In the classical wave theory of light, intensity was associated with the squares of the maximum amplitudes of the electric and magnetic fields. In the particle theory of light, what property is associated with the intensity of the light? I know that according to the particle theory, the kinetic energy of the electrons ejected from a metal does not depend on the intensity of light directed at the metal, but rather on of the frequency of the light. However, this doesn't really answer the question. Can someone please explain to me the role of intensity in the particle theory of light? Thanks!