A person can see clearly only up to a distanc | vedclass

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(C) The person is suffering from myopia (nearsightedness) as he cannot see objects beyond $25 \, cm$. To correct this,a concave lens is required.Given

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Concave,$-2.0 \, D$

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(C) The person is suffering from myopia (nearsightedness) as he cannot see objects beyond $25 \, cm$. To correct this,a concave lens is required.Given:Object distance $u = -50 \, cm$ (the position where he wants to read).Image distance $v = -25 \, cm$ (his far point,where the virtual image must be formed).Using the lens formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$$\frac{1}{f} = \frac{1}{-25} - \frac{1}{-50} = -\frac{2}{50} + \frac{1}{50} = -\frac{1}{50}$So,$f = -50 \, cm = -0.5 \, m$.The power of the lens is $P = \frac{1}{f(m)} = \frac{1}{-0.5} = -2.0 \, D$.Thus,a concave lens of power $-2.0 \, D$ is required.

$A$ person can see clearly only up to a distance of $25 \, cm$. He wants to read a book placed at a distance of $50 \, cm$. What kind of lens does he require for his spectacles and what must be its power?

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