Question

Doppler effect for light differs from that for sound in regards that:
[THIS QUESTION HAS MULTIPLE CORRECT OPTIONS]

 $$\left(\text{A}\right)$$ The relative frequency shift is smaller for light than for sound
 $$\left(\text{B}\right)$$ The velocity addition valid for sound is not true for light waves
 $$\left(\text{C}\right)$$ The Velocity of light is very large as compared to the sound
 $$\left(\text{D}\right)$$ Light waves are electromagnetic waves but sound waves are mechanical

Answer 1

Hint:There is a very important difference between the doppler effect for light and sound. For sound waves the relative velocity of sound changes if the listener gains velocity, but for the light wave according to the theory of Relativity the speed of light is always fixed no matter whenever the source and the visitor gain velocity w.r.t each other.

Note that the speed of light is very large compared to any other waves or particles.

The doppler effect of a sound wave depends upon the medium but for the light waves, there is no such medium dependency.

Complete step by step answer:
The doppler effect of a wave is the changes in the frequency of the wave due to the relative motion of the wave and an observer.

If there is a relative motion between a sound source and an observer, the observer feels the change in sharpness of the sound – this is called the doppler effect of the sound wave.
The light wave has also a doppler effect. When a relative motion occurs between the light source and an observer the changes in the frequency and intensity of light seem to the observer i.e the color of light becomes a change for the observer – this is called the doppler effect of light.

Now, There is a difference in the doppler effect of the sound wave and the light wave. For sound waves the relative velocity of sound changes if the listener gains velocity, but for the light wave according to the theory of Relativity the speed of light is always fixed no matter whenever the source and the visitor gain velocity w.r.t each other.

And it is also notable that the speed of light is $c=3\times {10}^8$, which is very high and greater than any waves or object in the universe.

We know that the sound wave is a mechanical wave and that’s why it needs a medium to transmit. So the doppler effect of the sound also depends upon the medium. The light wave is an electromagnetic wave and that’s why it does not need any medium to transmit and so the doppler effect of the light does not depend upon the medium.
So, the effect of Doppler effect for light that differs from the sound in regards that –

Option$$\left(\text{C}\right)$$-The Velocity of light is very large as compared to the sound and

Option$$\left(\text{D}\right)$$-Light waves are electromagnetic waves but sound waves are mechanical.

Hence the right answer is in option $$\left(\text{C}\right)$$ and $$\left(\text{D}\right)$$.

Notes:It is easy to see the doppler effect for a sound wave but not for the light wave because for occurring the doppler effect the relative velocity between the source and the observer should be equivalent to the velocity of that wave.
For the sound wave, the relative velocity becomes equivalent to the velocity of sound but the velocity of light is very high than the relative velocity. Hence for light waves, it is not easy to see the doppler effect.