Question

A convex lens has focal length 20 cm. Calculate at what distance from the lens should the object be placed so that it forms an image at 40 cm on the other side of the lens. State the nature of the image formed.

Answer 1

$f=20cm$

and $v=40cm$

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

$⟹\frac{1}{40}-\frac{1}{u}=\frac{1}{20}$

$⟹\frac{1}{u}=\frac{-1}{40}$

$⟹u=-40cm$

magnification $m=\frac{v}{u}=\frac{40}{-40}=-1$

Hence, the image formed is real , inverted and of same size as that of the object.