Question

A farsighted person cannot see objects placed closer to 50 cm. Find the power of the lens needed to see the objects at 20 cm.

Answer 1

Given :

u = – 20 cm

v = – 50 cm

The lens formula is given by

1/v-1/u=1/f

On putting the values, we get:

1/f=1/-50 -1/-20    

=3/100

⇒f=100/3 cm = 13 m

∴ Power of the lens = 1/f= 3 D

Answer 2

Hey !!

Given data,

u = - 20 cm

v = - 50 cm

Now, By applying lens formula

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

Substuting the values, we get

→ $\frac{1}{f} = \frac{1}{-50} = \frac{-1}{-20}$

→ $\frac{3}{100}$

=> 13 cm

Power of lens

$\frac{1}{f} = 3 D$

GOOD LUCK !!