Define power of lens with it’s unit. The focal length of a lens is – 5 m, name the type of lens

Solution

Power of a lens is defined as the reciprocal of its focal length.

                             i.e. P=1/f

Its S.I. unit is dioptre(D). Dioptre is the unit of power of a lens whose focal length is in metres.

Now, given focal length -5 m.

as P=1/f,

So, P=1/-5=-0.2

so power of the lens is -0.2 D and nature of the lens is concave as the focal length is -ve.

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Power of a lens is its ability to converge or diverge the rays of light falling on it. Power of a lens is equal to reciprocal of the focal length of the lens.SI unit of power is dioptre( D)the type of lens is concave lens
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