How do you calculate the size of the critical angle for total internal reflection???

Question

How do you calculate the size of the critical angle for total internal reflection???

Answer 1

It comes from Snell's law:

n1 sin(angle1) = n2 sin(angle2)

Set angle1 = 90 degrees.  If n1 is for air or vacuum, the whole left-hand-side is simply 1, so solve for angle2:

n2 sin(angle2) = 1

(They should tell you what n2 is in the problem statement, or give you enough information to figure it out.)