Question

The focal length of a concave lens is 20 cm. If an object is placed at a distance of 50 cm in front of this concave lens, where is the image formed? What is the nature of the image?

Answer 1

Focal length $f=-20cm$

Object distance $u=-50cm$

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

Or $\frac{1}{v}-\frac{1}{(-50)}=\frac{1}{-20}$

We get $v=-14.3cm$

Since, v is negative. So image formed is virtual.

Hence, virtual image is formed at a distance of $14.3cm$ in front of the lens.