To a stationary man the frequency of a sound source moving towards the man appears to be

Options

A. lower than the original frequency
B. same as the original frequency
C. higher than the original frequency
D. lower as well as higher than the original frequency depending upon the speed of the source.

Answer

To solve the question regarding the frequency of a sound source moving towards a stationary observer, we can follow these steps:

### 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. When the source of sound is moving towards the observer, the frequency perceived by the observer increases.

**Hint**: Remember that the Doppler effect applies to all types of waves, including sound waves.

2. **Visualizing the Scenario**:
Imagine a sound source (like a car horn) moving towards a stationary observer. As the car approaches, it emits sound waves that travel towards the observer.

**Hint**: Picture the sound waves as concentric circles (wavefronts) expanding outward from the source.

3. **Wavefronts and Frequency**:
As the sound source moves closer, the distance between consecutive wavefronts decreases. This means that more wavefronts reach the observer in a given time period.

**Hint**: Think about how the speed of the source affects the spacing of the wavefronts.

4. **Calculating Apparent Frequency**:
The apparent frequency (the frequency heard by the observer) is greater than the actual frequency emitted by the source because the observer receives more wavefronts per second.

**Hint**: Recall that frequency is defined as the number of wavefronts passing a point per second.

5. **Conclusion**:
Since the source is moving towards the observer, the frequency of the sound appears to be higher than the original frequency emitted by the source.

**Final Answer**: The frequency of a sound source moving towards a stationary man appears to be **higher than the original frequency**.

### Summary of the Answer:
The correct option is that the frequency appears to be higher than the original frequency when the sound source is moving towards the observer.