The Doppler Effect: Impact of Relative Motion on Light Waves

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Discussion Overview

The discussion revolves around the Doppler effect as it pertains to light waves and the implications of relative motion between a light source and a receiver. Participants explore theoretical scenarios involving sound and light, comparing their behaviors under different conditions of motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes two scenarios involving a moving light source and a receiver, suggesting that both situations appear identical when both are moving at speeds less than the speed of sound, but differ when considering speeds greater than sound speed due to the medium of wave propagation.
  • Another participant argues that even if a stationary medium for light exists, Special Relativity would still provide a more effective framework for understanding the behavior of light, as it removes the need to detect such a medium.
  • One participant speculates whether a moving source could increase the intensity of the wave in the forward direction, linking this idea to the Doppler effect and the headlight effect.
  • A later post questions whether any experiments have been conducted to measure the intensity of light from a moving source.

Areas of Agreement / Disagreement

Participants express differing views on the implications of a stationary medium for light and the relevance of Special Relativity. The discussion includes speculative ideas about the intensity of waves from moving sources, indicating a lack of consensus on these points.

Contextual Notes

Participants acknowledge the complexity of the scenarios discussed, particularly regarding the role of the medium in wave propagation and the implications of relative motion on observed phenomena.

Who May Find This Useful

This discussion may be of interest to those exploring the Doppler effect, the nature of light, and the implications of Special Relativity in physics.

mananvpanchal
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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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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.
 
ghwellsjr said:
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.
 
mananvpanchal said:
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
 

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