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 $