Hello, How can one prove that (using the wave theory of light) a bigger intensity would give a greater exit velocity of the electron? I'm looking for something beyond the heuristic "more energy in the wave implies more energy in the electron". Note: in case I'm giving of a crackpot vibe: I don't have the intention to go against the usual interpretation of this experiment (i.e. implying light are particles), I just want to understand its convincing power better. EDIT: an aside Q: was it in the classical theory (i.e. Maxwell's equations describing light as wave) already clear that there was a relation between frequency and energy? Or is that only since quantum theory?