5 3  Power of a lens
Power of a lens is a measure of the convergence or
divergence, which a lens introduces in the light falling on
it Clearly, a lens of shorter focal length bends the incident
light more,  while converging it in case of a convex lens
and diverging it in case of a concave lens The power P of
a lens is defined as the tangent of the angle by which it
converges or diverges a beam of light parallel to the
principal axis falling at unit distance from the optical
centre (Fig