Question

The angle of incidence for an equilateral prism of refractive index so that the ray is parallel to the base inside the prism is

• A. ${30}^o$
• B. ${20}^o$
• C. ${60}^o$
• D. ${45}^o$
• E. ${75}^o$

Answer 1

The correct option is C ${60}^o$

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

Using Snell's Law,

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

$⟹i={60}^{\circ }$