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) Refractive index of glass, μ = 1.5
Speed of light, c = 3 × 10⁸ m/s
Speed of light in glass is given by the relation,

Hence, the speed of light in glass is 2 × 10⁸ m/s.
 

(b) The speed of light in glass is not independent of the colour of light. The refractive index of a violet component of white light is greater than the refractive index of a red component. Hence, the speed of violet light is less than the speed of red light in glass. Hence, violet light travels slower than red light in a glass prism.