Definition
The ability of a lens to converge or diverge depends on its focal length. For example:
- Convex lens of short focal length bends light rays through large angles by focusing them closer to the optical centre.
- Concave lens of very short focal length cause high divergence.
The degree of convergence or divergence of light rays by a lens is expressed in terms of its power. It is the reciprocal of its focal length.
Formula
SI Unit
The SI unit of power of a lens is ‘dioptre’, denoted by letter D.
- 1D is the power of a lens whose focal length is 1 Meter.
- Thus,
The power of a convex lens is positive while concave lens is negative.
Combination of power
Backlinks
Flashcards
What is the power of a lens? ? The degree of convergence or divergence of light rays by a lens is expressed in terms of its power. It is the reciprocal of its focal length.
The ability of a lens to converge or diverge depends on its {{focal length}}.
The SI Unit of power of lens is {{dioptre}}.
The power of a convex lens is {{positive}}
The power of a concave lens is {{negative}}
What is the formula of power of a lens? ?