Question

a person needs a lens of power -4. D what kind of defect he is suffering from name the corrective lens find its focal length

Answer 1

He is suffering from Myopia .

Answer 2

The person is suffering from myopia because power is negative and Concave lens has negative power and concave lens is used to correct the defect of vision called myopia.

Power = 1/f

-4=1/f

f=1/-4

f= - 0.25m or -25cm

Hence focal length is -25cm or - 0.25m