Question

A person uses a concave lens of focal length $50cm$. What is the power of the lens?

Answer 1

Step 1 - Given data.

The focal length is $f=-50cm=-0.50m$. (The focal length of a concave lens is negative.)

Step 2 - Formula used

The power $\left(P\right)$ of the lens is given as

$P=\frac{1}{f}$.

Step 3 - Finding the power of the lens.

Substitute the values into the formula to calculate the power of the lens.
$$\begin{gathered} P=\frac{1}{f} \\ P=\frac{1}{-0.50m} \\ P=-2D \end{gathered}$$

Hence, the power of the lens is $-2D$.