Ans. POWER OF A LENS
The reciprocal of the focal length of a lens is called its power.
Power of lens P = 1/focal length (in metres) Unit: The SI unit of power of a lens is Dioptre, denoted by D. If f is expressed in
metres so that 1D = 1 m .
Dioptre
The power of a lens is one Dioptre whose focal length is one metre.