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  • A person 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 of the corrective lens? (c) What is the nature of the corrective lens?

A person 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 of the corrective lens?
(c) What is the nature of the corrective lens?

Answers (1)

Ans.
(a) Power of lens is given as negative, so she is suffering from myopia.
(b) Power, P = -4.5 D, focal length, f =?
P = 1/f
f = 1/P
f = 1/-4.5 = -0.222m = -22.2cm
(c) If focal length is positive, then lens to be used is convex lens.
If focal length is negative, then lens to be used is concave lens.
The nature of the corrective lens required here is concave.

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