Question

What is meant by power of lens? What does its sign (+ve or –ve) indicate? Stats its S.I. unit. How is this
unit related to focal length of a lens?

Answer 1

the ability to converge or diverge the rays at certain angles is known as power of lens. and the +ve sign shows that the lens is concave and the -ve sign shows that the lens is convex ...
the si unit of power is dioptre
which is 1 D = 1/f

Answer 2

power of lens is p=1/f in meters i.s unit of lens is dioptre