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DPP-5 Capacitor
1. The capacity of a parallel plate condenser is 5 F . When a glass plate is placed between the plates of the
conductor, its potential becomes 1 / 8 th of the original value. The value of dielectric constant will be

(1) 1.6 (2) 5 (3) 8 (4) 40

2. A capacitor is charged by using a battery which is then disconnected. A dielectric slab is then slipped between
the plates, which results in
(1) Reduction of charge on the plates and increase of potential difference across the plates
(2) Increase in the potential difference across the plate, reduction in stored energy, but no change in the
charge on the plates
(3) Decrease in the potential difference across the plates, reduction in the stored energy, but no change in
the charge on the plates
(4) None of the above
3. A parallel plate condenser has a capacitance 50 F in air and 110 F when immersed in an oil. The dielectric
constant ' k ' of the oil is
(1) 0.45 (2) 0.55 (3) 1.10 (4) 2.20
4. Separation between the plates of a parallel plate capacitor is d and the area of each plate is A . When a slab
of material of dielectric constant k and thickness t(t  d ) is introduced between the plates, its capacitance
becomes
0 A 0 A
(1) (2)
 1  1
d  t1   d  t1  
 k  k
0 A 0 A
(3) (4)
 1  1
d  t1   d  t1  
 k  k

5. In a parallel plate condenser, the radius of each circular plate is 12 cm and the distance between the plates is
5 mm . There is a glass slab of 3 mm thick and of radius 12 cm with dielectric constant 6 between its plates. The
capacity of the condenser will be
(1) 144  10 9 F (2) 40 pF
(3) 160 pF (4) 1 .44 F
6. The true statement is, on increasing the distance between the plates of a parallel plate condenser
(1) The electric intensity between the plates will decrease
(2) The electric intensity between the plates will increase
(3) The electric intensity between the plates will remain unchanged
(4) The P.D. between the plates will decrease
7. There is an air filled 1 pF parallel plate capacitor. When the plate separation is doubled and the space is filled
with wax, the capacitance increases to 2 pF . The dielectric constant of wax is
(1) 2 (2) 4 (3) 6 (4) 8
8. The capacity and the energy stored in a parallel plate condenser with air between its plates are respectively
Co and Wo . If the air is replaced by glass (dielectric constant = 5) between the plates, the capacity of the
plates and the energy stored in it will respectively be
W0 Co Co Wo
(1) 5 Co , 5Wo (2) 5 Co , (3) , 5Wo (4) ,
5 5 5 5
9. Force of attraction between the plates of a parallel plate capacitor is
 q2 q2 q q2
(1) (2) (3) (4)
2 0 AK  0 AK 2 0 A 2 0 A 2 K
10. A capacitor of capacity C is connected with a battery of potential V in parallel. The distance between its
plates is reduced to half at once, assuming that the charge remains the same. Then to charge the capacitance
upto the potential V again, the energy given by the battery will be
(1) CV 2 / 4 (2) CV 2 / 2 (3) 3 CV 2 / 4 (4) CV 2
11. N identical spherical drops charged to the same potential V are combined to form a big drop. The potential
of the new drop will be
(1) V (2) V / N (3) VN (4) V  N2/3
12. One plate of parallel plate capacitor is smaller than other, then charge on smaller plate will be
(1) Less than other (2) More than other
(3) Equal to other (4)Will depend upon the medium between them
13. A 6 F capacitor is charged from 10 volts to 20 volts . Increase in energy will be
(1) 18  10 4 J (2) 9  10 4 J (3) 4 .5  10 4 J (4) 9  10 6 J
14. The expression for the capacity of the capacitor formed by compound dielectric placed between the plates of
a parallel plate capacitor as shown in figure, will be (area of plate  A )
0 A
(1)
 d1 d 2 d 3 
 
K  K  K 
 1 2 3  d1 d3
0 A
(2)
 d1  d 2  d 3 
 
K K K 
 1 2 3  K1 K2 K3

 0 A(K1 K 2 K 3 )
(3)
d1 d 2 d 3
d2
 AK 1 AK 2 AK 3 
(4)  0    

 d1 d2 d3 
15. The intensity of electric field at a point between the plates of a charged capacitor
(1) Is directly proportional to the distance between the plates
(2) Is inversely proportional to the distance between the plates
(3) Is inversely proportional to the square of the distance between the plates
(4) Does not depend upon the distance between the plates
16. The capacity of a condenser in which a dielectric of dielectric constant 5 has been used, is C . If the dielectric
is replaced by another with dielectric constant 20, the capacity will become
C C
(1) (2) 4 C (3) (4) 2C
4 2
17. Four plates of equal area A are separated by equal distances d and are arranged as shown in the figure.
The equivalent capacity is

A B

2 0 A 3 0 A 3 0 A 0 A
(1) (2) (3) (4)
d d d d
18. The capacitor of capacitance 4 F and 6 F are connected in series. A potential difference of 500 volts applied
to the outer plates of the two capacitor system. Then the charge on each capacitor is numerically
(1) 6000 C (2) 1200 C (3) 1200 C (4) 6000 C
19. A parallel plate capacitor with air as medium between the plates has a capacitance of 10 F . The area of
capacitor is divided into two equal halves and filled with two media as shown in the figure having dielectric
constant k1  2 and k 2  4 . The capacitance of the system will now be
(1) 10 F
(2) 20 F
k1 k2
(3) 30 F
(4) 40 F
20. Three capacitors are connected to D.C. source of 100 volts shown in the adjoining figure. If the charge
accumulated on plates of C1 , C 2 and C 3 are qa , qb , qc , qd .qe and q f respectively, the
100 2F 3F 4F
(1) qb  qd  q f  C
9
a b c d e f
(2) qb  qd  q f  0
(3) qa  qc  qe  50 C
(4) qb  qd  q f 100 Volts

21. n identical condensers are joined in parallel and are charged to potential V . Now they are separated and
joined in series. Then the total energy and potential difference of the combination will be
(1) Energy and potential difference remain same
(2) Energy remains same and potential difference is nV
(3) Energy increases n times and potential difference is nV
(4) Energy increases n times and potential difference remains same
22. Three capacitors each of capacitance 1F are connected in parallel. To this combination, a fourth capacitor of
capacitance 1F is connected in series. The resultant capacitance of the system is
4 3
(1) 4 F (2) 2 F (3) F (4) F
3 4
23. Five capacitors of 10 F capacity each are connected to a d.c. potential of 100 volts as shown in the adjoining
figure. The equivalent capacitance between the points A and B will be equal to [CPMT 1986, 88; MP PMT 1999]
10F 10F
(1) 40 F
A B
(2) 20 F 10F

(3) 30 F 10F 10F

(4) 10 F 100 Volt

24. Three capacitors of capacitances 3 F, 9 F and 18 F are connected once in series and another time in
C  
parallel. The ratio of equivalent capacitance in the two cases  s  will be
 Cp 
(1) 1 : 15 (2) 15 : 1 (3) 1:1 (4) 1:3
25. Four condensers each of capacity 4 F are connected as shown in figure. VP  VQ  15 volts . The energy stored
in the system is
(1) 2400 ergs 4F
(2) 1800 ergs
4F 4F
(3) 3600 ergs P Q
4F
(4) 5400 ergs
26. Four condensers are joined as shown in the adjoining figure. The capacity of each is 8 F . The equivalent
capacity between the points A and B will be
(1) 32 F
(2) 2 F
A
(3) 8 F
B
(4) 16 F
27. The capacities and connection of five capacitors are shown in the adjoining figure. The potential difference
between the points A and B is 60 volts . Then the equivalent capacity between A and B and the charge on
5 F capacitance will be respectively
(1) 44 F; 300 C 5F 9F
A
(2) 16 F; 150 C
12F 10F 8F
(3) 15 F; 200 C
(4) 4 F; 50 C B

28. In the circuit shown here C1  6 F, C 2  3 F and battery B  20 V . The switch S 1 is first closed. It is then opened
and afterwards S 2 is closed. What is the charge finally on C 2
C2 3F
(1) 120 C
S2
(2) 80 C C1 6F

(3) 40 C
S1
(4) 20 C
B = 20V
29. A parallel plate capacitor of area A, plate separation d and capacitance C is filled with three different dielectric
materials having dielectric constants k 1 , k 2 and k 3 as shown. If a single dielectric material is to be used to
have the same capacitance C in this capacitor, then its dielectric constant k is given by
A/2 A/2
K1 K2 d/2
d
K3

A
A = Area of plates
1 1 1 1 1 1 1
(1)    (2)  
k k 1 k 2 2k 3 k k 1  k 2 2k 3
k1k 2
(3) k   2k 3 (4) k  k 1  k 2  2k 3
k1  k 2

30. Two capacitors A and B are connected in series with a battery as shown in the figure. When the switch S is
closed and the two capacitors get charged fully, then
2F 3F

A B

10 V S

(1) The potential difference across the plates of A is 4V and across the plates of B is 6V
(2) The potential difference across the plates of A is 6V and across the plates of B is 4V
(3) The ratio of electrical energies stored in A and B is 2 : 3
(4) The ratio of charges on A and B is 3 : 2