Find the power of a lens with a focal length of 90mm (giving your answer to the nearest whole number).

1. ### Break Down the Problem

We need to find the power of a lens given its focal length. The formula for calculating the power $P$ of a lens is given by:

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

where $P$ is in diopters (D) and $f$ is the focal length in meters.

2. ### Relevant Concepts

We need to convert the focal length from millimeters to meters before applying the formula, since the standard unit for focal length in this formula is meters.

Given:

• Focal length $f = 90 \text{ mm} = 0.090 \text{ m}$

3. ### Analysis and Detail

Now we will calculate the power of the lens:

$P = \frac{1}{0.090}$

Calculating this gives:

$P = \frac{1}{0.090} \approx 11.11 \, \text{D}$

4. ### Verify and Summarize

Rounding $11.11 \, \text{D}$ to the nearest whole number gives us $11 \, \text{D}$.

Final Answer

The power of the lens is $11 \, \text{D}$.