Physics (AS & A Level) · Feb / March 2023 · Paper 12 · Question 20

In a progressive water wave, two particles, P and Q, on the surface of the water, are a fixed horizontal distance apart. P and Q oscillate vertically. At time t = 0, the wave is as shown. [diagram of wave with particles P and Q labelled, and 'surface of water'] Which graph best represents the variation with time t of the phase difference φ between the oscillation of the water particle P and the oscillation of the water particle Q?

1. A[graph A: φ against t, cosine-like curve starting at maximum φ at t=0]
2. B[graph B: φ against t, sine-like curve starting at 0 and going negative]
3. C[graph C: φ against t, straight line with positive gradient starting negative]
4. D[graph D: φ against t, horizontal line at constant positive φ]

As printed in the paper