Which of the following is the correct formula for measuring power of a lens?
Answer & explanation
Correct answer: option 2
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.