A ray of light is incident at an angle $i$ on one surface of a prism of small angle $A$. It emerges

Question

A ray of light is incident at an angle $i$ on one surface of a prism of small angle $A$. It emerges normally from the opposite surface. If the refractive index of the material of the prism is $\mu$, the angle of incidence $i$ is nearly equal to

Professor PC Thomas Classes · Answer

Since the ray emerges normally, the angle of refraction at the second surface is zero, making the first angle of refraction $r_1=A$; thus, by Snell's Law and the small-angle approximation ( $\sin 	heta \approx 	heta)$, we get $i \approx \mu A$.