Light - Reflection and Refraction — Question 16

Given,

P = -2.0 D

f = ?

We know,

Power of lens (P) = $\dfrac{1}{\text{focal length}}$

As the given power is negative hence, we can say that the lens used is concave in nature.

Substituting the value of power in formula we get,

-2 = $\dfrac{1}{\text{f}}$

f = - $\dfrac{1}{\text{2}}$

f = -0.5 m

Therefore, focal length is -0.5 m and it is a concave lens.