Question

Find the focal length of a lens of power $+4.0D$. What type of lens is this?

Answer 1

Step 1: Given data.

Let the focal length be $\left(f\right)$.

The power of the lens is $P=$ $+4.0D$.

Step 2: Find the focal length.

We know that,

$\begin{array}{rcl}P(indiopter)& =& \frac{1}{f(\mathrm{in}\mathrm{meters})}\\ 4& =& \frac{1}{f(\mathrm{in}\mathrm{meters})}\\ f(\mathrm{in}\mathrm{meters})& =& \frac{1}{4}\end{array}$

Therefore the focal length is $\frac{1}{4}mor25cm.$.

Since the focal length is positive, it is a convex lens.