A source emits sound at a fixed constant frequency f . If the source moves away from you, the frequency you hear is
A) the same as f.
B) higher than f.
C) lower than f.
D) unrelated to f.

Question

Quizplus · Accepted Answer

When a source moves away from you, the frequency of the sound waves reaching you decreases, resulting in a lower perceived frequency (known as a Doppler shift). This is shown by the Doppler equation: f' = f(v +-vd)/(v +-vs), where f' is the perceived frequency, f is the emitted frequency, v is the speed of sound, vd is the velocity of the detector, and vs is the velocity of the source. Since the source is moving away from the detector, vs is positive, and the denominator becomes v + vs, which is greater than v - vs. Therefore, f' must be less than f, and the answer is C.

A Source Emits Sound at a Fixed Constant Frequency F