Doppler Effect
Doppler effect
The Doppler effect, named after Christian Doppler, is the change in frequency and wavelength of a wave as perceived by an observer moving relative to the source of the waves. For waves that propagate in a wave medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analysed separately. For waves which do not require a medium, such as light or gravity in special relativity, only the relative difference in velocity between the observer and the source needs to be considered.
[pic]
[pic]
A source of waves moving to the left. The frequency is higher on the left, and lower on the right.
| |
Doppler first proposed the effect in 1842 in the monograph Über das farbige Licht der Doppelsterne und einige andere Gestirne des Himmels - Versuch einer das Bradleysche Theorem als integrierenden Teil in sich schliessender allgemeiner Theorie (On the coloured light of the binary refracted stars and other celestial bodies - Attempt of a more general theory including Bradley's theorem as an integral part).[1] The hypothesis was tested for sound waves by the Dutch scientist Christoph Hendrik Diederik Buys Ballot in 1845. He confirmed that the sound's pitch was higher as the sound source approached him, and lower as the sound source receded from him. Hippolyte Fizeau discovered independently the same phenomenon on electromagnetic waves in 1848 (in France, the effect is sometimes called "effet Doppler-Fizeau"). It is often overlooked that in Doppler's publications (and also Einstein's in his discussion of the Doppler effect) he explicitly acknowledges that his formulae are only approximate since he made several mathematical approximations in his derivation. Doppler's derivation is repeated more or less verbatim in most modern textbooks but often
The Doppler effect, named after Christian Doppler, is the change in frequency and wavelength of a wave as perceived by an observer moving relative to the source of the waves. For waves that propagate in a wave medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analysed separately. For waves which do not require a medium, such as light or gravity in special relativity, only the relative difference in velocity between the observer and the source needs to be considered.
[pic]
[pic]
A source of waves moving to the left. The frequency is higher on the left, and lower on the right.
| |
Doppler first proposed the effect in 1842 in the monograph Über das farbige Licht der Doppelsterne und einige andere Gestirne des Himmels - Versuch einer das Bradleysche Theorem als integrierenden Teil in sich schliessender allgemeiner Theorie (On the coloured light of the binary refracted stars and other celestial bodies - Attempt of a more general theory including Bradley's theorem as an integral part).[1] The hypothesis was tested for sound waves by the Dutch scientist Christoph Hendrik Diederik Buys Ballot in 1845. He confirmed that the sound's pitch was higher as the sound source approached him, and lower as the sound source receded from him. Hippolyte Fizeau discovered independently the same phenomenon on electromagnetic waves in 1848 (in France, the effect is sometimes called "effet Doppler-Fizeau"). It is often overlooked that in Doppler's publications (and also Einstein's in his discussion of the Doppler effect) he explicitly acknowledges that his formulae are only approximate since he made several mathematical approximations in his derivation. Doppler's derivation is repeated more or less verbatim in most modern textbooks but often