Find the position of an object, which when placed in front of a concave mirror of radius of curvature 40 cm produces a virtual image, which is twice the size of the object.

Explanation

Here, R =-40 cm, m = + 2(+ sign for virtual image)
u=?
From `m= -v/u=2: v = -2u`
As `(1)/(v) + 1/u =(1)/(f) =2/R :. 1/-2u + 1/u = 2/-40, (1)/(2u) = -1/20, u = -10cm`. The object must be placed at 10 cm in front of the mirror.