Photon. It is a term introduced by quantum mechanics into electromagnetic theory to designate a particle of light , or a quantum of electromagnetic energy . The particle aspect of a photon was correlated with the expression of a constant and quantized angular momentum (Planck constant), and its energy was given by the product of this angular momentum constant for a frequency term . The accepted physical and geometric representation of the photon involves the mathematical description of a fiber of light, forming beams or bundles that are represented stochastically by a ray .


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  • 1 General
  • 2 Photodissociation
  • 3 Technological applications
  • 4 Photon Structure
  • 5 See also
  • 6 Source


Photons are carriers of all forms of electromagnetic radiation (EM), not just light . Different types of EM radiation correspond to different types of energy per photon. Gamma rays and X-ray photons have the highest amount of energy, and radio frequency photons have the least amount of energy, while photons from ultraviolet , infrared , and visible light have average energy.

Photons travel at the speed of light, which is: 299,792,458 kilometers per second (approximately 186,282.4 miles per second). Photons have no mass , no electrical charge .



Photons are small portions of light and other types of electromagnetic radiation. Sometimes photons separate molecules. When this occurs, it is called [[photodissociation].

When a photon collides with a molecule, it transfers energy to it. Molecules have chemical bonds that keep atoms attached to each other inside. If the chemical bonds are broken, the molecule breaks down. Sometimes photons have enough energy to break the bonds in a molecule . A photon of ultraviolet (UV) “light” has more energy than one of visible light. Ultraviolet photons can cause photodissociation more easily than photons in visible light.

Photodissociation occurs a lot in Earth ‘s atmosphere . In air , there are many chemical reactions, and photodissociation provides energy for many of them. For example, photodissociation helps create smog. It also helps ozone formation.

Technological applications

Photons have many applications in technology. Examples have been chosen that illustrate the applications of photons per se, and not other optical devices such as lenses, etc. whose operation can be explained under a classical theory of light. Laser is an extremely important application.

Individual photons can be detected by various methods. The classic photomultiplier tube is based on the photoelectric effect; a photon that strikes a sheet of metal starts an electron, which in turn initiates an avalanche of electrons. CCD integrated circuits use a similar effect in semiconductors; an incident photon generates a detectable charge in a microscopic capacitor. Other detectors like Geiger counters use the ability of photons to ionize gas molecules , leading to a detectable change in their conductivity.

Planck’s energy formula E = hν is often used by design engineers and chemists, both to calculate the energy change resulting from the absorption of a photon, and to predict the frequency of light emitted in an energy transition Dadaist. For example, the emission spectrum of a fluorescent lamp can be designed using gas molecules with different levels of electronic energy and adjusting the typical energy with which an electron collides with the gas molecules inside the lamp.

Under some conditions, an energy transition can be excited by means of two photons, said transition not occurring with the photons separately. This allows microscopes with higher resolutions, because the sample absorbs energy only in the region where the two different colored rays overlap significantly, which can be much less than the excitation volume of an individual beam. Furthermore, these photons cause less damage to the sample, since they are of lower energy.

In some cases, two energy transitions can be coupled so that when one system absorbs a photon, another nearby system steals its energy and re-emits a photon at a different frequency. This is the basis for resonance energy transfer between fluorescent molecules, which is used to measure molecular distances.

Photon Structure

According to quantum chromodynamics, a real photon can interact as a point particle, or as a collection of quarks and gluons, that is, as a hadron. The structure of the photons is not determined by the traditional valence quark distributions as in a proton, but by fluctuations of the point photon in a collection of partons.


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