Question

Light enters a diamond, reflects internally several times, and then refracts back into air. What is the critical angle for diamond, given the speed of light in diamond is 1.24x108 m/s ?

Answer 1

First, calculate the refraction index:

$$n=\frac{c}{v}=\frac{3\cdot10^8}{1.24\cdot10^8}=2.42.$$

the critical angle for air as surrounding medium is

$$\theta_c=\text{arcsin}\frac{1}{n}=\text{arcsin}\frac{1}{2.42}=24.4°.$$