Doppler effect(redirected from Christian J. Doppler)
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A change in the observed frequency of a wave, as of sound or light, occurring when the source and observer are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart. The motion of the source causes a real shift in frequency of the wave, while the motion of the observer produces only an apparent shift in frequency. Also called Doppler shift.
[After Christian Andreas Doppler (1803-1853), Austrian physicist and mathematician who explained the phenomenon.]
(General Physics) a phenomenon, observed for sound waves and electromagnetic radiation, characterized by a change in the apparent frequency of a wave as a result of relative motion between the observer and the source. Also called: Doppler shift
[C19: named after C. J. Doppler (1803–53), Austrian physicist]
Dop′pler effect`(ˈdɒp lər)
a phenomenon characterized by a change (Dop′pler shift`) in the frequency of waves, as light or sound waves, observed when the wave source is moving relative to the observer.
[1900–05; after C. J. Doppler (1803–53), Austrian physicist]
As the source of sound waves (the ambulance) moves closer to the observer, the frequency of the sound waves and pitch of the sound become higher. As the source moves away from the observer, the frequency and pitch become lower.
The apparent change in the frequency of waves, as of sound or light, when the source of the waves is moving toward or away from an observer.
Did You Know? When a car rushes past you on the road with the driver holding down the horn, you hear the horn change tone: it's higher pitched than normal as the car approaches and lower pitched as it departs. That's because of the Doppler effect. Sound waves spread outward in all directions from the horn. The forward motion of the car compresses the sound waves traveling ahead of the car, making the wavelengths shorter. Sound having shorter wavelengths has higher frequency and therefore higher pitch—what you hear if the car is moving towards you. Behind the car, however, the sound waves are drawn apart. Longer wavelengths mean lower frequency and lower pitch, which is what you hear once the car rushes past. The Doppler effect works on light waves, too; in fact, this was how scientists determined that the universe is expanding. The light from galaxies and other distant celestial objects is shifted toward the red end of the spectrum (a phenomenon called red shift). Red light has the longest wavelengths of visible light. The pioneering astronomer Edwin Hubble reasoned that the red shift was due to the Doppler effect: the galaxies are speeding away from us, drawing out the wavelengths of the light emitted behind them, and the universe as a whole is expanding.
The phenomenon evidenced by the change in the observed frequency of a sound or radio wave caused by a time rate of change in the effective length of the path of travel between the source and the point of observation.
Apparent change in the frequency of light waves or sound waves due to the relative motion of the observer and the source of the waves.