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, `+2.25` diopter
B. concave, `-0.25` diopter
C. concave, `-0.2` diopter
D. convex, `+0.15` diopter

Answer

B

Explanation

Here, `u=400cm=4m,v=oo,f=?`
Using lens formula `(1)/(v)-(1)/(u)=(1)/(f)`
or `(1)/(oo)-(1)/(4)=(1)/(f)"or"f=-4m`
Lens should be concave.
Power of lens `=(1)/(f)=(1)/(-4)=-0.25D`