Question

The angle of a prism is ‘A’. One of its refracting surfaces is
silvered. Light rays falling at an angle of incidence 2A on
the first surface returns back through the same path after
suffering reflection at the silvered surface. The refractive
index m, of the prism is : [2014]
(a) 2 sin A (b) 2 cos A
(c) 1/2 cos A
(d) tan A

Answer 1

Explanation:

As the light retrace he path

sin i / sinr = n

sin (2A) / sin A = n

Sin2Ф =2sinФ cosФ

n = 2cosA