Question

The magnitude of the focal length of a diverging less is 20 cm. What is the power of this lens?

• A. 5D
• B. 2.5D
• C. -5D
• D. -2.5D

Answer 1

The correct option is C

-5D

The focal length should be in meter to get the power in terms of diaopter
Now, |f| = 20 cm
Since, the less is diverging; f is negative
Hence,
f = -20 cm
= $-\frac{1}{5}m$
$\therefore P=\frac{1}{f}=\frac{-1}{\frac{1}{5}}=-5D$