Question

Two plane mirrors are inclined to each other at an angle of ${70}^{\circ }$ as shown in figure. A ray of light PO incident at some angle $i$ on the mirror $M_1$ falls on the other mirror $M_2$ after reflection, and also becomes parallel to the plane mirror $M_1$ after another reflection. Find the value of $i$.

Answer 1

As the final reflected ray is parallel to mirror $M_1$ hence, $\theta ={70}^{\circ }\text{(Correcponding angles)}In\Delta ACO{70}^{\circ }+{70}^{\circ }+i=180140+i=180\Rightarrow i=180-140={40}^{\circ }i={40}^{\circ }$