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For sound waves, the Doppler's formula f...

For sound waves, the Doppler's formula for frequency shift differs slightly between the two situation :
(i) source at rest , observer moving (ii) source moving , observer at rest.
The exact Doppler formulae for the case of light waves in vacuum, are however, strictly identical for the two situations in case of light travelling in a medium ?

Text Solution

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We know that sound is a mechanical wave and it requires a medium to propagate. Situations (i) and (ii) may be identical as far as source and observer.s relative motion is concerned, but with respect to medium the motion of the observer is different in two cases. Therefore, we cannot expect, Doppler formulae for sound to be identical for (i) and (ii). For light waves in vacuum, we can never distinguish between (i) and (ii). Here only the relative motion between the source and the observer is important and the relativistic Doppler formula is the same for (i) and (ii).
When we talk about propagation of light in a medium, once again like sound waves, the two situation are not identical and we should expect to Doppler formulae for this case to be different for the two situations (i) and (ii).
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