A wave undergoes reflection from a rigid boundary. One of its characteristic parameters that changes is

Options

A. frequency
B. phase
C. velocity
D. wavelength

Answer

To solve the question regarding the reflection of a wave from a rigid boundary and which characteristic parameter changes, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Reflection at a Rigid Boundary**:
When a wave hits a rigid boundary, it reflects back. The nature of the boundary (rigid) affects how the wave behaves upon reflection.

2. **Identifying Characteristic Parameters of Waves**:
The key parameters of a wave include frequency, wavelength, velocity, and phase.

3. **Analyzing Changes Upon Reflection**:
- **Frequency**: The frequency of a wave is determined by the source of the wave and remains constant during reflection.
- **Velocity**: The velocity of the wave in a given medium does not change upon reflection, as it is dependent on the properties of the medium.
- **Wavelength**: Since the frequency and velocity remain unchanged, the wavelength also remains constant during reflection.
- **Phase**: Upon reflection from a rigid boundary, the wave undergoes a phase change. Specifically, the phase of the reflected wave changes by π radians (or 180 degrees).

4. **Conclusion**:
Based on the analysis, the only characteristic parameter that changes when a wave reflects off a rigid boundary is the phase.

Therefore, the correct answer is **Option B: Phase**.