When source of sound moves towards a stationary observer, the wavelength of sound received by him

Options

A. decreases while frequency increases.
B. remains the same whereas frequency increases.
C. increases and frequency also increases
D. decreases while frequency remains the same

Answer

To solve the question regarding the effect on the wavelength of sound when a sound source moves towards a stationary observer, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Scenario**:
- We have a sound source that is moving towards a stationary observer.
- As the source moves, it emits sound waves that travel towards the observer.

2. **Doppler's Effect**:
- The phenomenon that occurs when the source of sound moves relative to an observer is known as the Doppler Effect.
- When the source moves towards the observer, the sound waves get compressed, leading to an increase in the frequency of the sound heard by the observer.

3. **Relationship Between Frequency and Wavelength**:
- The relationship between the speed of sound (v), frequency (f), and wavelength (λ) is given by the equation:
\[ v = f \cdot \lambda \]
- Here, v is the speed of sound in the medium, f is the frequency, and λ is the wavelength.

4. **Effect of Increasing Frequency**:
- Since the sound source is moving towards the observer, the frequency (f) of the sound waves increases.
- If the speed of sound (v) in the medium remains constant (which it does, as the medium is unchanged), an increase in frequency must result in a decrease in wavelength.

5. **Conclusion**:
- Therefore, when the source of sound moves towards the stationary observer, the wavelength of the sound received by the observer decreases.

### Final Answer:
- The wavelength of sound received by the observer decreases.