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
convex, + 2.25 diopter
concave, - 0.25 diopter
concave, - 0.2 diopter
convex, + 0.15 diopter
As we learnt in
Optical power of a mirror -
- wherein
focal length with sign and is in meters unit of power = diopter
This person wants to increase the farther distance from 400 cm to . Hence he must use a lense who will form image of an object which is place at infinity to 400 cm.
Hence focal length of the lens = 400 cm.
It must be concave
P = =
Option 1)
convex, + 2.25 diopter
This solution is incorrect.
Option 2)
concave, - 0.25 diopter
This solution is correct.
Option 3)
concave, - 0.2 diopter
This solution is incorrect.
Option 4)
convex, + 0.15 diopter
This solution is incorrect.