In 1905, Einstein proposed a theory of the photoelectric effect using a concept first put forward by Max Planck that light consists of tiny packets of energy known as photons or light quanta. Each packet carries energy formula_1 that is proportional to the frequency formula_2 of the corresponding electromagnetic wave. The proportionality constant formula_3 has become known as the Planck constant. The maximum kinetic energy formula_4 of the electrons that were delivered this much energy before being removed from their atomic binding is