Answer to Question #295145 in Optics for Somti

Question

A student is only able to read the lecture notebook when it is held at 65.00cm from his eyes. What focal length and power must the lenses of his reading glasses have to bring his near point to the normal value

Answer 1

Answer

Let focal length is f.

u=-65cm

v=-25cm

Using formula

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

Putting all values

$\frac{1}{-25}+\frac{1}{65}=\frac{1}{f}$

$\frac{65-25}{65\times25}=\frac{1}{f}$

$\frac{1}{f}=0.025\\=f=40.63cm$

So power of lenses

$P=\frac{1}{f}=2.46$