The power P of a lens of focal length f is given by the relation, P=1f
(i) Power of the lens used for correcting distant vision =−5.5D
Focal length of the required lens, f=1P=1−5.5=−0.181m
The focal length of the lens for correcting distant vision is −0.181 m.
(ii) Power of the lens used for correcting near vision =+1.5D.
Focal length of the required lens, f=1P
f=11.5=+0.667m
The focal length of the lens for correcting near vision is 0.667 m.