# MCQ Questions for Class 12 Physics Chapter 2 Electrostatic Potential and Capacitance with Answers

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## Electrostatic Potential and Capacitance Class 12 MCQs Questions with Answers

Question 1.
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

Answer: (b) 100 V

Question 2.
A charge q is distributed over two spheres of radii r1 and r2 such that their surface densities are equal. What is the ratio of their potential.
(a) $$\frac {r_1}{r_2}$$
(b) $$\frac {r_1^2}{r_2}$$
(c) $$\frac {U_1^3}{r_2^3}$$
(d) none of these

Answer: (a) $$\frac {r_1}{r_2}$$

Question 3.
A hollow metal sphere of radius 5 cm is charged such that the potential on its surface is 10 V. The potential at a distance of 2 cm from the centre of sphere is:
(a) Zero
(b) 10 V
(c) 5 V
(d) $$\frac {10}{3}$$ V

Answer: (b) 10 V

Question 4.
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

Answer: (d) V ∝ r-2

Question 5.
Two insulated charged spheres of radii 20 cm and 25 cm respectively and having an equal charge q are connected by a copper wire and then they are separated.
(a) Both spheres will have the same charge q.
(b) Charge on sphere of radius 20 cm will be more than that of radius 25 cm.
(c) Charge on sphere of radius 20 cm will be lesser than that of 25 cm.
(d) Charge on each will be zq.

Answer: (c) Charge on sphere of radius 20 cm will be lesser than that of 25 cm.

Question 6.
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 numericaly:
(a) 2 µC
(b) 3 µC
(c) 0
(d) 9 µC

Answer: (a) 2 µC

Question 7.
Three capacitors of capacitances 3µF, 9µF and 18 µF are conected 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

Answer: (a) 1 : 15

Question 8.
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.

Answer: (b) 48 component capacitors.

Question 9.
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 10.
The capacity of an isolated conducting sphere of radius r is proportional to:
(a) r²
(b) $$\frac {1}{r}$$
(c) $$\frac {1}{r^2}$$
(d) r

Question 11.
Van-de Graff Generator produces a voltage nearly:
(a) 106 V
(b) 108 V
(c) 104 V
(d) none of these.

Answer: (a) 106 V

Question 12.
The dielectric strength of air at N.T.P. is 3 × 106 V/m. Then the maximum charge that can be given to a spherical conductor of radius 3 m is
(a) 3 × 10-1 C
(b) 3 × 10² V
(c) 3 × 10-3 C
(d) 3 × 10-4 C

Answer: (c) 3 × 10-3 C

Question 13.
The maximum potential upto which the conductor can be charged in Q12 is
(a) 9 × 105 V
(b) 9 × 106 V
(c) 9 × 107 V
(d) 9 × 108 V.

Answer: (b) 9 × 106 V

Question 14.
ABC is a right angled ∆ with AB = 3 cm, BC = 4 cm, AB = 5 cm. Charges of +15 stat. C, -12 and 20 stat Coulomb are placed at A, B, C respectively. The electric potential energy of three charges is:
(a) 180 ergs
(b) 4 × 5 × 3 ergs
(c) – 60 ergs
(d) (20 + 15 – 12) ergs.

Answer: (c) – 60 ergs

Question 15.
The work done in moving the three charges to infinite separation is:
(a) 180 ergs
(b) 60 ergs
(c) – 60 ergs
(d) (20 + 15 -12) ergs.

Answer: (b) 60 ergs

Fill in the Blanks

Question 1.
The charge on the earth cannot be neutralized because ………………..

Lightning and thunder storms are the continuous phenomenon all over the world which send a charge equal to 1800 C per second into the earth and hence – 5 × 105 C charge is maintained on earth.

Question 2.
A potential difference of the order or ……………….. is created between the earth and the bottom of the cloud.

Question 3.
The top of ……………….. and the surface of the earth form a spherical capacitor of capacitance ………………..

Answer: Stratosphere, 0.09 F (= 0.1 F).

Question 4.
Force between the plates of a capacitor is ……………….. which varies ……………….. as the area of the plates and is independent of the ………………..

Answer: $$\frac {1}{2}$$, $$\frac {q^2}{ε_0KA}$$, inversely, separation between the plates.

Question 5.
When a dielectric slab is introduced by disconnecting the battery from the capacitor, then q = ………………..
V = ………………..
σ = ………………..
E = ………………..
U = ………………..
C = ………………..

q = q0
σ = σ0
E = $$\frac {V_0}{K}$$
U = $$\frac {U_0}{K}$$
C = KC0.

Question 6.
If the medium surrounding the conductor is charged, then the potential of the conductor is ………………..

Question 7.
If at any point E = 0, then V may or may not be ……………….. e.g. inside a charged conductor E = ……………….. but V is ………………..

Answer: Zero, Zero, not zero.

Question 8.
Electric potential at a point on the equitorial line of a dipole is ……………….. but $$\vec{E}$$ is ………………..

Answer: Zero, not equal to zero.

Question 9.
Two equipotential surfaces cannot intersect each other because ………………..