A person can see clearly object only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use will be
convex, +0.15 diopter
convex, +2.25 diopter
concave, –0.25 diopter
concave, –0.2 diopter
Explanation:
$\dfrac{1}{v} – \dfrac{1}{u} = \dfrac{1}{f}$
$\dfrac{1}{–4m} – \dfrac{1}{\infty} = \dfrac{1}{f}$
f = – 4m
power = $\dfrac{1}{f} = \dfrac{1}{–4}$ = – 0.25D