Notes

SI unit of Power of a Lens is ‘Dioptre’ …

SI unit of Power of a Lens is ‘Dioptre’. It is denoted by the letter D. If f is expressed in meters, then, power is expressed in diopters. Thus, 1 diopter is the Power of a Lens whose focal length is 1 meter.
1 D = 1 m-1
The power of a convex lens is positive and that a concave lens is negative.