The Doppler effect is the change in the frequency of a wave as observed by someone who is moving relative to the source of the wave. When the source of the wave moves toward the observer, the waves are compressed, leading to a higher observed frequency (or pitch, in the case of sound). Conversely, when the source moves away from the observer, the waves are stretched out, resulting in a lower observed frequency. This effect occurs with all types of waves, including sound, light, and water waves
. For example, the familiar change in pitch of a passing ambulance siren is due to the Doppler effect: the siren sounds higher in pitch as it approaches and lower as it moves away, even though the siren itself emits a constant frequency
. The Doppler effect depends on the relative motion between the source and the observer. If either the source or the observer is moving, the frequency perceived changes. For sound waves, the motion is relative to the medium (usually air), but for electromagnetic waves like light, the effect depends only on the relative velocity between source and observer
. In summary, the Doppler effect is:
- A change in observed wave frequency due to relative motion between source and observer.
- Causes waves to be perceived at a higher frequency when the source approaches and lower frequency when it recedes.
- Applies to all wave types, including sound and light.
- Explains everyday phenomena like the changing pitch of passing vehicles and is used in astronomy to measure the speed of stars and galaxies
