What is meant by power of a lens? What is its SI units ? Define one dioptre.
Answers
Power of lens is the ability of the lens to converge the rays of light falling on it. Definition: The power of a lens is the reciprocal of its focal length in meters. It is represented by the letter P. The power P of a lens of focal length f is given by f = 1/P.
The SI unit of power is dioptre .
1 dioptre is SI unit of the power of a lens whose focal length is 1 metre. It is denoted by the letter D. Thus 1D = 1 m-1. Simply, when focal length ‘ f ‘ is expressed in metres, then, power is expressed in dioptres. The power of a convex lens is positive and that of a concave lens is negative.
The power of lens is defined as the reciprocal as it's focal length. It is represented by the letter P . The power of a lens of focal length F is given by p=1/f .
The SI unit of power of a lens is ‘dioptre’.
1dioptre is the power of a lens whose focal length is 1 metre . 1D =1 m-1