Nooper needs a lens of power `- 4.5 D` for correction of her vision.
(a) What kind of defect in vision is she suffering from ?
(b) What is the focal length and nature of corrective lens ?
(c) Draw ray diagrams showing the defected eye and correction for the defect.
(d) What are the causes of this defect ?

Explanation

(a) The kind of defect in vision Nooper is suffering from is Myopia or short sighedness, i.e., she cannot see the distant objects properly.
(b) `f = (100)/(P) = (100)/(-4.5) = -22.2 cm`
The corrective lens is concave lens.
( c)
(d) Two possible causes of this defect are :
(i) increase in the length of eye ball, as if distance of ratina from the eye lens has increased.
(ii) decrease in focal length of eye lens, when eye is fully relaxed. This is as if ciliary muscles holding the eye lens do not relax fully and have some tension.
.