Q20 of 216 Page 461

A person is unable to see distinctly the words printed on a newspaper. Name the defect of vision he is suffering from. Draw ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.

It is given that a person is unable to see distinctly the words printed on a newspaper. This means person is not able to see the nearby objects clearly. The defect of vision the person is suffering from is hypermetropia.


i. This defect is also called as far-sightedness.


ii. A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.


iii. This is because the light rays from a close by object are focussed at a point behind the retina.



The possible causes of hypermetropia are:


i. The focal length of the eye lens is too long.


ii. The eyeball has become too small.


This defect can be corrected by using a convex lens of appropriate power. This is shown in the figure below:



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