Question

Find the focal length of a lens of power -2.0 D. What type of lens is this?

Answer 1

Step 1: Given data:

Power of lens (P )= -2.0 D

Step 2: Finding the focal length

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

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

Putting the value of $P$ from the given data.

$f=\frac{1}{-2.0}$

$f=-0.5$

Focal length is $-0.5m$.

As the value of focal length is negative. It represents that the lens is concave.