Question

The speed of light in air as compared to vacuum is

• A. Less
• B. More
• C. Same
• D. None of these

Hint:

Light travels fastest in a vacuum. Any medium, including air, will slow it down. The denser the optical medium, the slower the light travels.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The speed of light is constant in a vacuum but changes when it travels through a transparent medium. The refractive index (\(n\)) of a medium describes how much the speed of light is reduced in that medium.

Step 2: Key Formula or Approach:
The refractive index (\(n\)) is defined as the ratio of the speed of light in a vacuum (\(c\)) to the speed of light in the medium (\(v\)):
\[ n = \frac{c}{v} \]

Step 3: Detailed Explanation:
By definition, the refractive index of a vacuum is exactly 1. Air is a physical medium, and its refractive index is slightly greater than 1 (approximately \(n_{air} \approx 1.0003\)).
Using the formula, \(v = \frac{c}{n}\). Since \(n_{air} > 1\), the speed of light in air (\(v_{air}\)) will be slightly less than the speed of light in a vacuum (\(c\)).
Although for many calculations the speed of light in air is approximated to be the same as in a vacuum, it is technically and factually less.

Step 4: Final Answer:
The speed of light in air is less than the speed of light in a vacuum.