Question

A person wears eye glasses of focal length f = -70 cm. What is the far point of the person? [2 MARKS]

Answer 1

Explanation: 2 Marks

Given:

$f=-70cm$, f is negative, it is a case of Myopia.

let $u=-\infty$ because we want the eye to be able to see objects kept at infinity which is the far point of a normal eye.

We know, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

By substituting, $\frac{1}{v}-\frac{1}{-\infty }=\frac{1}{-70cm}$

$\frac{1}{v}-0=\frac{1}{-70cm}$

$\frac{1}{v}=\frac{1}{-70}$

$v=-70cm$

Therefore the far point of the person's eye is at 70cm in front of his eyelens(indicated by -ve sign)