Doppler Effect - II

The Doppler effect is described as the change in the observed frequency of the sound waves, whenever the source of waves is moving with respect to an observer.

For instance, when a fire truck approaches a man, the sound waves that are emitted bunch up, creating an upward shift in frequency, which is interpreted as a high pitch.

However, when the fire truck recedes away, the waves spread out and the man observes an apparent downward shift in frequency, which is interpreted as low pitch.

In another case, when a man approaches a stationary fire truck, he strikes more wave crests, resulting in high-frequency sound. Conversely, when the man moves away, he strikes fewer wave crests, resulting in a lower frequency of sound.

Thus, the Doppler effect can be observed for two cases: first, when the source moves towards or away from the stationary observer, and second, when the observer moves towards or away from the stationary source.