fotoelektrikus

Fotoelektrikus is a term used in physics to describe phenomena and devices involving the interaction of light with electrons. It most often refers to the photoelectric effect and to photoelectric sensors and related equipment.

In the photoelectric effect, electrons are ejected from a material, typically a metal, when light of sufficient energy shines on it. Light is treated as photons with energy hf. An electron is emitted only if hf exceeds the work function phi of the material. The excess energy hf − phi becomes the kinetic energy of the emitted electron, which can be measured by the stopping potential. The emission rate depends on light intensity, while the maximum kinetic energy depends on frequency. Albert Einstein explained the effect in 1905 by introducing the photon concept, a foundational result for quantum theory.

History and significance: The phenomenon was observed in the late 19th and early 20th centuries and provided crucial evidence for the quantum nature of light. Einstein’s explanation earned broad recognition, with subsequent experiments confirming the relation between photon energy and electron emission.

Applications: Photoelectric devices include sensors that generate or interrupt electrical signals in response to light, as well as photocathodes used in vacuum tubes and electron multipliers. The related photovoltaic effect in semiconductors enables solar cells to convert light into electricity by generating and collecting charge carriers, though via a solid-state process rather than electron emission into vacuum.

See also: photoelectric effect; photoemission; work function; photoconductivity; photocathode; photovoltaics.