Information AboutElectronvolt |
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One electronvolt is a very small amount of energy: : 1 eV = 1.602 176 53(14) J . 1 An in-depth discussion of how the CODATA constants were selected and determined. (or approximately 0.160 A J) The unit electronvolt is accepted (but not encouraged) for use with SI . It is widely used in Solid State , Atomic , Nuclear , and Particle Physics , often with Prefixes m, k, M, G or T. In a recorded lecture from 1961 Richard Feynman apologized to his students for this failure by atomic physicists to use the appropriate SI unit (which would be the Atto joule): "A single atom is such a small thing that to talk about its energy in joules would be inconvenient. But instead of taking a definite unit in the same system, like 10−20 J, In Chemistry , it is often useful to have the molar equivalent, that is the kinetic energy that would be gained by a Mole of electrons passing through a potential difference of one volt. This quantity is equal to 96.48538(2) KJ/mol . Ionization Energies and other atomic properties are often quoted in electronvolts, especially in older texts. USING ELECTRONVOLTS TO MEASURE MASS Albert Einstein reasoned that energy is equivalent to Mass , as famously expressed in the Mass-energy Equivalence formula ''E'' = ''mc''&2 (1.0000 Kg = 89.876 PJ ). It is thus common in particle physics, where mass and energy are often interchanged, to use eV/''c''&2 or even simply eV as a unit of mass. For example, an electron and a Positron , each with a mass of 0.511 MeV/c&2, can annihilate to yield 1.022 MeV of energy. The Proton has a mass of 0.938 GeV/c&2, making GeV a very convenient unit of mass for Particle Physics . :1 eV/c&2 = 1.783 kg :1 keV/c&2 = 1.783 kg :1 MeV/c&2 = 1.783 kg :1 GeV/c&2 = 1.783 kg :1 TeV/c&2 = 1.783 kg :1 PeV/c&2 = 1.783 kg :1 EeV/c&2 = 1.783 kg See: Orders Of Magnitude (mass) In some older documents, and in the name Bevatron , the symbol "BeV" is used, which stands for "billion-electron-volt"; it is equivalent to the GeV (gigaelectronvolt). ELECTRONVOLTS AND ENERGY For comparison:
ELECTRONVOLTS AND PHOTON PROPERTIES The energy ''E'', frequency ''f'', and wavelength λ of a photon are related by : where ''h'' is Planck's Constant and ''c'' is the Speed Of Light . For example, the spectrum of visible light consists of wavelengths ranging from 400 nm to 700 nm. Photons of visible light therefore have energies ranging from : to :. An electronvolt is also the energy of an infrared photon with a wavelength of approximately 1240nm. 10eV would correspond to ultraviolet of 124nm, etc. USING ELECTRONVOLTS TO MEASURE TIME AND DISTANCE In Particle Physics , distances and times are sometimes expressed in inverse electronvolts via the conversion factorsK. Hagiwara et al, ''Review of Particle Physics'', Phys. Rev. D66, 010001 (2002)
In these units, the Mean Lifetime of an unstable particle can be reexpressed in terms of its ''decay width'' (in eV) via . For example, the B0 Meson has a mean lifetime of 1.542(16) Picosecond s, or a decay width of 4.269(44) x 10-4 eV, and its mean decay length is = 462 m. ELECTRONVOLTS AND TEMPERATURE In certain fields, such as : : For example, a typical Magnetic Confinement Fusion plasma is 15 keV, or 174 megakelvins. REFERENCES SEE ALSO EXTERNAL LINKS
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