Question

At what distance should an object be placed from a convex lens of focal length $18cm$ to obtain an image at $24cm$ if on the other side. What will be the magnification produced in this case?

Answer 1

By using lens formula

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

where v=24cm ,f=18cm

$\frac{1}{24}-\frac{1}{u}=\frac{1}{18}$

from this we get $u=-72cm$

magnification of lens is $m=\frac{v}{u}$

$m=\frac{24}{-72}=-\frac{1}{3}$