What is meant by power of lens? What does its sign (+ ve or -ve) indicate? State its S.I. unit. How is this unit related to focal length of a lens?
(i) Power of lens: It is its ability to converge or diverge a beam of light.
(ii) Positive Power (+ ve) of a lens indicates converging ability of a lens as in the case of convex lens. Negative power (-ve) indicates the diverging ability as in the case of concave lens.
(iii) S.I. unit of power is dioptre (D).