Photoelectric effect
Emission of electrons from materials caused by electromagnetic radiation.
The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, solid state, and quantum chemistry to draw inferences about the properties of atoms, molecules and solids. The effect has found use in electronic devices specialized for light detection and precisely timed electron emission.
- field
- Condensed matter physics, solid state physics, quantum chemistry
- known_for
- Emission of electrons from materials upon exposure to light, leading to the concept of photons and wave–particle duality
Lore & Background
The experimental results of the photoelectric effect disagree with classical electromagnetism, which predicts that continuous light waves transfer energy to electrons, which would then be emitted when they accumulate enough energy. An alteration in the intensity of light would theoretically change the kinetic energy of the emitted electrons, with sufficiently dim light resulting in a delayed emission. The experimental results instead show that electrons are dislodged only when the light exceeds a certain frequency—regardless of the light's intensity or duration of exposure. Because a low-frequency beam at a high intensity does not build up the energy required to produce photoelectrons, as would be the case if light's energy accumulated over time from a continuous wave, Albert Einstein proposed that a beam of light is not a wave propagating through space, but discrete energy packets, which were later popularised as photons by Gilbert N. Lewis.
Reader's Guide
The photoelectric effect is significant because it provided key evidence for the quantum nature of light and electrons. The experimental results contradicted classical electromagnetism, leading Albert Einstein to propose that light consists of discrete energy packets, later called photons. This work influenced the formation of the concept of wave–particle duality. The effect is used in electronic devices for light detection and precisely timed electron emission. Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons. The phenomenon is also related to other effects where light affects the movement of electric charges, including the photoconductive effect, the photovoltaic effect, and the photoelectrochemical effect.
Did You Know?
- The photoelectric effect is most readily observed from metals and other conductors.
- The time lag between the incidence of radiation and the emission of a photoelectron is less than 10⁻⁹ second.
- The stopping potential is the retarding voltage that stops the most energetic photoelectrons.
- The angular distribution of photoelectrons is highly dependent on the polarization of the incident light.
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