Question

The image obtained with a convex lens is erect and its length is `4` times the length of the object. If the focal length of lens is `20 cm`, calculate the object and image distances.

Answer 1

Here, `f = 20cm, m = +4`, for correct image.
From `m = (f)/(u + f)`
`4 = (20)/(u + 20) , u = - 15cm`
From `m = (f - v)/(f)`
`4 = (20 - v)/(20) , v = - 60 cm`