Question

A convex lens of focal length $3cm$ forms a real image at $24cm$ from its optic centre. Calculate the distance of the object from the lens.

Answer 1

Given: Focal length, $f=3cm$

Since image formed is real it will be on opposite side of lens hence

Image distance, $v=24cm$

To find: $Objectdistance,u$

From lens formula,

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$\frac{1}{24}-\frac{1}{u}=\frac{1}{3}$

$\frac{1}{u}=\frac{1}{24}-\frac{1}{3}$

$u=\frac{-24}{7}cm$