Refraction through prisms

We will consider the refraction of monochromatic light through prisms. The effect of different wavelengths is considered elsewhere.
Firstly right angled prisms. Since the critical angle for a glass-air boundary is 42^o any light which hits the boundary at 45^o will be totally internally reflected. This explains the following three diagrams (Figures 1,2 and 3).



Figure 3 shows how right- angled prisms are used in (a) a periscope and (b) in prismatic binoculars