Question

Reading glasses of what power are needed for a person whose near point is 125 cm , so that he can read a computer screen at 54 cm ? Assume a lens-eye distance of 2.0 cm .

Answer 1

Answer:

1.11 dioptre

Explanation:

$d_{i}$ = Distance of the image = - (125 - 2) = - 123 cm

$d_{o}$ = Distance of the object = 54 - 2 = 52 cm

$f$ = Focal length of the lens

Using the equation

$\frac{1}{d_{o}} + \frac{1}{d_{i}} = \frac{1}{f}$

$\frac{1}{52} + \frac{- 1}{123} = \frac{1}{f}$

$f = 90.1$ cm

Power of the lens is given as

$P = \frac{100}{f}$

$P = \frac{100}{90.1}$

$P = 1.11$ Dioptre