When light travels from one medium to another, which are separated by a sharp boundary, the characteristic which does not change is

Options

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

Explanation

To solve the question, we need to determine which characteristic of light does not change when it travels from one medium to another. The options provided are frequency, wavelength, velocity, and amplitude.

### Step-by-Step Solution:

1. **Understanding the Properties of Light**:
- Light behaves as a wave when it travels through different media. Each of these properties (frequency, wavelength, velocity, and amplitude) can be affected by the medium through which the light is traveling.

2. **Frequency**:
- The frequency of light is determined by the source of the light. When light transitions from one medium to another, the frequency remains constant. This is because the frequency is a property of the source and does not depend on the medium.

3. **Wavelength**:
- The wavelength of light is related to its speed and frequency by the equation:
\[ v = f \cdot \lambda \]
where \(v\) is the velocity of light in the medium, \(f\) is the frequency, and \(\lambda\) is the wavelength. Since the speed of light changes when it enters a different medium, the wavelength must also change to maintain the relationship.

4. **Velocity**:
- The velocity of light changes when it moves from one medium to another. For example, light travels slower in denser media compared to less dense media. This change in speed affects both the wavelength and amplitude.

5. **Amplitude**:
- The amplitude of light can also change when it enters a different medium. This change can be due to reflection and refraction at the boundary between the two media.

6. **Conclusion**:
- Since the frequency is the only characteristic that does not change when light travels from one medium to another, we conclude that the correct answer is **frequency**.

### Final Answer:
The characteristic which does not change when light travels from one medium to another is **frequency**.

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