A-Level H2 Physics 3

Question 1

What is Coulomb's Law?

Accepted Answer

F = kQ₁Q₂/r²

Answer

Coulomb's Law: F = kQ₁Q₂/r² (or F = Q₁Q₂/4πε₀r²), giving the electrostatic force between two point charges, where k = 9×10⁹ N m² C⁻².

Question 2

A particle of charge q moves with velocity v perpendicular to a magnetic field B. What force acts on it?

Accepted Answer

F = qvB

Answer

The magnetic force on a moving charge: F = qvB sin θ. When velocity is perpendicular to B (θ = 90°), sin θ = 1, so F = qvB.

Question 3

What is meant by 'half-life' in radioactive decay?

Accepted Answer

The time for the activity (and number of undecayed nuclei) to halve

Answer

Half-life (t½) is the time taken for the number of undecayed nuclei (or the activity) of a radioactive sample to decrease to half its original value.

Question 4

A simple pendulum has period T = 2π√(L/g). If L is quadrupled, how does T change?

Accepted Answer

T doubles

Answer

T ∝ √L. If L is quadrupled (×4), T changes by √4 = 2. So T doubles.

Question 5

What is the phenomenon of 'interference' in waves?

Accepted Answer

The superposition of two coherent waves producing regions of constructive and destructive interference

Answer

Wave interference occurs when two coherent waves superpose: where crests meet (in phase), constructive interference creates large amplitude; where crest meets trough (antiphase), destructive interference creates zero amplitude.

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A-Level H2 Physics 3