The power of a lens is + 0.2 D. Calculate its focal length.

Given:

Power of the lens, $P$ = $+$0.2 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-

$0.2=\frac {1}{f}$

$f=-\frac {1}{0.2}$

$f=-\frac {10}{2}$

$f=-5m$

Thus, the focal length of the lens $f$ is 5 m, and the negative sign $(-)$ implies that the lens is diverging in nature. Hence, it is a concave lens.

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Updated on: 10-Oct-2022

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