(a) A student cannot see clearly a chart hanging on a wall placed at a distance of 3m from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes.
(b) Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.
(c) What do you mean by the 'Power of Accommodation' of human eye?

Explanation

(a) The students is suffering from Myopia. It is the defect of the eye vision due to which a person can see the near objects clearly, but he cannot see the far objects clearly.
Causes of myopia. Myopia is caused
- due to the elongation of the eye ball.
- due to decrease in the focal length of the eye lens. The eye lens becomes more convergent.
Myopia can be corrected by using a concave lens of suitable focal length in the spectacles of such a person.

(c) Eye lens can change its focal length according to the distance of the object from the eye, with the help of its ciliary muscles. This phenomenon is known as 'Power of Accomodation' of the eye.