(a) State two laws of refraction of light.

OR

(b) Define the term absolute refractive index of a medium. A ray of light enters from vacuum to glass of absolute refractive index 1.5. Find the speed of light in glass. The speed of light in vacuum is $3 \times 10^{8} \mathrm{~m / s}$.

(a) The two laws of refraction of light are:

1. The incident ray, the refracted ray and the normal to the interface at the point of incidence all lie in the same plane.
2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media.

OR

(b) The absolute refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium. It is denoted by the symbol n.

Speed of light in glass = Speed of light in vacuum / Absolute refractive index of glass

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

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