1. The problem statement, all variables and given/known data Let's just say some photons hit the anode in a photo-tube, and the light's frequency is the threshold frequency. Will the electrons have momentum when they leave the electron? Or will they simply leave the electron, only to come back because of the closer proximity anode's electric field? Or, will the electron displacement get electrons from lower down in the anode, until the cathode is positively charged, and the electrons are attracted to it? 3. The attempt at a solution I thought that it was the last option, where electrons from atoms lower down in the anode gave electrons to the higher-up part, and this continued until the cathode was positively charged? I also don't know if the electrons leave the atom with any momentum. I know that they have zero Ek relative to the nucleus, but does this mean that they don't have momentum and will just stop?