Question

A farsighted boy has a near point at 2.3 m and requires eyeglasses to correct his vision. Corrective lenses are available in increments in power of 0.25 diopters. The eyeglasses should have lenses of the lowest power for which the near point is no further than 25 cm. The correct choice of lens power for eyeglasses, in diopters, is:

Answer 1

Answer:

P = 3.5 D

Explanation:

As we know that convex lens is to be used to make the near point of eye to be correct

So we will have

$\frac{1}{d_i} + \frac{1}{d_o} = \frac{1}{f}$

here we have

$d_i = 2.3 m = 230 cm$

$d_o = 25 cm$

now plug in all values into the formula

$-\frac{1}{230} + \frac{1}{25} = \frac{1}{f}$

$f = 28 cm$

now for power of lens

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

$P = \frac{1}{0.28} = 3.5 D$

so the power in dioptre is

P = 3.5 D