Question

The focal length of a convex lens is 25 cm. What is its power ?

Answer 1

Power of the lens is always the reciprocal of the focal length of the lens.
Focal length of the lens = f = 25 cm = 0.25 m
So, power of the lens, $P=\frac{1}{f}$

$P=\frac{1}{0.25}$

P = 4 D
Since power of a lens is positive which shows that, the lens is a converging lens.
Hopefully it helps.

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