Question

A converging lens forms a five fold magnified image of an object. The screen is moved towards the object by a distance d = 0.5 m, and the lens is shifted so that the image has the same size as the object. Find the lens power and the initial distance between the object and the screen.

Answer 1

In the first case image us five tunes magnified. Hence, |v| = 5|u|, In the second case image and object are of equal size. Hence, |v| = |u|. From the two figures,

Using the lens formula for both the cases,

Solving these three equations, we get

x = 0.1875 m and f = 0.15625 m

Therefore, initial distance between the object and the screen = 6x = 1.125 m

Power of the lens,