The power of a lens is, −2 D. What is its focal length?

Given:

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

$-2=\frac {1}{f}$

$f=-\frac {1}{2}$

$f=-0.5m$

Thus, the focal length of the lens $f$ is 0.5 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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