question_answer

What is meant by power of a 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?

Answer:

The ability of lens to converge or diverge the light rays is called its power. The positive sign is for converging lens or a convex lens. The negative sign is for diverging lens or a concave lens. The S.I. unit of power is dioptre.

\[\text{Power=}\frac{\text{1}}{\text{Focal length(in metres)}}\]