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Class 12 Physics MCQ Questions of Electric Charges and Fields with Answers?

Answer 1

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Practice MCQ Question for Class 12 Physics chapter-wise 

1. The surface considered for Gauss’s law is called

(a) Closed surface
(b) Spherical surface
(c) Gaussian surface
(d) Plane surface

2. Which of the following statements is not true about Gauss’s law?

(a) Gauss’s law is true for any closed surface.
(b) The term q on the right side of Gauss’s law includes the sum of all charges enclosed by the surface
(c) Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry
(d) Gauss’s law is based on the inverse square dependence on distance contained in the coulomb’s law

3. A charge Q is placed at the centre of the line joining two point charges +q and +q as shown in the figure. The ratio of charges Q and q is

(a) 4
(b) 1/4
(c) -4
(d) -1/4

4. ​​​​​​Electric field lines provide information about

(a) field strength
(b) direction
(c) nature of charge
(d) all of these

5. The unit of electric dipole moment is

(a) newton
(b) coulomb
(c) farad
(d) debye

6. Which one of the following is the unit of electric field?

(a) Coulomb
(b) Newton
(c) Volt
(d) N/C

7. If sphere of bad conductor is given charge then it is distributed on:

(a) surface
(b) inside the surface
(c) only inside the surface
(d) None

8. The dielectric constant of a metal is:

(a) 0
(b) 1
(c) ∞
(d) -1

9. When placed in a uniform field, a dipole experiences:

(a) a net force
(b) a torque
(c) both a net force and torque
(d) neither a net force nor a torque

10. A soap bubble is given a negative charge, then its radius:

(a) increases
(b) decreases
(c) remains unchanged
(d) may increase or decrease

11. Figure shows electric field lines in which an electric dipole P is placed as shown. Which of the following statements is correct?

(a) The dipole will not experience any force
(b) The dipole will experience a force towards right
(c) The dipole will experience a force towards left
(d) The dipole will experience a force upwards

12. A point charge + q is placed at a distance d from an isolated conducting plane. The field at a point P on the other side of the plane is

(a) directed perpendicular to the plane and away from the plane
(b) directed perpendicular to the plane but towards the plane
(c) directed radially away from the point charge
(d) directed radially towards the point charge

13. A hemisphere is uniformly charged positively. The electric field at a point on a diameter away from the centre is directed

(a) perpendicular to the diameter
(b) parallel to the diameter
(c) at an angle tilted towards the diameter
(d) at an angle tilted away from the diameter

14. Assertion: The positive charge particle is placed in front of a spherical uncharged conductor. The number of lines of forces terminating on the sphere will be more than those emerging from it.

Reason: The surface charge density at a point on the sphere nearest to the point charge will be negative and maximum in magnitude compared to other points on the sphere.

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

15. Charge is the property associated with matter due to which it produces and experiences

(a) electric effects only
(b) magnetic effects only
(c) both electric and magnetic effects
(d) None of these

16. A body is positively charged, it implies that

(a) there is only positive charge in the body.
(b) there is positive as well as negative charge in the body but the positive charge is more than negative charge
(c) there is equal positive and negative charge in the body but the positive charge lies in the outer regions
(d) negative charge is displaced from its position

17. Which of the following is the best insulator?

(a) Carbon
(b) Paper
(c) Graphite
(d) Ebonite

18. Two spheres A and B of exactly same mass are given equal positive and negative charges respectively. Their masses after charging

(a) remains unaffected
(b) mass of A > mass of B
(c) mass of A < mass of B
(d) Nothing can be said

19. If an electron has an initial velocity in a direction different from that of an electric field, the path of the electron is

(a) a straight line
(b) a circle
(c) an ellipse
(d) a parabola

20. Electric lines of force about a negative point charge are

(a) circular anticlockwise
(b) circular clockwise
(c) radial, inwards
(d) radial, outwards

21. Gauss's law is valid for

(a) any closed surface
(b) only regular close surfaces
(c) any open surface
(d) only irregular open surfaces

22. You are traveling in a car during a thunderstorm. In order to protect yourself from lightning, you would prefer to

(a) Touch the nearest electric pole
(b) Take shelter under a tree
(c) Get out and crouch on the ground
(d) Remain in the car

23. Out of gravitational, electromagnetic, Vander Waals, electrostatic and nuclear forces; which two are able to provide an attractive force between two neutrons 

(a) Electrostatic and gravitational
(b) Electrostatic and nuclear
(c) Gravitational and nuclear
(d) Some other forces like Vander Waals

24. +2C and +6C two charges are repelling each other with a force of 12 N. If each charge is given –2C of charge, then the value of the force will be 

(a) 4 N (Attractive)
(b) 4 N (Repulsive)
(c) 8 N (Repulsive)
(d) Zero

25. Two identical conductors of copper and aluminium are placed in an identical electric field. The magnitude of induced charge in the aluminum will be 

(a) Zero
(b) Greater than in copper
(c) Equal to that in copper
(d) Less than in copper

Answer 2

1. Answer : (c) Gaussian surface

Explanation: The surface that we choose for the application of Gauss’s law is called Gaussian surface.

2. Answer : (c) Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry.

Explanation: Gauss's law is often useful towards a much easier calculation of electrostatic field when the system has some symmetry. This is facilitated by the choice of a suitable Gaussian surface.

3. Answer : (d) -1/4

Explanation: For the system to be in equilibrium, net force on q = 0 or \(\frac{Qq}{4\pi\varepsilon_0x^2}+\frac{qq}{4\pi\varepsilon_0(2x)^2}=0\)

or \(Q=\frac{-q}{4}\)​ or  \(\frac{Q}{q}=-\frac{1}{4}\)

4. ​​​​​​Answer : (d) all of these

Explanation: The electric field lines are the curves which gives the information about the electric field. Thus, the electric field lines provide information about field strength, direction of electric field and nature of the electric charge.

5. Answer : (d) debye

Explanation: The SI unit for electric dipole moment is the coulomb-meter (C⋅m). The debye (D) is another unit of measurement used in atomic physics and chemistry.

6. Answer : (d) N/C

Explanation: The units of the electric field in the SI system are newtons per coulomb (N/C), or volts per meter (V/m); in terms of the SI base units they are kg⋅m⋅s⁻³⋅A⁻¹.

7. Answer : (d) None

Explanation: As the charge is given to the conductor, according to the guass law, or the gaussian surface the charge will be equally distributed outside the surface of the sphere. The bad conductor conductivity will decreases but the charge will be there. The charge will be distributed outside the surface not on the inside surface.

8. Answer : (c) ∞

Explanation: The dielectric constant of metals is infinite. The dielectric constant of metal is infinite as the net electric field inside the metal is zero.

9. Answer : (b) a torque

Explanation: An electric dipole placed in a uniform electric field experiences a torque that aligns the dipole parallel to the direction of the electric field with zero net force. In a uniform electric field, both the point charges comprising the dipole will experience force, equal in magnitude and opposite in direction.

10. Answer : (a) increases

Explanation: The charge will be distributed uniformly over the surface of the bubble by symmetry. Therefore, when a negative charge is given to the soap bubble, then its radius will increase.

11. Answer : (c) The dipole will experience a force towards left

Explanation: The spacing between electric lines of force increases from left to right. Therefore, E on left is greater than E on right. Force on +q charge of dipole is smaller and to the right. Force on −q charge of dipole is bigger and to the left. Hence the dipole will experience a force towards the left.

12. Answer : (a) directed perpendicular to the plane and away from the plane

Explanation: When a point charge +q is placed at a distance d from an isolated conducting plane, some negative charge develops on the surface of the plane towards the charge and an equal positive charge develops on opposite side of the plane. Hence, the field at a point P on the other side of the plane is directed perpendicular to the plane and away from the plane as shown in figure.

13. Answer : (a) perpendicular to the diameter

Explanation: When the point is on the diameter and away from the centre of hemisphere which is charged uniformly and positively, the component of electric field intensity parallel to the diameter cancel out. So the electric field is perpendicular to the diameter.

14. Answer : (d) If both the Assertion and Reason are incorrect

Explanation: No. of lines entering the surface = No. of lines leaving the surface.

15. Answer : (c) both electric and magnetic effects

Explanation: A charge is a property associated with the matter due to which it experiences and produces an electric and magnetic field. Charges are scalar in nature and they add up like real numbers. Also, the total charge of an isolated system is always conserved.

16. Answer : (c) there is equal positive and negative charge in the body but the positive charge lies in the outer regions

Explanation: A body is positively charged, it implies that there is positive as well as negative charge in the body but the positive charge is more than negative charge.

17. Answer : (d) Ebonite

Explanation: Whereas Ebonite is a very good material for insulators as it does not allow free flow of electrons and acts as a very good material for an insulator.

18. Answer : (c) mass of A < mass of B

Explanation: A loses electrons and B gains electrons. Therefore, mass of A < mass of B.

19. Answer : (d) a parabola

Explanation: The path is a parabola, because initial velocity can be resolved into two rectangular components, one along \(\vec E\) and other ⊥ to \(\vec E\) . The former decreases at a constant rate and later is unaffected. The resultant path is therefore a parabola.

20. Answer : (c) radial, inwards

Explanation: For a single negative point charge, electric lines of force are radial and inwards.

21. Answer : (a) any closed surface

Explanation: Gauss's law states that flow through any closed surface is a measure of the total charge inside. So, Gauss law is valid for closed surfaces. Gauss's law is valid only for the symmetric body charge distribution such as spherical, cylindrical, plane symmetry. It is also a valid other medium such as dielectric medium.

22. Answer : (d) Remain in the car

Explanation: It is better to remain in the car, as it provides earthing to charges without harming us. The metal body of the car conducts the charges to the earth without letting it enter our body. The chances of lightning striking a high-rise object are more. So we should never stand near a tower, a building, or a tree, etc. 

23. Answer :(c) Gravitational and nuclear

Explanation: Attractive force between two neutrons may be due to gravitational forces or due to nuclear forces.

24. Answer : (d) Zero

Explanation: On adding -2C to both, one charge becomes neutral and hence Coulomb's force equals zero.

25. Answer : (c) Equal to that in copper

Explanation: Since the magnitude of the external electric field is the same, the induced charge will be the same in both copper and aluminum. 

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