Question

Explain why a fire engine’s siren sounds lower in pitch after the fire engine passes you.  

Answer 1

When a sound source is moving toward you, you hear a higher frequency than the source is putting out, and when the source is moving away from you, you hear a lower frequency than the real one. The whole process is called the Doppler effect. It works with light too.

Answer 2

Explanation:

Doppler effect: It is the phenomenon which occurs when there is relative motion between listener and source.

In this phenomenon, there is an apparent change in the frequency. There is an increase or decrease in frequency.

The frequency gets lower when the source and the listener are moving away from each other.

The frequency gets higher when the source and the listener are moving towards each other.

The pitch depends on the frequency. When the frequency increases then the pitch of the sound gets louder. When the frequency decreases then the pitch of the sound gets lower.

In the given problem, a fire engine's siren sounds lowers in pitch after the fire engine passes. Here, the source and the listener are moving away from each other. The frequency gets lower. Then, the pitch of the sound will also get lower.