Critical Angle Prism: Find Theta with n=1.90

[Aeighme]

Homework Statement

A corner reflector is to be made from a triangular prism with index of refraction n = 1.90, as shown in the diagram below. What is the maximum angle, with respect to the normal to the front surface of the prism, (theta), such that total reflection will occur?
http://capa.sci.geneseo.edu/teacher/capalibrary/Graphics/Gtype73/prob02.gif (link to image)

Homework Equations

sin(critical angle)=(n1/n2)

The Attempt at a Solution

Tried using that equation, failed miserably.

 

[tiny-tim]

Hi Aeighme!

sin(critical angle)=(n1/n2)

No … that's the equation for the maximum angle from glass (or whatever) into air.

You need the ordinary sinθ₁/sinθ₂ = n₂/n₁