Question

Noopur need a lens of power _4.5 for correctingof her vision . a ) what kind of defect in vision is she suffering from ? b) what is the focal length and nature of the corrective lens. c) draw ray diagram showing the. a) defect of eye and correction for this defect . d ) what are the causes of this defect?

Answer 1

It is given that the power of the lens 'P' = -4.5.

a) She has Myopia, since the power of the lens is negative.

b) Focal length: $f=\frac{1}{P}=\frac{-1}{4.5}=0.22\:cm$

The lens is concave.

c) See the image below for (i) the defected eye and (ii) correction of the defect.

d)Cause of the defect is eye elongation.

Answer 2

THE AMSWERS ARE AS FOLLOWS;

Answer (a)

• Since the power of the lens is in negative. Noopur is suffering from Myopia.
• It is also knwwn as near-sightedness which causes distant objects to appear blurry.
• In myopic eyes the light focuses in front of the retina and not on it.
• Types - Simple, Degenerative, Pseudomyopia, Nocturnal myopia, Instrumental and induced.

Answer (b)

• It is known that power of a lens is the reciprocal of its focal length.
• Therefore, Focal length = 1/Power of lens.
• Focal length = 1/-4.5 = - 0.22 m.
• The nature of the lens is concave.

Answer (c) Please refer to the picture for the diagram.

Answer (d)

• The causes of myopia are genetic, environmental and conditions such as diabetes, uveitis and systemic lupus erythematosus.

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