Question

As demonstrated by the Doppler effect, why does a siren sound higher pitched as a vehicle drives toward a person, then lower pitched as the vehicle drives away?

A) Change in frequency
B) Change in amplitude
C) Change in wavelength
D) Change in speed

Answer 1

The siren of a vehicle sounds higher pitched as it approaches and lower pitched as it moves away due to the Doppler effect, which is a change in frequency of the sound waves reaching the observer.

Step-by-step explanation:

The Doppler effect explains why a siren sounds higher pitched as it drives toward a person and lower pitched as it drives away. This phenomenon is due to a change in frequency (A) of the sound waves that reach the listener's ears. When the source of the sound approaches, the sound waves are compressed, leading to a higher pitch. As the vehicle moves away, the sound waves are stretched, resulting in a lower pitch. The effect is more dramatic the closer and faster the vehicle moves past the observer. This shift in frequency affects all kinds of sources in motion, such as motorcycles, race cars, airplanes, and trains passing by a stationary observer.