The apparent change in frequency of a sounding source and observer in relative motion is

Options

A. phenomenon of beats
B. Doppler effect
C. stationary waves
D. resonance

Answer

To solve the question regarding the apparent change in frequency of a sounding source and observer in relative motion, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept**: The phenomenon where the frequency of a wave changes due to the relative motion between the source of the sound and the observer is known as the Doppler Effect.

2. **Identifying Variables**:
- Let \( F \) be the actual frequency of the source.
- Let \( V \) be the speed of sound in the medium.
- Let \( V_o \) be the speed of the observer.
- Let \( V_s \) be the speed of the source.

3. **Doppler Effect Formula**: The general formula for the observed frequency \( F' \) when both the source and the observer are in motion is given by:
\[ F' = F \frac{V + V_o}{V - V_s} \]
- Here, \( V + V_o \) is used when the observer is moving towards the source, and \( V - V_s \) is used when the source is moving towards the observer.

4. **Considering Different Scenarios**:
- If both the source and observer are moving towards each other, the frequency increases.
- If the observer is moving away from the source, the frequency decreases, and we would use \( V - V_o \) in the numerator.
- If the source is moving away from the observer, we would use \( V + V_s \) in the denominator.

5. **Conclusion**: The apparent change in frequency due to the relative motion of the source and observer is a manifestation of the Doppler Effect. The formula encapsulates how the frequency changes based on their velocities and the speed of sound.

### Final Answer:
The apparent change in frequency of a sounding source and observer in relative motion is known as the **Doppler Effect**.

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