State the laws of refraction

(i) The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane.
(ii) The ratio of the sine of angle of incidence to the sine of the angle of refraction is a constant and this constant is called the index of refraction or refractive index.
Mathematically, Sin i/Sin r =$n_{2}$ / $n_{1}$