Relative Doppler Effect

View attachment relative_doppler_effect.bmp

The image shows four points. "A" is source of light and "B" is receiver, and "a" and "b" represents co-ordinate points.

"A" is moving with constant speed to "B". "B" feels doppler effect.
If "B" moving with constant speed to "A", then also "B" feels doppler effect.

Statement 1: This two situations seems identical.

We can imagine "A" as sound source and "B" as sound receiver.
If "A" is moving with constant speed < sound speed to "B". "B" feels doppler effect.
If "B" is moving with constant speed < sound speed to "B". then also "B" feels doppler effect.

Now, suppose the situation where speed of "A" or "B" > sound speed.

Imagine, that "A" coming to "B" from far beyond "a" with grater speed then sound speed. B is situated at point "b".
when "A" reaches to "a", "A" starts producing sound, but sound cannot reach to "B" before "A".

In another situation "B" coming to "A" from far beyond "b" with grater speed then sound speed. "A" is situated at point "a".
When "B" reaches to "b", "A" starts producing sound, but now situation is different then before. "B" can receives sound before "B" reaches to "A".

So, the change in speed differs the identity of situation.
So, the situations ( < sound speed ) also weren't identical, it seems that those were identical.

Here is something which stops situations to be identical. Medium of wave. The air.
In first situation "A" is moving relative to medium, but in second "A" is stationary to medium.

We cannot create the same situation with light, since nothing can travel faster than light.
But, there is SOMETHING in which light travels.
And if "relative to medium" can change outcomes, then is the "Statement 1" right????

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ghwellsjr
Gold Member
Even if there is a stationary SOMETHING in which light travels so that LET is a true representation of what is really happening in nature, we still wouldn't be able to tell. Special Relativity would still be a better way to account for all the facts of nature because it would free us up from being concerned about trying to measure or detect that stationary SOMETHING.

Even if there is a stationary SOMETHING in which light travels so that LET is a true representation of what is really happening in nature, we still wouldn't be able to tell. Special Relativity would still be a better way to account for all the facts of nature because it would free us up from being concerned about trying to measure or detect that stationary SOMETHING.

Thanks George.

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If source is moving: can it increase intensity of wave little bit in forward direction? I have no experimental evidence, this is just a thinking.

Thanks.

If source is moving: can it increase intensity of wave little bit in forward direction? I have no experimental evidence, this is just a thinking.

Thanks.
Yes. Probably you mean the Doppler effect, in which the energy is intensified. There is also the headlight effect, in which the directionality is intensified. see: http://demonstrations.wolfram.com/TheHeadlightEffect/

Harald

(disclaimer: I did not verify that page)

Hello All,

Is there any experiment done to measure intensity of moving light source?

Thanks