A person with defective vision is unable to s | vedclass

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Question

(A) This person suffers from hypermetropia (farsightedness). For the corrective lens, the object distance $u = -30 \ cm$ and the image must be formed

Vedclass · Accepted Answer

Convex lens, $37.5 \ cm$, $+2.67 \ D$

Vedclass · Answer

(A) This person suffers from hypermetropia (farsightedness). For the corrective lens, the object distance $u = -30 \ cm$ and the image must be formed at the person's near point $v = -150 \ cm$. Using the lens formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$. $\frac{1}{f} = \frac{1}{-150} - \frac{1}{-30} = \frac{-1 + 5}{150} = \frac{4}{150}$. $f = \frac{150}{4} = +37.5 \ cm = +0.375 \ m$. The positive sign indicates a convex lens. Power $P = \frac{1}{f(	ext{in } m)} = \frac{1}{0.375} = +2.67 \ D$.

$A$ person with defective vision is unable to see objects nearer than $1.5 \ m$. He wants to read books at a distance of $30 \ cm$. Find the nature, focal length, and power of the lens he needs in his spectacles.

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