Change in frequency due to Doppler's effect is produced when

Options

A. the source and the observer are moving in the same direction
B. the source and the observe are both at rest
C. there is a relative motion between the source and the observer
D. there is a resultant motion between the source and observer.

Answer

C

Explanation

According to Doppler's effect, when a source of sound or an observer or both are in motion relative to air, there is an apparent change in the frequence of sound as heard by the observer.