A person is suffering from a myopic defect. H | vedclass

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Question

(A) For a myopic eye,a concave lens is used to correct the vision.Given:Object distance $u = -60 \,cm$ (the distance at which the person wants to see)

Vedclass · Accepted Answer

Concave lens of $20 \,cm$ focal length

Vedclass · Answer

(A) For a myopic eye,a concave lens is used to correct the vision.Given:Object distance $u = -60 \,cm$ (the distance at which the person wants to see).Image distance $v = -15 \,cm$ (the far point of the myopic eye).Using the lens formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$.Substituting the values: $\frac{1}{f} = \frac{1}{-15} - \frac{1}{-60}$.$\frac{1}{f} = -\frac{1}{15} + \frac{1}{60} = \frac{-4 + 1}{60} = -\frac{3}{60} = -\frac{1}{20}$.Therefore,$f = -20 \,cm$.The negative sign indicates a concave lens of focal length $20 \,cm$.

$(I)$ Presbyopia	$(A)$ Sphero-cylindrical lens
$(II)$ Hypermetropia	$(B)$ Convex lens of proper power may be used close to the eye
$(III)$ Astigmatism	$(C)$ Concave lens of suitable focal length
$(IV)$ Myopia	$(D)$ Bifocal lens of suitable focal length

$A$ person is suffering from a myopic defect. He is able to see clear objects placed at $15 \,cm$. What type and of what focal length of lens should he use to see clearly the objects placed $60 \,cm$ away?

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