A person can see objects clearly only when they lie between `50cm` 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

Options

A. Convex, +0.15 diopter
B. Convex, +2.25 diopte
C. Concave, –0.25 diopter
D. Concave, –0.2 diopter

Answer

C

Explanation

If the object is at infinity, its image is formed at distance 400 cm
`(1)/(v) - (1)/(u) = (1)/(f) rArr (1)/(- 4m) - (1)/(infty) = (1)/(f)`
`rArr f = -4 m rArr " Power " = (1)/(f) = (1)/(-4) = -0.25 `D.