Physics 11 H.
Name:_________________
Date: ________________
Calculating the Critical angle
When light is incident upon a medium of lesser index of refraction, the ray is bent away from the
normal, so the exit angle is greater than the incident angle. Such reflection is commonly called
"internal reflection". The exit angle will then approach 90° for some critical incident angle Θc,
and for incident angles greater than the critical angle there will be total internal reflection.
Let's consider two different media - creatively named medium i (incident medium) and medium r
(refractive medium). The critical angle is the
that gives a
value of
If this information is substituted into Snell's Law equation, a generic equation for predicting the
critical angle can be derived. The derivation is shown below.
6. Calculate the critical angle for diamond.
7. What is the critical angle for a glass that has an index of refraction of 1.500?