Question: which one of the following is the correct expression for the energy of the photon?
Answer: The energy of a photon is E = hf = hc/λ and the momentum of the photon is p = hf/c = h/λ = E/c. The relativistically correct expression for the energy of the electron is Ee = (pe2c2 + me2c4)1/2. The initial momentum of the electron is (nearly) zero.