1. The problem statement, all variables and given/known data A photon with of 13600eV energy interacts with a hydrogen atom at rest and ejects the electron (photoelectrically) in the direction in which the photon was travelling. If 13.6 eV is required to eject the electron, find the speed of the photoelectron and the momentum and energy of the recoiling photon. 2. Relevant equations Energy of a Photo: E = h*f Photo electric effect: KEmax = hf - phi Momentum for a photon: p = h / lamda Compton Effect: lamda ' - lamda = h / Me*c (1 - Cos theta) 3. The attempt at a solution Now I'm confused. In class we learned about the photoelectric effect and the Compton Scattering separately. I understand and can do problems about both concepts. What I don't understand here is the ejection of the electron. Is the electron ejected due to the photoelectric effect or due to a collision with the photon? I know that Phi is 13.6eV. This energy will be lost due to pulling the electron out of the atom. Is the Kinetic energy of the ejected electron coming from the collision with the photon. Thanks for the help!