Question

How do we calculate the number of images formed by a pair of plane mirrors?

What will be the number of images if not calculated as a fraction?

Calculate the number of images formed if the angle between the mirrors is 1) 50° 2) 72°.

Answer 1

We can find the number of images formed if we know the angle between the plane mirrors.

This is given by the formula:

Number of images = $\frac{360}{\theta }-1$ if $\frac{360}{\theta }$ is even

The number of images = $\frac{360}{\theta }$ if it comes odd and when the object is placed asymmetrically.

The number of images = $\frac{360}{\theta }-1$ when $\frac{360}{\theta }$ is odd and the object is kept symmetrically.

If the number of images = $\frac{360}{\theta }$ is a fraction, then the number of images formed will be equal to its integral part.

1)If the angle is 50°

Number of images = $\frac{360}{50}$ = 7.2

We take 7 as the number of images formed as the image will not be taken as a fraction.

2) If the angle is 72°

Number of images = $\frac{360}{72}$ = 5 (consider object kept asymmetrically)