Question

Which lens is more convergent one with focal lenth 20 cm or one with focla length 40cm?

Answer 1

Converging power depends on the thickness of the lens.

The thickness is directly proportional to the focal length.

If focal length is more, thickness will will be more.

Hence 40 cm lens will be more thick.

Thus it will have more converging power .

It is because the light has to travel through a relatively more distance and then refract.