1.Coulomb’s law is applicable for which type of charges?
(A) Moving charges
(B) Stationary charges
(C) Both moving and stationary charges
(D) None of these
Answer: (B) Stationary charges
Explanation: Coulomb’s law gives the force between two point charges that are stationary. It states that the electrostatic force between two charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.
2. The SI unit of electric charge is:
(A) Coulomb
(B) Newton
(C) Joule
(D) Farad
Answer: (A) Coulomb
Explanation: The SI unit of electric charge is the coulomb (C), where 1 Coulomb is the amount of charge transported by a current of 1 ampere in 1 second.
3. The force between two charges separated by 1 meter is 9 N. If the distance is halved, the force becomes:
(A) 18 N
(B) 36 N
(C) 4.5 N
(D) 2.25 N
Answer: (B) 36 N
Explanation: According to Coulomb’s law: F ∝ 1 / r2
When the distance is halved, the force increases by a factor of 4. Hence, 9×4=36 N.9 \times 4 = 36 \, N.9×4=36N.
Mcq on electrostatics class 12 chapter 1
4. The value of the permittivity of free space (ε0) is:
(A) 8.854 × 10−12 C2N−1m−2
(B) 9 × 109 Nm2 C−2
(C) 1.6 × 10−19 C
(D) 6.67 × 10−11 Nm2kg−2
Answer: (A) 8.854×10−12 C2N−1m−2
Explanation: The permittivity of free space is a fundamental physical constant that defines the strength of the electrostatic force between electric charges in a vacuum.
5. The electric field due to a point charge is:
(A) Constant everywhere
(B) Directly proportional to distance from the charge
(C) Inversely proportional to distance squared
(D) Zero at infinity
Answer: (C) Inversely proportional to distance squared
Explanation: The electric field due to a point charge is given by: E = kQ / r2
It decreases as the square of the distance from the charge.
6. A positively charged rod is brought near a neutral conductor. The charge induced on the near and far sides of the conductor is:
(A) Positive on both sides
(B) Negative on both sides
(C) Negative on the near side and positive on the far side
(D) Positive on the near side and negative on the far side
Answer: (C) Negative on the near side and positive on the far side
Explanation: By the principle of electrostatic induction, opposite charges accumulate on the closer side, and like charges are repelled to the far side.
Mcq on electrostatics class 12 chapter 1
7. The unit of electric field is:
(A) Newton per Coulomb
(B) Joules per meter
(C) Farad per meter
(D) Coulomb per meter
Answer: (A) Newton per Coulomb
Explanation: The electric field is defined as force per unit charge, with SI unit N / C.
8. Electric potential due to a point charge at a distance r is:
(A) V = kQ / r
(B) V = kQ / r2
(C) V = kQr
(D) V = kQ2
Answer: (A) V = kQ / r
Explanation: Electric potential due to a point charge is given by the formula: V = kQ / r Where k is Coulomb’s constant.
9. The work done in bringing a unit positive charge from infinity to a point in an electric field is:
(A) Potential energy
(B) Kinetic energy
(C) Electric potential
(D) Capacitance
Answer: (C) Electric potential
Explanation: Electric potential is defined as the work done to bring a unit positive charge from infinity to a specific point in an electric field.
10. The capacitance of a parallel plate capacitor increases with:
(A) Increase in the distance between the plates
(B) Decrease in plate area
(C) Insertion of a dielectric medium
(D) Decrease in dielectric constant
Answer: (C) Insertion of a dielectric medium
Explanation: Inserting a dielectric increases the permittivity of the medium, thereby increasing the capacitance.
11. Two point charges +3 μC and −3 μC are placed 5 cm apart in air. The electric field at the midpoint between them is:
(a) Zero
(b) Directed towards the negative charge
(c) Directed towards the positive charge
(d) None of these
Answer: (a) Zero
Explanation: The electric field due to equal and opposite charges at the midpoint cancels each other out, resulting in zero net electric field.
12. The unit of electric field is:
(a) N/C
(b) V/m
(c) Both (a) and (b)
(d) J/C
Answer: (c) Both (a) and (b)
Explanation: Electric field E is defined as force per unit charge, so E = F / q, with units N/C or equivalently V/m.
13. Coulomb’s law is valid for:
(a) Point charges only
(b) Finite-sized bodies
(c) Both point charges and extended bodies
(d) None of these
Answer: (a) Point charges only
Explanation: Coulomb’s law strictly applies to point charges, but it can be approximated for larger bodies.
14. The permittivity of free space is represented by:
(a) μ0
(b) ϵ0
(c) k
(d) None of these
Answer: (b) ϵ0
Explanation: ϵ0 is the permittivity of free space, with a value of 8.854×10−12 C2N−1m−2
15. The force between two point charges is 36 N. If the distance between them is halved, the force becomes:
(a) 9 N
(b) 72 N
(c) 144 N
(d) 18 N
Answer: (c) 144 N
Explanation: According to Coulomb’s law, F∝1 / r2. When distance is halved, force increases by a factor of 4, hence 36 × 4 = 144 N.
16. Electric potential due to a point charge is:
(a) Inversely proportional to distance
(b) Directly proportional to distance
(c) Independent of distance
(d) None of these
Answer: (a) Inversely proportional to distance
Explanation: Electric potential due to a point charge is given by: V = kQ / r
17. The SI unit of electric potential is:
(a) Coulomb
(b) Joule
(c) Volt
(d) Newton
Answer: (c) Volt
Explanation: Potential is defined as work done per unit charge, with SI unit volt (V).
18. A capacitor is connected to a battery. What happens when the plate separation increases?
(a) Capacitance increases
(b) Capacitance decreases
(c) Charge increases
(d) Voltage increases
Answer: (b) Capacitance decreases
Explanation: Capacitance is given by C = ϵ0A / d so increasing distance reduces capacitance.
19. The energy stored in a capacitor is given by:
(a) QV
(b) 1 / 2 CV2
(c) CV
(d) 1 / 2QV
Answer: (b) 1 / 2CV2
Explanation: Energy stored in a capacitor is derived using the work done to charge the capacitor.
20. The equivalent capacitance of two capacitors connected in parallel is:
(a) C1 + C2
(b) C1C2 / C1 + C2
(c) 1 / C1+1 / C2
(d) None of these
Answer: (a) C1 + C2
Explanation: In parallel, capacitances add up to give the total capacitance.
21. According to Gauss’s Law, the electric flux through a closed surface depends on:
(a) Shape of the surface
(b) Charge enclosed by the surface
(c) Size of the surface
(d) None of these
Answer: (b) Charge enclosed by the surface
Explanation: Gauss’s law states: Φ = Qenclosed / ϵ0
22. The electric field due to an infinitely long charged wire varies as:
(a) r
(b) 1 / r
(c) 1 / r2
(d) r2
Answer: (b) 1 / r
Explanation: For a long charged wire, E∝1 / r, where r is the distance from the wire.
23. In a conductor, electric field is:
(a) Zero
(b) Maximum
(c) Infinity
(d) Uniform
Answer: (a) Zero
Explanation: Inside a conductor, electrostatic equilibrium ensures zero electric field.
24. When a dielectric is inserted between capacitor plates, its capacitance:
(a) Increases
(b) Decreases
(c) Remains the same
(d) Becomes zero
Answer: (a) Increases
Explanation: Inserting a dielectric increases the capacitance by a factor of the dielectric constant k.
25. Work done in moving a charge in an equipotential surface is:
(a) Maximum
(b) Zero
(c) Minimum
(d) Infinity
Answer: (b) Zero
Explanation: No work is required to move a charge along an equipotential surface.
26. The capacitance of a parallel plate capacitor depends on:
(a) Plate area
(b) Distance between plates
(c) Dielectric constant
(d) All of these
Answer: (d) All of these
Explanation: Capacitance formula: C = ϵ0ϵrA / d
27. Electric field inside a charged spherical conductor is:
(a) Zero
(b) Uniform
(c) Infinity
(d) Varies with radius
Answer: (a) Zero
Explanation: Inside a conductor, the electric field is zero in electrostatic equilibrium.
28. The potential at a distance ‘r’ from a point charge ‘Q’ is given by:
(a) V = kQ / r
(b) V = Q / 4πϵ0r
(c) V = kQ / r2
(d) V = Q / r
Answer: (a) V = kQ / r
Explanation: Potential due to a point charge follows the inverse distance law.
29. The SI unit of permittivity is:
(a) F / m
(b) C / m2
(c) N m2 / C2
(d) V/m
Answer: (a) F / m
Explanation: Permittivity ϵ\epsilonϵ has units farad per meter.
30. If the distance between two charges is doubled, the force between them becomes:
(a) One-fourth
(b) Double
(c) Half
(d) Four times
Answer: (a) One-fourth
Explanation: Coulomb’s law: F ∝ 1 / r2, hence doubling distance reduces force by 1/4.
31. A parallel plate capacitor is charged and disconnected. If the plates are pulled apart:
(a) Voltage increases
(b) Capacitance increases
(c) Charge increases
(d) Energy decreases
Answer: (a) Voltage increases
Explanation: V ∝ d / C, increasing distance increases voltage.
32. Dielectric constant is also known as:
(b) Absolute permittivity
(c) Permeability
(d) None of these
Answer: (a) Relative permittivity
Explanation: Dielectric constant ϵr is the ratio of permittivity of the material to free space.
33. Two charges of +4 µC and -6 µC are placed 12 cm apart in air. The magnitude of the electrostatic force between them is approximately:
(A) 15×10−3 N
(B) 18×10−3 N
(C) 20×10−3 N
(D) 30×10−3 N
Answer: (B) 18×10−3 N
Explanation: The electrostatic force is given by Coulomb’s law: F = k × ∣ q1×q2 ∣ / r2
Where:
- K = 9 × 109 Nm2 / C2
- q1 = 4×10−6 C, q2 = −6 × 10−6 C
- r = 0.12 m
F = 9 ×109 × 4 ×10−6 × 6×10−6 / (0.12)2 = 18 × 10−3 N
34. The electric field at a point due to a point charge is inversely proportional to:
(A) Charge
(B) Distance
(C) Square of distance
(D) Cube of distance
Answer: (C) Square of distance
Explanation: The electric field due to a point charge is given by: E = k × q / r2
It is inversely proportional to the square of the distance from the charge.
35. Which of the following statements is true about electric field lines?
(A) Electric field lines start from negative and end at positive charges.
(B) Electric field lines form closed loops.
(C) Electric field lines never intersect.
(D) Electric field lines are parallel to equipotential surfaces.
Answer: (C) Electric field lines never intersect.
Explanation: Electric field lines do not intersect because if they did, it would imply two different directions of the electric field at a single point, which is impossible.
36. The work done in moving a charge between two points in an electric field depends on:
(A) The path taken
(B) Initial position only
(C) Final position only
(D) Initial and final positions
Answer: (D) Initial and final positions
Explanation: The work done in moving a charge in an electric field is given by the change in potential energy, which depends only on the initial and final positions, not the path followed (conservative field).