1. The problem statement, all variables and given/known data Consider a photon that is barely capable of causing a photoelectric effect when it strikes a sodium plate having a work function of 2.55eV. 2. Relevant equations Find the minimum energy level n for a hydrogen atom that can be ionized by such a photon, and the speed of the released electron far from the nucleus. Can someone explain to me what is this "ionize" term used in this question mean, because I don't know how to proceed? 3. The attempt at a solution I'm thinking "ionize" here means "exciting the atom" and if that is so, Ef - Ei = 2.55eV. Also I first found out the energy levels for hydrogen : -13.6eV, -3.4eV, -1.51eV, -0.85eV... So I'm thinking that I need to find the correct pair of Ef - Ei that will give 2.55eV so that I can determine the minimum energy level n for the hydrogen atom. Please correct me where I'm wrong.