Q. The refractive index of the material of a prism is $\sqrt{2}$ and the angle of the prism is 30°. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is
A) 30°
B) 45°
C) 60°
D) zero
Explanation
[Solution] To retrace, the ray must hit the mirror normally, so r = A = 30°; $\sin i = \sqrt{2}\sin 30^\circ = 1/\sqrt{2}$, i = 45°. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.