Question

A person cannot see distinctly objects kept beyond 2m. This defect can be corrected by using a lens of which power?

Answer 1

Hint: The near point is the minimum distance up to which a person can see while the far point is the maximum distance up to which a person can see properly. When any defects arise in these points then it may lead to unclear vision.

Complete answer:
When the person cannot see distinctly objects kept beyond 2m, then he is suffering from myopia. In this condition, the person cannot see the objects that are placed far away but can clearly see the objects that are nearly placed, and the condition is termed as nearsightedness. This defect can be corrected by using the concave lens of the power -0.5 D.
The nearsightedness condition arises when the lens of the eye is unable to converge the rays because the rays come from a very short distance and thus it becomes difficult to diverge those rays more than the far rays.

Additional information
The condition opposite to myopia is hypermetropia where the person is suffering from farsightedness.
In this condition, the lens of the eye is unable to diverge because the rays come from a very long distance, and the retina of the eye is unable to focus on them. This results in the eye using more powers to bend the rays and causes an eye defect.
To correct this defect the person must use convex lenses.
The power of the lens is measured in the SI unit Dioptre.

Note:
To understand the concept of the eye defect better the students must see the image formation through the position of the object and the lens with the help of the diagrams. These eye defects mostly occur in the person above the age of 40 but sometimes it may occur in the children as well.