(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 xx 10^(8) 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?

Explanation

(a) `2.0xx10^(8)ms^(-1)`
(b) No. The refractive index, and hence the speed of light in a medium, depends on wavelength. [When no particular wavelength or colour of light is specified, we may take the given refractive index to refer to yellow colour.] Now we know violet colour deviates more than red in a glass prism, i.e. nv > nr . Therefore, the violet component of white light travels slower than the red component.