Hi guys, I've got a little conceptual question here. I became a little confused after my exam. Firstly, I understand that in the photoelectric effect, the electrons either accept all or none of the energy from the particular incident photon and the photon must have a minimum frequency before the electrons can be emmitted and this frequency is characteristic of the material irradiated. What's the difference in this case?: For example, in a hydrogen atom, there are different orbits for electrons and they have different energy levels, of which the lowest is closest to the nucleus at -13.6eV if I remember right. There cannot be any other orbits hence the fixed amount of energy at each level. Say when I put electrons with an amount of energy which is enough to remove the electron from nucleus (ionisation energy) through the atom, why is it that electrons can accept different amounts of energy from the incident electrons and transit between different energy levels instead of accepting all becoming a "free electron? An example for hydrogen, I inject electrons (also, must it always be electrons, can it be photons?) of 13.6eV passing through the hydrogen gas. By principle since the hydrogen electrons accept all the energy, wouldn't it remove the electrons from the attraction of the nucleus? Why is it possible still for it to accept a certain amount to excite it to say level 2, 3, 4.. etc? When it only accepts a certain amount of energy for excitation, where does the rest of the energy go to? Thanks apologise for the poor expression.