Question

please answer it fast tomorrow exam

Answer 1

Doppler effect (or doppler shift) is the change in frequency of a wave, for an observer, moving relative to the source of the wave. A common experience of doppler shift is, when a train sounding siren approaches and receds an observer, the frequency of the sound will be seem to be high as it approaches and low as it passes the observer.


Doppler effect cannot be observed when the source of sound and observer are stationary.
Bcoz to observe Doppler effect, there should be a relative motion between the source and the observer.