Question

An object at a distance of 30 cm from a convex lens gets its images at the same distance on the other side. Find the focal length of the lens.​

Answer 1

Given:

Distance of the object = $30$ cm

Distance of the image = $30$ cm

To find:

The focal length of the lens ($f$)

Formula used:

$\frac1f\;=\;\frac1v\;+\;\frac1u$

Where, $f$ is the focal length of the lens

$v$ is the distance of the image

$u$ is the distance of the object

Explanation:

$\frac1f\;=\;\frac1{30}\;+\;\frac1{30}$

$\frac1f\;=\;\frac2{30}\;$

$f\;=\;15\;cm$

Answer:

Therefore, the focal length of the lens is $15$ cm