If a person can't see the object that is placed at a distance less than 50 cm, then what type of defect he is suffering from? Also tell the nature of lens and calculate the power of the lens so that he can clearly see the object that is placed at 25 cm from the eye.

Explanation

Defect from which the person suffering=Long sightedness
Given
value of u=-25cm
Value of v=-50cm
Use the lens formula
(1/v)+(1/u)=1/f
Put the values of u and v in the above given formula
(1/-50)+(1/-25)=1/f
f=50cm =5m
Power of lens=2D
To correct this defect, convex lens with power 2D is required to be used.