Question

What is the critical angle for total internal reflection at the interface between
diamond and air?

Answer 1

The critical angle for total internal reflection is given by:

$$\theta_c = \arcsin\left( \dfrac{n_2}{n_1} \right)$$

where $n_2 = 1$ is the refractive index for air and $n_1\approx 2.42$ is the refractive index of diamond. Thus, obtain:

$$\theta_c = \arcsin\left( \dfrac{1}{2.42} \right) \approx 24.4\degree$$

Answer. $24.4\degree$.