Question

(a) The refractive index of glass is 1.5. What is the speed of light in glass? (Speed of light in vacuum is 3.0 × 108 m s–1) (b) Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?

Answer 1

(a)

Given,

Refractive index of glass μ=1.5

Speed of light in vacuum c=3× 10 8   ms -1

Let, v be the speed of light in glass.

The expression for the light of speed in any medium is,

v= c μ

Thus, speed of light in glass is,

v= 3× 10 8 1.5 =2× 10 8   ms -1

(b)

The speed of light in glass depends on the color of light. Since, the refractive index of the violet color is greater than red color, thus the speed of the violet light will be less than red light in glass. Therefore, the violet component of white light travels slower than the red component.