The Doppler effect is an effect produced by a moving source of sound or electromagnetic waves due to the relative motion of a so
urce or a receiver. If an emergency vehicle approaches Bob and moves away from Jill, how does the frequency of the siren change? A) Neither Bob or Jill perceive any change in the frequency of the siren. B) As an emergency vehicle approaches Bob the frequency appears to increase. C) As an emergency vehicle moves away from Jill the frequency appears to increase. D) Bob does not notice any change until the vehicle passes him and the siren increases.
B) As an emergency vehicle approaches Bob the frequency appears to increase.
Explanation:
As mentioned Doppler effect is related to the waves produced by a moving source. When moving towards the observer, the frequency of the wave will seem to increase and while moving away from the observer, the frequency will seem to decrease.
Here, the vehicle is moving towards Bob and away from Jill. This means, the frequency of the siren will seem to increase while approaching Bob and frequency will seem to decrease while moving away from Jill.
