Question

A source of light lies on the angle bisector of two plane mirrors inclined at an angle $\theta$. The values of $\theta$, so that the light reflected from one mirror does not reach the other mirror will be

• A. $\theta \ge {120}^0$
• B. $\theta \ge {90}^0$
• C. $\theta \le {120}^0$
• D. $\theta <{30}^0$

Answer 1

The correct option is A $\theta \ge {120}^0$

$I_1$ \& $I_2$ are 2 images of object 0 in mirrors $M_1$ a $M_2$ respectively for the condition $\to$ light reflected from ane mirrny should not reach other mirror $-$

maximum images should be 2

$\ast$ number of images (n) $\underset{–}{L}2$ for

2. plane mirror system indined at angle Q formula for number of images $\Rightarrow$

$\begin{array}{c}\Rightarrow \frac{{560}^{\circ }}{Q}\cdot -1\le n(\text{here}n=2)\\ \Rightarrow \frac{{360}^{\circ }}{Q}⩽2+1\\ \Rightarrow {120}^{\circ }\le Q\end{array}$

$\therefore$ option ' $A$ ' is correct.