The power of a lens is +2.0D. Its focal length should be :(a) 100 cm (b) 50 cm (c) 25 cm (d) 40 cm

(b) 50 cm

Explanation

Given:

Power of the lens, $P$ = $+$2.0 D

To find:  Focal length of the lens, $f$.

Solution:

Power of a lens is given by-

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

Substituting the given values we get-

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

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

$f=+0.5m=+50cm$

Thus, the focal length of the lens is 50 cm. The minus sign $(+)$ indicates that the lens is converging in nature means it is a convex lens.