MCQ Electric Potential and Capacitance Chapter 2 Physics Class 12

1. If an electron is brought towards another electron, the electric potential energy of the system

a) increases ✓

b) decreases

c) becomes zero

d) remains the same

2. Equal charges are given to two spheres of different radii. The potential will:

a) Be more on bigger sphere

b) Be more on smaller sphere ✓

c) Be equal on both the spheres

d) Depend on the nature of the materials of the spheres

3. A, B & C are three points in a uniform electric field.The electric potential is

a) Maximum at C

b) Same at all the three points A, B & C

c) Maximum at A

d) Maximum at B ✓

4. A charge ‘Q’ is supplied to a hollow metallic conductor. Which of the following is true?

a) Electric field inside it is same as on the surface

b) Electric potential inside is zero

c) Electric potential inside it is constant ✓

d) Electric potential on the surface is zero

5. The diagram shows four pairs of large parallel conducting plates. The value of electric potential is given for each plate. Rank the pairs according to the magnitude of the electric field between the plates, least to greatest.

a) 1, 2, 3, 4

b) 4, 3, 2, 1

c) 2, 3, 1, 4

d) 2, 4, 1, 3 ✓

Assertion-Reasoning type questions

Read the following questions and choose any of the following four responses.

1. Assertion: Two adjacent conductors, carrying the same positive charge have no potential difference between them.
Reason: The potential of a conductor does not depend upon the charge given to it.

(a) If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

(b) If both Assertion and Reason are true and the Reason is not a correct explanation of the Assertion.

(d) If both Assertion and Reason are false ✓

2. Assertion: One may have zero potential but non-zero electric field at a point in space.
Reason: Electric potential is a scalar quantity.

(a) If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.

(b) If both Assertion and Reason are true and the Reason is not a correct explanation of the Assertion. ✓

(d) If both Assertion and Reason are false

Case/Source based questions:

For the various charge systems, we represent equipotential surfaces by curves and line of force by full line curves. Between any two adjacent equipotential surfaces, we assume a constant potential difference. The equipotential surfaces of a single point charge are concentric spherical shells with their centres at the point charge. As the lines of force point radially outwards, so they are perpendicular to the equipotential surfaces at all points.

Choose the most appropriate alternative for each of the following questions:

1. Identify the wrong statement

a) Equipotential surface due a single point charge is spherical

b) Equipotential surface can be constructed for dipoles too

c) The electric field is normal to the equipotential surface through the point

d) The work done to move a test charge on the equipotential surface is positive ✓

2. Nature of equipotential surface for a point charge is

a) Ellipsoid with charge at foci

b) Sphere with charge at the centre of the sphere ✓

c) Sphere with charge on the centre of the sphere

d) Plane with charge on the surface

3. The work done to move a unit charge along an equipotential surface from A to B

a) Must be defined as ∫ ⃗ ⃗ ⃗⃗

b) Is zero

c) Can have a non-zero value

d) Both (A) & (B) are correct ✓

4. A spherical equipotential surface is not possible

a) Inside a uniformly charged sphere

b) Inside a spherical condenser

c) For a dipole ✓

d) For a point charge

Capacitors MCQS

1. A parallel plate capacitor is charged by a battery. Once it is charged battery is removed. Now a dielectric material is inserted between the plates of the capacitor, which of the following does not change?

(a) electric field between the plates

(b) potential difference across the plates

(d) energy stored in the capacitor.
Ans. (c)

2. Four capacitors, each of 2 μF, are connected as shown. What will be the equivalent capacitor across the points A, B?

(a) 0.5 μF

(b) 2 μF

(d) 4 μF

Explanation: All the capacitors are connected in parallel. So the equivalent capacitance will be 8 μF.

3. A capacitor is charged by a battery. The battery is removed and another identical uncharged capacitor is connected in parallel. The total electrostatic energy of resulting system

(a) increases by a factor of 4.

(b) decreases by a factor of 2. ✓

(d) increases by a factor of 2

Explanation: (b) Using, Vnet = V/2 , U = ½ CnetVnet²

4. Two metal spheres are separately charged and then brought in contact, so

(a) total charge on the two spheres is conserved. ✓

(b) total energy of the two spheres is conserved.

(d) None of the above

Explanation: According to the law of conservation of charge, total charge on the two spheres is conserved.

5. Two identical capacitors are joined in parallel, charged to a potential V, separated and then connected in series, the positive plate of one is connected to the negative of the other. Which of the following is true?

(a) The charges on the free plate connected together are destroyed.

(b) The energy stored in this system increases.

(d) The potential difference remains constant.

6. A battery does 200 J of work in charging a capacitor. The energy stored in the capacitor is

(a) 200 J

(b) 100 J ✓

(d) 400 J

U = ½ C V2
W = C V2
U = W / 2 = 100 J (half of work is lost in heat)

7. Capacitors C 1 is 10 μF and C2 is 20 μF are connected in series across a 3 kV supply, as shown. What is the charge on the capacitor C1 ?

(a) 45000 μC

(b) 20000 μC ✓

(d) 10000 μC

8. The energy stored in the capacitor as shown in Fig. (a) is 4.5 × 10–6 J. If the battery is replaced by another capacitor of 900 pF as shown in Fig. (b), then the total energy of the system is ________

(a) 4.5 × 10–6 J

(b) 2.25 × 10–6 J ✓

(d) 9 × 10–6 J

Assertion and Reason Questions

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

1. Assertion : If the distance between parallel plates of a capacitor is halved and dielectric having dielectric constant is three inserted between the plates of capacitor, then the capacitance becomes 6 times.
Reason : Capacity of the capacitor does not depend upon the nature of the material.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect. ✓
(d) If both the Assertion and Reason are incorrect.

2. Assertion : Two metal plates having charges Q, –Q face each other at some separation and are dipped into an oil tank. If the oil is pumped out, the electric field between the plates increases.
Reason : Electric field between the plates, Emed = Eair/K

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. ✓
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

3. Assertion: Polar molecules have dipole moment.

Reason: In polar molecule, the centres of positive and negative charges coincide even when there is no external field

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect. ✓

4. Assertion: A capacitor is a device which stores electric energy in the form of electric field.
Reason: Net charge on the capacitor is always zero

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. ✓
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

Case study base question:

Capacitance is the ratio of the change in the electric charge of a system to the corresponding change in its electrical potential. Capacitor consists of two metal plates which are filled with dielectric. When a voltage is applied to these plates an electric current flows charging up one plate with a positive charge with respect to the supply voltage and the other plate with an equal and opposite negative charge. The generalized equation for the charge stored in a capacitor is given by q=CV, where C is the capacitance of the capacitor

1. The capacitance of a capacitor does not depend on

a) Area of plates

b) Separation between the plates

c) Applied potential difference ✓

d) Dielectric constant

2. 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. C0 and Q0 are the capacitance and charge of the capacitor before the introduction of the dielectric.

a) C=C0/2 ; Q=2Q0

b) C=2C0 ; Q=Q0/2

c) C=C0/2 ; Q=Q0/2

d) C=2C0 ; Q=2Q0 ✓

3. Capacity of a parallel plate condenser can be increased by

(a) increasing the distance between the plates

(b) increasing the thickness of the plates

(d) decreasing the distance between the plates ✓

4. In a charged capacitor, the energy is stored in

(a) the negative charges

(b) the positive charges

(d) both (a) and (b)

Source Based Questions:

Read the source given below and answer any four out of the following questions:

If two or more capacitors are connected in series, the overall effect is that of a single (equivalent) capacitor having the sum total of the plate spacing of the individual capacitors. If two or more capacitors are connected in parallel, the overall effect is that of a single equivalent capacitor having the sum total of the plate areas of the individual
capacitors. (figure (a) shows parallel combination and (b) shows series combination)

1. Capacity can be increased by connecting capacitors in:

a) parallel ✓

b) series

c) both a and b

d) none of these

2. Three capacitors having a capacitance equal to 2μF, 4μF and 6μF are connected in parallel. Calculate the effective parallel capacitance:

a) 12/11 μF

b) 11 μF ✓

c) 12 μF

d) 13 μF

3. When capacitors are connected in the series _______________ remains same.

a) voltage

b) capacitance ✓

c) charge

d) resistance

4. Four 10 μF capacitors are connected in series, calculate the equivalent capacitance.

a) 1.5 μF

b) 2.5 μF ✓

c) 3.5 μF

d) 4.5 μF

Source: Kendriya Vidyalaya Sangathan, Hyderabad Region