Give scientific reasons for the following statements:
To rectify the defect of far-sightedness or hypermetropia, convex lens of suitable focal length is used as corrective lens.

Explanation

The eye lens of a person having defect of far-sightedness as hypermetropia, does not become thick as per the requirement and so the rays after being refracted by the eye lens get focussed behind retina. So nearby objects cannot be seen clearly.
If a person having defect of far-sightedness, uses convex lens of suitable focal length, then light rays become slightly convergent. Hence, the image can be formed on retina.
Thus, if the image is formed on retina, then the nearby object may be seen clearly.