When light travels from air to water, which parameter does not change?

Options

A. Wave length
B. Frequency
C. Velocity
D. All of these.

Answer

To determine which parameter does not change when light travels from air to water, we need to analyze the properties of light as it transitions between different media. The parameters we are considering are wavelength, frequency, and velocity.

### Step-by-Step Solution:

1. **Understanding the Parameters**:
- **Velocity (V)**: The speed of light changes when it moves from one medium to another due to the different refractive indices of the media.
- **Wavelength (λ)**: The wavelength of light changes when it enters a different medium. It is related to the velocity and frequency by the equation \( V = f \cdot \lambda \).
- **Frequency (f)**: The frequency of light remains constant when it travels from one medium to another.

2. **Analyzing Velocity**:
- When light travels from air (with a refractive index of approximately 1) to water (with a refractive index of about 1.33), its velocity decreases. The relationship can be expressed as:
\[ V_{water} = \frac{V_{air}}{\mu} \]
- Here, \( \mu \) is the refractive index of water. Thus, the velocity changes.

3. **Analyzing Wavelength**:
- The wavelength of light is also affected when it enters a new medium. The new wavelength can be expressed as:
\[ \lambda_{water} = \frac{V_{water}}{f} \]
- Since the velocity changes, the wavelength will also change.

4. **Analyzing Frequency**:
- The frequency of light is determined by the source and does not change when light moves from one medium to another. This can be understood from the equation:
\[ f = \frac{V}{\lambda} \]
- Since the frequency is constant, it remains unchanged regardless of the medium.

5. **Conclusion**:
- Among the parameters considered (wavelength, frequency, and velocity), the only parameter that does not change when light travels from air to water is **frequency**.

### Final Answer:
**Frequency does not change when light travels from air to water.**

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