Question

A certain far-sighted person cannot see objects closer to the eye than 60cm clearly .Calculate the power of a converging lens to enable a man to see an object at 20cm

Answer 1

Answer:

For the person's range of clear vision to be equal to that of average man, the image of an object kept at the least distance of distinct vision, that is, 0.25 m, must be at the least distance of distinct vision of far-sighted man by the correcting lens.

Thus using

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

$\frac{1}{ - 1} = \frac{1}{ - 0.25} = \frac{1}{f}$

Thus , power of the lens is ,

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