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 ?

Explanation

`P = (1)/(f)`.
For obtaining more convergent light, power of lens must be larger. Therefore, its focal length must be smaller, Therefore, the lens of `f = 20 cm` will provide more convergent light.