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

Explanation

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 vission.
Object distance, u - infinity - `oo`
Image distance, v=-8cm, Focal length=f
According to the lens formula
`1/v-1/u = 1/f`
`- 1/80 - 1/oo = 1/f`
`1/f =- 1/80`
`f =- 80 cm = - 0.8 m`
We know , power , P = 1/f(in meter)
`P = (1)/(-0.8) = - 1.25D`
A concave lens of power -1.25D is required by the person to correct his defect .