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

The person is suffering from an eye defecte called mypia. In this defect the image is formed in front of the retian. Hence , a concave lens is used to correct this defect of vision
Object distance , u= infinity =`oo`
Image distance ,v=-80cm
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 cm
We known,
Power ,`P=(1)/(f("in meteres"))`
`p=(1)/(-0.8)=-1.25D`
A concave lens of power -1.25 D is required by the person to correct his defect.