Question

A converging lens has a focal length $40cm$. Calculate its power.

Answer 1

• A converging lens is a lens whose power is Positive.
• The relationship between power and focal length of the lens

$$\begin{gathered} Powerofthelens=\frac{100}{Focallengthofthelens\left(cm\right)} \\ \Rightarrow Poweroflens=\frac{100}{40} \\ \Rightarrow Poweroflens=+2.5D \end{gathered}$$

Hence the power of the converging lens is $+2.5D$.