Refraction through a prism?

Question

A horizontal light ray is incident on a crown glass prism as shown in the figure below where alpha = 40°. Find the angle of deviation delta of the ray--the angle that the ray emerging from the prism makes with the incident ray.

here is the figure given

https://chip.physics.purdue.edu/protected/GiambattistaEMimg/chapter-23/fig-053.gif

Answer 1

I am using 1.50 as the coefficient of refraction for crown glass.

As the two lower angles of the prism are each 70 deg, the angle of incidence at the first surface is 20 deg.

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

sin(20) / sin(r) = 1.50

r = 13.18 deg.

Angle of incidence at the second face is:

40 - 13.18

= 26.82 deg.

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

sin(s) / sin(26.82) = 1.50

s = 42.59 deg.

The deviation required is:

delta = s - 20

= 22.6 deg.