Question

A car's horn emits a constant frequency as it accelerates away from a stationary listener. Which of the following quantities actually changes for the listener?

I. Frequency of the sound
II. Pitch of the sound
III. Amplitude of the sound
IV. Loudness of the sound

Answer 1

The observer experiences a change in both the perceived frequency and pitch of the sound due to the Doppler effect, while amplitude and loudness are not directly changed by the effect.

Step-by-step explanation:

When a car's horn emits a constant frequency while accelerating away from a stationary listener, the listener experiences a change in the perceived frequency and pitch of the sound due to the Doppler effect. The Doppler effect explains why the frequency (and thus the pitch) appears higher as the source approaches and lower as it moves away, even though the actual frequency produced by the source remains the same. However, the amplitude of the sound waves, which contributes to the loudness, does not change because it is determined by the source's power output and is separate from any relative motion between the source and observer. Loudness may subjectively seem to change due to environmental factors and distance, but it is not directly altered by the Doppler effect.