A light ray falling at an angle of 45° with the surface of a clean slab of ice of thickness 1.00 m is refracted into it at an angle of 30°. Calculate the time taken by the light rays to cross the slab. Speed of light in vacuum = 3 x 108 ms-1.

5.44 ns

When the light ray will fall on the slab of ice, then the

light ray will refract and it will change its path because of change in medium. The light is travelling from rarer medium to denser medium hence the ray will be refracted towards the normal of the ice slab by the angle 30 degree. The relation between the angle of incident, angle of refraction, the refractive index of the mediums and the velocity of the light ray in different medium is given by Snell’s law.

Angle of incidence i= 45°

Angle of refraction r= 30°

Using the Snell’s law

Distance travelled by light in the slab is x