A photon of initial energy Ei=2.4E3 eV collides with a free electron, initially stationary. What is the maximum energy that the electron can aquire in this collision? -we know that conservation of energy requires that the Kinetic energy of the eletron gained must equal that lost by the photon so (delta)Ephoton=(delta)Eelectron I considered finding the final energy using (delta)lambda=(h/mec)(1-cos(theta)) where =(h/mec) is the compton wavelength=0.02426A which can be rearranged hc/(delta)E=(0.02426A)(1-cos(theta)) My question is, how do we find the final energy of the photon without knowing the angle of deflection? Or can we assume that the electron and photon both move in opposite directions? Thanks!