Question

Long sightedness is caused by the eyeball being too short. It can be corrected by the use of a:
A. convergent lens
B. plane mirror
C. divergent lens
D. concave mirror

Answer 1

Hint: Long sightedness which is additionally referred to as hypermetropia is caused when the eyeball is too short. To find the solution of the required question we need to find where the image is formed in such eyes, and how it can be corrected.

Complete step-by-step answer:
A person suffering from hypermetropia can see distant objects clearly but cannot see nearby objects distinctly. The near point, or the person, is farther away from the normal near point which is 25 cm. Such a person has to keep a reading material much beyond the 25 cm from the eye to be comfortable for reading. This is because the light rays from a close by object are focussed at a point behind the retina.
This defect arises either because (i) when the focal length of the eye lens is too long, or (ii) the eyeball becomes too small. This defect can be corrected by using a converging or convex lens of appropriate power.

So, the correct answer is “Option A”.

Note: The normal vision of an eye is from 25cm to infinity. But in some situations, the eye is unable to focus the image of the object on the retina, so in such cases the person is said to suffer from eye defects. Defects other than hypermetropia are myopia and presbyopia. Myopia is also known as nearsightedness; it is caused when the eyeballs get elongated or due to excessive curvature of eye lens. Presbyopia is caused when the eye loses its power of accommodation. It occurs in old age due weakening of the ciliary muscles and diminishing flexibility of the eye lens.