Question

as an emergency vehicle approaches bob and moves away from jill, how does the frequency of the siren change to the driver of the vehicle? a as an emergency vehicle approaches bob the frequency increases. b as an emergency vehicle moves away from jill the frequency decreases. c the frequency of the siren does not change despite appearances. d bob does not notice any change until the vehicle passes him and the siren increases.

Explanation:

The Doppler - effect is related to the relative motion between the source of a wave (the siren) and the observer. For the driver of the emergency vehicle, there is no relative motion between the siren (source) and the driver (observer). So, the frequency of the siren as perceived by the driver does not change.

Answer:

C. The frequency of the siren does not change despite appearances.