Question

An object is kept $60$ $cm$ from a lens gives a virtual image $20$ $cm$ in front of lens. What is the focal length of the lens? Is it converging lens or diverging lens?

Answer 1

From lens formula, $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

$=\frac{1}{(-20)}-\frac{1}{(-60)}=-\frac{2}{60}$

$\Rightarrow f=-30cm$

Since the focal length is negative. It is a diverging lens.