With increase in temperature of the medium, its refractive index

Options

A. increases
B. decreases
C. remains same
D. either (a) or (b)

Answer

To solve the question regarding the behavior of the refractive index of a medium with an increase in temperature, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Refractive Index**: The refractive index (denoted as \( \mu \)) of a medium is defined as the ratio of the speed of light in vacuum to the speed of light in that medium. It is a measure of how much light slows down when it enters a medium.

2. **Effect of Temperature on Medium**: As the temperature of a medium increases, the density of that medium generally decreases. This is because the particles in the medium gain kinetic energy and move apart from each other.

3. **Relation Between Density and Refractive Index**: The refractive index is inversely related to the density of the medium. As the density decreases (due to an increase in temperature), the refractive index also decreases.

4. **Conclusion**: Therefore, with an increase in temperature of the medium, its refractive index decreases. This means that the correct answer to the question is that the refractive index decreases.

### Final Answer:
With an increase in temperature of the medium, its refractive index decreases.

---