Three plane mirrors are placed as shown in the figure. A light ray striking the first mirror at an angle of incidence ${60}^{\circ }$, after reflections at all the three mirrors, becomes opposite to the initial direction. Find the value of $\theta$.



Take angle of incidence to be equal at all the mirrors.

Q.

Two mirrors are kept at an angle ${60}^{\circ }$ between them as shown in the fig. A ray of light strikes the first mirror and after reflection strikes the second mirror. If the final reflected ray goes parallel to the first mirror, calculate the angle of incidence.

Q. Two plane mirrors are arranged as shown in the figure. A ray has been incident on one of the mirrors at an angle of ${40}^{\circ }$. The deviations produced in the incident ray after three successive reflections will be

Q. 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 $i$.

Q.

A ray of light strikes a plane mirror PQ at an angle of incidence of ${30}^{\circ }$, is reflected from the plane mirror and then strikes a second plane mirror QR placed at right angles to the first mirror. The angle of reflection at the second mirror is : (a) ${30}^{\circ }$ (b) ${45}^{\circ }$ (c) ${60}^{\circ }$ (d) ${90}^{\circ }$ Draw a ray-diagram to illustrate your answer.

Q. Find angle $\theta$ for which a light ray incident at angle ${60}^{\circ }$ on the horizontal mirror becomes vertical after two successive reflections at the shown plane mirrors. Draw ray diagram forth event. ($\theta$ is angle between plane mirrors)