Question

According to doppler's effect, the apparent frequency of sound may change if the wave source is:

• A. traveling toward the observer
• B. traveling away from the observer
• C. approaching or retreating from the observer
• D. not traveling
• E. oscillating

Answer 1

The correct option is C approaching or retreating from the observer

Doppler's effect is valid only when there is a relative motion between the source of sound and the observer.

Thus the apparent frequency of sound may change if the wave source is either approaching or retreating (moving away) from the observer.