The Doppler Effect
3 marks · EasyThe diagram below shows wavefronts produced by a stationary and a moving sound source.
Identify which set of wavefronts shows the effect of movement.
Explain how the spacing of these wavefronts demonstrates the Doppler effect.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) The set of circles centred on point R show the effect of movement. · must show identification of moving wavefronts
(b) The wavefronts are closer together in front (direction of movement), showing a shorter wavelength and higher frequency (pitch). Behind, wavefronts are spread further apart, showing a longer wavelength and lower frequency. · must show compressed ahead, stretched behind, explains frequency/wavelength change
Must show: identification of moving-source wavefronts
Common mistakes: Just naming without explanation.; Not relating spacing to frequency/wavelength.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies the moving-source set as the circles centred on R.
B2 (b) · 1 mark · States that wavefronts are closer together (compressed) ahead/shorter, and further apart (stretched) behind/longer.
B3 (b) · 1 mark · Links this to higher frequency at front, lower at back (the Doppler effect).
Worked solution
a) The circles centred on point R represent the moving source and show the Doppler effect. b) In front of R, the wavefronts are closer together, causing a higher frequency (shorter wavelength). Behind R, the wavefronts are spaced out, showing lower frequency (longer wavelength).