Dopper's effect is sound in addition of relative velocity between source and observer, also depends while source and observer or both are moving. Doppler effecct in light depennd only on the relative velocity of source and observer. The reason of this is

Options

A. Einstein mass-energy relation
B. Einstein theory of relativity
C. Photoelectric effect
D. none of the above

Explanation

To solve the question regarding the Doppler effect in sound and light, we will analyze the statements provided and derive the correct reasoning behind the differences in how the Doppler effect applies to sound and light.

### Step-by-Step Solution:

1. **Understanding the Doppler Effect**:
- The Doppler effect refers to the change in frequency (or wavelength) of a wave in relation to an observer moving relative to the source of the wave. This effect is observed in both sound and light waves.

2. **Doppler Effect in Sound**:
- For sound waves, the Doppler effect is influenced by the relative motion of both the source and the observer. If either the source or the observer is moving, the frequency of the sound heard will change.
- This is because sound requires a medium (like air) to travel, and the speed of sound is constant in that medium. The relative velocities of the source and observer affect how the sound waves compress or stretch, leading to a change in frequency.

3. **Doppler Effect in Light**:
- In contrast, the Doppler effect for light depends solely on the relative velocity of the source and the observer. This is because light does not require a medium to travel; it moves at a constant speed (the speed of light) in a vacuum regardless of the motion of the source or observer.
- Therefore, the frequency shift observed in light is only a function of the relative velocity between the source and observer.

4. **Reason for the Difference**:
- The reason the Doppler effect in light depends only on the relative velocity is rooted in Einstein's theory of relativity. According to relativity, the speed of light is constant for all observers, regardless of their motion relative to the source of light. This leads to the conclusion that the frequency shift due to the Doppler effect in light is independent of the motion of the observer or source, as long as their relative velocity is considered.

5. **Conclusion**:
- Given the options provided in the question, the correct answer is that the reason the Doppler effect in light depends only on the relative velocity of the source and observer is due to **Einstein's theory of relativity**.

### Final Answer:
The correct option is **Einstein's theory of relativity**.