Refraction of Light at Plane Surfaces — Question 5

(a) As we know that light is an electromagnetic wave and it travels with same speed for all wavelength, which is equal to 3 x 10⁸.

Hence, the ratio of speeds of light of wavelength 4000Å (i.e. violet light) and 8000Å (i.e. red light) in vacuum = 1:1.

(b) The refractive index of a medium is defined as the ratio of the speed of light in vacuum (or air) to the speed of light in that medium.

$μ =\dfrac{\text{Speed of light in vacuum or air (c) }}{\text {Speed of light in that medium (V)}} \\[0.5em]$

Denser medium has a higher refractive index. Hence, the speed of light in such medium is lower in comparison to the speed of light in a medium which has a lower refractive index.