Doppler effect
Doppler effectWith, wave（ sound wave and light wave and radio wave () with relativity with observer such as sound source illuminant speed, the wave frequency differing, it is the phenomenon which is observed. When occurrence source gets near, the vibration of the wave being stuffed, frequency becomes high, when it goes away conversely, the vibration being extended, becomes low.
For example, the occasion where the ambulance and the like passes, when getting near, when sound of the siren is audible high, going away the fact that it is audible low is something due to this phenomenon.
This phenomenon concerning sound was for a long time known, but the Austrian physicist,Christian DopplerYou discovered the mathematical relational expression between speed and frequency, you proved with experiment.
When the observer and the sound source move, identical direct line the sound source S (Source) from observer O (Observer) make the direction which faces correct, as for frequency of the sound wave which is audible in the observer,
- < Math> F'=f\times {V-v_ {0} \over V-v_ {\rm s}} < /math>
With it becomes. Here,F : Frequency of the sound wave which the sound source puts out,V ： speed of sound、V0 : The speed where the observer moves,VS : The speed where the sound source moves
Doppler effect of light
The similar effect happens even with in case of light, light from the illuminant where it goes away is visible reddish, (Red shift) Light from the illuminant which gets near is visible bluish, (Blue one deviation). But, as for propagation of light special relativity, the Doppler effect of the usual wave the phenomenon which is different is shown.
As for cause of in the first place Doppler effect, wave source and observer waveMediumThere is a place where interval of the wave crest changes because it has speed vis-a-vis, but as for light with wave source and the speed of the observer alwaysLuminous flux C In order so to be spread, because it is visible, it differs from the case where method of changing the interval of the mountain is the usual wave. In addition, in case of light, when wave source is exercising, method of advancing the time with respect to wave source is visible lately by the special relativistic effect. The effect to which frequency of the light which comes out of wave source with this is visible small is added.
With the effect above, when the illuminant S to direction of angle θ it is exercising at speed V considered as observer O, as for frequency ν of the light with O ',
- < Math> \nu'=\nu\times {\sqrt {1- (V/c) ^2} \over 1- (V/c) \cos \theta} < /math>
With it becomes. Here,ν : Frequency of the light which the illuminant puts out,V : Speed of the illuminant which was seen from the observer,C : Luminous flux,θ : The direction where the illuminant where you saw from the observer moves (θ =0: When it faces to the observer)
As for being important, in case of light the illuminant exercising to immediate side vis-a-vis the observer, when it does not have the speed of gaze direction, (θ=90°) So frequency of light changing, it is to be visible. ThisSide Doppler effectWith you say.
As for Doppler effect of lightStar rainbow (star bow)There is a theory that observation is possible as.
Related item
- physics - wave motion theory
