Light enters a medium (refractive index `gt` 1) from vacuum. Which property will remain unchanged?

Options

A. Wavelength
B. Frequency
C. Speed
D. All of them

Explanation

To solve the question of which property of light remains unchanged when it enters a medium with a refractive index greater than 1 from vacuum, we can analyze the properties of light as it transitions between different media.

### Step-by-Step Solution:

1. **Understanding the Properties of Light**:
- When light travels from one medium to another, certain properties change while others remain constant. The main properties to consider are speed, wavelength, and frequency.

2. **Speed of Light**:
- The speed of light in a medium (V) is given by the formula:
\[ V = \frac{c}{n} \]
where \(c\) is the speed of light in vacuum (approximately \(3 \times 10^8 \, m/s\)) and \(n\) is the refractive index of the medium. Since \(n > 1\), the speed of light in the medium will be less than in vacuum.

3. **Wavelength of Light**:
- The wavelength of light in a medium (\(\lambda\)) is related to its wavelength in vacuum (\(\lambda_0\)) by the formula:
\[ \lambda = \frac{\lambda_0}{n} \]
Again, since \(n > 1\), the wavelength in the medium will be shorter than in vacuum.

4. **Frequency of Light**:
- The frequency (\(f\)) of light is given by the relation:
\[ f = \frac{V}{\lambda} \]
In a transition from vacuum to a medium, the frequency remains constant. This is because frequency is determined by the source of the light and does not change when light enters a different medium.

5. **Conclusion**:
- Therefore, when light enters a medium with a refractive index greater than 1 from vacuum, the property that remains unchanged is the **frequency** of the light.

### Final Answer:
The property that will remain unchanged is the **frequency** of the light.