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Question

(A) The person is suffering from myopia (nearsightedness) because he cannot see distant objects clearly.For a myopic eye, the far point is limited to

Vedclass · Accepted Answer

$-2.5 \, D$

Vedclass · Answer

(A) The person is suffering from myopia (nearsightedness) because he cannot see distant objects clearly.For a myopic eye, the far point is limited to $40 \, cm$.To correct this defect, we need to use a concave lens that forms a virtual image of an object at infinity at the person's far point $(40 \, cm)$.Here, the object distance $u = \infty$ and the image distance $v = -40 \, cm$.Using the lens formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$.$\frac{1}{f} = \frac{1}{-40} - \frac{1}{\infty} = -\frac{1}{40} \, cm^{-1}$.Thus, the focal length $f = -40 \, cm = -0.4 \, m$.The power of the lens $P$ is given by $P = \frac{1}{f(	ext{in } meters)}$.$P = \frac{1}{-0.4} = -2.5 \, D$.

$A$ person cannot see objects clearly placed at a distance of more than $40 \, cm$. He is advised to use a lens of power:

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