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?

(A) The power $(P)$ of a lens is defined as the reciprocal of its focal length $(f)$ in meters,expressed as $P = \frac{1}{f(m)}$.
This indicates that power is inversely proportional to the focal length $(P \propto \frac{1}{f})$.
$A$ lens with a shorter focal length has a higher power and thus a greater ability to converge light rays.
Comparing the two lenses,the lens with a focal length of $20\, cm$ has a higher power than the lens with a focal length of $40\, cm$.
Therefore,the lens with a focal length of $20\, cm$ will provide more convergent light.