Describe and explain the photoelectric effect.

Consider a single photon (a particle of light) of a particular energy striking the surface of a metal. If the energy of this photon exceeds the work function of the metal, it will remove a single electron - itself with a particular kinetic energy - from the surface of the metal (extra energy is required to bring the electron to the surface otherwise). For a photon of energy hf (that is, the product of the Plank constant h - 6.626x10³⁴ - and the photon's frequency f), a metal with work function o, the ejected electron's kinetic energy K_e can therefore be given by K_e= hf - o. In other words, the interaction obeys the law of energy conservation, as the excess energy not 'used' by the photon to overcome the work function is transferred into kinetic energy. The photon will not remove an electron if its energy is lower than the work function of the metal. This is because light is quantum in nature, meaning is has both particle and wave-like properties: the photoelectric effect is an example of light displaying the former. Was light only a wave, increasing the intensity of the light shone upon the metal surface would see an electron removed, as in the wave model intensity and energy are proportional. For a particle, however, intensity is obsolete as, no matter how many photons you direct at the surface, the energy of each individual particle remains the same.