Calculate the distance at which an object should be placed in front of a convex lens of focal length 10 cm to obtain a virtual image of double its size.

Explanation

Here, `u=?, f=10 cm, m= +2`, as image is virtual.
As `m = v/u=2, v=2u`
As `(1)/(v) - 1/u = (1)/(f), (1)/(2u) - 1/u = 1/10`
or `- (1)/(2u) = 1/10`, `u = -5 cm`
Therefore, object should be placed at a distance of 5 cm from the lens.