Question

Two plane mirrors are inclined to each other at an angle $\theta$. A ray of light is reflected first at one mirror and then at the other. The total deviation of the ray is

• A. ${360}^o-2\theta$
• B. ${240}^o-20$
• C. $20$
• D. ${180}^o-\theta$

Answer 1

The correct option is A ${360}^o-2\theta$

$\angle BAD=x$ $\angle ABD+y$ is two incidence angle

$\Rightarrow \angle OBA=90-y$ $\angle OAB=90-x$

$\Delta OAB;\theta +90-y+90-1=180$

$\Rightarrow x+y=\theta$

Total deviation is $2(90-x)+2(90-y)$

$=360-2(x+y)$

$=360-2\theta$