How does the frequency perceived by a moving observer change as they approach a sound source?

• A. It remains the same
• B. It decreases
• C. It increases
• D. It oscillates

Answer: (C)

When a moving observer approaches a sound source, the frequency of the sound they perceive increases due to the Doppler effect. This phenomenon occurs because the sound waves emitted from the source are compressed in the direction of the observer’s movement. As the observer gets closer, each successive wave is encountered more frequently than if the observer were stationary. Therefore, the observer hears a higher frequency than what is emitted by the source.

In contrast, if the observer were moving away from the sound source, they would perceive a decrease in frequency. As for options regarding it remaining the same or oscillating, these do not accurately reflect the behavior described by the Doppler effect in this scenario. The essential concept is that the perceived frequency increases as the distance between the observer and the source decreases.