The photoelectric effect, first observed by the German scientist Henrich Hertz in 1887, forms the basis of operation of modern technologies such as CCD cameras, solar cell technology and other light sensitive devices. The principle is that electrons can be released from the surface of a metal if given enough energy. Einstein’s explanation, for the photoelectric effect, for which won him the noble prize in physics in the miracle year of 1905 is this:
Einstein made use of the equation at the heart of Planck’s description of blackbody radiation, E=hf, and applying it not to the little oscillators within atoms, but to the electromagnetic radiation itself. He stated that light behaves as a stream of packets of energy which he called quanta or photons each with energy hf. Although photons possess no mass, they do have momentum and it takes one quantum of light to eject one electron from an atom.
When light is incident on a metallic surface, electrons may be released, providing that the frequency of the light exceeds a certain critical threshold called the ‘work function’ donated by the Greek letter phi Φ. This constant depends on the nature of the material upon which the light is incident. This condition is so that an electron can absorb enough energy from the incident light so that it can overcome the electrostatic attraction between itself and the positively charged nucleus. In other words, electrons can be thought of as being in a depression called a potential well that confines them inside the material. As the frequency of the light increases, the result will be more energetic photoelectrons, while, increasing the illumination intensity will result in more electrons being released.
E = Φ + K