A transparent solid rod in the shape of a cuboid has refractive index $\sqrt 3$ The cuboid is kept in air, light enters midpoint (0) of one end of rod as shown . What should be the incident angle $\theta$ Such that when the refracted ray grazes along the wall.

Question

 

$(a)\;\sin ^{-1} \sqrt 3 \\ (b)\;\sin ^{-1} \sqrt 2 \\ (c)\;\sin ^{-1} \frac{\sqrt 3}{2} \\ (d)\;\sin ^{-1} \frac{1}{\sqrt 3}$