A ray of light travelling in the direction `1/2 (hati+sqrt(3)hatj)` is incident on a plane mirror. After reflectiion, it travels along the direction `1/2(hati -sqrt(3)hatj)`. The angle of incidence is

Options

A. `30^(@)`
B. `45^(@)`
C. `60^(@)`
D. `75^(@)`

Answer

a.

Explanation

Let anglel between the directions of incident ray and reflected ray be `theta`
`costheta=(1)/(2)(hat(i)+sqrt(3)hat(j))*(1)/(2)(hat(i)-sqrt(3)hat(j))`
`=-(1)/(2)`
`theta=120^(@)`