Question

A person can see clearly objects 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
(1) convex, +2.25 diopter
(2) concave, -0.25 diopter
(3) concave, -0.2 diopter
(4) convex, +0.15 diopter

Answer 1

Explanation:

he had myopia

with far point 400cm

1/f = 1/v - 1/u

1/f = 1/-4m - 1 /infinity

1/f = 1/-4m - 0

f = -4m

power of lens = 1/f = 1/-4m

- 0.25D