1. The problem statement, all variables and given/known data "A photon of energy E collides with an electron at rest. Calculate the maximum amount of Energy Ek that may be transferred to the electron. Make a graph of Ek versus E, labeling the scale in electronvolts. 2. Relevant equations Transfer = Ek = E - mc^2*E/(mc^2 + 2E) 3. The attempt at a solution So, I'm not sure if I have the correct equation, the reason why is: I take the derivative of the function and set it equal to 0 E = -mc^2 and then I plug that value into my function of Ek and I get 0.. but how can the max value for energy transfer be 0? I understand the -mc^2 conceptually saying perfect back scattering but I'm not sure.