A man cannot see clearly the objects beyond a | vedclass

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(D) The man is suffering from myopia (nearsightedness),as he cannot see objects beyond $20 \, cm$. To correct this defect,the lens must form a virtual

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$20 \, cm$ concave

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(D) The man is suffering from myopia (nearsightedness),as he cannot see objects beyond $20 \, cm$. To correct this defect,the lens must form a virtual image of an object placed at infinity $(u = \infty)$ at the man's far point $(v = -20 \, cm)$. Using the lens formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$. Substituting the values: $\frac{1}{f} = \frac{1}{-20} - \frac{1}{\infty}$. Since $\frac{1}{\infty} = 0$,we get $\frac{1}{f} = -\frac{1}{20}$. Therefore,$f = -20 \, cm$. $A$ negative focal length indicates a concave lens. Thus,a concave lens of focal length $20 \, cm$ is required.

$A$ man cannot see clearly the objects beyond a distance of $20 \, cm$ from his eyes. To see distant objects clearly,he must use which kind of lenses and of what focal length?

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