Which of the following does not affect the apparent frequency in doppter effect?

Options

A. Speed of source
B. Speed of observer
C. Frequency of source
D. Distance between source and observer

Explanation

To determine which factor does not affect the apparent frequency in the Doppler effect, we can analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding the Doppler Effect**:
The Doppler effect describes how the frequency of a wave changes for an observer moving relative to the source of the wave. The apparent frequency (\(f'\)) can be calculated using the formula:
\[ f' = f \left( \frac{v + v_o}{v - v_s} \right) \]
where:
- \(f\) = frequency of the source
- \(v\) = speed of sound in the medium
- \(v_o\) = speed of the observer (positive if moving towards the source)
- \(v_s\) = speed of the source (positive if moving away from the observer)

2. **Analyzing the Options**:
- **Speed of Source (\(v_s\))**: This affects the apparent frequency because it is included in the formula. If the source moves, the frequency perceived by the observer changes.
- **Speed of Observer (\(v_o\))**: This also affects the apparent frequency. If the observer moves, the frequency they perceive changes as well.
- **Frequency of Source (\(f\))**: This is the original frequency emitted by the source and directly influences the apparent frequency.
- **Distance Between Source and Observer**: This does not appear in the formula for apparent frequency. While distance may affect the intensity of the sound, it does not affect the frequency perceived by the observer.

3. **Conclusion**:
The factor that does not affect the apparent frequency in the Doppler effect is the **distance between the source and observer**.

### Final Answer:
The correct option is **distance between source and observer**.