alleryA source of sound moves forward. What happens to the wavelength ahead of it?
AIt becomes longer ahead of the source
BIt becomes shorter ahead of the source
CIt is unchanged ahead of the source
DIt falls to zero ahead of the source
Answer & Solution
Correct answer: B. It becomes shorter ahead of the source
1. A moving source keeps emitting while it travels forward.
2. Each new compression is released closer to the one before it, in the direction of travel.
3. So the wavelength is shorter in the direction the source is moving.
4. Behind the source the compressions spread out, so the wavelength there is longer.
_Source: OpenStax Physics (high school, CC BY 4.0), Ch 14 "Sound", section 14.3 Doppler Effect and Sonic Booms_
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