The refractive power of a lens of focal length $40 \mathrm{~cm}$ is
A) $-2.5 \mathrm{D}$.
B) $2.5 \mathrm{D}$.
C) $0.40 \mathrm{D}$.
D) $0.16 \mathrm{D}$.
E) $4.0 \mathrm{D}$.

Question

Quizplus · Accepted Answer

The refractive power $P$ of a lens is given by the formula $P = \frac{1}{f}$, where $f$ is the focal length in meters. Converting $40 \mathrm{~cm}$ to meters gives $0.4 \mathrm{~m}$. Thus, $P = \frac{1}{0.4} = 2.5 \mathrm{D}$.

The Refractive Power of a Lens of Focal Length 40 cm40 \mathrm{~cm}40 cm

The Refractive Power of a Lens of Focal Length $40 \mathrm{~cm}$