# Capacitors and Dielectrics MCQ Type Questions for ISC Class-12

(a) π/2
(b) π
(c) zero
(d) 3π/2

Question 8 In which of the following forms is the energy stored in a capacitor?
(a) Charge
(b) Potential
(c) Capacitance
(d) Electric field

Question 9 The capacitance of a capacitor will decrease if we introduce a slab of:
(a) copper
(b) aluminium
(c) zinc
(d) None of these

Ans- (d) None of these

Question 10 Two capacitors of capacitance 6 µF and 4 µF are put in series across a 120 V battery. What is the potential difference across the 4 µF capacitor ?
(a) 72 V
(b) 60 V
(c) 48 V
(d) zero

Question 11
Capacitance of a parallel plate air capacitor depends on

(a)Thickness of conducting plates

(b)Charge on the conducting plates

(c)Area of the conducting plates

(d)Distance of separation between the conducting plates

Solution (b) 100 V

Question 12 Electric potential V due to an electric dipole is related to the distance r of the observation point as:
(a) V ∝ r
(b) V ∝ r-1
(c) V ∝ r²
(d) V ∝ r-2

Ans-: (d) V ∝ r-2

Question 13  A capacitor is connected to a cell of emf E having some internal resistance r, the potential across the:
(a) cell is < E
(b) cell is E
(b) cell is > E
(d) capacitor is E

Question 14  Dielectric strength of a medium is 2 KV mm-1. What is the maximum potential difference that can be set up across a 50 µm specimen without puncturing it.
(a) 10 V
(b) 100 V
(c) 1000 V
(d) 10,000 V

Ans- (b) 100 V

Question 15 A capacitor is connected across a battery and the plate separation of capacitor is increased without removing the battery, then:
(a) capacitance will increase
(b) charge stored will increase
(c) energy stored will decrease
(d) potential difference will increase

Answer: (c) energy stored will decrease

Question 16  A parallel plate air capacitor with no dielectric between the plates is connected to the constant voltage source. How would capacitance and charge change if dielectric of dielectric constant K=2 is inserted between the plates. Cand Qare the capacitance and charge of the capacitor before the introduction of the dielectric.

(b)  C=C0/2 ; Q=2Q0

(b)  C=2C; Q=Q0/2

(c)  C=C0/2 ; Q=Q0/2

(d)   C=2C; Q=2Q0

Ans (d)   C=2C; Q=2Q0

Question 17. Two capacitors of capacitance 6 µF and 4 µF are put in series across a 120 V battery. What is the potential difference across the 4 µF capacitor ?
(a) 72 V
(b) 60 V
(c) 48 V
(d) zero

Ans (a) 72 V

Question 18. Two capacitors of 3 µF and 6 µF are connected in series with a battery of P.d. 12 V. The P.d. across 3µF and 6µF
capacitors respectively will be :
(a) 8 V, 4 V
(b) 6 V, 6 V
(c) 4 V, 8 V
(d) 9 V, 3 V

Answer: (a) 8 V, 4 V

Question 19  A parallel plate air capacitor is given a charge of 3 µC. A sheet of dielectric constant 3 is inserted so that it completely fills the gap between the plates. The induced charge on each face of the sheet is numerically:
(a) 2 µC
(b) 3 µC
(c) 0
(d) 9 µC

Ans- (a) 2 µC

Question 20 Minimum number of capacitor of 2µF each required to obtain a capacitance of 5µF will be:
(a) 4
(b) 3
(c) 5
(d) 6

Question 21 A parallel plate capacitor of capacitance C is connected to a battery and is charged to a potential difference V. Another capacitor of capacitance 2C is similarly charged to a potential difference 2V. The charging battery is then disconnected and the capacitors are connected in parallel to each other in such a way that the positive terminal of one is connected to the negative terminal of the other. The final energy of the configuration is

a Zero

b 3CV2/2

c 25CV2/6

d 9CV2/2

Ans  (b) 3CV2/2

Question 22 A parallel plate air capacitor is connected to a battery. The quantities charge, voltage, electric field, and energy associated with this capacitor are given by Q0, V0, Eand U0 respectively. A dielectric slab is now introduced to fill the space between the plates with battery still in connection. The corresponding quantities are now given by Q, V, E and U are related to previous quantities as

a Q> Q0

b V> V0

c E> E0

d U> U0

Ans  (a) and (d)
Question 22
The effective capacitance of a capacitor is reduced when capacitors are connected in

a  series

b parallel

c series-parallel combination

d  none of the above

Ans  (a) series

Question 23 When a dielectric slab is introduced between the plates of a parallel plate capacitor which remains connected to a battery then charge on the plates relative to earlier charge is :
(a) more
(b) less
(c) less or may be more
(d) same

Question 24 Two identical conducting plates of plate area A are separated by a distance d to form a parallel plate air capacitor. Now a metal sheet of thickness d/2 is inserted between the plates of the capacitor. The ratio of capacitance before the insertion of plate and after the insertion of plate is

a  1:2

b  1:1

c  1:2

d  √2:1

Ans :- (a) 1:2

Question 25 The plates of a parallel plate air capacitor are charged to 100 V. A 2mm plate is inserted between the plates of the capacitor. To maintain the same potential difference , the distance between the capacitor plates is increased by 1.6mm. The dielectric constant of the plate is

a   1.25

b   5

c  2.5

d  4

Ans (b) 5

Question 26
Four capacitors are connected as shown below in the figure

Here C1=2μF , C2=3μF , C3=4μF and C4=5μF. The equivalent capacitance between A and B is

a  1.245 μF

b  4.446 μF

c  9 μF

d  3.27 μF

Ans (d) is the correct choice

Question 27
Consider the figure and value of capacitances given in the Question 9 if a 4Volt battery is connected between points A and B total charge stored on the capacitors would be

a   13.8μC

b    10 μC

c  22 μC

d   4 μC

Ans  (a) is the correct choice

Question 28 A parallel plate capacitor of capacitance C is connected to a battery and is charged to a potential difference V. Another capacitor of capacitance 2C is connected to another battery and is charged to potential difference 2V. The charging batteries are now disconnected and the capacitors are connected in parallel to each other in such a way that the positive terminal of one is connected to the negative terminal of the other. The final energy of the configuration is
(a) 2
(b) 2
(c) 2
(d) zero

Ans (a) is the correct option

Question 29  A parallel plate capacitor is connected to a battery as shown below

Consider two situations:

A: Key K is kept closed and plates of capacitors are moved apart using insulating handle.
B: Key K is opened and plates of capacitors are moved apart using insulating handle.
Choose the correct option(s).
(a) In A : Q remains same but C changes.
(b) In B : V remains same but C changes.
(c) In A : V remains same and hence Q changes.
(d) In B : Q remains same and hence V changes.

Ans   (c) and (d)

Question 30
Three capacitors of capacitances 3µF, 9µF and 18 µF are connected once in series and then in parallel. The ratio of equivalent capacitances Cs/Cp will be:
(a) 1 : 15
(b) 15 : 1
(c) 1 : 1
(d) 1 : 3

Ans  (a) 1 : 15

Question 31 A number of capacitors, each of capacitance 1 µF and each one of which gets punctured if a potential difference just exceeding 500 V is applied are provided. Then an arrangement suitable for giving a capacitor of capacitance 3 µF across which 2000 V may be applied requires at least:
(a) 4 component capacitors.
(b) 48 component capacitors.
(c) 3 component capacitors.
(d) 12 component capacitors

Question 32 Five equal capacitors, each with capacitance C are connected as shown. The equivalent capacitance between A and B is.

(a) 5 C
(b) C
(c) C/5
(d) 3C.

Question-33  A capacitor is charged by using a battery which is then disconnected. A dielectric slab then slipped between the plates, which results in
(a) reduction of charge on the plates and increase of potential difference across the plates.
(b) increase in the potential difference across the plate, reduction in stored energy, but no change in the charge on the plates.
(c) decrease in the potential difference across the plates, reduction in the stored energy, but no change in the charge on the plates.
(d) none of these

Answer: (c) decrease in the potential difference across the plates, reduction in the stored energy, but no change in the charge on the plates.

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