A concave mirror has a focal length of 20 cm. Find the position or positions of an object for which the image-size is double of the object-size.

Explanation

Converging mirror is concave mirror.
`:. f = - 20cm,m = +-2,u=?`
From `m= v/u = +-2 " " v= +-2u`.
From `(1)/(v) + 1/u =(1)/(f)`
`(1)/(+-2u) +(1)/(u) =(1)/(-20)`
On solving, we get `u = -30cm` and `u = -10cm`