Question 30
Observe the illustration below. Imagine a fire truck with its siren left on is parked at a fire station and a listener some distance away can perceive the siren at the same frequency at which it is emitted. Now consider how this situation changes when the truck is moving with a constant velocity towards the stationary observer. While the frequency of the fire engine's siren as heard by a person on the firetruck has not changed, the waves in the direction of the truck's motion bunch up as the fire truck is catching up to its own sound waves. This shifting of electromagnetic spectrum depending upon one’s relative motion to the emitting source is called_______.
