Chapter 30, Problem 14A

To determine

To distinguish: Far sighted and near sighted vision.

Explanation of Solution

Introduction:

Human eyes is the most sensitive part of our body and is most vital organs also as it enables to see the colourful world. However it is unable to adjust its accommodation, it suffers from some defects too namely: farsightedness, near sightedness and astigmatism.

A normal eye can clearly see objects placed at far point from eye (at infinity) and also at near point of eye (25 cm). But growing age and some other factors make this power of accommodation to gradually decrease and the defects in eye arise.

Far sighted vision also called farsightedness or hypermetropia is a defect in which the person can clearly see far objects but is unable to see nearby objects. In such defect, the image is formed behind the retina and it is corrected by using convex lens. It is caused because of large focal length of eye lens or the eye ball is too short.

Near sighted vision also called near-sightedness or myopia is a defect in which the person can clearly see nearby objects but is unable to see far objects. In such defect, the image is formed in front of retina and it is corrected by using concave lens. It is caused because of the focal length of eye lens is too small to converge the image at retina or the eye ball is too long.

Conclusion:

Hence, a person with far sighted vision cannot see nearby objects clearly while a person with near sighted vision cannot see far objects clearly.