Question

A person needs a lens of power -5.5 diopters for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 diopters. What is the focal length of the lens required for correcting (i) distant vision (ii) near vision?

Answer 1

(i) Correcting distant vision

$f=\frac{1}{P}=1/(-5.5)=-0.18m$

(ii) Correcting near vision

$f=\frac{1}{P}=\frac{1}{1.5}=0.67m$