Question

If an object is placed 23 cm from a converging lens, the image formed is slightly smaller than the object. If the object is placed 21 cm from the lens, the image formed is slightly larger than the object. The approximate focal length of the lens is:; (a) 11 cm (b) 10 cm; (c) 18 cm (d) 20 cm

Answer 1

Answer:

Focal length of the lens is 11cm.

Explanation:

Since the object lies at a point beyond 2f so, the image formed will be a little smaller or diminished and when the object is present in between f and 2f the image will be a little bigger.

So, we can conclude that 21cm and 23cm are the points in between which lies the 2f so, 22cm lies between the 21 and 23cm. Hence, the focal length of 2f will be equal to 22cm.

Therefore, on solving we will get that 2f = 22 cm.

So, f = 11 cm .