Question

The Doppler effect is applicable to
(A) Light waves only
(B) Sound waves only
(C) Both sound and light waves
(D) None of the above

Answer 1

Hint: The Doppler effect occurs when the motion of wave source and observer is relative. The common example is the ambulance’s sound and shift of red light. Doppler effect refers to change in any type of wave frequency during the relative motion of wave source and observer. So the Doppler effect occurs in every type of wave.

Complete step by step answer:
If the source of waves or observer or both in moving condition with respect to each other or with respect to its medium, the observed frequency is more or less than the source’s actual frequency. This phenomenon is called the Doppler effect.
For example, In figure A is the source of the wave and B is the observer. In figure \[(1)\]the source and the observer are in a static position. The pitch of every wavefront is the same and comes with the same speed to the observer. But in figure \[(2)\] the source of waves is coming towards the observer and all the wavefronts are the same but the respective speed of each wavefront is relatively different due to the motion of the source.

figure \[(1)\]

figure \[(2)\]

If these wavefronts are wavefront of sound then the pitch of the frequency changes relatively and If these wavefronts are wavefront of the light wave then the pitch of light frequency changes relatively. So the Doppler Effect is applicable for both sound and light waves.
So the answer is (C).

Additional Information:
The formula of Doppler Effect in any medium in any condition is,
\[{{f}_{o}}={{f}_{s}}(\dfrac{{{v}_{m}}\pm {{v}_{o}}}{{{v}_{m}}\pm {{v}_{s}}})\]
  Where \[{{f}_{o}}\] is observed frequency
\[{{f}_{s}}\] is frequency of source
 \[{{v}_{m}}\] is velocity of medium
\[{{v}_{o}}\] is the velocity of the observer
 And \[{{v}_{s}}\] is velocity of source.

Note: The Doppler effect can be observed in any type of wave-like sound wave, lightwave, water wave. We used to feel the Doppler effect in sound waves for example police vehicles or ambulances but note that we can’t feel in other waves because the relative speed of waves in other mediums is about the speed of light and only the speed of sound waves is in our region.