Question

A man with deffecrive eyes cannot see distinct objext mote than 60cm what is the power of the lrns used

Answer 1

so it's a case of myopia (nearsightness)

the far point should be at infinite which is now at 60cm = 0.6m

use lens formula

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

from this we can calculate the power of lens used i.e $p= \frac{1}{f}$ in meter

so u = ∞

v= 0.60

by putting the values in the formula we get

$\frac{1}{f}= -\frac{1}{0.6}$   (∵ 1/∞=0)

so power = 1/f= -1.66 D