Gaokao Exam Gaokao Physics: Electromagnetism 2 — Questions and Answers
Question 1: Two charges +Q and −Q are separated by distance d. The electric potential at the midpoint between them is:
- Zero (Correct answer)
- kQ/(d/2)
- 2kQ/d
- −kQ/(d/2)
Correct answer: Zero
Potential is a scalar; V = kQ/(d/2) + k(−Q)/(d/2) = 0.
Question 2: A charged particle of mass m and charge q enters a region of crossed electric and magnetic fields (E perpendicular to B). For the particle to travel undeflected, its speed must be:
- E/B (Correct answer)
- B/E
- qE/mB
- mB/qE
Correct answer: E/B
For equilibrium: qE = qvB, so v = E/B regardless of mass or charge.
Question 3: A transformer has 500 primary turns and 50 secondary turns. If the primary voltage is 220 V, the secondary voltage is:
- 22 V (Correct answer)
- 2200 V
- 110 V
- 44 V
Correct answer: 22 V
V₂/V₁ = N₂/N₁ → V₂ = 220 × (50/500) = 22 V.
Question 4: Faraday's law states that the magnitude of the induced EMF in a loop is equal to:
- The rate of change of magnetic flux through the loop (Correct answer)
- The total magnetic flux through the loop
- The product of magnetic field and area
- The rate of change of current in the loop
Correct answer: The rate of change of magnetic flux through the loop
Faraday's law: |EMF| = |dΦ/dt|, where Φ is the total magnetic flux.
Question 5: An electron (e = 1.6×10⁻¹⁹ C) is accelerated through a potential difference of 500 V. Its kinetic energy gained is:
- 8×10⁻¹⁷ J (Correct answer)
- 4×10⁻¹⁷ J
- 1.6×10⁻¹⁶ J
- 3.2×10⁻¹⁶ J
Correct answer: 8×10⁻¹⁷ J
KE = qV = 1.6×10⁻¹⁹ × 500 = 8×10⁻¹⁷ J.
Question 6: A solenoid with 1000 turns, length 0.5 m, and cross-sectional area 4 cm² carries a current of 2 A. Its self-inductance is approximately: (μ₀ = 4π×10⁻⁷ T·m/A)
- 2.01×10⁻³ H (Correct answer)
- 4.02×10⁻³ H
- 1.00×10⁻³ H
- 8.04×10⁻³ H
Correct answer: 2.01×10⁻³ H
L = μ₀N²A/l = 4π×10⁻⁷ × 10⁶ × 4×10⁻⁴ / 0.5 ≈ 2.01×10⁻³ H.
Question 7: In a circuit, a 12 V battery with internal resistance 1 Ω is connected to an external resistance of 5 Ω. The terminal voltage of the battery is:
- 10 V (Correct answer)
- 12 V
- 8 V
- 6 V
Correct answer: 10 V
I = 12/(5+1) = 2 A; terminal voltage = 12 − 2×1 = 10 V.
Gaokao Exam Gaokao Physics: Electromagnetism 2
Two charges +Q and −Q are separated by distance d.
The electric potential at the midpoint between them is: