Objective 204.4.2-10: Explain the Doppler Effect.
Write an essay explaining the Doppler Effect. Be sure to explain what the observed effect is, why it occurs, and give specific examples that include at least two different types of waves.
If you’ve ever had the bad luck to have been the recipient of a speeding ticket, or noticed how the sound of an approaching vehicle has a higher pitch as it’s moving toward you and a lower pitch as it moves away from you, you’ve experienced what’s known as the Doppler Effect.
The Doppler Effect, named for physicist Christian Doppler, is the apparent change in frequency of a wave through a medium with respect to an observer. When a stationary source emits a wave (sound, light, electromagnetic, etc.) through a medium at a constant frequency, the wave propagates outward in all directions with a constant wavelength. Observers on either side of the source will experience the wave at the same frequency. When the source of the wave begins to move through the medium, like in the case of a passing car, the source of the wave closes the distance between one crest of the wave and the next, causing the waves to “bunch up” ahead of the source, decreasing the wavelength in front of it, and increasing the wavelength behind it. The result is that any observer ahead of the wave will experience an apparent increase in frequency of the wave, and any observer behind it will experience a decrease in the frequency of the wave.
The Doppler Effect is most often associated with sound waves, like in the example of the passing car, but can apply to any kind of wave. In the unfortunate case of the speeding ticket mentioned above, the Doppler Effect is used with electromagnetic waves to measure the speed of your car as it passes a stationary police car equipped with a radar-emitting device, or “radar gun”. The radar gun emits electromagnetic waves, or pulses, at a constant rate, which...