There are two laws of refraction.

First law of Refraction of light:

The incident ray, refracted ray and the normal at the point of incidence, all lie in same plane.

In given Figure ray AO, OB and ON all lie in same plane i.e. plane of paper.

Second law of Refraction of light: The ratio of sine of angle of incidence (sin i) to the sine of angle of refraction (Sin r) is constant for a given pair of media.

Where ‘i’ is the angle of incidence and ‘r’ is the angle of refraction.

This constant is called refractive index. It has no units.