Question

A convex lens has a focal length of 20.0 cm. At what distance from the lens 5 cm tall object be placed so that it forms an image 15 cm from the lens? Also, calculate the size of the image formed.

Answer 1

Just use the formula of lens 1/v-1/u =1/f

Answer 2

f=20cm
I=5cm
v=15cm
$\frac{1}{f } = \frac{1}{v} - \frac{1}{u}$
$\frac{1}{u} = \frac{1}{v} - \frac{1}{f}$

$m = \frac{ - v}{u}$