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

(N/A) $1$. Refraction through a prism: When a light ray $PQ$ enters a triangular glass prism $ABC$,it undergoes refraction at the first surface $AB$ and bends towards the normal $NN'$.
$2$. Inside the prism,the ray travels as $EF$ and bends away from the normal $MM'$ at the second surface $AC$,emerging as ray $FS$.
$3$. The incident ray $PQ$ is extended forward,and the emergent ray $FS$ is extended backward to meet at point $G$.
$4$. Angle of deviation: The angle $D$ formed between the direction of the incident ray and the direction of the emergent ray is known as the angle of deviation.