Question

An object is placed 50 cm from a lens produces a virtual image at a distance of 10 cm in front of the lens. Draw a diagram to show the formation of image and calculate the focal length of the lens.

Answer 1

Distance of object from the mirror $u=-50$ cm

Distance of image from the mirror $v=-10$ cm

For lens, we know

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

$\frac{1}{f}=\frac{1}{-10}-\frac{1}{-50}$

$f=-12.5cm$

It is a concave lens.