CBSE 12th Electrostatic Potential And Capacitance Predicted Questions 2025: Physics Preparation

1

What is the shape of the equipotential surfaces for a uniform electric field?

2

Two thin wire rings, each having a radius R, are placed at a distance d apart with their axis coinciding. The charges on the two rings are +q and -q. What is the potential difference between the centre of two rings?

3

Two charged conductors - A and B, are kept close to each other. If the charge on conductor A is increased, the potential on conductor B will?

4

Find the force between the plates of a parallel-plate capacitor with capacitance C, separation d, and potential V.

5

A small conducting sphere of radius r carrying a positive charge q is placed concentrically inside a large hollow conducting shell of radius R (R > r). This outer shell has charge Q on it. Show that if these spheres are connected by a conducting wire, the charge will always flow from the inner sphere to the outer sphere, irrespective of the magnitude of the two charges.

6

A positively charged particle is released from rest in a uniform electric field. What is the electric potential energy of the charge?

7

When the separation between two charges is increased, what happens to the electric potential energy of the charges?

8

An electric dipole of dipole moment p is kept in a uniform electric field E. What will be the amount of work done to rotate it from the position of stable equilibrium to that of unstable equilibrium?

9

A parallel plate capacitor (A) of capacitance C is charged by a battery to voltage V. The battery is disconnected and an uncharged capacitor (B) of capacitance 2C is connected across A. Find the ratio of:

• final charges on A and B.
• total electrostatic energy stored in A and B finally and that stored in A initially.

10

Derive an expression for the electric potential at any point along the axial line of an electric dipole.

11

An electric dipole consisting of charges +q and -q separated by a distance L is in stable equilibrium in a uniform electric field E. what is the electrostatic potential energy of the dipole?

12

The electric potential on the axis of an electric dipole at a distance 'r' from its centre is V. Then what will be the potential at a point at the same distance on its equatorial line?

13

Four charges -q, -q, +q and +q are placed at the corners of a square of side 2L. What is the electric potential at point A midway between the two charges +q and +q?

14

Which of the following is not the property of an equipotential surface?

• They do not cross each other True
• The work done in carrying a charge from one point to another on an equipotential surface is zero.
• For a uniform electric field, they are concentric spheres
• They can be imaginary spheres

15

An electric dipole of length 2 cm is placed at an angle of 30° with an electric field 2 × 105 N/C. If the dipole experiences a torque of 8 × 10-3 Nm, the magnitude of either charge of the dipole is (Evaluate).

16

A capacitor of unknown capacitance is connected across a battery of V volt. A charge of 360 C is stored in it. When the potential across the capacitor is reduced by 120 V, the charge stored in the capacitor becomes 120 C. Calculate V and the unknown capacitance. What would have been the charge on the capacitor if the voltage were increased by 120 V?

17

An electric dipole moment 2 × 10-8 Cm in a uniform electric field experiences a maximum torque of 6 × 10-4 Nm. What is the magnitude of the electric field?

18

Which of the following materials can be used to make a Faraday cage?

• Plastic
• Glass
• Copper
• Wood

19

Example of a real-world Faraday cage is:

• car
• plastic box
• lighting rod
• metal rod

20

What is the electrical force inside a Faraday cage when it is struck by lightning?

• The same as the lighting
• Half that of the lighting
• Zero
• A quarter of the lighting

21

Three capacitors, each of 4 uF are to be connected in such a way that the effective capacitance of the combination of 6 uF. This can be achieved by connecting

• All three in parallel
• All three in the series
• Two of them connected in series, and the combination in parallel to the third
• Two of them connected in parallel, and the combination in series to the third

22

At what rate does the electric field change between the plates of a square capacitor of side 5 cm if the plates are spaced 1.2 mm apart and the voltage across them is changing at a rate of 60 V/s?

23

A +3.0 nC charge Q is initially at rest at a distance of r, = 10 cm from a + 5.0 nC charge q fixed at the origin. The charge Q is moved away from q to a new position at r2 = 15 cm. In this process of work done by the field?

24

A capacitor of unknown capacitance is connected across a battery of V volts. The charge stored in it is 360 C. When the potential across the capacitor is reduced by 120 V, the charge stored in it becomes 120 C. Calculate:

(i)The potential V and the unknown capacitance C.

(ii) What would be the charge stored in the capacitor, if the voltage applied had increased by 120 V?

25

The magnitude of the electric field (in NC-1) in a region varies with the distance r (in m) as E = 10r + 5. By how much does the electric potential increase in moving from point at r = 1 m to a point at r = 10 m.

26

Derive the expression for the electric potential due to an electric dipole at a point on its axial line.

27

Depict the equipotential surfaces due to an electric dipole.

28

Derive the expression for the capacitance of a parallel plate capacitor having plate area A and plate separation d.

29

Two charged spherical conductors of radii Ry and Re when connected by a conducting plate respectively. Find the ratio of their surface charge densities in terms of their radii.

30

Draw the equipotential surfaces corresponding to a uniform electric field in the z-direction.