Question

A light beam is being reflected by using two mirrors, as in a periscope used in submarines. If one of the mirrors rotates by an angle θ, the reflected light will deviate from its original path by the angle(a) 2θ(b) 0°(c) θ(d) 4θ

Answer 1

answer : option (a) 2θ

explanation : Let incident ray made A angle with horizontal plane mirror, so, incident angle = reflected angle = (90 - A) as shown in figure.

now, plane mirror is rotated by angle θ
so, new refracted ray made angle with new normal = (90 - A - θ)
old refracted rays made angle with new normal = (90 - A + θ)

so, angle between them = (90 - A + θ) - (90 - A - θ) = 2θ

hence, option (a) is correct.