A far sighted person has his near point 50 cm. Find the power of lens he should use to see at 25 cm clearly.

In order for a person to see the object at 25cm clearly, the lens should make an image of the object at 25cm distance at a distance of 50 cm.Hence,u=−25cm=−0.25mv=−50cm=−0.5mThus, Power=1/f=1/v−1/u=+2D