How many times is a ray of light reflected by two plane mirrors placed parallel and facing each other?

Step 1: Formula for image formation at an angle

We know that the number of images formed by two mirrors inclined towards each other at an angle $\theta$ is given by

$n=\frac{360}{\theta }-1$

In the question, the mirrors are parallel to each other, therefore they are placed at an angle $0°$

Hence $\theta =0°$

Step 2: Calculate the number of images

Therefore, the number of images formed by these two mirrors,

$n=\frac{360}{0}-1$

$=\infty -1$

$=\infty$

Hence, the number of images formed by two parallel mirrors are $\infty$.