The Doppler effect
2 marks · EasyDescribe how the wavelength of sound waves changes in front of a moving source compared to behind it.
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In front of the moving source, the wavelength is shorter; behind the source, the wavelength is longer.
Also accept: The waves are compressed in front making the wavelength shorter, and stretched out behind making the wavelength longer.; Wavelength decreases in front and increases behind the source.; Shorter wavelength in front, longer behind.
Common mistakes: Frequency is lower in front; No change in wavelength
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Marking points
B1 · 1 mark · States that waves in front are shorter/compressed.
B1 · 1 mark · States that waves behind are longer/stretched.
Worked solution
In front of the moving source, the sound waves are compressed so the wavelength is shorter. Behind the source, the waves are stretched so the wavelength is longer.