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 ?

Explanation

The remedial lens should make the objects at infinity appear at the far point.
For object at infinity, `u = - oo`.
Far-point distance of the defected eye, `v = -80 cm`.
By lens formula,
`(1)/(f) = (1)/(v) - (1)/(u) = (1)/(-80) - (1)/(- oo) = -(1)/(80) + 0 = -(1)/(80)`
or f = - 80 cm.
Power `P = (100)/(f("in cm")) = (100)/(-80) = -1.25 D`.
Negative sign shows that the remedial lens is a concave lens.