Question

Q.A man who wears glasses of power +3D must hold a book at least 25 cm. away to see the print clearly. How far away would

the newspaper have to be if he took off the glasses and still wanted clear vision?

18.

Answer 1

In absence of glasses, he should hold the newspaper at a distance of -1 m away from his eyes for clear vision

EXPLANATION:

Given here u = -0.25

And $\mathrm{f}=\frac{1}{p}$

which is equal to $\left(\frac{1}{3}\right) \mathrm{m}$

From the lens formula

$\mathrm{P}=\frac{1}{f}$

$=\frac{1}{v}-\frac{1}{u}$

We have

$3=\frac{1}{v}-\frac{1}{-0.25}$

Hence, $\frac{1}{v}=3-4$

Therefore v = -1 m

Hence, the lens shifts the object from 25 cm to 1 m for clear vision, that is, the man’s near point is 1 m.  

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