Question

A convex lens of focal length 30 cm produces a real image 3 times magnified .Find the object distance

Answer 1

Given:f = 20 cm

m = -3 = v/u

v = -3u

Lens formula: 1/v - 1/u = 1/f

                         1/(-3u) - 1/u = 1/20

        - 4/(3u) = 1/20

            3u = - 4 x 20

               u = -80/3 = - 26.6 cm

The object is at a distance of 26.6 cm to the left from the optic centre of the lens.