Question

What is the critical angle of a diamond having a refractive index
of 2.42? Use air as the second medium. Air has the refractive
index 1.00.

Answer 1

14.9
24.4
36.6
40.9

Answer 2

Snell's law is
\[n_1\sin\theta_1 = n_2\sin\theta_2\]
Let's say material 1 is diamond and material 2 is air.
The critical angle \(\theta_1 = \theta_c\) in diamond is reached when the angle in air is \(\theta_2 = 90^\circ\)

Therefore
\[2.42 \sin\theta_c = 1.00 \sin90^\circ = 1\]
solve for \(\theta_c\)