Question

What is the angle of incidence for an equilateral prism of refractive index $\sqrt{3}$ so that the ray is parallel to the base inside the prism?

• A. ${30}^{\circ }$
• B. ${45}^{\circ }$
• C. ${60}^{\circ }$
• D. Either ${30}^{\circ }$ or ${60}^{\circ }$

Answer 1

The correct option is C ${60}^{\circ }$

From geometry, $r={90}^{\circ }-{60}^{\circ }={30}^{\circ }$

Using Snell's Law,

$\sin i=\mu \sin r=\sqrt{3}\sin {30}^{\circ }=\frac{\sqrt{3}}{2}$

$⟹i={60}^{\circ }$