Question

A person needs a lens of power -4.5 D for correction of her vision (i)what kind of vision she ia suffering from.
(ii) focal length of corrective lensm
(iii)natureof corrective lensm

Answer 1

1.She is suffering from myopia 2.Focal lenght of corrective lens is -0.22... i.e -0.23 3.corrective lens is concave lens

Answer 2

She is suffering from short-sightedness or myopia.

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• Given,

Power of the corrective lens = -4.5D

To find,

The focal length of the corrective lens.

Solution,

We have to calculate the focal length of the given corrective lens,by using the following mathematical formula :

Power of the lens = 1/focal length

P = 1/f

-4.5= 1/f  [By,putting the given values.]

-4.5f = 1

f = 1/-4.5

f = -0.22

Hence,the focal length of the given corrective lens is -0.22 metres or 22 metres.

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• Here,the disease is myopia. So,the corrective lens will be a concave lens.