Question

A person is unable to see object distinctly placed within 50cm from his eyes:
1) Name the defect.
2) Mention type of lens reqd.

Answer 1

answer : (1) Hypermetropia

(2) convex lens

explanation : we know, Hypermetropia (far-sightedness) is a common eye condition where nearby objects appear blurred, but your vision is clearer when looking at things further away.

here, A person is unable to see object distinctly placed within 50cm from his eyes, so the person is suffering from Hypermetropia.

Hypermetropia is caused due to,

decrease in the length of eyeball

increase in focal length of eye lens.

so, this defect can be corrected using convex lens of appropriate focal length.

Answer 2

Answer:

If a person is able to see objects placed beyond normal sight of vision, but is unable to see objects placed within normal sight of vision, then the defect is known as Hypermetropia.

It is also known as Far-sightedness.

According to the question, the normal sight of vision is 50 cm. Also, the person is not able to see objects placed within 50 cm. This means he is able to see objects placed beyond 50 cm. Therefore it is a case of Hypermetropia.

To correct this defect, a lens called as convex lens is used. This can converge the light rays, and therefore forms the image in the retina of the eye.

Since Normal sight of vision is 50 cm, the power can be calculated as:

⇒ Power = 1 / Focal Length ( in m )

⇒ Power = 1 / 0.5 = 2 D

Therefore the power of lens needed for correcting the above defect is + 2 Diopters.