Question

What is the nature and the focal length of the lens that will form virtual image having one quarter the dimensions of an object spaced 40cm from the lens

Answer 1

Focal length is given by;

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

$\frac{1}{10}+\frac{1}{40}=\frac{1}{f}$

solving you find$\frac{1}{8}$

Therefore, the focal length is 8 cm.

The nature of the lens is convex because the power is positive