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Explanation: The SI unit of electric charge is Coulomb (C), defined as the amount of charge transported by a constant current of one ampere in one second.
2. Quantization of electric charge implies that:
A. Charge cannot be destroyed
B. Charge exists in discrete packets (q = ±ne)
C. Total charge in the universe is constant
D. Charge can be divided infinitely
Answer: B. Charge exists in discrete packets (q = ±ne)
Explanation: Quantization of charge means that total charge on a body is always an integral multiple of the basic fundamental charge e (where e = 1.6 × 10^-19 C).
3. When a glass rod is rubbed with silk, the glass rod becomes:
A. Negatively charged
B. Positively charged
C. Neutral
D. Magnetized
Answer: B. Positively charged
Explanation: During friction, electrons are transferred from the glass rod to silk, leaving the glass rod with a deficiency of electrons and thus a positive charge.
4. According to Coulomb’s Law, the electrostatic force between two point charges is inversely proportional to:
A. Distance between them
B. Square of the distance between them
C. Product of their charges
D. Cube of the distance between them
Answer: B. Square of the distance between them
Explanation: Coulomb's Law states that F = k * (q1 * q2) / r^2, which shows force is inversely proportional to the square of the distance (r^2).
5. What is the value of permittivity of free space (ε₀)?
A. 9 × 10^9 N m²/C²
B. 8.854 × 10^-12 C²/N m²
C. 1.6 × 10^-19 C
D. 6.67 × 10^-11 N m²/kg²
Answer: B. 8.854 × 10^-12 C²/N m²
Explanation: Permittivity of free space (ε₀) is a physical constant equal to approximately 8.854 × 10^-12 C²/N m².
6. If the distance between two charges is doubled, the electrostatic force between them will become:
A. Double
B. Half
C. Four times
D. One-fourth
Answer: D. One-fourth
Explanation: Since F is inversely proportional to r^2, doubling the distance (2r) reduces the force to 1/(2)^2 = 1/4th of its original value.
7. The dimensional formula for Electric Field Intensity is:
A. [M L T^-2 A^-1]
B. [M L T^-3 A^-1]
C. [M L T^-3 A^1]
D. [M L^2 T^-3 A^-1]
Answer: B. [M L T^-3 A^-1]
Explanation: Electric Field E = Force / Charge = [M L T^-2] / [A T] = [M L T^-3 A^-1].
8. Electric field lines around a isolated positive point charge are:
A. Radially inwards
B. Radially outwards
C. Circular clockwise
D. Parallel straight lines
Answer: B. Radially outwards
Explanation: Field lines start from a positive charge and extend to infinity, acting radially outwards.
9. Which of the following is NOT a property of electric field lines?
A. They start from positive charge and end at negative charge
B. Two field lines can cross each other
C. They do not form closed loops
D. Tangent to a field line gives direction of electric field
Answer: B. Two field lines can cross each other
Explanation: Two electric field lines can never intersect because if they did, there would be two directions of electric field at the point of intersection, which is impossible.
10. Electric dipole moment is a vector quantity directed from:
A. Positive charge to negative charge
B. Negative charge to positive charge
C. Center to positive charge only
D. Perpendicular to dipole axis
Answer: B. Negative charge to positive charge
Explanation: By convention, the direction of electric dipole moment (p = q × 2a) is directed from the negative charge to the positive charge.
11. What is the SI unit of Electric Dipole Moment?
A. Coulomb / meter
B. Coulomb-meter (C m)
C. Newton / Coulomb
D. Volt-meter
Answer: B. Coulomb-meter (C m)
Explanation: Electric dipole moment p = q × 2a, so its SI unit is Coulomb × meter (C m).
12. The torque acting on an electric dipole of dipole moment 'p' placed in a uniform electric field 'E' is given by:
A. τ = p · E
B. τ = p × E
C. τ = p / E
D. τ = p + E
Answer: B. τ = p × E
Explanation: Torque τ = p E sinθ, which in vector form is represented as the cross product τ = p × E.
13. An electric dipole experiences maximum torque in a uniform electric field when angle between 'p' and 'E' is:
A. 0°
B. 45°
C. 90°
D. 180°
Answer: C. 90°
Explanation: Since τ = pE sinθ, maximum torque occurs when sinθ = 1, i.e., θ = 90°.
14. What is the net force experienced by an electric dipole placed in a uniform electric field?
A. Maximum
B. Zero
C. Depends on angle
D. Infinite
Answer: B. Zero
Explanation: The two equal and opposite forces (+qE and -qE) acting on opposite charges cancel out, making the net force zero.
15. The electric field at a point on the axial line of a short electric dipole varies with distance 'r' as:
A. E ∝ 1/r
B. E ∝ 1/r²
C. E ∝ 1/r³
D. E ∝ r²
Answer: C. E ∝ 1/r³
Explanation: For a short dipole, electric field on axial position E = (1/4πε₀) * (2p/r³), which means E is inversely proportional to r³.
16. What is the ratio of electric field intensity on the axial line to the equatorial line for a short dipole at the same distance?
Explanation: Flux Φ = E · A = (N/C) * m² = N m²/C, which is equivalent to Volt-meter (V m).
18. According to Gauss’s Law, total electric flux through any closed surface is equal to:
A. ε₀ times enclosed charge
B. 1/ε₀ times net charge enclosed
C. Zero always
D. Infinite
Answer: B. 1/ε₀ times net charge enclosed
Explanation: Gauss's Law states that total electric flux Φ = q_enclosed / ε₀.
19. If a closed surface encloses an electric dipole, the total electric flux through the surface will be:
A. q / ε₀
B. 2q / ε₀
C. Zero
D. Dependent on size of surface
Answer: C. Zero
Explanation: A dipole consists of charges +q and -q, so net enclosed charge q_net = 0. Hence, flux Φ = 0 / ε₀ = 0.
20. The electric field due to an infinitely long straight uniformly charged wire varies with distance 'r' as:
A. Directly proportional to r
B. Inversely proportional to r
C. Inversely proportional to r²
D. Independent of r
Answer: B. Inversely proportional to r
Explanation: For a long charged wire, E = λ / (2πε₀ r), showing that E is inversely proportional to r (1/r).
21. Electric field intensity inside a uniformly charged thin spherical shell is:
A. Maximum
B. Zero
C. Same as on surface
D. Variable
Answer: B. Zero
Explanation: Inside a charged hollow sphere/shell, charge enclosed by a Gaussian surface is zero, so electric field E = 0.
22. What is the SI unit of Surface Charge Density (σ)?
A. C / m
B. C / m²
C. C / m³
D. C m
Answer: B. C / m²
Explanation: Surface charge density σ = Charge / Area = Coulomb / meter² (C/m²).
23. Electric field intensity near an infinite thin plane sheet of charge with uniform surface density σ is:
A. E = σ / ε₀
B. E = σ / (2ε₀)
C. E = 2σ / ε₀
D. E = 0
Answer: B. E = σ / (2ε₀)
Explanation: By Gauss's Law, the electric field near a thin infinite sheet of charge is uniform and equal to E = σ / (2ε₀).
24. What is the dielectric constant (relative permittivity K) of water?
A. 1
B. 80 (or 81)
C. Infinity
D. Zero
Answer: B. 80 (or 81)
Explanation: Water has a high relative permittivity/dielectric constant of approximately 80 at room temperature, drastically reducing forces between ions.
25. How many electrons constitute 1 Coulomb of negative charge?
A. 6.25 × 10^18 electrons
B. 1.6 × 10^-19 electrons
C. 6.25 × 10^19 electrons
D. 9.1 × 10^31 electrons
Answer: A. 6.25 × 10^18 electrons
Explanation: Using q = ne, n = q / e = 1 / (1.6 × 10^-19) = 6.25 × 10^18 electrons.
This page contains a chapter-wise objective practice set. Try the questions without checking the answer first, then use the explanation to understand the point you missed. The current page contains 25 questions, so you can practise in smaller sets when you are revising.
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After the practice set, write down the question numbers you missed and revise only those concepts once more. This makes MCQ practice more useful than repeatedly attempting the same questions without reviewing mistakes.
