Question

The power of a lens is 5D. Find its focal length.

Answer 1

Step 1: Given

Power, $\mathrm{P}=5\mathrm{D}$

Step 2: Formula used

$f=\frac{1}{P}$ where f is the focal length of the lens,

Step 3: Calculations

By substituting the values in the above formula, we get

$f=\frac{1}{5}$

$f=0.2m$

$$\begin{gathered} f=0.2\times 100cm \\ f=20cm \end{gathered}$$

Therefore, the focal length of the lens is $20\mathrm{cm}$.