Question

The focal length of a concave lens is 2 m, calculate the power of the lens.

• A. $-0.5D$
• B. $-1.0D$
• C. $+0.5D$
• D. $+1.0D$

Answer 1

The correct option is A $-0.5D$

Focal length of concave lens, $F=-2m$
Power of lens, $P=$ $\frac{1}{f}$
$P=-0.5dioptre$.

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.