Question

Question 16
Find the focal length of a lens of power -2.0 D. What type of lens is this?

Answer 1

Power of lens, $\left(P\right)=-2.0D$
$P=\frac{1}{f\left(inmetres\right)}orf=\frac{1}{P}$
$f=\frac{1}{-2.0}=-0.5m$
The focal length, f = -0.5 m
A concave lens has a negative focal length. Hence, it is a concave lens.