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Practice MCQ Question for Class 12 Physics chapter-wise 

1. If a conductor has a potential V ≠ 0 and there are no charges anywhere else outside, then

(a) there must be charges on the surface or in¬side itself
(b) there cannot be any charge in the body of the conductor
(c) there must be charges only on the surface
(d) both (a) and (b) are correct

2. A parallel plate air capacitor is charged to a potential difference of V volts. After disconnecting the charging battery the distance between the plates of the capacitor is increased using an insulating handle. As a result the potential difference between the plates

(a) increases
(b) decreases
(c) does not change
(d) becomes zero

3. 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 plated connected together are destroyed.
(b) The energy stored in ths system increases
(c) The potential difference between the free plates is 2V
(d) The potential difference remains constant

4. Two spherical conductors each of capacity C are charged to potential V and -V. These are then connected by means of a fine wire. The loss of energy is

(a) zero
(b) 1/2 CV²
(c) CV²
(d) 2 CV²

5. Two copper spheres of the same radius, one solid and the other hollow, are charged to the same potential. Which will have more charge?

(a) Solid sphere
(b) Hollow sphere
(c) Both will have an equal charge
(d) None of these

6. A bird sitting on a high power line:

(a) gets killed instantly
(b) gets a mild shock
(c) gets a fatal shock
(d) is not affected practically

7. Choose the SI unit of electric potential energy :

(a) Joule
(b) Coulomb
(c) Netwon per coulomb
(d) Erg

8. 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

9. The electric potential of earth is taken as:

(a) zero
(b) infinity
(c) unity
(d) None of these

10. A positively charged particle is released from rest in an uniform electric field. The electric potential energy of the charge

(a) remains a constant because the electric field is uniform
(b) increases because the charge moves along the electric field
(c) decreases because the charge moves along the electric field
(d) decreases because the charge moves opposite to the electric field 

11. Equipotentials at a great distance from a collection of charges whose total sum is not zero are approximately

(a) spheres
(b) planes
(c) paraboloids
(d) ellipsoids

12. The electric potential inside a conducting sphere

(a) increases from centre to surface
(b) decreases from centre to surface
(c) remains constant from centre to surface
(d) is zero at every point inside

13. It becomes possible to define potential at a point in an electric field because electric field

(a) is a conservative field
(b) is a non-conservative field
(c) is a vector field
(d) obeys principle of superposition

14. There are two metallic spheres of same radii but one is solid and the other is hollow, then

(a) solid sphere can be given more charge
(b) hollow sphere can be given more charge
(c) they can be charged equally (maximum)
(d) None of the above

15. The positive terminal of 12 V battery is connected to the ground. Then the negative terminal will be at

(a) – 6 V
(b) + 12 V
(c) zero
(d) – 12 V

16. 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 the sphere is

(a) zero
(b) 10 V
(c) 4 V
(d) 10/3 V

17. Energy is stored in a capacitor in the form of

(a) electrostatic energy
(b) magnetic energy
(c) light energy
(d) heat energy

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

(a) the negative charges
(b) the positive charges
(c) the field between the plates
(d) both (a) and (b)

19. Capacitors are used in electrical circuits where appliances need more

(a) voltage
(b) current
(c) resistance
(d) power

20. Assertion : Electric field is discontinuous across the surface of a spherical charged shell.

Reason : Electric potential is continuous across the surface of a spherical charged shell

(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct

21. A table tennis ball that has been covered with conducting paint is suspended by a silk thread so that it hangs between two plates, out of which one is earthed and other is connected to a high voltage generator. This ball

(a) Is attracted towards high voltage plate and stays there
(b) Hangs without moving
(c) Swing backward and forward hitting each plate in turn
(d) Is attracted to the earthed plate and stays there

22. If a unit positive charge is taken from one point to another over an equipotential surface, then-

(a) Work is done on the charge
(b) Work is done by the charge
(c) Work done is constant
(d) No work is done

23. When one electron is taken towards the other electron, then the electric potential energy of the system -

(a) Decreases
(b) Increases
(c) Remains unchanged
(d) Becomes zero

24. Equipotential surfaces associated with an electric field which is increasing in magnitude along the x-direction are

(a) Planes parallel to yz-plane
(b) Planes parallel to xy-plane
(c) Planes parallel to xz-plane
(d) Coaxial cylinders of increasing radii around the x-axis

25. If the dielectric constant and dielectric strength be denoted by k and x respectively, then a material suitable for use as a dielectric in a capacitor must have

(a) High k and high x
(b) High k and low x
(c) Low k and low x
(d) Low k and high x

Answer :

1. Answer : (c) there must be charges only on the surface

Explanation: If a conductor has a non zero potential and there are no charges anywhere else outside, then there must be charges on the surface of the conductor or inside the conductor. There cannot be any charge in the body of the conductor.

2. Answer : (a) increases

Explanation: When battery is disconnected and the distance between the plates of the capacitor is increased then capacitance increases and charge remains constant. ∴ Potential difference increases.

3. Answer : (c) The potential difference between the free plates is 2V

Explanation: The charges on the inner plates are bound. Capacitance is halved. So, potential difference is doubled but energy stored remains unchanged.

4. Answer : (c) CV²

Explanation: Here, loss of energy

\(=\frac{C_1C_2(V_1+V_2)^2}{2(C_1+C_2)}\)

\(=\frac{CC(V+V)^2}{2(C+C)}\)

5. Answer : (c) Both will have an equal charge

Explanation: We know that the charges reside on the surface of a conductor. Here the two copper spheres are two conductors. So the charge uniformly distributed on the surface on the both sphere. We know that potential at the surface is \(V=\frac{kq}{R}\) . As the both spheres have same radius and charged to same potential so they will have equal charge.

6. Answer : (d) is not affected practically

Explanation: A bird is not affected practically because both of its legs are at same potential thus, current cannot flow through its body.

7. Answer : (a) Joule

Explanation: The SI unit of electric potential energy is joule (named after the English physicist James Prescott Joule). In the CGS system the erg is the unit of energy, being equal to 10⁻⁷ Joules.

8. Answer : (a) more

Explanation: When dielectric is introduced, the capacitance will increase and as the battery remains connected, so the voltage will remain constant. Hence according to Q = CV the charge will increase.

9. Answer : (a) zero

Explanation: Electric potential of earth is taken as zero, because the capacitance of earth is taken infinite.

10. Answer : (c) decreases because the charge moves along the electric field

Explanation: In a uniform electric field, when a positively charged particle is released from rest, it moves along the electric field, that is from higher potential to lower potential. Therefore, electric potential energy of charge decreases.

11. Answer : (a) spheres

Explanation: For a collection of charges, whose total sum is not zero, equipotentials at large distances must be spheres only.

12. Answer : (c) remains constant from centre to surface

Explanation: Electric potential inside a conductor is constant and it is equal to that on the surface of conductor.

13. Answer : (a) is a conservative field

Explanation: It becomes possible to define potential at a point in an electric field because electric field is a conservative field.

14. Answer : (c) they can be charged equally (maximum)

Explanation: Because in case of metallic sphere either solid or hollow, the charge will reside on the surface of the sphere. Since both spheres have same surface area, so they can hold equal maximum charge.

15. Answer : (d) – 12 V

Explanation: When negative terminal of battery is grounded, positive terminal of battery is at +12V . When positive terminal is grounded, the negative terminal will be at −12V.

16. Answer : (b) 10 V

Explanation: Hollow metal sphere = spherical shell

Electric field inside shell = 0

B is Potential in constant inside thin shell

potential at surface = potential at centre 

=10 V.

17. Answer : (a) electrostatic energy

Explanation: Energy stored in a capacitor is in the form of electrical potential energy, and it is thus related to the charge Q and voltage V on the capacitor.

18. Answer : (c) the field between the plates

Explanation: Electrostatic energy of a condenser lies in the field in between the plates of the condenser.

19. Answer : (b) current

Explanation: Capacitors are commonly used in electronic devices to maintain their power supply and some appliances need rapid current so they can start. So the capacitors are used in electrical circuits where appliances need current. 

20. Answer : (b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion

Explanation: Electric field is zero inside the spherical charged shell and it is \(\frac{\sigma}{\varepsilon_0}\pi\) outside. So it is discontinuous across the surface. Electric potential is continuous across the surface.

21. Answer : (c) Swing backward and forward hitting each plate in turn

Explanation: When the other piate is connected to the high voltage generator, the negative charge induced on the ball cause attraction. When it strikes the +ve plate charge distribution again takes piace.This causes repulsion. Hence, the ball swings backward and forward hitting each plate in turn.

22. Answer : (d) No work is done

Explanation: Since the potential at each point of an equipotential surface is the same, the potential does not change while we move a unit positive charge from one point to another. Therefore work done in the process is zero.

23. Answer : (b) Increases

Explanation: when an electron is brought near another electron, the work has to be done against the repulsive force since like charges repel each other. This work done is stored in the form of electrostatic potential energy and hence the electric potential energy of the system increases.

24. Answer : (a) Planes parallel to yz-plane

Explanation: Any surface which has same electrostatic potential at every point is called an equipotential surface. Electric field is always perpendicular to an equipotential surface. Therefore x-direction is perpendicular only to yz plane.

25. Answer : (a) High k and high x

Explanation: High K means good insulating propetry and high x means able to withstand electric field gradient to a higher value.

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