King Edward Medical University Entry Test Physics Electrostatics — Set 3

Electrostatics MCQs set 3 for King Edward Medical University Entry Test Physics — 20 solved questions.

King Edward Medical University Entry Test Physics Electrostatics — Set 3

  1. Question 1

    Q1. An electric field of 200 N/C exists at a point. What force acts on a +5 μC charge placed there?

    • A) 1×10⁻³ N (opposite field direction)
    • B) 1×10⁻³ N (same field direction)
    • C) 2×10⁻³ N (perpendicular to field)
    • D) 0 N (no movement)

    Answer: 1×10⁻³ N (same field direction)

    Explanation: F = qE. Option A incorrectly assumes negative charge direction.

  2. Question 2

    Q2. A parallel plate capacitor stores 1.5×10⁻⁶ C when charged to 24 V. What is its capacitance?

    • A) 6.25×10⁻⁸ F
    • B) 6.25×10⁻⁵ F
    • C) 6.25×10⁻² F
    • D) 6.25×10⁻⁴ F

    Answer: 6.25×10⁻⁸ F

    Explanation: C = Q/V. Option B divides instead of multiplies by voltage.

  3. Question 3

    Q3. An electric dipole with moment p = 4×10⁻⁶ C·m experiences a torque of 1.2×10⁻³ N·m in a 300 N/C field. What is the angle between p and E?

    • A) 30°
    • B) 45°
    • C) 60°
    • D) 90°

    Answer: 30°

    Explanation: τ = pE sinθ. Option B uses cosine instead of sine in calculation.

  4. Question 4

    Q4. A spherical shell of radius 20 cm carries +8 μC. What is the electric field at 10 cm from the center?

    • A) 720 N/C inward
    • B) Zero (conductor interior field)
    • C) 360 N/C outward
    • D) 450 N/C outward

    Answer: Zero (conductor interior field)

    Explanation: Conductors in electrostatic equilibrium have zero interior field. Option C uses Coulomb’s Law incorrectly.

  5. Question 5

    Q5. Three capacitors, 2 μF, 4 μF, and 6 μF, are connected in series. What is their equivalent capacitance?

    • A) 12 μF
    • B) 1.09 μF
    • C) 12/6 μF
    • D) 6 μF

    Answer: 1.09 μF

    Explanation: 1/Ceq = 1/C₁ + 1/C₂ + 1/C₃. Option D adds capacitors directly.

  6. Question 6

    Q6. An electron (mass 9.1×10⁻³¹ kg) enters a 2000 N/C electric field. What acceleration does it experience?

    • A) 3.52×10¹⁴ m/s² (opposite field)
    • B) 3.52×10¹⁴ m/s² (same field)
    • C) 1.76×10¹⁴ m/s² (perpendicular)
    • D) 0 m/s² (no acceleration)

    Answer: 3.52×10¹⁴ m/s² (opposite field)

    Explanation: a = qE/m. Option B forgets electron’s negative charge direction.

  7. Question 7

    Q7. A 10 μF capacitor is charged to 12 V. What energy is stored?

    • A) 720 μJ
    • B) 120 μJ
    • C) 72 μJ
    • D) 60 μJ

    Answer: 720 μJ

    Explanation: U = ½CV². Option D uses U = CV² instead of ½CV².

  8. Question 8

    Q8. A 2 μC charge creates a potential of 360 V at a point. What is the distance to that point?

    • A) 0.5 m
    • B) 1.0 m
    • C) 2.0 m
    • D) 5.0 m

    Answer: 0.5 m

    Explanation: V = kq/r. Option C squares the distance instead of solving for it.

  9. Question 9

    Q9. Two charges, +3 μC and -3 μC, are 6 mm apart. What is their dipole moment?

    • A) 1.8×10⁻⁸ C·m
    • B) 1.8×10⁻⁵ C·m
    • C) 5.4×10⁻⁵ C·m
    • D) 9.0×10⁻⁸ C·m

    Answer: 1.8×10⁻⁵ C·m

    Explanation: p = qd. Option A uses 2d instead of d.

  10. Question 10

    Q10. A dielectric (κ=3) is placed between a 4 μF capacitor. What is the new capacitance if the capacitor remains connected to a battery?

    • A) 12 μF
    • B) 4 μF
    • C) 2/3 μF
    • D) 18 μF

    Answer: 12 μF

    Explanation: C = κC₀. Option B assumes voltage remains constant.

  11. Question 11

    Q11. A 500 N/C field is perpendicular to a 0.2 m² surface. What is the electric flux?

    • A) 100 N·m²/C
    • B) 250 N·m²/C
    • C) 500 N·m²/C
    • D) 0 N·m²/C

    Answer: 100 N·m²/C

    Explanation: Φ = EA cosθ. Option B omits cosine factor.

  12. Question 12

    Q12. A 10 μF and 5 μF capacitor are connected in parallel. What is their equivalent capacitance?

    • A) 15 μF
    • B) 3.3 μF
    • C) 5 μF
    • D) 10 μF

    Answer: 15 μF

    Explanation: Ceq = C₁ + C₂. Option B assumes series connection.

  13. Question 13

    Q13. Two +4 μC charges are placed 10 cm apart. What is the electric potential at the midpoint?

    • A) 0 V
    • B) 720×10³ V
    • C) 360×10³ V
    • D) 180×10³ V

    Answer: 0 V

    Explanation: Potentials cancel due to equal magnitude and opposite direction. Option B adds instead.

  14. Question 14

    Q14. A 2 μC charge moves from 600 V to 200 V. How much work is done?

    • A) 8×10⁻⁶ J
    • B) 4×10⁻⁶ J
    • C) 12×10⁻⁶ J
    • D) 0 J

    Answer: 8×10⁻⁶ J

    Explanation: W = qΔV. Option B uses 200 V instead of 400 V difference.

  15. Question 15

    Q15. An infinite line charge with λ = 5×10⁻⁶ C/m produces a field of 9×10⁴ N/C. What is the distance from the line?

    • A) 0.5 m
    • B) 0.25 m
    • C) 0.1 m
    • D) 2 m

    Answer: 0.5 m

    Explanation: E = λ/(2πε₀r). Option C uses 2π instead of π.

  16. Question 16

    Q16. A parallel plate capacitor has plates with area 0.5 m² separated by 2 mm. Calculate the capacitance if the dielectric constant is 3.6.

    • A) 8.0 nF
    • B) 4.0 nF
    • C) 2.0 nF
    • D) 1.8 nF

    Answer: 8.0 nF

    Explanation: Capacitance C = ε₀εᵣA/d. Forbids using area without units conversion or ignoring dielectric constant.

  17. Question 17

    Q17. Two charges +2μC and -2μC are separated by 0.1 m. Calculate the electric dipole moment.

    • A) 0.2 μC·m
    • B) 0.4 μC·m
    • C) 2.0 μC·m
    • D) 4.0 μC·m

    Answer: 0.2 μC·m

    Explanation: Dipole moment p = q × 2a. Confuses distance between charges vs arm length.

  18. Question 18

    Q18. A capacitor stores 50 J of energy when charged to 10 V. Calculate its capacitance.

    • A) 0.5 F
    • B) 1.0 F
    • C) 2.5 F
    • D) 5.0 F

    Answer: 1.0 F

    Explanation: Energy U = ½ CV². Misuses energy formula as U = CV or U = ½ V²/C.

  19. Question 19

    Q19. What electric field is required to suspend a 2 g oil drop with charge -3e in air?

    • A) 2.1 × 10⁵ N/C
    • B) 6.5 × 10⁶ N/C
    • C) 9.8 × 10⁴ N/C
    • D) 1.3 × 10³ N/C

    Answer: 6.5 × 10⁶ N/C

    Explanation: E = mg/q. Mixes gravitational acceleration with electrostatic force magnitude.

  20. Question 20

    Q20. Three capacitors 2 μF, 3 μF, and 6 μF are connected in series. Calculate the equivalent capacitance.

    • A) 1.1 μF
    • B) 1.5 μF
    • C) 0.8 μF
    • D) 0.5 μF

    Answer: 1.1 μF

    Explanation: 1/C_eq = Σ1/C. Confuses series with parallel formula for capacitors.

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Level 1

An electric field of 200 N/C exists at a point. What force acts on a +5 μC charge placed there?