Answer;
A. Longer
C. Shorter
The sound of a police siren that is moving away has shorter wavelengths, and one that is approaching has longer wavelengths.
Explanation;
- The pitch of the sound heard depends on the frequency of the sound wave. A higher frequency corresponds to a high pitch. Therefore, when the police siren is approaching an observer, the observed frequency increases and thus the observer hears a higher pitch.
- Conversely, when the police siren is moving away from an observer, then the frequency decreases and thus, the pitch of the sound heard is lower.
- A higher frequency corresponds to a shorter wavelength, therefore, the shorter the wavelength, the higher the frequency, and the higher the pitch, of the sound.