The Doppler effect
2 marks · EasyWhy does the Doppler effect happen for both sound and light waves? Give a reason in terms of wave properties.
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The Doppler effect occurs for all waves because when the source moves, the spacing of the wavefronts changes. This alters the wavelength and frequency seen by an observer.
Also accept: It happens for all waves because the relative motion between the source and the observer changes the wavefront spacing.; Because a moving source just changes the wavelength and therefore the frequency for any type of wave.
Common mistakes: Only happens for sound; It is caused by loudness changes
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Marking points
B1 · 1 mark · States that it happens for all waves (sound and light or all waves).
B1 · 1 mark · Mentions change in wavefront spacing, wavelength, or frequency due to motion.
Worked solution
The Doppler effect happens for all waves, not just sound, because moving the source changes how close the wavefronts are together. This changes the observed wavelength and frequency.