Explain the refraction of light through a triangular glass prism using a labelled ray diagram. Hence, define the angle of deviation.

The refraction of light through a triangular glass prism is shown below. A ray of light PE is entering from air to glass at the first surface AB. The light ray EF on refraction has bent towards the normal.
At the second surface AC, the light ray FS has entered from glass to air and bent away from normal. The angle made by extending incident ray(EH) with the emergent ray(FS) is called angle of deviation.