When ultraviolet radiation is shone onto a zinc plate, electrons are emitted from the surface. Explain why the emitted electrons have a range of kinetic energies rather than all having the same kinetic energy.

Each photon transfers its energy to a single electron – one‑to‑one interaction. The photon energy, (h
u), is first used to overcome the work function, (phi), which is the energy required to liberate an electron from the metal surface. The excess energy, (h
u-phi), becomes the electron’s kinetic energy. Electrons that are not at the surface must travel through the metal to reach the surface; during this journey they lose energy through collisions with other electrons and lattice atoms. Consequently, electrons originating from deeper layers lose more energy before escaping, so their final kinetic energy is lower. Electrons produced at the surface lose the least energy and therefore have the maximum kinetic energy. Thus, the emitted electrons exhibit a range of kinetic energies rather than a single value.