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.