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

The power of a lens is related to its focal length as
`P=(1)/("f (in m)")`
For greater convergent light, lens of higher power and smaller focal length is needed i.e., the lens of focal length 20 cm is needed for the same.