(a) The refractive index of glass is 1.5. What is the speed of light in glass?
(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?

Explanation

(a) Given, refractive index ,` mu = 1.5`
Speed of light in vacuum , `c = 3.0 xx 10^8 ms^(-1)`
As , `mu = c/upsilon`
`implies upsilon = c/(mu) = (3 xx 10^8)/(1.5) = 2 xx 10^8 m s^(-1)`
The speed of light in glass is `2 xx 10^8 m s^(-1)`
(b) No, because the refractive index as well as the speed of a component of light depen on its wavelength. The refractive index for violet light is greater than that for red light. Therefore, the violet light travels slower in glass prism.