Question

What is the focal length of a convex lens if the minimum distance between an object and its real image formed by it is 42 cm?​

Answer 1

Answer:

Let the distance between the object and its real image formed by convex lens be d1 .

Let the distance of the object from lens be x,so,the image distance from the lens is (d-x).

Then, x= 2d± d 2 −4fd

For real values of x,

d 2 ≥4fd

that is ,d≥4f

The minimum distance between an object and its real image in a convex lens is 4f.