# (i) The refractive index of glass is 1.5.

Question:

(i) The refractive index of glass is 1.5. What is the speed of light in glass? Speed of light in a vacuum is ( 3.0 x 108 m s-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?

Solution:

(i) Refractive Index of glass, $\mu=1.5$

Speed of light, c = 3 × 108 ms-1

The relation for the speed of light in a glass is: $v=\frac{c}{\mu}$

The relation for the speed of light in a glass is: $v=\frac{c}{\mu}$

$=\frac{3 \times 10^{8}}{1.5}=2 \times 10^{8} \mathrm{~m} / \mathrm{s}$

Hence, the speed of light in glass is 2 × 108 m s-1

(ii) The speed of light is dependent on the colour of the light. For a white light, the refractive index of the violet component is greater than the refractive index of the red

component. So, the speed of violet light is less than the speed of the red light in the glass. This will reduce the speed of violet light in glass prism when compared with

red light.