Light of constant intensity is incident on a metal surface, causing electrons to be emitted. State and explain why the rate of emission of electrons changes as the frequency of the incident light is increased. My answer: As frequency increases, energy of photons also increases, so more energy is available per electron, so more electrons can escape and rate of emission increases Book's answer: at higher frequency, fewer photons (per second) for same intensity, so rate of emission decreases. (Allow argument based on photoelectric efficiency) I totally don't understand what the book is saying. Why fewer photons at higher frequency? And what is photoelectric efficiency? Someone please explain to me, thanks.