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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 :

The person is suffering from an eye defect called myopia. In this defect, the image is formed in front of the retina. Hence, a concave lens is used to correct this defect of vision.

Object distance, u = infinity = ?

Image distance, v = - 80 cm
Focal length = f

According to the lens formula,

Using \(\frac{1}{f} = \frac{1}{v} – \frac{1}{u} \)

\(\frac{1}{f} = \frac{1}{-80} + \frac{1}{-infinity} \)

\(\frac{1}{f} = - \frac{1}{80} + (-0)\)
f = -80 cm
f = -0.8 m
Power = \(\frac{1}{f} \)
= \(\frac{1}{(-0.8)} \)
= -1.25 D

The nature of lens required to see the distant objects clearly is convex lens is power -1.25 D.

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