Question

A person suffering myopia his far distance is 5m what is the focal length of his eyes

Answer 1

Given:

A person suffering myopia his far distance is 5m.

To find:

Focal length of his corrective lens?

Calculation:

Since the person is suffering from myopia, he needs CONACVE LENS, so that the object at infinity forms a virtual object at 5 m.

$\rm \: \dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u}$

$\rm \implies \dfrac{1}{f} = \dfrac{1}{( - 5)} - \dfrac{1}{ ( - \infty)}$

$\rm \implies \dfrac{1}{f} = \dfrac{1}{( - 5)} - 0$

$\rm \implies \dfrac{1}{f} = \dfrac{1}{( - 5)}$

$\rm \implies \: f = - 5 \: m$

Now, power of the lens required:

$\rm \:P = \dfrac{1}{f \: (in \: metres)}$

$\rm \implies \:P = \dfrac{1}{ - 5}$

$\rm \implies \:P = - 0.2 \: D$

So, power of lens required is -0.2 Dioptre.