Hey people, I'm doing some last minute revision for my physics A-level (not literally last minute, i have a few days till the exam) and I need something clarifying. The photoelectric effect is supposed to demonstrate particle behaviour of light. From what I have read, the energy of the photoelectrons is independent of the intensity of the light, but dependent on its frequency. Supposedly that means that light is a particle, but I can't see why. I think it has something to do with the equation [tex]E = hf - \phi[/tex]. My text book says that the photoelectric effect is explained by saying the "the energy exchanged with the wave is always [tex]nhf[/tex] where n is an integer". By why does n have to be integer? Why can't n be any number? Thanks in advance.