(a) The near point of a hypermetropic person is at `75 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 ?
(b) In what way does the corrective lens help the person above ? Does the lens magnify objects held near the eye ?
( c) The person above prefers to remove his spectacles while looking at the sky. Explain why ?

Explanation

Here, distance of near point, `x' = 75 cm`., distance of book, `d = 25 cm, f = ?`
As `f = (x'd)/(x' - d), f = (75 xx 25)/(75 - 25) = (75 xx 25)/(50) = 37.5 cm`
Thus, `P = (100)/(f) = (100)/(37.5) = 2.66 D`. As `f` is positive, the corrective lens is convex.