Which of the following is the correct formula for measuring power of a lens?

P = \(\frac{1}{f}\)

The power of a lens is defined as the reciprocal of its focal length. It is represented by the letter P.

The power P of a lens of focal length f is given by, 

P = \(\frac{1}{f}\)

The SI unit of power of a lens is ‘dioptre’. It is denoted by the letter D.

If f is expressed in metres, then, power is expressed in dioptres.

Thus, 1 dioptre is the power of a lens whose focal length is 1 metre. 1D = 1m^–1.