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

Answer

The focal length of the lens is -30 cm and the lens is diverging in nature i.e., concave.

Explanation

Given: Object distance (u)=-60 cm,
image distance (v)=-20 cm
To find: Focal length (f), type of lens
Formula: `(1)/(f)=(1)/(v)-(1)/(u)`
Calculation: From formula, `(1)/(f)=(1)/(-20)-(1)/(-60)=(-3-(-2))/(30)`
`therefore" "(1)/(f)=(-1)/(30)`
`therefore" "f=-30 cm`
Since, the focal length is negative, the lens is diverging in nature i.e., concave lens