Explain the phenomena of total internal reflection in right angle prism.

Explanation

Prisms designed to bend light by `90^@` or by `180^@` make use of total internal reflection figure (a) and (b).

In the first two cases, the critical angle `i_c` for the material of the prism must be less than `45^@`.
Such a prism is also used to invert images without changing their size figure (c).