Gaokao Physics: Electromagnetism Flashcards

Three resistors of 6 Ω, 3 Ω, and 2 Ω are connected in parallel. What is the equivalent resistance?

Answer: 1 Ω

1/R = 1/6 + 1/3 + 1/2 = 1/6 + 2/6 + 3/6 = 1; R = 1 Ω.

A wire of resistance R is stretched to twice its original length. Its new resistance is:

Answer: 4R

Stretching to twice the length doubles L and halves cross-sectional area A (volume conserved); R = ρL/A increases by factor 4.

A uniform electric field E = 500 V/m exists between two parallel plates separated by d = 0.02 m. The potential difference between the plates is:

Answer: 10 V

V = Ed = 500 × 0.02 = 10 V.

According to the right-hand screw rule, the magnetic field lines around a straight current-carrying wire form:

Answer: Concentric circles in planes perpendicular to the wire

By Ampere's law, the magnetic field around a long straight wire forms closed circular loops centred on the wire.

Electromagnetic induction was discovered experimentally by:

Answer: Michael Faraday

Faraday discovered electromagnetic induction in 1831 through experiments with changing magnetic flux.

A 60 W light bulb operates on a 120 V AC supply. The resistance of the filament during operation is:

Answer: 240 Ω

P = V²/R → R = V²/P = 120²/60 = 240 Ω.

The work done in moving a charge of +3 μC from a point at potential 20 V to a point at potential 80 V is:

Answer: 1.8×10⁻⁴ J

W = q(V₂ − V₁) = 3×10⁻⁶ × (80 − 20) = 3×10⁻⁶ × 60 = 1.8×10⁻⁴ J.