If the power of a lens is -2D, what is its focal length?(a) +50 cm (b) -100 cm< (c) -50 cm (d) +100 cm
(c) -50 cm
Explanation
Given,
Power of lens = P = $-2D$.
As, power is in negative sign $(-)$, it means it is a diverging lens or concave lens.
We know that,
$Power=\frac{1}{focal\ length\ (in\ meters)}$
Putting the given value in the formula we get-
$-2=\frac{1}{f}$
$f=\frac{1}{-2}$
$f=0.5m$
$f=50cm$
Hence, the focal length of the combination will be $50cm$.
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