When a sound wave is reflected from a wall the phase difference between the reflected and incident pressure wave is:

Options

A. `0`
B. `pi`
C. `pi//2`
D. `pi//4`

Explanation

To solve the question regarding the phase difference between the reflected and incident pressure wave when a sound wave is reflected from a wall, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reflection of Sound Waves**:
- When a sound wave encounters a rigid boundary (like a wall), it reflects back. The behavior of the wave at this boundary is crucial to determining the phase difference.

2. **Behavior at a Rigid Boundary**:
- At a rigid boundary, the particles of the medium cannot vibrate. This means that the wave reflects in such a way that it creates a node at the boundary. A node is a point where there is zero displacement of the medium.

3. **Interference of Waves**:
- The incident wave and the reflected wave interfere with each other. At the boundary, where the wave reflects, the condition for constructive interference leads to a situation where the pressure variation is maximized.

4. **Phase of Reflected Wave**:
- The reflected wave maintains the same phase as the incident wave because the pressure variation is maximum at the boundary. This means that the peaks and troughs of the reflected wave align with those of the incident wave.

5. **Calculating Phase Difference**:
- Since the reflected wave has the same phase as the incident wave, the phase difference between the two waves is zero.

6. **Conclusion**:
- Therefore, the phase difference between the reflected and incident pressure wave when a sound wave is reflected from a wall is **0 radians**.

### Final Answer:
The phase difference between the reflected and incident pressure wave is **0 radians**.