Question

When light passes from air to a medium its speed reduces to 40%. The velocity of light in air is 3 × 108 ms-1. What is refractive index of the medium?

Answer 1

Answer:

2.5.

Explanation:

The refractive index of a medium is defined as the ratio of speed of light in the vacuum ( or air ) $c$ to the speed of light in that medium $v$.

$n = \dfrac cv$

Given:

• $c = 3\times 10^8\ m/s$.

• $v = 40\% \text{ of }c\\=\dfrac{40}{100}\times 3\times 10^8\\=1.2\times 10^8\ m/s.$

Using,

$n= \dfrac cv\\=\dfrac{3\times 10^8}{1.2\times 10^8}\\=2.5.$

It is the refractive index of the medium.