Question

There are two plane mirrors placed at some angle $\theta$ with each other. A ray incident on the first mirror travels parallel to the second mirror after reflection and then after reflection it travels parallel to the first mirror. Find the angle $\theta$ between the mirrors.

• A. $90^{\circ }$
• B. $60^{\circ }$
• C. $120^{\circ }$
• D. $30^{\circ }$

Answer 1

Answer: (B)

$\delta =90+\alpha -\theta$
$90+\alpha -\theta =\theta$ and $90-\alpha =\theta$
$180-\theta =2\theta$
$\theta =60^{\circ }$