Page 2 - Lesson note power of a lens

Power of a lens is the ability to converge or diverge the ray of light falling on it.

Power of a lens is defined as reciprocal of focal length of the lens.

 The power P of a lens of focal length f is given by
P=1/f

A lens of small focal length has large power of converging or diverging a parallel
beam of light.

 Power of a convex lens is positive and that of a concave lens is negative.
 The SI unit of power of a lens is ‘diopter’. It is denoted by the letter D.
 Power of lens is 1 diopter if its focal length is 1 m.

Power of combination of lenses :

If a number of lenses are placed in close contact, then the power of the
combination of lenses is equal to the algebraic sum of the powes of
individual lenses..

P=p1+p2.......

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