A lens has a focal length of, −10 cm. What is the power of the lens and what is its nature?

Given:

Focal length, $f$ = $-$10 cm = $-$0.1 m

To find: Power of the lens, $P$, and its nature.

Solution:

Power of a lens is given by:

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

Substituting the given values we get-

$P=\frac {1}{-0.1}$

$P=-\frac {10}{1}$

$P=-10D$

Thus, the power of the lens $P$ is 10 D, and the negative sign $(-)$ implies that the lens is concave in nature. 

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Updated on: 10-Oct-2022

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