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

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

Answer 1

Answer: (B)

concave, - 0.25 diopter

Answer 2

$\frac{1}{v} - \frac{1}{u}=P$

$\frac{1}{-4 m} - \frac{1}{\infty} =P$
$P = - 0.25\ D$
And lens is concave.

So, the correct option is (B): concave, - 0.25 diopter.