Explain the phenomenon of total internal reflection in a right-angled prism.

(N/A) Prisms designed to deviate light by $90^{\circ}$ or $180^{\circ}$ utilize the phenomenon of total internal reflection,as shown in figures $(a)$ and $(b)$.
In these cases,the angle of incidence at the prism face is $45^{\circ}$. For total internal reflection to occur,the critical angle $i_{c}$ for the material of the prism must be less than $45^{\circ}$.
Such prisms are also used to invert images without changing their size,as illustrated in figure $(c)$.