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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.
Solution:
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 $f=-50\ cm$
Therefore,
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.
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