Gaokao Physics: Electromagnetism Flashcards

Coulomb's law states that the force between two point charges is proportional to:

Answer: The product of the charges divided by the square of the distance

Coulomb's law: F = kq₁q₂/r², force proportional to charge product and inversely proportional to distance squared.

The magnetic force on a current-carrying conductor of length L carrying current I in a field B at angle θ is:

Answer: F = BIL sinθ

The Ampere force is F = BIL sinθ, maximum when current is perpendicular to the field.

A 10 μF capacitor is charged to 100 V. The energy stored in the capacitor is:

Answer: 0.05 J

U = ½CV² = ½ × 10×10⁻⁶ × 100² = 0.05 J.

When the distance between two parallel plates of a capacitor (connected to a battery) is doubled, the capacitance:

Answer: Halves

C = ε₀A/d; doubling d halves C.

In an AC circuit, the root-mean-square (rms) voltage across a 10 Ω resistor is 20 V. The average power dissipated is:

Answer: 40 W

P = V_rms²/R = 400/10 = 40 W.

An alpha particle (charge +2e) moves at 2×10⁶ m/s perpendicular to a 0.3 T magnetic field. The magnitude of the force on it is: (e = 1.6×10⁻¹⁹ C)

Answer: 1.92×10⁻¹³ N

F = qvB = 2 × 1.6×10⁻¹⁹ × 2×10⁶ × 0.3 = 1.92×10⁻¹³ N.

Kirchhoff's voltage law (KVL) states that:

Answer: The algebraic sum of all voltages around any closed loop is zero

KVL is based on conservation of energy: the sum of voltage rises and drops around any closed loop equals zero.