Question

The power of a lens is 2D. What is it's focal length?

Answer 1

f=1/P=1/2D
f=0.5m
f=50cm

Answer 2

Bonjour!

$power = \frac{1}{focal \: length}$

Given Power = 2D

So,
$= > focal \: length = \frac{1}{power} \\ \\ = > focal \: length = \frac{1}{2} \\ \\ = > focal \: length = 0.5 \: meter$


Hope this helps...:)