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== 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 [[kilogram|kg]] = 89.876 [[petajoule|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.
 
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:
 
*The typical atmospheric molecule has a kinetic energy of about [[1 E-21 J|1/40 eV]]. This corresponds to [[room temperature]].
 
== Electronvolts and photon properties ==
 
The energy ''E'', frequency ν, and wavelength λ of a photon are related by
An electronvolt is also the energy of an infrared photon with a wavelength of approximately 1240nm. 10eV would correspond to UV 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 factors<ref>K. Hagiwara et al, ''Review of Particle Physics'', Phys. Rev. '''D66''', 010001 (2002)</ref>
 
In these units, the [[exponential decay|mean lifetime]] <math>\tau</math> of an unstable particle can be reexpressed in terms of its ''decay width'' <math>\Gamma</math> (in eV) via <math>\Gamma = \hbar/\tau</math>. For example, the [[List of mesons|B<sup>0</sup> meson]] has a mean lifetime of 1.542(16) [[picosecond]]s, or a decay width of 4.269(44) x 10<sup>-4</sup> eV, and its mean decay length is <math>c\tau</math> = 462 <math>\mu</math>m.
 
== Electronvolts and temperature ==
In certain fields, such as [[plasma physics]], it is convenient to use the electronvolt as a unit of temperature. The conversion to [[kelvin]]s (symbol: uppercase K) is defined by using ''k<sub>B</sub>'', the [[Boltzmann constant]]:
 
For example, a typical [[magnetic confinement fusion]] plasma is 15 keV, or 174 megakelvins.
 
== See also ==
*[[Orders of magnitude (energy)]]
*[[Thermodynamics]]
 
== Verwysings ==
{{verwysingsVerwysings}}
 
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