When light passes from a denser medium to a rarer medium

Options

A. Velocity of light increases
B. Velocity of light decreases
C. Velocity of light remains unchanged
D. Velocity of light becomes infinity

Answer

To solve the question, "When light passes from a denser medium to a rarer medium, what will be the difference in the velocity of light?" we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Refractive Index**:
The refractive index (μ) of a medium is defined as the ratio of the speed of light in vacuum (or air) to the speed of light in that medium. Mathematically, it is expressed as:
\[ \mu = \frac{c}{v} \]
where \( c \) is the speed of light in vacuum (approximately \( 3 \times 10^8 \) m/s), and \( v \) is the speed of light in the medium.

2. **Identify the Relationship Between Refractive Index and Velocity**:
From the definition, we can see that:
\[ v = \frac{c}{\mu} \]
This indicates that the speed of light in a medium is inversely proportional to its refractive index.

3. **Compare Denser and Rarer Mediums**:
- A denser medium has a higher refractive index (μ > 1), which means that the speed of light in that medium (v) is lower.
- A rarer medium has a lower refractive index (μ < 1), which means that the speed of light in that medium (v) is higher.

4. **Conclusion on the Change in Velocity**:
When light transitions from a denser medium (higher μ) to a rarer medium (lower μ), the refractive index decreases, leading to an increase in the velocity of light. Therefore, the velocity of light increases when moving from a denser medium to a rarer medium.

5. **Final Answer**:
The velocity of light will **increase** when it passes from a denser medium to a rarer medium.