We know from definition, power of a lens is defined as the ability of a lens to converge or diverge incoming light rays. So, a lens of higher power would converge or diverge light rays to a greater extent. Now, the focal length of a lens is also related to its diverging or converging ability but it varies inversely.
Thus, the relation between power and focal length is inverse such that power is given as the reciprocal of the focal length of a lens.
