Richard Feynman in his Physics lectures and diagrams show a free electron emitting a photo and/ or absorbing a photon. He (They?) always show the electron being deflected. My question is if the photon has no mass how can or why does the electron react by being deflected in motion? If it is a way to show the change in the energy state of the electron which would change its velocity or mass wouldn't it be an instantaneous step change rather than a change it the angle of motion?