Q. The angle of prism is 'A'. One of its refracting surfaces is silvered. Light rays falling at an angle of incidence 2A on the first surface return back through the same path after suffering reflection at the silvered surface. The refractive index μ of the prism is :
A) 2 sin A
B) 2 cos A
C) $\frac{1}{2}\cos A$
D) tan A
Explanation
[Solution] To retrace its path the ray must hit the silvered face normally, so r = A. Then sin 2A = μ sin A ⇒ μ = 2 cos A. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.