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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.
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