , _ - U f )

R

••••

V i dy 5: Cho d o a n mach xoay chieu RLC mac n o i tie'p v a i R = 100 Q va cugn

i ' ^
C. 64 V.

•

tan cp =

R'.ZI

=> (p = — > 0 : d i e n ap som pha h o n i , U K la n/6 => Chon A.

gia trj cue d a i t h i thay gia trj cue dai d o

: B. 136 V.

Z, = ^
Zc

d i e n ap hieu d u n g 6 hai dau cupn cam dat

Vv ( f

vM. . . o . i J •

=>« = - = > Chon A.
6
•

mac no! tie'p g o m dien tro thuan R, tu dien
CO dien d u n g C va cupn cam thuan c6 d o

:

'•\siAiS}\h

Cach 1: D u a vao gian d o vec t o ta nhan thay u s o m pha h o n UK la a va

V i du 2: ( D H - 2 0 n ) Dat dien ap xoay chieu

dau tu d i e n bang 36 V . Gia t r j cua U la

../v;

C. t r o n g mach c6 cgng h u o n g di?n.

Chil y: V&i cac bai toan chi lien quan den cac U hoqc cdc do lech pha ta nen dit)i<^

A . 80 V.

n'^i' V - ? ! / ' ; ' ./V;/-, v..

: ilVK,:)£';3

A . d i e n ap hieu d u n g tren dien t r o g i a m .
B. cong sua't toa nhiet tren toan mach g i a m .
C. d i e n ap hieu d u n g tren cugn cam thuan g i a m .
D . d i e n ap hieu d u n g tren cugn cam t h u a n tang.

)>0)i»vOt;i =

<;! U>'K \
f\n,- B V ; ' r I .
.• -

i •


Bo tr^ hicn

tliiic

V^t li LTDtl tren henh

VTV2. t^p 2 - Chu VSn

Cty Trmn nrv

Bien

Huong dan

Huang dan

Dieu kicn etc xay ra cong h u o n g va U i m . i x Ian l u g t la:

Khi

Cong h i i d n g <=> Z] | = ZQ

U

Zc

U[,T,ax => U J . UK(^- nen URC tre pha h o n u la 7t/2. D o d o : (p = -7i/4.

V i U K C = U = 100 V nen tarn giac A M B v u o n g can tai A , suy ra tam giac A E M

= z.•c

R2 => Z^i <

: D i e u nay cc ngiiTa la kiii

Z^

dang cong h u o n g ne'u tang L thi se tie'n den gia t r i Z1.2 ngiiia la U L tang dan
\if-f den gia t r j cue dai => Chon D .

t l w 'rA>h. ;<> _<«Kb

lyk nvit;

v u o n g can tai E => Uc = U R => Zc = 100 Q
=> C =

0,1.10,-3
-(F) =>ChonC.

a)Z|

7C

V i d y 9: Cho doan mach RLC mac noi tiep, v o l cuon cam t h u a n cc d o t u cam L

V i d u 7: Cho mach dien xoay chieu RLC co cuon thuan cam L c6 the thay d o i
gia t r i duoc. D u n g ba v o n ke'xoay chieu c6 dien t r o rat Ion de d o dien ap
jf.l: hieu d u n g tren m o i phan tir. Dieu c h i n h gia trj cua L t h i thay dien ap hieu

thay d o i d u g c . D i e n ap xoay chieu giua hai dau doan m a c h l u o n o n d i n h .
Cho L thay d o i . K h i L = L i thi dien ap hieu d u n g giCra hai ban t u dien c6 gia
trj Ian nhat, dien ap hieu d u n g giOa hai dau dien tro R bang 220 V. K h i L = L 2

d u n g cue dai tren cuon cam IcSn gap 2 Ian dien ap hieu d u n g cue dai tren

thi dien ap hieu d u n g g i i i a hai dau cuon cam c6 gia t r j Ion nhat va bang 275

dien tro. H o i dien np hieu d u n g cue dai tren cuon cam gap bao nhieu Ian

V, dien ap hieu d u n g giua hai d a u dien t r a bang 132 V . L i i c nay dien ap

dien ap hieu d u n g cur dai tren tu?
A. 3 Ian.

B.

4 Ian.

hh.-tim ©^'^ '^V^ t f

xyi w

t

C. 3 Ian.

Jfoi

D . 2/^/3 Ian.

hieu d u n g g i u a hai ban tu dien la
A. 96 V.

u

/"

u

Uc = max => Cong hucing => U R = U = 220(V)

=u

ULH,.,. «

u

0 1 URC

ul

+ U?,c = U - + uf, + U^-

=

=> 275^ = 220^ +132^ + Uc => Uc = 99(V) => Chon D.
b. Khi C thay doi tint dieu kien Ucm

l.mav

R

Cach 1 :
It

Theo bai ra: Ui.m.ix = 2 U K i n . i x hay — ^
+ R\3

D . 99 V .

C. 457 V.
Huong dan

K h i L thay doi t h i
U

'

B. 451 V.

Huong dan

m

O VVn Kbang Vl^t

Uc = IZc =

7 R^.(Z,

V i d u 8: M o t doan mach A B g o m hai doan mach j c;,

R

u

|(R'+Z^)-^V-2ZL-^-- + 1

^^^^ + bx + c

A M va M B mac noi tiep. Doan mach A M c6

b
<=> ax" + bx + c = min o x =

dien tro R = 100 Q mac noi tiep v o i tu dien c6 '
dien d u n g C. D o a n mach M B c h i c6 cuon

^(R' + Zf,)-2ZcZi,+Z^

f

U

Uc =

•Chon D.

hii

'

cam t h u a n v o l d o t u cam L thay d o i d u g c .
D a t dien ap u = 100 V2 cos(1007rt + n/i) ( V )
• ' vao hai dau doan mach A B . D i e u chinh L de
dien ap hi^u d u n g tren cuon cam cue dai, k h i
d o UAM = 100 N/2 cos(1007xt + ep) ( V ) . Gia trj cua
C va cp Ian l u g t la
A . 0,2/71 (mF) v a - 7 i / 3 .

B. 0,l/7i (mF) v a - T C / 3 .

C. 0,1/71 (mF) va -7t/4.

D . 0,05/7t (mF) va -7i/4.

l':iv„iU.,i

B

A

UZc

UZc

1
<=>—=

2a

ZC

.

= max

-I

. =oZc =

»

R^+Z^

'''''''

R ' + Z ^

UZc

Thay bieu t h u c Zc vao Uc = ,
yR^+(ZL-Zc)

t i n h ra: U C m a x ~

U^R^ +
^

Zl

^ach 2: D u n g gian d o vec to.
Ta co: sina =

AM

Z^M

AN

ZA N

R

A p d u n g d i n h ly ham so sin cho tam giac A N B :
sinp

^
sina

. U , = - ^ ^ = max«P = 90"=^0lURL

sina

161


B6

trpkiSn thiic V4t li LTDH

tr€n kenh

u

t^pZ-Chu

VTV2.

Bicn

V^n

C/!M V- ^(^w tiitjch CO nhieu dien tra thuan thi khi dp dung cong thi'ec tren can thay

u

R = l R -

sin a

Khi do:

AN'

Y j du 2: C h o mach dien no'i tiep g o m dien t r o 30^/2 0. cuon day c6 d o tir cam

= MN.NB «

= ZMN-ZNB »

R' +

= Z^-Z, => Z ^ =
Z,

0,3-42 In ( H ) va dien t r o thuan 30>/2 Q va t u xoay c6 dien d u n g thay d o i C .
D i e n ap giCra hai d a u doan mach: u = 240\/2 coslOOTtt (V). K h i C = Cm t h i
dien ap hieu d u n g giira hai dau t u dien dat gia t r i cue dai U m . Gia t r j cua Cm
va Urn ian i u g t la
A. 1 6 ( H F ) v a l 5 8 ( V ) .

.clnjfj / i d noi.-'i H.i?-
=o)L

U^R^Tzf

100^(6072) + ( 3 0 ^ )

R

60V2

B
,,2

U^; = U +

,,2

^

,,2

+ U,

, ^

ii = b + c

->

^•%> C

= U | ( U ( ^ . - U , )<=>lr = b c

•

U ' = U f ( U e - U| ) o b - = ab'

.UR

]

1

U-

UR,_

i^iih

1

1

1

n

D

c

.30V2

Xt^fYi

• ^,l«^iO

ulit

R
KhiC
=

UJR-+Zf

o Z,. =

uV^i

\iUi\

0

,

-„

,

gia t r i . Dieu c h i n h C de thay d o i d u n g khang Zc cua t u t h i thay: K h i Zc = 50
d u n g tren tu I o n nhat. T i n h dien t r o R.

R'+Z?P =

162

14QtR'^r

7

l^R

=

U-'R

R2+(Z,,-Ze)

C.5V2Q.

D.5Q.

,

dan

- = max o Zc = Z L = 5 0 ( n ) fp* ^;w|:^ "'^^'',^f'

:

KI.

( V ) . T i m C de dien ap hieu

« 297(V)

,

Wi^."

, .1

R^ + Z f ^ 20- +140^ _ 1000
ZL

B.5VTOQ.

-

R^ + Z

10072 cosiOOTit

20

R

'It.

(i)Z(-

Huang

d u n g giira hai d a u tu dien dat gia t r j cue dai. T i m gia t r i cue dai d o .
•of i
Hu6itg dan
Cmnx

lU.

Q t h i cong sua't tieu t h u cua mach Ion nha't, i
l,4/7i(H), dien t r o thuan 30 Q va tu xoay c6 dien d u n g thay d o i C. Dien ap

U

o)

V i du 3: C h o doan mach xoay chieu R L C v o i dien d u n g C co the thay d o i duoc

V i d u 1: C h o mach dien n o i tiep g o m dien t r o 20 Q cuon day c6 d o t u cam
giua hai dau doan mach: u =

I

= -^""^^ICio"^ ( F ) => CHon D .

A.5V3Q.
o Z, =

dan

• n O O ' t - ' ' ! ••-'Ij cr:x'!.''i^5; cr.;r-v'^^

= 30V2(Q)

U
.V P(> . 0

D . 15 (|.tF) va 120 (V). nl of.t

.4
Huong

Z,

'

' B. 15 (^F) va 158 ( V ) .

C. 16 (nF) va 120 (V).
M

2

\

50
• Chon B.
V i du 4: M a c h dien g o m dien tro thuan R = 150Q,

;

ijsuf.

cuon thuan cam L = 2/n H va t u dien co dien
d u n g C bien d o i mac no'i tiep vao hai d a u A , B
CO dien ap u = 120 V^coslOOrct (V). K h i C thay

doi t u 0 de'n rat Ion t h i dien ap hieu d u n g giiia

no

hai ban tu
A . tang tLi 120 V den 200 V roi giam ve 0.

<Bfia>,

^

B. tang t u 0 de'n 200 V roi giam ve 0.

,j

z.
163


Ba

tr^

hicn

tliiic

V.il

l i I.

roil

VTV2, t$p 2~Chu

l i c i i Itcnh

VSu

BlSn

Cty TimnMTV

C. tang tu 120 V den 220 V roi giam ve 0
D. giam tu 120 V den 0 roi tang den 120 V.
Huang dan
u

12oVl50^ + 200^
Cmax

Zc =

150

R

Dua vao do tlii

= 200(V)

UOZr

7R^+(ZL-Zcf
'C = 0=>Zc =<x.=>Uc = U = 120(V)
thay: • C=oo=>Zc =0=>Uc =0

- - r^..

A A M B : A M = ^ 2 0 0 ^ - 1 6 0 ^ = 120

UZc

= IZ^- =

7^50^ +(200-Zef
.'I -

^
,

;

Vi^t

Vi dy 7: Dat dien ap xoay chieu c6 gia tri hieu dung 160 V vao hai dau doan
mach RLC noi tiep. Khi do dien ap tren doan RL l§ch pha nil so voi dien ap
hai dau doan mach, dien ap hifu dung tren ty bang 200 V. Dien ap hi^u
dung tren dien tro R la
C 9 6 V . j,.;,^^,. D.40V.

A. 120 V.
B. 72 V.
Huang d&n
,. <

150^ + 200^
= 312,5(Q)
200

R'+Zf

nvvHKhang

theo Zc ta

••> >

• Chon C.

A A M B : A H . M B = A B . A M => U R . 2 0 0 = 160.120 => U R = 9 6 ( V )

(a:?<:VO^. a ( . r

=>ChonA.

C = C„ =^Ze=312,5(Q)=^Uc,„,,=200(V)

*

200V

L

V i du 5: (DH-20n) Dat dien ap xoay chieu u = UN/2 coslOOTtt ( U khong doi, t
A

tinh bang s) vao liai dau doan mach mac noi tiep gom dien tro thuan R,
cuon cam thuan c6 do tu cam 0,2/?: H va tu dien c6 dien dung C thay doi
duoc. Dieu chinh dien dung ciia tu dien de dien ap hieu dung giOa hai ban
tu dien dat gia trj eye dai. Gia trj cue dai do bang U V3 . Dien tro R bang
A. 10 n .

U Cniiix

• (1 o-j
UVR^+Z[
R

J

B. 20 V2 Q.
C. 10 72 Q.
Huongdan
UV3 =

UVR^

+20^

D. 20 Q. J sfi '.
iUialj

.o„uu; .ixi i w .

• R = - 7 L = 10V2 ( Q ) => Chon C.

Vi dy 6: Mach dien R L C noi tiep dang xay ra cong huang. Neu chi giam dien
dung tu dien mot lugng ra't nho thi
A. dien ap hieu dung tu khong doi.
B. dien ap hieu dung tren dien tro thuan khong doi.
C. dien ap hieu dung tren tu tang.
D. di^n ap hieu dung tren tu giam.
, , , Hwang dan
Cong hadng : Z,-, = Z ,
Ucmnx khl

: Zc2

= —

= Z,, +

> Z ci

-I.

Liic dau: Z ^ = ZL < ^ ^

Uc
Sau do, Zc tang dan thi Uc cung tang dan
den gia tri cue dai Ucmnx => Clion C.

.

'»
•

,\

Vi du 8: Mach dien no'i tiep gom cuon day c6 do ty cam L, di?n tro thuan R va
tu xoay CO dien dung thay doi C. Dien ap giiia hai dau doan mach:
u = 30>/2 coslOOTtt (V). Dieu chinh C de dien ap hieu dyng tren ty dien dat
gia tn eye dai va bang 50 V. Khi do dien ap hieu dung tren cuoc day la
A.20(V).

B.40(V).

C. lOO(V).

D. 30 (V).

Huang dan
U = OR + 0 ,

+ O r = OR, + O r

^ R L^
U e w^« U l U

^

u

RL

n

,
T

,

,

=7U^-U^ =40(V) =>ChonB.

Vi dy 9: Mot cuon day mac noi tiep voi ty dien c6 dif n dung C thay doi duoc
roi mac vao nguon dien xoay chieu u = Uocoscjt (V). Thay doi C de dien ap
hieu dung tren tu circ dai thi gia trj eye dai diing bang 2Uo. Dien ap hieu
dyng giiia hai dau cuon day liic nay la
..
B.
3Uo.
A. 3,5Uo.
C. U o V 3 ; 5 .

D. 72 Uo.
Huang dan

U = URL + U C
Ucmax«UlOR,

=> Chon C.


Cty
B o trf/ Men tliirc

Chu

V^t I t L T B l l t r e n henh

VTV2.

y: Khi thai/ dot C dc Uomx tin dong dicn sc. i:6in pha hun dien ap Id a sao cho:
R

tan a = -

Tram

JVTV

D VVHKhang

Vlft

t^p 2 - Chu V^n B i g n

\

Dat vac A B m o t d i e n ap: UAB = 120 s/Z costOOTtt ( V ) . D i e u c h i n h C de tong
dien ap h i e u d u n g (UAM + UMD) dat gia trj cue dai. T i m gia trj cue dai cua
tong so nay.

U,

V i d u 10: Cho mach d i e n xoay chieu noi tiep g o m dien t r o R , cuon day thuan
cam va t u d i e n c6 dien d u n g thay d o i . D i e n ap giira hai dau doan mach c6

A . 240 V.

-

B. 120 V3V.

C.120V.

••.

D. I20V2V.
Huong dan

gia t r i hieu d u n g U . K h i dien d u n g thay d o i de d i e n ap hieu d u n g tren tu
cue dai t h i d o n g d i e n qua mach sam pha hon dien ap g i i i a hai dau mach la
7i/3. D i e n ap hieu d u n g tren tu eye dai la

A.U.

B. 2 U .

Iv''

-

-

i ' , ' . .iA

C.U^/3.

. 5,u.,\ii.'..

i

u,

v.A
. AME = 6O''

D.2U/73.

=:>
Huang dan
T u gian do vec to, xet tam giac A M B : U C m a x

R

X e t A A E M : tanAME = H I

U

2U

sin a

Vs

A p d u n g d j n h l i h a m so sin cho A A M B :
Chon D.

Y i d u 11: M a c h d i e n xoay chieu A B mac n o i tiep g o m ba doan theo d i i n g t h u

AB

AM

MB

AM + MB

510 60"

sin a

sinp

sina + sinP

U A M + U MB

t y A M , M N va N B . Doan A M chi cuon cam thuan, doan M N chiia ampe ke
h' t u o n g n o i tiep v o i d i e n t r a va doan N B chi c6 t u d i e n c6 dien d u n g C thay
doi dugc. K h i dieu chinh dien d u n g t o i gia t r | Co t h i UAN va UAB v u o n g pha.

•

. a+p
a-p
2 sin
-cos —
2
2

=>(U^M + U ^ i j ) = 2ABsin60"cos^^Y^ = max <=> a = p

D i e u c h i n h t u tir C > Co t h i dien ap hieu d u n g tren tu d i e n

K h i do; ( U A M + ^MB)^,^

= 120^3(V) ^ Chon B .

A . tang, so chi ampe ke tang.

Chu y: Co thephoi hap dieu kien cue tri vai gidn do vec la dcviet bieu thiec u va i.
V i du 13: Cho doan mach A B theo t h u t u g o m dien t r a R mac n o i tiep v a i cuon

B. g i a m , so'chi ampe k e g i a m .
C. g i a m , so chi ampe k e t a n g .

thuan cam L n o i tiep v o i t u d i e n c6 dien d u n g C thay d o i dugc. G g i M la

l'^' D . tang, so'chi ampe ke g i a m .

d i e m n o i L v o i C. Dat vao 2 dau doan mach d i e n ap xoay chieu UAB =

,

Huang dan
C = C'o

U

1

^

100^y2 cos(100Ttt + (pu) V . Thay d o i C de dien ap hieu d u n g tren doan A M
cue dai t h i bieu thuc dien ap tren do la UAM = 200\/2 cos(1007tt - 71/6) V . Xac

U-^Cmax

K h i C > Co t h i Zc cang xa v i t r i cue dai nen Uc

d j n h (pu. Thay d o i C de dien ap hieu d u n g tri^n t y cue dai vie't bieu thuc dien

g i a m , n h u n g Zc tie'n dan den v j t r i cong

ap tren doan A M va M B liic nay.

h u a n g nen I tang=> Chon C.

,, doi ta da diing dink ly ham so sin:
C

.

J

Huang dan

' '"

>!/!. Chii y : Khi dung gidn do vec ta detim

^

'

= max

Khi U ^ u = I Z ^ M = U

a

b

c

g.^^

sinB

sinC

. Neu hai todn yen cau titn

'

b+c
, . B+C
B-C
2 sin
cos
2
2
V i du 12: D o a n mach A B n o i tiep g o m hai doan mach A M va M B D o a n mach
A M la m o t cuon day c6 d i e n t r a thuan R = 4 0

N/3

Q

Z L = Zc <=> Mcich c6 cgng

>^+(Z,-Zcf
h u a n g nen ve gian do vec to n h u h i n h 1.

b _ c _
b+c

sinB sinC sinB + sinC

va d o t u cam L =

0,4/7t

H , doan mach M B la m o t t u dien c6 dien d u n g C thay d o i dugc, C c6 gia trj
h i i u han va khac k h o n g .

^

Uimax khi L thay doi hoac Ucmax khi C thay

dieu kien de (b + c) = max thi ta dp dung tinh chat cua day ti so bang nhau:
a
sin A

^^^

T u g i a n do vec ta: cos^^^^ =
=> ^3^1^ = 60" => UAB

la n/3

(pu =

=^

L

»-

C*

tre pha b a n UAM

-n/2

hay u^[j =]00V2cos lOO-nt-^ ( V ) .

,

/
200//

U,

/
100
Hinh 1

B
Hinh 2


no trp kian thac

Vft If LTDH

Iren

kenh

VTV2. t^p 2 - Chu VSn

Blen

K h i Ucnwx => U ± U R L ' ve gian d o vec to n h u h i n h 2.

•.

Ctj' TnaiH MTV D VVH Khang

=^ ( Z L I

A M = 100tan60° = 100V3(V)
u^,^ s6m pha hdn u l a

= 100V6cos 1 0 0 . t - ^ +

2

cuon cam k h i Z L = Z L I gap hai Ian k h i Z L = ZL2. Gia trj Z L I bang

jm

-r^'^-mt^

B.0,7572.

A. 50Q.

B. 150Q.

C. 20 Q.
Huang

p, = P2

7

C 0,75.

Huang

=4.

Z, =

U u = 2 U L2

D.2V2.^^,;r

dan

ZLI

R

+ Z f =3Z, = > Z , =

R

UZLI:

VR'+(ZLI-ZC)'

=20 (n)

M./

>^+(ZL2-ZC}

Chon C. i

4/7C ( H ) va k h i L = L2 = 2/71 (H) t h i mach d i e n c6 cung cong suat P = 200 W .
Gia t r j R b a n g
A . 50 Q.

B. 150

C. 20
Huang

4. H a i gia tri L, C c6 cung I, P, U R , U i , Uc.

Z L I + ZL2

P, = P2 =^ Z, = Z2 => Zc =:i

a. Khi L thay doi hai gid tri L i va L2 c6 cung I, Uc, UR, P thi
Z, = Z2

^R^ + ( Z L , -Zcf=^R'+

.:^(ZL,-Ze) =
Z] = Z2

(Z,,2 - Zc f

-(Z,,-Ze)^Zc=^i4^

R
R
— =
Z;
Z2

COSip, = C0S^P2

9] =

P =•
•

.

' :. 5

U^R

R^ + ( Z L I

• 200 = •

- Zc)'

fi.

1) Zc =

-^P2

ra: ZLQ =

+ ZL2

dan

= 300(Q)

"

200'R
,

hoac L = L2 = 3 L i t h i c u o n g d o hieu d u n g qua m a c h n h u n h a u . T r i so'Li la
Huang
i>i
168

=P2 =>Zi = Z 2

+(z,, -Zcf

D . l,5/7r ( H ) .

dan
= VRH(ZL2

-Zc)'

.

'

,

„

Z L I + Z L2

URmax, Pmax) tkl ZLO = Zc. TU dO SUy

L, + L 2
h

="—;—

C = 100/7t ()aF) v a cuon day t h u a n cam c6 d o t u cam L thay d o i . N e u L = L i

C. 0,5/71 ( H ) .

1

R = 100(f^) =>ChonD.

+ ( 4 0 0 - 300)^

j^i^- ^.^^ huang (Lmx, Uomx,

' d a u doan mach mac n o i tiep g o m d i f n t r o t h u a n R, t u d i e n c6 d i e n d u n g

B. l / 7 i ( H ) .

D . 100 Q. \

Chu y: Khi L thay doi hai gia trj Li va Li c6 ciing I, Uc, UR, P thi

V i dvi 1: D a t d i e n ap xoay chieu u = UocoslOOTct (V) (Uo k h o n g doi) vao hai

A.2/7t(H).

: => Z L I - 2ZL2

ap xoay chieu c6 bieu thuc u = 200 V2 coslOOTtt ( V ) . Thay d o i L , k h i L = L i =

2^y2

- = 0,75V2U => - = 0,7572 =^ Chon B.

R

UZL2

= 2.^

k h o n g d o i ; L t h u a n cam va thay d o i duoc. D a t vao hai d a u d o a n mach dien

_RJ

U^R^+Z^

•z =

dan

V i d y 3: M a c h d i e n xoay chieu g o m ba dien t r o R, L, C mac no'i tiep. R va C

R
U^R

D. lOQ.

Z2 => Z L I + Z1.2 = 2Zc = 30(n)

ZL2=io(n)

= U Cmax

Chon C.

c u o n g d o hieu d u n g qua mach n h u n h a u . D i e n ap h i ^ u d u n g a hai dau

d o i t h i d i ^ n ap hieu d u n g cue d a i tren R, L va C Ian l u g t la x, y va z. N e u z/y

Z

(H)

thay d o i . D i e u c h i n h L de cam k h a n g Ian l u g t la Z i . = Z L I va Z L = ZL2 t h i

• " A M =200V2COS i o o . t - : ^ - : ! i ( V ) ^

R, cuon cam t h u a n L va t u dien c6 dien d u n g C thay d o i d u o c . K h i C thay
^

71

0)

^j(V)

V i dv 14: Dat d i e n ap xoay chieu vao hai dau doan mach no'i tiep g o m d i e n tro

= 3thiz/xbang

0,5

Z , 1 + 3ZLI = 200 => Z L I = 50(n) => L , =

t r o t h u a n R, t u d i e n c6 d u n g k h a n g 15 Q va cuon cam t h u a n c6 d o t u cam L

t r i pha hdn u ^ g la - s

A.2^/2/3.

= 2Zc = 200 (fi)

+

Y i d u 2: D a t d i e n ap xoay chieu vao hai d a u ddan mach mac n o i tiep g o m dien

MB = - i ^ = 200(V)
cos60"
"MB

- Z c ) = - (ZL2 - Z c ) ^

Vl^t

,

2)

Z,=Z2

R

R

Zl ~ Z

<^
• => COSCPi = C0S<P2 => tPl = -
w"
Dong dim trong hai truang hap lech pha nhau Id la.

(khiL, > L 2 )

= -a < 0 ,
.
(khiLi[(f>2 = +a > 0
Ml

^

• t.'V"*- ^; *>"''•'••
169