A converging lens has a focal length 40cm. Calculate its power.
Powerofthelens=100Focallengthofthelens(cm)⇒Poweroflens=10040⇒Poweroflens=+2.5D
Hence the power of the converging lens is +2.5D.
A person has near point of his vision shifted to 50 cm. What lens must be used to see an object placed at 25 cm from the eye? What is the power of the lens?