Draw a path of light ray passing through a prism. Label angle of incidence and angle of deviation in the ray diagram.
A ray of light PQ is incident on one of its faces at point E, making an ∠PEN, also called the angle of incidence ∠i, at the point of incidence. NN' being the normal at the point of incidence.
As the ray of light enters the transparent material, it moves from air, a rarer medium, to a denser medium. Refractive index μ of the material of the block being more than that of air. The ray of light is refracted and bends towards the normal.
The ray of light moves in a straight path through the block and impinges the other face of the block at F. As it emerges out of the block, it moves from a denser to a rarer medium, and therefore, bends away from the normal MM' at point F. Once out of the block it proceeds again along a straight line path RS as the emergent ray.