(a) The refractive index of glass is `1.5`. What is the speed of light in glass ? (Speed of light in vaccum is `3 xx 10^(8) ms^(-1)`).
(b) Is the speed of light in glass independent of 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.