Question

A person cannot see clearly distance more than 40 cm . How much power of lens he should be advised to use?

Answer 1

HERE IS THE SOLUTION;

◆According to the question;

u= -40 Cm 【 Near Point 】

v = -∞

f=?

◆ Formula Used

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u} \\ \\ \frac{1}{f} = \frac{1}{ - \infty } - \frac{1}{40} \\ \\ \frac{1}{f} = - \frac{1}{40} \\ \\ = > f = - 40 \: cm$

◆ Using Lens Formula;

P= ?

f= -40 Cm

$p = \frac{1}{f} \\ \\ p = \frac{1}{ - 40} \\ \\ p = \frac{100}{ - 40 } \\ \\ p = - 2.5 \: d$

So, the power is -2.5 D.

HOPE IT HELPS