Question

The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

Answer 1

Myopia:-

1. The person is suffering from myopia and hence needs a concave lens to correct the defect.
2. The lens should be such that an object at infinity must form its image at the far point.

Now, the distance of the far point $x=80$ cm

To view distant objects correctly, the focal length of the corrective lens $f=-x=-80$ cm

Power of the lens P (in meters) $=\left(\frac{1}{{\displaystyle \frac{1}{-80}}}\right)=\frac{1}{-.8}=1.25$

The lens is concave of power $=-1.25D$

Therefore, a concave lens of power $-1.25D$ is required by the individual to correct his defect.