Photoelectric Effect Essay, Research Paper

Photoelectric Effect

Photoelectric Effect is the formation and liberation of electrically charged particles in matter, usually metals, when it is irradiated by light or other electromagnetic radiation. The term photoelectric effect designates several types of interactions. In the external photoelectric effect, electrons are liberated from the surface of a metallic conductor by absorbing energy from light shining on the metal’s surface. This is the form that we generally associate photoelectric effect with.

Study of the external photoelectric effect played an important role in the development of modern physics. Experiments beginning in 1887 showed that the external photoelectric effect had certain qualities that could not be explained by the theories of that time, in which light and all other electromagnetic radiation was considered to behave like waves. For example, as the light shining on a metal becomes increasingly intense, the classical wave theory of light suggests that the electrons that absorb the light will be liberated from the metal with more and more energy. However, experiments showed that the maximum possible energy of the ejected electrons depends only on the frequency of the incident light, and is independent of the light’s intensity.

In 1905, in an effort to explain how the external photoelectric effect occurs, Albert Einstein suggested that light could be considered to behave like particles in some instances, and that the energy of each light particle, or photon, depends only on the wavelength of the light. To explain the external photoelectric effect, he envisioned light as a collection of projectiles hitting the metal. A free electron in the metal that is struck by a photon absorbs the photon’s energy. If the photon is energetic enough, the electron is ejected from the metal. Einstein’s theory explained many features of the external photoelectric effect, including why the maximum energy of electrons ejected from a metal is independent of the intensity of the light itself. Einstein’s theory was later verified through further experimentation. His explanation of the photoelectric effect, with its demonstration that electromagnetic radiation can behave like a collection of particles in some situations, contributed to the development of quantum theory.

*Much of this information comes from Encarta Encyclopedia s Photoelectric Effect listing.