Write down the 4-momentum of a particle with energy and 3-momentum p. State the relationship between the energy and wavelength of a photon.
An electron of mass is at rest at the origin of the laboratory frame: write down its 4 -momentum. The electron is scattered by a photon of wavelength travelling along the -axis: write down the initial 4-momentum of the photon. Afterwards, the photon has wavelength and has been deflected through an angle . Show that
where is the speed of light and is Planck's constant.