The optician's prescription for a spectacle lens is marked+ 0.5 D. What is the: (a) nature of spectacle lens?
(b) focal length of spectacle lens ?
(a) nature of spectacle lens is Convex lens
(b) Power of a lens = +0.5 D
P = 1/f
f = 1/P = 1/(+0.5) = +2 m
Focal length is 2 m.