A ray of light falls on a plane mirror. When the mirror is turned, about an axis at right angle to the plane of the mirror through `20^(@)`, the angle between the incident ray and new reflected ray is `45^(@)`. Find the angle between the incident ray and original reflected ray.

Options

A. `35^ (@)` or `50^ (@)`
B. `25^(@)` or `65^(@)`
C. `45^(@)` or `5^(@)`
D. None of these

Answer

D

Explanation

Let i is the angle between incident ray and original reflected ray, Then initial angle between them will be `180^(@)-2i`. When mirror is rotated by `20^(@)` , then reflected ray will rotate by `40^(@)`
`:. 180^(@) -2i+- 40^(@) =45^(@)`
Solving we get, `
i=47.5^(@) or 87.5^(@)`.