A convex lens converges the light rays falling on it whereas a concave lens diverges the light rays falling on it.
The power of a lens is a measure of the degree of convergence or divergence of the light rays falling on it.
The power of a lens is defined as the reciprocal of its focal length in metres.
Power = 1 / focal length (m)
A lens of short focal length has more power whereas a lens of long focal length has less power.
The unit of the power of a lens is dioptre.
The power of a convex lens is positive
The power of a concave lens is negative.
In order to calculate the power of a lens , we need its focal length in metres.
Power of a combination of lenses :
1.If two lenses are placed in contact , the combination has a power equal to the algebraic sum of the powers of two lenses.
P = P1+ P2 , 1/f = 1/f1 + 1/f2
