CBSE Class 10 Science 2018 · Paper 31(B) · Question 12
A person needs a lenses of power D for the correction of his vision.
- (a)Name the defect of vision the person is suffering from. Write two causes of this defect.
- (b)What is the nature and focal length of the corrective lenses ?
Answer
Hypermetropia, caused by a long eye-lens focal length or a small eyeball; the lens is convex, cm.
(a) The power is positive, so the corrective lens is converging: the person suffers from hypermetropia (far-sightedness), that is, can see distant objects clearly but not nearby objects.
Two causes: (i) the focal length of the eye lens is too long; (ii) the eyeball has become too small.
(b) The corrective lens is convex (converging), with focal length .
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