Question

In the given figure, two mirrors P and Q are situated at an angle of ${60}^o$ with each other and a ray of light is incident on mirror P at an angle of ${55}^o$. What is the value of angle A if the ray again reflected by the mirror Q?

• A. ${35}^o$
• B. ${55}^o$
• C. ${50}^o$
• D. ${70}^o$

Answer 1

Answer: (C)

${50}^o$

A ray of light incident on mirror P
at an angle = ${55}^o$
$\therefore \angle i=90-{55}^o={35}^o$
$\therefore \angle r=\angle i={35}^o$
Hence $\angle B={180}^o-({55}^o+{35}^o+{35}^o)$
$={180}^o-{125}^o={55}^o$
$\therefore \angle C={180}^o-({60}^o+{55}^o)={180}^o-{115}^o$
$={65}^o$
= $\therefore \angle A=2[{90}^o-{65}^o]=2\left[{25}^o\right]={50}^o$