Question

The power of a lens is $–2D$. What is its focal length?

Answer 1

STEP 1:Given data

The power of the lens is $P=-2D$

STEP 2: Finding the focal length of the lens

Using the relation between power and the focal length of the lens;

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

where the power is in Dioptre (D) and the focal length of the lens is taken in metres.

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

$f=\frac{1}{-2D}$

$f=-0.5m$

$f=-50cm$

Hence, the focal length of the lens is $f=-50cm$.