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Sha went to a doctor and said that he co...

Sha went to a doctor and said that he could not see distant objects clearly. Doctor tested and prescribed a lens of power - 0.75 D.
a. what is the eye defect of sha ?
b. Why did the doctor prescribe a lens - 0.75 D ?
c. What type of lens is this ?

Text Solution

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a. Short sight
b. Power of lens = - 0.75 d
`therefore` Focal length , f = `(-1)/(P) = (-1)/(0.75) = (-100)/(75) = (-4)/(3) ` m
A short sighted person can see only nearby object clearly. By using a concave lens of power - 0.75 D, the image is made to fall on the retina.
c. the concave lens
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