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?

Soln:

Power of lens is inversely proportional to the focal length of the lens. Lens with focal length 20 has more power than lens with focal length 40 cm. Lens with higher power should be used to obtain more convergent light.