Question

How are power and focal length of a lens related? You are provided with two lenses of focal length 20 cm and 40 cm respectively. Which lens will you use to obtain more convergent light?

Answer 1

The power of the lens is the reciprocal of the focal length.

Mathematically, `"Power"  ("P") = 1/("focal length"  ("f"))` 

The high power of the lens indicates less focal length and more converging power. Therefore, the lens of focal length 20 cm is more converging.