Question

A far sighted man can see from $50cm$ to infinity. The power of the lens required to enable him to read books is (least distance of clear vision = $25cm$)

• A. +2 D
• B. +0.5 D
• C. +1.5 D
• D. +2.5 D

Answer 1

The correct option is A +2 D

Apply concept of object and image.
If book kept at $25cm$ is seen at $50cm$,
$u=-25cmv=-50cm\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\frac{-1}{50}+\frac{1}{25}=\frac{1}{f}\Rightarrow f=50cm\Rightarrow P=+2D$