Photoelektrischem

Photoelectric emission, also known as the photoelectric effect, is the release of electrons from a material, typically a metal surface, when illuminated by light with sufficient energy. In German, the phenomenon is called the Photoelektrischer Effekt; “Photoelektrischem” is a declined form of the adjective used in phrases such as photoelektrischer Effekt or photoelektrischen Emission.

Historically, the effect was first observed by Heinrich Hertz in 1887 and investigated in more detail by Philipp Lenard. In 1905 Albert Einstein proposed a quantum explanation, introducing the concept of photons. He showed that light energy is quantized and that ejection occurs only if a single photon carries energy hν greater than the work function φ of the material. The maximum kinetic energy of emitted electrons is E_k,max = hν − φ. Emission begins only above a threshold frequency, and the kinetic energy increases with frequency while the emission rate depends on light intensity.

Experimentally, the effect demonstrates key quantum properties of light: a threshold behavior, linear dependence of kinetic energy on frequency, and a linear relationship between light intensity and the number of emitted electrons (above threshold). Measurements of stopping potential and photocurrent provide direct estimates of photon energy and the work function.

Applications and significance include the use of photoelectric emission in photodetectors, photoelectron spectroscopy, and certain light-sensing devices. The phenomenon is distinguished from the photovoltaic (or solar) effect, where light generates charge separation without ejecting electrons. The discovery of the photoelectric effect played a pivotal role in establishing quantum theory and the photon concept.