# 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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