Gaokao Physics: Electromagnetism Flashcards

Two charges +Q and −Q are separated by distance d. The electric potential at the midpoint between them is:

Answer: Zero

Potential is a scalar; V = kQ/(d/2) + k(−Q)/(d/2) = 0.

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:

Answer: E/B

For equilibrium: qE = qvB, so v = E/B regardless of mass or charge.

A transformer has 500 primary turns and 50 secondary turns. If the primary voltage is 220 V, the secondary voltage is:

Answer: 22 V

V₂/V₁ = N₂/N₁ → V₂ = 220 × (50/500) = 22 V.

Faraday's law states that the magnitude of the induced EMF in a loop is equal to:

Answer: The rate of change of magnetic flux through the loop

Faraday's law: |EMF| = |dΦ/dt|, where Φ is the total magnetic flux.

An electron (e = 1.6×10⁻¹⁹ C) is accelerated through a potential difference of 500 V. Its kinetic energy gained is:

Answer: 8×10⁻¹⁷ J

KE = qV = 1.6×10⁻¹⁹ × 500 = 8×10⁻¹⁷ J.

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)

Answer: 2.01×10⁻³ H

L = μ₀N²A/l = 4π×10⁻⁷ × 10⁶ × 4×10⁻⁴ / 0.5 ≈ 2.01×10⁻³ H.

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:

Answer: 10 V

I = 12/(5+1) = 2 A; terminal voltage = 12 − 2×1 = 10 V.