Talk:Electronvolt

The name of the unit

The name of the unit must be electron-volt because those two (the charge on the electron and the volt) are multiplied together. This is just like the following:
newton-meter, foot-pound, pound-foot, kilowatt-hour, and ampere-hour.
If you have a hard time understanding the ampere-hour, this is a rating for storage batteries. At a fixed "bus voltage" at the output (set by the power electronics), volts times ampere-hours works out in energy, and if multiplied by 3600, the result works out in joules. The real job of a storage battery is to store energy, and then release it as required.
The foot-pound is a unit of energy, but the pound-foot is a unit of torque. In the SI, energy is measured in joules, but the newton-meter is a unit of torque.
98.67.162.130 (talk) 20:48, 1 September 2012 (UTC)

Comments

Decay width is used several times on this page but never explained.
Arlesterc 21:42, 10 February 2007 (UTC)

It looks like decay width is used only once in the article, and is defined in terms of the mean lifetime immediately. I italicized the term in the article just to make it clear that it's a newly introduced term. HEL 22:49, 10 February 2007 (UTC)

I think maybe it would be worthwhile to add conversions between the electronvolt and other major physics units, as in High Energy physics energy is used to measure just about everything including, distances masses, times, etc.

Lyuokdea 15:10 July 21, 2005 (US Central)

Rather silly question. How many significant digits do we want for unit relations? For example, the most accurate value known for the relation in this article is 1 eV = 1.602 176 462(63) x 10^-19 J, where the number in parenthesis is the uncertainty of the last two digits.

Why not give that value then? I would prefer a clearer term than "uncertainty" though. Do they mean standard error? AxelBoldt

Yes, estimated standard deviation. The most recent recommended values are the "1998 CODATA recommended values". Their values and uncertainties can be found in http://physics.nist.gov/cuu/Constants
AstroNomer

I appologise for my mistake in editing, I wasn't thinking, and I assumed that you meant Joules even though it said eV.
Jedi Dan 17:43 Apr 23, 2003(UTC)

"Electron volt" yields 44,000 Google hits, "electronvolt" 1650. Is most of the world wrong? Is there an authoritative source for the correct term? If it is "electronvolt", then we should move the page.
Tannin 12:21 May 13, 2003 (UTC)

Authoritative source: NIST See: http://physics.nist.gov/cuu/Units/outside.html

Please move the page, I do not know how to do it.
User:Vargenau

If NIST has gotten it wrong, then there is little hope for the rest of us! I'll move the page in a moment. This can be one more of those little things that we at Wikipedia have got right, even though the majority get it wrong. Given enough eyes to look for them, sooner or later there will be no more mistakes left here. Well spotted, Vargenau.
Tannin

I just modified the units in the "As a unit of mass" section, the example refered to the mass of electron and positron with MeV units (energy) when it meant MeV/c² (mass).
8/13/2009 —Preceding unsigned comment added by 186.136.39.153 (talk) 20:02, 13 August 2009 (UTC)

Electronvolts and kinetic energy: Temperature of a particle

A single particle has no temperature, because temperature is a property of a body consisting of many particles. The average kinetic energy of particles of a gas is approximately ${\overline {\mathrm {E_{kin}} }}={\frac {f}{2}}\cdot k_{B}\cdot \mathrm {T}$. Where $f$ is the number of degrees of freedom of the gas particles and $k_{B}$ is the Boltzmann constant. For an ideal gas $f$ is 3. So the relation between average kinetic energy of the particles and the temperature of the gas is $\mathrm {T} ={\overline {\mathrm {E_{kin}} }}\cdot {\frac {2}{f}}\cdot {\frac {1}{k_{B}}}$. In the case of an ideal gas the constant of proportionality is ${\frac {2}{3}}\cdot 11605{\frac {K}{eV}}$. See also Maxwell-Boltzmann distribution equation (17). --Hardy 15:20, 6 November 2005 (UTC)

Can someone more knowledgable than I implement the above correction (see last line of "Electronvolts and kinetic energy"). Thanks. Anthony Chivetta 06:12, 13 February 2006 (UTC)

Hardy's right, but the standard Kelvin <-> eV conversion is defined to be like it is. - mako 09:49, 19 February 2006 (UTC)

Help!

Hey, I'm getting ready for the SAT physics test, and I seem to be getting some strange info. about the eV. In my book, it says 1eV=1.6x10(-19) Joules, but then it says something about 1eV= 6.25x10(18)eV/Joules... Does anybody know what this is supposed to mean, and if so could they add it to the article? Thanks

1 eV = 1.6x10(-19) J, therefore 1 Joule = 6.25x10(18)eV. Hope that helps... I'm not sure what they mean by eV/J though as both eV and J are units of energy. The definition means that multiplying one eV by e, the charge on an electron (not the natural logarithmic e) gives you Joules. e = 1.6x10(-19) Coulombs. There. Clear as mud. MilleauRekiir 15:23, 11 August 2006 (UTC)

I am trying to understand what is going on with the Large Hadron Collider. I saw something that said 1 tetraelectronvolt was equal to the energy of a flying mosquito. I don't have a realistic idea of how much energy that is. Is there a generally recognizable equivalent to how much energy is contained in a tetraelectronvolt?claimman75 (talk) 02:03, 1 December 2009 (UTC)

jev

I have never before heard anyone pronounce GeV as jev, I would say its commonly refered to G-E-V, at least Canadian particle physics curcits. As well, the Proton is not a Typical baryon, in fact it is probably the least typical of them all because it and the neutron are the only ones that don't decay. I would probably go a little further and say that no Baryon can be seen as representative of them all, the only thing they all have in common is each having 3 quarks.--Jason

At RHIC everybody said "jev". It may be an American midwest kind of thing, as my fusion professor, originally from Illinois, said "jev" and "jigawatts". From personal experience, it's much faster to say "jev" and "rick", as opposed to G-E-V and R-H-I-C, especially if you say them often. - mako 09:49, 19 February 2006 (UTC)

French speakers also pronounce "jev". Urhixidur 15:01, 21 March 2006 (UTC)

In England, we refer to both jay-eV and gee-eV (probably most common). I guess with midwest, french and Canadian collaborators, my research group has no hope of a standard pronounciation... MilleauRekiir 15:26, 11 August 2006 (UTC)

I've heard gee-ee-vee and jev used interchangeably. Also in use but much less common is a monosyllabic pronunciation of TeV as "tev", as in Tevatron. (I've never actually heard RHIC spelled out. Also the only place I ever heard anyone pronounce gigawatt as jigawatt was in "Back to the Future"....) HEL 02:25, 9 October 2006 (UTC)

I just added in the intro that 1V = 1J/C so that it is easier to understand where the electron volt gets its units of joules from. I hate it when wikipedia users make the descriptions so convoluted and hard to understand. The people who look at these articles are attempting to learn something about the subject... the way some of these articles are compiled makes it impossible to do so.

Errors in "Electronvolts and time" section

There are some errors in the Electronvolts and time section. First of all, expressing time and distance in inverse eV units is based on the usual "particle physics units" hbar = c = 1. Then time is hbar/E, not hbar/2E. Likewise, distance is hbar*c/E. It's true that eV units are used as an alternate way to express the lifetimes of unstable particles, in the form of the (total) width $\Gamma =1/\tau$ where $\tau$ is the lifetime (not the half-life). Also, what's an exotic kernel? HEL 00:30, 9 October 2006 (UTC)

Here are the relevant numbers:

• hbar = 6.582 118 89(26) x 10^-22 MeV s
• hbar c = 197.326 960 2(77) MeV fm

Citation is K. Hagiwara et al, Review of Particle Physics, Phys. Rev. D66, 010001 (2002). The parentheses notation (26) means the uncertainty is plus or minus 26 in the last two digits quoted. fm is a Fermi or femtometer, 10^-15 m. Also the lifetime $\tau$ is the thing that appears in the decay exponential, exp(-t/$\tau$). The half-life $\tau _{1/2}$ is related to the lifetime by $\tau _{1/2}=ln(2)\tau$. (By the way, does anyone know how to get rid of those spurious dashes that sometimes follow math-mode expressions?) HEL 02:40, 9 October 2006 (UTC)

I rewrote this section. The old content is here: (forgot to sign comment - sorry! HEL 17:54, 9 October 2006 (UTC) )

Electronvolts and time

A very brief length of time can be measured with eV. The uncertainty principle gives ${\Delta }E\,\cdot \,{\Delta }t\ {\geq }\ {\frac {\hbar }{2}}$. A time can correspond to an energy, and when the length of time is very brief (less than an attosecond), the measure is less significant for the observer if expressed in seconds. The conversion is carried out by :

${\frac {\hbar }{2}}{\frac {1}{eV}}={\frac {1.054\ 571\ 68\times 10^{-34}\ {\mbox{J}}\cdot {\mbox{s}}}{2\times 1.6022\times 10^{-19}{\mbox{J}}}}=3.29101135938\times 10^{-16}{\mbox{s}}$

This kind of length is encountered in half-lifes of exotic kernels. For example, the half-life of the ⁸C is 230keV (1.43×10^-21 s).

How much is 1.0000 kg

one kilogram, or ten thousand kilograms? Im referring to this section 1.0000 kg = 89.876 PJ 194.145.96.51 (talk) 15:26, 31 January 2008 (UTC)

That would be 1 kg, as per:

$E=mc^{2}\longrightarrow {1\ {\mbox{kg}}\times {\left(2.998\times {10^{8}}\right)^{2}}{\mbox{m}}\cdot {\mbox{s}}^{2}=89.88\times 10^{15}\ {\mbox{J}}}$ Eutactic (talk) 03:26, 9 May 2008 (UTC)

Electron volt and Electronvolt

Nobody outside of a government building has ever, to my knowledge, called it an "electronvolt".Likebox (talk) 19:33, 18 July 2008 (UTC)

I suspect a government conspiracy. Seriously though, I suggest that "electronvolt" is an acceptable/preferred spelling based on the observation that the IUPAC Gold Book/Green Book has an entry for "electronvolt" but none for "electron volt" (that I can find). IUPAC is, of course, an NGO. Eutactic (talk) 06:57, 19 July 2008 (UTC)

I get your point -- but this is the worst sort of social engineering. Everybody spells it "electron volt", then one day, some bureaucrat wakes up and says, "gosh it makes more sense as electronvolt, really!", convinces his three officemates (who agree because they want to be able to say later -- hey, remember when I helped you out with "electronvolt"?). Then, next thing you know, all official documents say "electronvolt", then NGO's start copying it, etc., etc.

To prevent this sort of thing, I think that usage should be determined by google search. In this case, 115,000 hits for "electron volt", most of them "of the people" (or outside the US), and 32,000 hits for "electronvolt", mostly official looking.Likebox (talk) 18:29, 19 July 2008 (UTC)

Obsolete J/eV value used almost throughout

Maybe back in 2002, the CODATA value was 1.602 176 53(14)×10⁻¹⁹ J, but it's 2008 now, and the value is 1.602 176 487(40)×10⁻¹⁹ J. Some of the equations need to be reworked because of this.

67.171.43.170 (talk) 23:10, 5 September 2008 (UTC)

Aw, awww ...

In SI units, it is the number which measures the charge of the electron with the unit changed from C to J. Is this really a good thing to write it that way? This suggests the (unaware) reader, that you can simply exchange C with J. However, C is unit of Charge (coulomb), J is unit of work (joule). Any suggestions to word this better? -andy 92.229.100.244 (talk) 12:18, 24 October 2008 (UTC)

Origin of the unit

I found that electron volt was first used in 1912 and in that time it was called "equivalent volt". Does anybody know who was the person to use it for the first time and in which publication did it appear? Thank you. Jan.Kamenicek (talk) 22:34, 13 April 2009 (UTC)

Richard Feynman quote

Ummh, this seems to completely miss the point. You have to define a new unit cause you don't know the exact ratio of 1.0 eV to 1.0 J, and if you used the same unit of measure you would be asserting that you did. The electron-volt can be used when you know the number of electrons, through counting, but not exact conversions, which can be continually improved. Just like the Avogadro constant.
Just look above at how the old number has become obsolete due to better measurements, this is the reason there has to be two different units.
I propose that a quote that just tells people to accept things on faith, accept things because that's the way its done, should be removed, even if it is from a lecturer with lots of credibility. The quote really says nothing besides that the two units are measuring the same thing.Scientus (talk) 16:11, 18 September 2009 (UTC)

Energy released by fusion seems wrong...

Could just be me, but the energy released from fusion seems like it should be much higher than quoted... it should be greater than fission... in the GeV range maybe? It says that fission produces more per particle than fusion, but fusion produces more energy per kilogram... just sounds like somebody's in the wrong order of magnitude? Does anyone have a source? Patricius12 (talk) 05:21, 2 November 2009 (UTC)

As a unit of energy

I find this section very confusing. "17.6 MeV: total energy released in fusion of deuterium and tritium to form helium-4 (also on average); this is 0.41 petajoule per kilogram of product produced, which is equivalent to the energy released in a 100-kiloton explosion of TNT." What the heck does that mean? Is 17.6 = to 100-kt of TNT? If not, why even mention TNT? If so, then how can one teraelectronvolt only been the same kinetic energy of a flying mosquito? —Preceding unsigned comment added by 70.68.138.99 (talk) 04:32, 25 November 2009 (UTC)

100-kt of TNT is equivalent to the energy released in fusion of tritium and deuterium, if in the process a kilogram of helium is produced. I agree it is a bit confusing. Terminus0 (talk) 18:47, 7 December 2009 (UTC)

Exa=10^18, so 300 EeV=300,000 PeV = 300,000,000 TeV = 3x10^20 eV, while Peta = 10^15, so 600 PeV = 600,000 TeV = 6x10^17 eV. comment added by 78.159.199.31 (talk) 09:17, 31 May 2010 (UTC)

Lightbulb

100 J is not 8000 TeV (or 8 PeV = 8*10^15 eV) —Preceding unsigned comment added by 72.92.76.143 (talk) 00:13, 2 April 2010 (UTC)

Requested move

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: page moved. Anthony Appleyard (talk) 14:01, 14 February 2010 (UTC)

---

Electron volt → Electronvolt —. It is the name used throughout all of science as far as I'm aware. All my textbooks, and all the journals I read, regardless of field (chemistry, thermodynamics, particle physics, solid state physics, ...) spell it that way. All other authoritative sources (such as BIPM, IUPAC, ...) also spell it that way. I don't ever recall seeing it spell "electron volt", other than in vulgarization articles found in magazines such as Popular Science from time to time. — Headbomb {^ταλκ_{κοντριβς} – WP Physics} 05:27, 6 February 2010 (UTC)

• Support move. M. L. McGlashan in "Physiochemical quantities and units" Pub. Royal Institute of Chemistry, 2nd Ed., 1971 has "electronvolt" and I am pretty sure later editions written by Ian Mills has it too. This is a very reputable source re units. --Bduke (Discussion) 05:58, 7 February 2010 (UTC)

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Hertz conversion seems wrong

I was trying to find the eV of a terahertz frequency signal. This led me to the NIST CODATA conversion factor [1] and several examples [2][3] [4] which seem to support using the Planck's constant h, not h/2pi, for the conversion factor. This makes sense to me in that the hertz here seem to be for the full revolution of a circle, not a unit length. I didn't want to mess with this article because I'm out of my expertise and I don't know if you have a different calculation more in mind, but that's the way I did it for the radio spectrum article to provide an eV reference. Wnt (talk) 19:37, 18 April 2011 (UTC)

Page Move

The rational for the previous move is incorrect. I am a physics student and all my textbooks and lecturers use electron Volt, not electronvolt. Electron Volt is clearly the most common term used by both physicists and the public at large. Unless anybody objects I will be moving this page. Electronvolt makes no sense linguistically either. The Proffesor (talk) 11:45, 23 May 2011 (UTC)

I agree. The term "electron volt" may be concatenated into a single word "electronvolt" by some people, but I've been working in semiconductor physics for well over thirty years, and this is not standard usage. (I just grabbed a couple of reference books off my desk, and checked. Nope, no "electronvolts.") An electron volt is one electron times one volt; concatenating the two together is like expressing electrical energy in "kilowatthours" or torque in "Newtonmeters" or workforce in "manyears". I don't know who voted on the previous "page move" vote, but it does not seem to reflect physics usage. Geoffrey.landis (talk) 16:41, 7 December 2011 (UTC)

My impression is that both are common, and a google search verifies this. Electron volt seems the more common, but BIPM uses electronvolt and American Physical Society seems to prefer electron-volt. Among the first 30 hits on a google search for electronvolt 6 uses electronvolt, 2 electron-volt and the rest electron volt. 89.253.103.60 (talk) 20:42, 8 December 2011 (UTC)

I will point out that the BIPM document linked is an English translation of a document in French. For all I know, electron-volt may be one work in French. Geoffrey.landis (talk) 20:40, 9 December 2011 (UTC)

Velocity

I think this article would benefit from a section on converting eV to velocity, most especially in reference to a free electon.

KE = 1/2 m v^2 where the mass of an electon is .511 MeV/c^2, and the kinetic energy of the electron is (just to make it easy) 511 eV, would result in a speed of

v = (2 KE/m) ^1/2 (with v in terms of c, the speed of light)

 =  (2 511 eV/(511 * 10^3) ^1/2
 = .04 times the speed of light

or, to put it in terms people have a gut feel for,

 = .04 c * (671 million miles per hour)

 =  26 million miles per hour

Also, doing the same thing for higher energies, like 1MeV, which is a typical value for an emitted beta particle, which requires calculating it assuming relativistic speed, but is too hard for me. — Preceding unsigned comment added by 74.38.229.40 (talk) 10:27, 3 September 2011 (UTC)