Question

If incident ray is kept fixed but mirror turns through an angle '$\theta$' clockwise, by what angle the reflected ray will turn through?

• A. $\theta$ clockwsie
  
• B. $\theta$ anti-clockwsie
• C. $2\theta$ clockwsie
• D. $2\theta$ anti-clockwsie

Answer 1

The correct option is C $2\theta$ clockwsie


Now the mirror turns by $\theta$ clockwise.


Here ${}^{\prime }{R}^{\prime }$ is the new reflected ray.
From the geometry of diagram we can write :
(Writing the sum of angles between $I$ and $R^{\prime }$ with respect to $R$ and $N^{\prime }$)

$\Rightarrow \alpha +\alpha +\delta =\alpha +\theta +(\alpha +\theta )$
$\therefore \delta =2\theta$, Clockwise