Question

under what condition in an arrangement of two plane mirrors incident ray and reflected I always parallel to each other whatever may be the angle of incidence so with the help of a diagram

Answer 1

Let there are two mirrors inclined at an angle theta and a ray light is incident on one of the mirror with angle of incidence as 'i' and the reflected ray is incident on the other mirror at an angle 'r'.

Answer 2

The incident ray and reflected ray will always be parallel to each other when the two plane mirrors will be placed at right angle i.e. 90° to each other.