Question

A horizontal light ray is incident on a crown glass prism as shown in the figure below where ? = 42.5

Answer 1

s the two lower angles of the prism are each 68.75 deg, the angle of incidence at the first surface is 21.25 deg

If r is the angle of refraction at the first surface:

sin(21.25) / sin(r) = 1.50

r = 13.9825 deg.

Angle of incidence at the second face is:

42.5 - 13.9825

= 28.5175 deg.

If s is the angle between the normal to the second face of the prism and the emerging ray:

sin(s) / sin(28.5175) = 1.50

s = 45.7367 deg.

The deviation required is:

delta = s - 20 = 45.7367 - 20 = 25.7368 deg.