Question

The focal length of a concave lens is $2m$. Calculate the power of the lens.

Answer 1

Power of lens (P) = $\frac{1}{f}$

Here, focal length, $f=-2m$

Therefore, $P=\frac{1}{-2}$

i.e., Power of the lens, $P=-0.5dioptre$

The diopter is the unit of measure for the refractive power of a lens. The power of a lens is defined as the reciprocal of its focal length in metres, or $P=\frac{1}{f}$, where $P$ is the power in diopters and $f$ is the focal length in metres.