The near point of a hypermetropic person is `50 cm` from the eye. What is the power of the lens required to enable him to read clearly a book held at `25 cm` from the eye ?

Explanation

Here, `u = -25 cm, v = -50 cm. f = ?`
From `(1)/(f)=(1)/(v)-(1)/(u)` , `(1)/(f)=(1)/(-50)+(1)/(25)=(1)/(50)` , `f = 50 cm` or `P = (100)/(f) = (100)/(50) = 2 D`
Positive sign of `f or P` indicates that the correcting lens must be convex.