 Trang 1
BT: 
A .  không phân nhánh RLC.
I.m
+P = UIcos + UIcos(2t + ) (1)
+P = UIcos = RI
2
.
+
P UIcos
(2)
+
Z
R


cos
( Cos  (3)
+B:

2
2
R
R
U
P RI U I
R
  
(4)


+  = 
2

  
thì: P = P
min
= 0.
+: P
hp
= rI
2
=

22
2
cosU
rP
(8)
 r ( .
+ (8) => cos 
hp
 cos. Q cos 0,85.
+cos
ên dây.
+  thng  
sao   1.

III
1.
max

,
Do U=Const nên 
max
thì (
R
ZZ
R
CL
2
)( 

) 
ng R và (Z
L
-Z
C
)
2
ta 

C
A
B
R
L
R
O
R
1
R

ZZ 2


R
ZZ
R
CL
2
)( 

)
min
là
CL
ZZ 2
lúc 
R=
LC
Z -Z
(9)

Z R 2
,
U
I
R2

;
R2
cos =

ZZ
U

.
a.  :
 : : 

1
H, C =

4
10.2

F , u
AB
= 200cos100t(V).

A.50 ;200W B.100 ;200W C.50 ;100W D.100 ;100W
 Ta có :Z
L
= L = 100 ; Z
C
=
C

1
= 50 ; U = 100
2
V


hay R =Z
L
-Z
C
= 50  => P
max
=
R
U
2
2
= 200W. A.
2 : . 
RL
= 100
2
V, U
C
= 200V. 
 g
4
10
()
2

CF

.
A. 100W B. 100
2

C

C
 Z
L

0


m

A. R
0
= Z
L
+ Z
C
. B.
2
m
0
U
P.
R

C.
2
L
m
C



2
cos100

A. R=120. B. R=60. C. R=400. D. R=60.
G HD: Z
L
= 100, Z
C
= 40, theo (9) R=|Z
L
 Z
C
| = 60 . 
Câu 3: 

1


4
10
3

120
2
cos100

A. P
max

=110W. C. P
max
=220W. D. P
max
=110
2
W.
 HD: Theo (11)
2
max
U
P
2R

= 110W .
Câu 5: 


AB
=200cos100t (V). Khi R=100

A. 2A. B.
2
A. C. 2
2
A. D.
2
2
A
 HD: Theo (10)

. B. 120. C. 60. D. 60
2
.
 HD: Theo (10)
Z R 2
=60
2
. .
Câu 8:  
                       u =
240cos(100t)V. Khi R = R
o

:
A. P = 115,2W B. P = 224W C. P = 230,4W D. P = 144W

 Trang 4
 HD:
L
= 200, Z
C
= 100 ) => R+r =|Z
L
 Z
C
| = 100.
2
max
LC
U

()
LC
RU
P
R Z Z



 
2
2
2
LC
U
R R Z Z 0
P
   
(13)

ph 
1
và R
2

- R
1
+ R
2
=


2


1
= P
2
 R
1
.R
2
= (Z
L
 Z
C
)
2
 
1
 +
2
 = /2
  và I
 a. Ta có P = I
2
R =
R
ZZ
R
U
R

R
ZZ
R
U
CL


=
2
2
2
2
)(
R
ZZ
R
U
CL




1
2
1
)(
R
ZZ
R
CL

ZZ
CL


 R
1
 R
2
= (Z
L
 Z
C
)
2
(
1
1
2
1
RR

)  R
1
.R
2
= (Z
L
 Z
C
)

2
)( 

min
T
R
ZZ
R
CL
2
)( 

 2 Z
L
 Z
C

: R =
R
ZZ
CL
2
)( 
 R = Z
L
 Z
C
 P
max
=

LC
U
ZZ
 Trang 5
+4: : 

1
H, C =
3
10
6


F , u
AB
= 200cos100t(V).
0W?
Ta có:
2
2 2 2 2
LC
22
LC
RU
P' I R P'R U R P'(Z Z ) 0 (*)
R (Z Z )
      

).100cos(.275 tU
AB


 
A.
)(45 R
B.
)(60 R
C.
)(80 R
D
:
)(100 
L
Z
;
)(40 
C
Z


)1(.
22
R
P
IRIP 

:
22

- 125R+ 3600 = 0

1
2
2
45
125 3600 0
80
R
RR
R


   




1
= 45 
2
= 80 n D
+: t L = 2/(H) C = 125.10
-6
/ (F)hai 

AB

= 150
2

CLCL
2
2
22
2
2
2
)()(
cos








R
R
2
2
)80200(
150


= 90 
R
R
2
120

FC



  giá

1
và R=R
2

21
.RR
?
A.
10.
21
RR
B.
1
21
10. RR
C.
2
21
10. RR
D.
4
21
10. RR


)1(.
)(

1
2
1
2
2
1
2
2
1
2
1
R
ZR
U
R
Z
U
RIP
C



Khi R=R
2

)2(.
)(

2
2
1
2
1
2
2
.
)(
.
(
R
ZR
U
R
ZR
U
CC



Hay:
42
21
10. 
C
ZRR
n D
+8: 


1
100 100   
L
Z .L .



Khi R=R
1
tiê :
2
2
1
11
22
1


L
U .R
P I R
( R Z )
(1)
Khi R=R
2

2
2
2
22

Hay:
2
12

L
R R Z
= 10
4
n D
+ 9: 
π
1

dung C=
2π
10
-4

 
AB
=200cos100
A. 50, 200. B. 100, 400. C. 50, 200. D. 50, 200.
HD:
L
= 100, Z
C
= 200, theo (13):
 
2
2

1
và R
2


2
12
U
RR
P

,

 
2
1 2 L C
R R Z Z (14)

(15)
C
A
B
R
L

1
và R
2
):

 
2
1 2 L C
R R Z Z
suy ra:
0 1 2
R R Rmax
1 2 0
2
.
P
R R R
P
 (16)

(17)

1
và R
2

max


2
1 2 0
max
1 2 0
.
2
.
R R R
P
R R R
P








Gii:  Imax? Tính giá tr này?
Cm kháng:
. 100( )
L

LC
LC
UR
U U U
I P I R
ZZ
Z R Z Z
R Z Z
R
R
     





Pmax khi
2
0
0
()
LC
ZZ
R
R



0
2

2
1 2 0
max
1 2 0
.
2
.
R R R
P
R R R
P








-T công thc tính công sut ta có:
2
2
1
1 1 1
22
1
.
.
()
LC

1 2 1 2 2 1 2 1
2 2 2 2
12
2 2 2
1 2 2 1 2 1 1 2 0
.
.
. . ( )( )
( ) ( )
. ( ) ( )( ) . ( ) (1).
LC
L C L C
L C L C
UR
U
P P R R R R R R Z Z
R Z Z R Z Z
R R R R R R Z Z R R Z Z R
       
   
         Trang 8

max
1 2 0
2
.
P

P
R

P =
2
max 0
0 0 1 2
2
12
2.
22
. . ( )
U
PR
R R R R VeTrai DPCM
U
P
RR
   


1. 
0


0

trên R là
A. P B. 2P C.
2

0
,  thì

0

0
là
A. 7,5 B. 15 C. 10 D. 50
HD: 
0
thì
0Max L C
P R Z Z  

Khi R
1
=R
0
+10 hay R
2
=R
0
-t =>
2
12 LC
R R ( Z Z )2
0 0 0

100. Khi R = R
1

A. 400 W. B. 220 W. C. 440W. D. 880 W.
 P
1
= P
2
=>
22
1
1
)(
CL
ZZR
R

=
22
2
2
)(
CL
ZZR
R

> (Z
L
 Z
C

21
2
RR
U

= 400W.  A
h 2: 
 
 
2
2
2 2 2
2
2
. . . 0
LC
LC
U
P RI R P R U R P Z Z
R Z Z
      



-et:
2
12
U
RR
P

1
+R
2
)=3600  U=60V. 
Câu 12: 


0

A. 60. B. 65. C. 130. D. 98,5.
HD: Theo (16)
0 1 2
R R R
R
0
=60 
Câu 13: 
2

R
1

2


 B.12;100W;  
Theo (16):
0 1 2
R R R
=12 Theo (13)  P

P
R

W. (1) Z
2
= 2R ,
2
2
2
U
P
R

(2)

1
2
200
100
22
P
P   
W. C
Câu 15: 
0


max

0

0

0
U
I
5.R

 
2
=
2
0
2U
5R


max
P4
0,8
P5

 P = 0,8P
max
.  D

 Trang 10
Câu 16: 
x

63,8CF

CLCL
2
2
22
2
)()( 





x
+ r = R
x

Z
L
; Z
C
=

6
10.8,63.314
1
2
1
fC

50
P = P

x
= 0, P

= 378,4 W. 

3. i k RLC.
  
C) sao cho
1
ωL =
ωC
(hay Z
L
=Z
C
) thì có 


Z
L
=Z
C
;
1
L
C


;
1

=0; 
u
= 
i
; cos=1 (22)
C
A
B
R
L
N
M

 Trang 11

U
LCmin
= 0. (23)
 
3.1
3.  

0
cos100

0

AB
cùng p
:

tan( ) 3 2
3
LC
LC
ZZ
Z Z R Z R
R


       
(1)
Và
2
22
2
200
U
P I R R U R
Z
   
(2)
- Khi u và I cùng pha ta có:
2
axm
U
P
R

(3)
- 

2
= 100
2
V
P = I
2
R =
R
Z
U
2
2

U và R P 

Z =
22
)(
CL
ZZR 
 Z
C
= Z
L

= 100

=> C =

4

ZR 
= 100
2

U
AM
 Z  Z
C
= Z
L
= 100

=> C
=

4
101


C
Z
(F) Z = R
=> U
vmax
=
AM
Z
R
U
=

HD: U
MBmin
=U
LCmin
= :
P=P
max
=U
2
/R=50W. 
3.2.
Câu 19: (ĐH2008) 

1
LC


 
 D. 
HD: P
max
 C
Câu 20: 

u
AB
=U
0
cos
A. 1. B.

R
L
C
A
B
R
L

 Trang 13
3.4
P
max
) ta suy ra

2
1
L=
ωC(25)
Câu 22:  

3
/5

A. 0,5/ (H). B. 5/ (H). C. 0,5 (H). D. 5 (H). HD: Z
L
= Z
C


 = 
0
P
max

0
1

LC


+  = 
1
 = 
2

R

khi
12
  

 
12
f f f
.
f

12



 
1
, 
2
, 
0
:
0 1 2 1 2
1
LC
   
   
 
12
f f f
(26)

+
axCM
U
khi:
2
22
2
1

4
10
()
2.

CF


100 2cos2
AB
u ft



 
: 
2
2
cos
U
P UI R
Z




max
khi Z
min



f
LC



= 100 (Hz).
C
A
B
R
L
N
M
C
A
B
R
L

 Trang 14

2 2 2 2
max
22
min
100
200
50
U U U

0
cost có U
0
 
  = 
1

 = 
2

A.
12
2
LC
   
. B.
12
1
.
LC
  
. C.
12
2
LC
   
. D.
12
1
.


A. 72 (Hz) B. 34,72 (Hz) C. 60 (Hz) D. 41,67 (Hz)
 Khi f = f
1
= 50 (Hz) :Z
C1
= 1,44 Z
L1

1
2
1
fC


1

LC =
2
1
2
4.44,1
1
f

(1)

2

Khi f = f

f

=
2
1
2
4.44,1
1
f



f
2
= 1,2 f
1
= 1,2 . 50 = 60(Hz) 


1

2

max
.

1

2






L
= Z
C
suy ra:

L1 L2
L
ZZ
Z
2


=>
12
LL
L
2

(29) (30)


C1 C2
L
ZZ
Z
2


=>
2
12
11
2L
CC

(31)

Theo (18) Z
L
= Z
C
:

C1 C2
C
ZZ
Z
2


22
max
UU
P =
22
:
LC
LC
R Z Z
Khi R Z Z




 sau: 2
max
2
U
P =
1

2
max
U
P =
1
:
2
LC
R
Khi Z Z f
LC
  

 sau: 6: 
2
cos 100

t (V). Khi C = C
1
=
4
10
4


  
. Tng tr:
2 2 2 2
11
( ) ( 400) .
L C L
Z R Z Z R Z     

- Công sut:
2
2
11
22
.
.
( 400)
L
UR
P I R
RZ


(1)
+Khi C = C2 =
4
10
2


F ta có:

(2)
 : P1 = P2 :
22
12
2 2 2 2

P P 300( ).
( 400) ( 200)
L
LL
U R U R
Z
R Z R Z
     
   


3
()
L
Z
LH

  
.
- Tìm R:
22
2
11
2 2 2 2

P
max
C
L
O
L
0
P

P
ma
x
O
C
0
P

P
max

 Trang 16
- H s công sut khi C = C1=
4
10
4


:
1
1


y khi
1
L=L
và khi
1
2
L
L=L =
2


1

A.
-4
1
4 3.10
L = (H);C= (F)
π 2π
B.
-4
1
4 10
L = (H);C= (F)
π 3π
C.
-4
1
2 10

L2
 Z
C
)
2
. Do Z
L1
 Z
L2
nên Z
L1
 Z
C
= Z
C
 Z
L2
= Z
C
-
2
1L
Z

=> 1,5Z
L1
= 2Z
C
(1)
tan

=
R
Z
L
4
1



1
+ 
2
=
2

=> tan
1
. tan
2
= -1 => Z
L1
2
= 16R
2
=> Z
L1
= 4R = 400 => L
1
=


0
công sut mt giá tr cc thêm
t C
1
vào mch MB công such gim mt na, tip tc mc thêm t C
2
vào m công sut
ca m C
2
là:
A. C
0

0
B. C
0

0
C. C
0
/3 hoc 2C
0
D. C
0

0

 Khi C= C
0
=> P

C
C b 0
Z
Z R C 2C
2
3Z
2
Z 3R C C
23

   



   


2

0

1

b


0

song song C
b
:
0 0 2 2 0
21
C C C C C
33
   


 Trang 17
19:   

L
= 2Z
C
  trong m

2
A C, L là:
A.
1
10
m

F và
2
H

B.

LC
UU
P
Z
R Z Z




LC
R Z Z
hay
( 2 )
C L C
R Z doZ Z

 
100 2( )
U
Z
I
  

Hay
22
( ) 100 2
LC
R Z Z  

11

200cos100
AB
ut




A.
1
L


H B.
1
2
L


H C.
2
L


H D.
4
L


H


UR
P I R R Z U
ZP
      
.
Mà
 
 
2
2
22
100 2 100 100
L C L
Z R Z Z Z      

0( ai)
200 2
200 ( )
100
L
L
L
Z lo
Z
Z L H
  






P
1
= P
2
B.

P
1
= P
2
/
2

C.

P
1
= 2 P
2
D.

P
1
=
2
P
2

:  R nt C:

Hay (2R)
2
= R
2
+
2
1C
Z


R =
3
1C
Z
mà Z
C1
=

CC
11
1



R =

C3
1
(1)









(2)
-
2
= Ucos(
3
) : Z
C2
=


3
11
2
C
C

(3)
So sánh (1) và (3) ta có: Z
C2
= R
p dùng u
2
:

2
2/
2
2
2
2
2
2
2



















(4)
So sánh (2) và (4) ta có: P

A.720W B.360W C.240W D. 360W
Câu 29:. 
3
L = H
10π

-4
2.10
C = F
π

.u =120 2 cos 100πt (V)

1


max

1
, P
max

A.
1 max
R 20 , P 360W  
B.
1 max
R 80 , P 90W  

C.

CL
ZZ
D.
2
LC R


Câu 32:            ).
= 15,9

u 120 2cos100 t(V)


A. 240W B. 96W C. 48W D. 192W
Câu 33:.  ).
R=100


2
L = H
π


R
L
C
A
B
Hình 32
R


A. 50W. B. 100W. C. 400W. D. 200W.
Câu 35.  h 34). R=100


2
L = H
π

A và N là:
AN
u = 200cos100πt (V)

h là:
A. 100W B. 50W C. 40W D. 79W
Câu 36: 

120 2 cos(120 )ut


 R
1
=18

,R
2
= 32

thì 
  

60 , ;
12
R L H C F


   
B.
3
0,6 10
80 , ;
12
R L H C F


   

C.
3
0,6 10
120 , ;
8
R L H C F


   
D.
3
1,2 10
60 , ;
8

10
. C. 75. D. 200.
HD: Theo (31)
C1 C2
L
ZZ
Z
2


= 200. .
Câu 41: 
1
=2.10
-4

2
=10
-4


A10
-4
 B.10
-4
 C. 2.10
-4
 D. 3.10
-4


L
C
A
M
N
B
Hình 3.5

 Trang 20
A.
40
B.
60
C.
50
D.
30

Câu 43:  
 

A. 50W. B. 100W. C. 400W. D. 200W.
Câu 44: 

A B C D(rad/s).
Câu 45: 
10 2cos100 ( )u t V




,
2
22( )R 
thì 
  
A. 120W. B. 484W. C. 240W. D. 282W.
Câu 48: 

200 2 os(100 )u c t


(V) khi
5
1
2,5.10 ( )C C F


và
5
2
5.10 ( )C C F



cùng cô
A B
C D
Câu 49:  

0

1
+ 
2
. B.
12
0
12


  
. C. 
0
= 
1
- 
2.
D.
2
0 1. 2
  


Câu 51: 
t


0.75
H



. D. 0,5.
Câu 54: 
2



/
A. 100W B.
100 3
W C. 50W D.
50 3
W

 Trang 21
Câu 55: 

tUu

cos2
(V) . Khi C = C
1


)3/cos(2

 tIi
(A). Khi C = C
2
 


21
2
4
)(
RR
RRU 

Câu 57: 
100R 




0
60


A.
3
LH


, P = 36W B.
1
3
LH


, P = 75W C.
1

hoặc
80R 
B.
20R 
hoặc
45R 

C.
25R 
hoặc
45R 
D.
45R 
hoặc
80R 

Câu 59: 


1

2


A.    
Câu 60: 
2


25

max
.
A. C=7F. B. 1F. C. 5 F. D. 3,43F.
HD
12
12
2C .C
C
CC


= 3,43F. 
Câu 63: -2009): 

1
và R
2


 Trang 22
C
A
B
R
2

L
M
R
1

22
12
1 2 1 1 2 2 1 2 1 2
2 2 2 2
12
(1) (2)& 2 2 (3)
CC
CC
RR
P P R I R I U U I I
R Z R Z
       



21
4 (4)RR

2
12
50 200
4
C
Z
RR     

Câu 64 -2010): 




1
= P
2
nên ta có:
2 2 2 2 2 2 2 2
12
1 2 1 2 1 2
3
( ) ( )
2
CC
L C L C L
ZZ
I R I R Z Z R Z Z R Z Z Z L H


            

Câu 65 (-2011): 
ft2cos2Uu 
h

1



và 8


2

3
f
12


 
1
:
 
4
3
.28
2
1
;62
2
1
1
1
1
1
11
 LCf
Z
Z
Cf
ZLfZ
C
L
CL

2


0
cos

t (U
0
và



LC
1
2



AM
và u
MB
là 90
0


A. 85 W B. 135 W. C. 110 W. D. 170 W.
Khi
LC
1
2


2
- 
1
= 90
0
=> tan
1.
tan
2
= -1

1
R
Z
C

1
R
Z
L
= -1 => Z
L
= Z
C
=
21
RR
(2)


RR
U

= P = 85W.  A
Câu 67: 
3


2



A. L =
2
2

(H);P= 160W. B.L =
3

(H); P = 173,2W C. L =

2
3
(H);P = 200W D.L =
3
2

(H); P = 100W

22

-4

:
C1
+ Z
C2
= 2Z
L


C

 là: Z
Ci
=
180
c
i
Z



1
là Z
C1
=
1
180
c
Z

L
= 600 ;
C
= 1200
Suy ra: Z
C1
= 200 = 10
-4
; Suy ra Z
C2
= 400 = 10
-4


Câu 69: Cho mach R,L,C mc ni tip, vi C có th i. n mch
n áp
100 2 cos(100 )( )u t V


.
R=100
3
n ti,
 /3. Công suât tiêu th c
 
1

2
 :P
1

ZZ
Z
2


=>
C2
L
3.Z
Z
2


-1+ 2 = /3 1 = -/6 ; 2 = /6 => -tan1= tan2
Ta có:
1
2
2
33
3
33
LL
LC
ZZ
ZZ
RR


    
<=>

=200 .Ta có
100
0,5
200
U
IA
Z
  

P= I
2
.R= (0,5)2
2
(0,5) 100 3 25 3( )W Trang 24
Hay:
22
22
22
. 100 .100 3
25 3( )
()
(100 3) (300 400)
LC
UR
PW
R Z Z
  

1

1


2

2

2

cos
2

1
+ cos
2

2
=
4
3

1
2
P
P

A. 1 B. 2 C. 3 D. 4
 P

1
=> cos
2

1
=
U
P
2
1
=
10
3
(2)
P
2
= UI
2
cos
2
= I
2
2
R
2
=> I
2
R
2
= Ucos

3
-
10
3
=
20
9
(4)

1
2
P
P
=
1
2
I
I

1
2
cos
cos


=
1
2
cos2
cos4

,U



1
LL
hay
2
LL
v
12
LL


12
,PP

12
3;PP


12
,


12
/2.
  



L1
- Z
C
)
2
}
P
2
= I
2
2
.R = U
2
.R/ { R
2
+ (Z
L2
- Z
C
)
2
}
Do P
1
= 3. P
2
ta có 3. { R
2
+ (Z
L1

)/R}
Suy ra R
2
= (Z
L1
- Z
C
).(Z
L2
- Z
C
) (2)
Thay vào ( 1) ta có: 3.(Z
L1
- Z
C
). (Z
L1
- Z
C
+ Z
L2
- Z
C
) = (Z
L2
- Z
C
). (Z
L1

= R
2
/3
Và theo (3) suy ra (Z
L2
- Z
C
)
2
= 3. R
2

Mà Cos 
1
= R/Z
1
= R/
3
2
2
R
R 
=
2
3
suy ra
1

= /6



.
+ P
R
= I
2
.R=
2
2
U .R
Z

22
LC
(R+r) (Z - Z )

+ Pr = I
2
.r =
2
2
U .r
Z

cos
d
=
d
r
Z

LC
U
P
2 Z Z



- 
Rmax

R
2
= r
2
+(Z
L
 Z
C
)
2
()

(12)

(17)
1: r =20 
0,8

A. 100 . B. 120 . C. 50 . D. 80 .
HD: Z
L
= 80, Z
C
= 40, theo (17): R
2
= r
2
+(Z
L
 Z
C
)
2
=2500  R=50  . 

II.  : (L,r,C,

không )

max
: Khi L,C,

không 
L
và Z
C
không thay 
không gây ra 