Find the focal length of a lens of power -2.0 D. What type of lens is this?

Given: Power of the lens $=-2.0\ D$

To do: To find the focal length and type of the given lens.


Relationship between the power of a lens and its focal length$\rightarrow$

We know the relationship between focal length and the power of the lens.

Focal length $\boxed{f=\frac{1}{power\ of\ lens(P)}}$

Here, $P\rightarrow$ Power of the lens

$f\rightarrow$ Focal length of the lens

It is given that power of the lens $P=-2.0\ D$

Or $f=\frac{1}{-2.0}$

Or $f=-0.5\ m$

Or $f=-50\ cm$


The focal length of the lens:

The focal length of the lens is $-0.5\ m$ or $-50 cm$.

Nature of the lens:

Since the focal length is negative. So, it is diverging in nature.

So it is a concave lens.

Updated on: 10-Oct-2022


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