Free Electrostatics MCQs with Answers
831 Electrostatics MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Electrostatics describes forces between charges through Coulomb's law, electric fields and field intensity, then uses electric potential to measure energy per unit charge. Capacitors store charge and electrical energy, with capacitance depending on geometry and dielectric material, not simply on the amount of charge present.
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Read the Electrostatics notesFree MDCAT chapter notes with key terms831 questions · page 13 of 42
- A. JC⁻¹
- B. Jm⁻³
- C. JV⁻¹
- D. JF⁻³
Explanation: Energy density is defined as energy per unit volume. The SI unit for energy is the Joule (J) and for volume is cubic meters (m³), making…
Correct answer: Jm⁻³- A. Reduction of charge on the plates and increase of potential difference across the plates
- B. Increase in the potential difference across the plates, reduction in stored energy, but no change in the charge on the plates
- C. Decrease in the potential difference across the plates, reduction in stored energy, but no change in the charge on the plates
- D. None of the above
Explanation: Since the battery is disconnected, the charge (Q) on the plates remains constant.
Correct answer: Decrease in the potential difference across the plates, reduction in stored energy, but no change in the charge on the plates- A. 9 × 10³ N/C toward q₁
- B. 18 × 10³ N/C toward q₂
- C. 27 × 10³ N/C toward q₂
- D. Zero
Explanation: The electric field at the midpoint is the vector sum of fields due to q₁ and q₂.
Correct answer: 27 × 10³ N/C toward q₂244. A point charge of +4 μC is placed at the origin. What is the electric potential at a point 3 m away?
- A. 1.2 × 10⁴ V
- B. 2.4 × 10⁴ V
- C. 3.6 × 10⁴ V
- D. 4.8 × 10⁴ V
Explanation: Electric potential due to a point charge is V = kq/r, where k = 9 × 10⁹ N·m²/C², q = 4 × 10⁻⁶ C, and r = 3 m.
Correct answer: 1.2 × 10⁴ V- A. Zero
- B. 4kq/a
- C. 4kq/(a√2)
- D. 2kq/a
Explanation: The potential at the center is the scalar sum of potentials due to each charge. The distance from each corner to the center is a/√2.
Correct answer: 4kq/a- A. Increases
- B. Decreases
- C. Remains constant
- D. Becomes zero
Explanation: Energy stored is U = (1/2)CV². If plates are separated, C decreases (C = ε₀A/d).
Correct answer: Increases- A. σ/ε₀
- B. Zero
- C. σR/ε₀
- D. σ/(4πε₀R)
Explanation: By Gauss's law, the electric field inside a uniformly charged spherical shell is zero, as the enclosed charge is zero.
Correct answer: Zero- A. 6 μF
- B. 2 μF
- C. 0.67 μF
- D. 1.5 μF
Explanation: For capacitors in series, 1/C_eq = 1/C₁ + 1/C₂ + 1/C₃ = 1/2 + 1/2 + 1/2 = 3/2. Thus, C_eq = 2/3 ≈ 0.67 μF.
Correct answer: 0.67 μF- A. 2 × 10⁻⁴ N·m
- B. 1 × 10⁻⁴ N·m
- C. Zero
- D. 4 × 10⁻⁴ N·m
Explanation: Torque on a dipole is τ = pE sinθ, where p = 2 × 10⁻⁹ C·m, E = 10⁵ N/C, and θ = 90° (sin 90° = 1). Thus, τ = (2 × 10⁻⁹)(10⁵) = 2 × 10⁻⁴ N·m.
Correct answer: 2 × 10⁻⁴ N·m- A. kq/r²
- B. Zero
- C. kq/(r² - a²)
- D. kq/(b - A)
Explanation: For r > b, the conducting shell's induced charges make it appear as if all charge q is at the center.
Correct answer: kq/r²- A. kq/(2a²) along +x
- B. 2kq/a² along -x
- C. kq/(√2a²) along +y
- D. Zero
Explanation: The electric fields due to the two charges at (a, 0) cancel out. Each charge produces a field of equal magnitude but opposite direction…
Correct answer: Zero- A. C/3
- B. C
- C. 3C
- D. 2C
Explanation: Capacitance is C = ε₀εrA/d. With a dielectric of εr = 3, the capacitance becomes 3C, as εr increases the permittivity.
Correct answer: 3C- A. 2.26 × 10⁵ N·m²/C
- B. 3.76 × 10⁴ N·m²/C
- C. Zero
- D. 1.13 × 10⁵ N·m²/C
Explanation: By Gauss's law, total flux through a closed surface is Φ = q/ ε₀, where q = 2 × 10⁻⁶ C and ε₀ = 8.85 × 10⁻¹² C²/N·m².
Correct answer: 3.76 × 10⁴ N·m²/C- A. kq/d
- B. Zero
- C. 2kq/d
- D. -kq/d
Explanation: Electric potential is a scalar. At the midpoint, distance to each charge is d/2.
Correct answer: Zero- A. 0.05 m
- B. 0.1 m
- C. 0.2 m
- D. Infinite
Explanation: In a uniform electric field, the force F = qE causes circular motion when velocity is perpendicular.
Correct answer: 0.2 m- A. V/2
- B. V
- C. 2V
- D. 4V
Explanation: Capacitance is C = ε₀A/d. With constant charge Q, potential is V = Q/C. If d doubles, C' = C/2, so V' = Q/(C/2) = 2Q/C = 2V.
Correct answer: 2V- A. λ/(2πε₀r)
- B. λ/(4πε₀r²)
- C. λ/(πε₀r²)
- D. Zero
Explanation: Using Gauss's law for an infinite wire, the electric field is E = λ/(2πε₀r), where λ is the linear charge density and r is the radial…
Correct answer: λ/(2πε₀r)258. A dipole with moment p is placed in a non-uniform electric field. The net force on the dipole is:
- A. Zero
- B. pE
- C. p(dE/dx)
- D. p/E
Explanation: In a non-uniform electric field, the forces on the dipole's charges do not cancel, resulting in a net force F = p(dE/dx), where dE/dx is…
Correct answer: p(dE/dx)- A. 10⁻³ J
- B. 2 × 10⁻³ J
- C. 10⁻⁴ J
- D. 5 × 10⁻⁴ J
Explanation: Energy stored in a capacitor is U = (1/2)CV². With C = 5 × 10⁻⁶ F and V = 20 V, U = (1/2)(5 × 10⁻⁶)(20)² = 2 × 10⁻³ J.
Correct answer: 2 × 10⁻³ J- A. Zero
- B. 3.6 × 10⁴ V
- C. -3.6 × 10⁴ V
- D. 1.8 × 10⁴ V
Explanation: Potential at the third corner is the sum of potentials due to both charges. Distance to each charge is 1 m.
Correct answer: Zero