Refractive index is minimum for

Options

A. vacuum
B. air
C. glass
D. diamond

Explanation

To determine which medium has the minimum refractive index among vacuum, air, glass, and diamond, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Refractive Index**:
The refractive index (μ) of a medium is defined as the ratio of the speed of light in vacuum (C) to the speed of light in that medium (V). Mathematically, it is expressed as:
\[ \mu = \frac{C}{V} \]

2. **Refractive Index in Vacuum**:
In a vacuum, the speed of light is at its maximum, which is C. Therefore, the refractive index in vacuum is:
\[ \mu_{vacuum} = \frac{C}{C} = 1 \]

3. **Refractive Index in Air**:
The speed of light in air is slightly less than in vacuum. Hence, the refractive index in air is:
\[ \mu_{air} > 1 \]
(exact value is approximately 1.0003).

4. **Refractive Index in Glass**:
The speed of light in glass is even lower than in air. Therefore, the refractive index in glass is:
\[ \mu_{glass} > 1 \]
(typically around 1.5).

5. **Refractive Index in Diamond**:
Diamond is an optically denser medium, and the speed of light in diamond is much lower than in air. Thus, the refractive index in diamond is:
\[ \mu_{diamond} > 1 \]
(approximately 2.42).

6. **Comparison of Refractive Indices**:
From the above calculations, we can summarize the refractive indices:
- Vacuum: μ = 1
- Air: μ > 1
- Glass: μ > 1
- Diamond: μ > 1

The only medium with a refractive index of 1 is vacuum, while all other mediums have a refractive index greater than 1.

### Conclusion:
The refractive index is minimum for **vacuum**.

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