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) Since the power of the spectacle has a plus sign $(+)$, it implies that it is a converging lens or convex lens.


(b) Given:

Power of the lens, $P$ = $+$0.5 D


To find: Focal length of the lens, $f$.


Solution:

Power of a lens is given by:

$P=\frac {1}{f}$

Substituting the given values we get-

$0.5=\frac {1}{f}$

$f=\frac {1}{0.5}$

$f=\frac {10}{5}$

$f=+2m$

Thus, the focal length of the lens $f$ is 2 m. 

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Updated on: 10-Oct-2022

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