Practice question · Multiple choice
An ambulance drives past you at constant speed with its siren on. Which best describes the pitch you hear?
Hints
- At constant approach speed, each wavefront is emitted a fixed fraction closer, the compression factor is constant.
- The pitch does not glide while it approaches; it jumps downward as the source passes you.
Show the answer
A. Steadily higher while approaching, lower after passing
Why
Constant velocity gives a constant Doppler shift: one fixed higher pitch inbound, one fixed lower pitch outbound, with a rapid slide only during the moment of passing. The familiar "eee-yooo" is two plateaus and a step, not a long glissando.
Practise Sound Waves and the Doppler Effect
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