Question

find the focal length of a lens of power 20 D .what type of lens is this ??answer fast...

Answer 1

$\huge{\mathcal{\blue{Answer}}}$

The focal length of a lens of power 20dioptre

$\large{dioptre=1/focal\:length}$

$\large{20D=1/focal\:length}$

$\large{focal\:length=1/20D}$

$\large{focal\:length=0.05cm}$

Type of lens :

Convex because there is a +ve sign in the power of the lens

Answer 2

The focal length of the lens is 5 cm and it is a convex lens.

Explanation:

Given that, the power of a lens 20 D. We need to find the focal length of the lens. We know that the reciprocal of focal length is called its power. It is given by :

$P=\dfrac{1}{f}\\\\f=\dfrac{1}{P}\\\\f=\dfrac{1}{20\ D}\\\\f=0.05\ m\\\\f=5\ cm$

So, the focal length of the lens is 5 cm. The focal length of a convex lens is positive. So, it is a convex lens.

Learn more,

Power of a lens

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