A child while playing with his father's spectacles, burnt a hole in a piece of tissue paper by focussing the image of the sun on the paper.
(a) Name the defect of vision his father is suffering from.
(b) List two causes of the defect.
( c) Draw a ray diagram to show this defect may be corrected using a suitable lens.

Explanation

(a) As a hole is burnt in the tissue paper paper by focussing the image of the sun on the tissue paper, therefore, the spectacle must carry a convex lens.
The defect of vision his father is suffering from is Hypermetropia or Long sightedness.
(b) Two causes of this defect are
(i) Decrease in length of the eye ball.
(ii) Increase in focal length of eye lens, when the eye is fully relaxed.
( c) The ray diagram `2.6` shows how this defect is corrected.
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