Question

A man is suffering from myopia, cannot see objects beyond $10.0m$ distinctly. What should be the type of corrective lens used to restore proper vision? Find the focal length and power of the lens?

Answer 1

A concave lens of suitable power should be used to restore proper vision.

The far point of a normal eye= $\infty$

The far point of the myopic eye= $10m$

Objject distance, $u=-\infty$

Image distance, $v=-10$

Using lens formula,

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

$\frac{1}{f}=\frac{1}{-10}-\frac{1}{\infty }$

$\frac{1}{f}=\frac{-1}{10}$

focal length, $f=-10m$

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

$P=\frac{1}{-10}=-0.1D$