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

(i) The refractive index of glass is 1.5. What is
the speed of light in glass? (Speed of light in vacuum is 3 x ${{10}^{8}}$ ${{ms}^{-1}}$)
(ii) 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?

(i) Here, refractive index µ = 1.5
v=? c = 3 x ${{10}^{8}}$ ${{ms}^{-1}}$

As, µ = c/v ====> v = c/µ = 3 x ${{10}^{8}}$/1.5
= 2 x ${{10}^{8}}$ ${{ms}^{-1}}$

(ii) No, the refractive index and the speed of light in a
medium depend on wavelength, i.e. colour of light.
We know that, ${ µ }{ v}$ >
${ µ }
{ r}$. Hence, violet component of white light travels slower than the red component.