Question 1

Paper 2Hard10 marks

A sound emitter moves uniformly through still air. At one instant, the distance between adjacent wavefronts is 0.646 m ahead of the emitter and 0.714 m behind it. The speed of sound in the air is 340 m s⁻¹. In a second arrangement, the emitter is stationary and a detector moves towards it at the speed found in (a). The emitter has the same frequency in both arrangements.

(a)

Determine the emitted frequency and the speed of the emitter. Show your reasoning.

[4]
(b)

Sketch wavefront diagrams for (i) the sound emitter moving towards a stationary detector and (ii) a stationary emitter with the detector moving towards it. Indicate the directions of motion and the relative spacing of the wavefronts.

[2]
(c)

Calculate the frequency detected in each sound arrangement. Give your answers to three significant figures.

[2]
(d)

A light beacon moves towards an observer. State how the detected frequency and wavelength compare with those emitted, and state one relevant difference between light waves and sound waves.

[2]

More C.5 Doppler effect questions