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(A) The person suffers from myopia (nearsightedness) because they cannot see objects beyond $400\, cm$.To correct this, we need to place a lens such t

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concave, $-0.25$ diopter

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(A) The person suffers from myopia (nearsightedness) because they cannot see objects beyond $400\, cm$.To correct this, we need to place a lens such that an object at infinity $(\infty)$ forms a virtual image at the person's far point $(400\, cm)$.Given: Object distance $u = -\infty$, Image distance $v = -400\, cm = -4\, m$.Using the lens formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$.Substituting the values: $\frac{1}{f} = \frac{1}{-4} - \frac{1}{-\infty} = -0.25\, m^{-1}$.Since the focal length $f$ is negative, the lens must be concave.The power of the lens $P = \frac{1}{f} = -0.25\, D$.

$A$ person can see objects clearly only when they lie between $50\, cm$ and $400\, cm$ from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens the person has to use will be

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