Question

What will be the power of a concave lens whose focal length is $2m$.

• A. $0.5D$
• B. $-0.5D$
• C. $-1D$
• D. $1.5D$

Answer 1

The correct option is B $-0.5D$

Given:
Focal length of concave lens, $f=-2m$
(concave lens has negative focal length)

Power is given by:
$P=\frac{1}{f}$
$P=\frac{1}{-2}$
$P=-0.5D$

Thus, the power of this concave lens is $-0.5D$.