Talk:Electronvolt

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Temperature eV/kB 1.1604505(20)×10^5 K is definitely wrong by a factor of 10! As one learns early on in the physics course at university KB * room temperature ≈ 1/40 eV! — Preceding unsigned comment added by Nayano2 (talk • contribs) 19:48, 11 November 2016 (UTC)[reply]

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

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)[reply]

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 appologize 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)[reply]

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 ${\displaystyle {\overline {\mathrm {E_{kin}} }}={\frac {f}{2}}\cdot k_{B}\cdot \mathrm {T} }$. Where ${\displaystyle f}$ is the number of degrees of freedom of the gas particles and ${\displaystyle k_{B}}$ is the Boltzmann constant. For an ideal gas ${\displaystyle f}$ is 3. So the relation between average kinetic energy of the particles and the temperature of the gas is ${\displaystyle \mathrm {T} ={\overline {\mathrm {E_{kin}} }}\cdot {\frac {2}{f}}\cdot {\frac {1}{k_{B}}}}$. In the case of an ideal gas the constant of proportionality is ${\displaystyle {\frac {2}{3}}\cdot 11605{\frac {K}{eV}}}$. See also Maxwell-Boltzmann distribution equation (17). --Hardy 15:20, 6 November 2005 (UTC)[reply]

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)[reply]

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

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)[reply]

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)[reply]

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 three 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)[reply]

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

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

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)[reply]

I just added in the intro that 1.0 V = 1.0 J/C so that it is easier to understand where the electron volt gets its units of joules from. I hate it when Wikipedia writers 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.

In the part of the United States where I come from, we say "jigawatts", "jigabytes", "jigohms", and "jigavolts" all the time. Personally, I don't see any reason for anyone to get argumentative about it and snapping off things like "I've never heard anyone say..." So what if you haven't? Are you the man who sings "I've been everywhere..." or are you Johnny Appleseed?
98.67.162.130 (talk) 21:07, 1 September 2012 (UTC)[reply]

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 ${\displaystyle \Gamma =1/\tau }$ where ${\displaystyle \tau }$ is the lifetime (not the half-life). Also, what's an exotic kernel? HEL 00:30, 9 October 2006 (UTC)[reply]

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 ${\displaystyle \tau }$ is the thing that appears in the decay exponential, exp(-t/${\displaystyle \tau }$). The half-life ${\displaystyle \tau _{1/2}}$ is related to the lifetime by ${\displaystyle \tau _{1/2}=ln(2)\tau }$. (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)[reply]

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

A very brief length of time can be measured with eV. The uncertainty principle gives ${\displaystyle {\Delta }E\,\cdot \,{\Delta }t\ {\geq }\ {\frac {\hbar }{2}}}$. 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 :

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

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).

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)[reply]

That would be 1 kg, as per:

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

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

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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. The electron-volt (abbreviated eV) is a unit of energy.
98.67.162.130 (talk) 20:48, 1 September 2012 (UTC)[reply]

A foot-pound is a compound unit (the unit foot and the unit pound). An electron however, is a particle, not a unit. If you want to build the same etymology, it would be an elementary charge-volt. Headbomb {talk / contribs / physics / books} 00:27, 2 September 2012 (UTC)[reply]

"Electron" in this case is a sort of unit (abbreviation of "electron charge"). On the other hand, "electron volt" means "volt of an electron", making no sense. — Mikhail Ryazanov (talk) 01:59, 7 May 2013 (UTC)[reply]

So first and foremost, this section begins by making the statement:

"By mass–energy equivalence, the electronvolt is also a unit of mass."

though it is true that energy and mass can be converted between eachother, mass units and energy units are not the same thing. You can never write "x electronvolts = y kilograms", It just doesn't work that way. Saying that electronvolts are a UNIT of mass is always wrong, saying mass can be expressed in terms of energy and energy can be (sort of) expressed in terms of mass is significantly more correct. The current wordage could prove to be misleading to readers who don't understand what is actually meant to be said.

Now, I don't think this section even really belongs in an article on a unit of measure, since it is something which pertains to energy in general and the units used have next to no relevance on the matter. In other words, talking about this does not tell someone anything more about electronvolts. If the statement about electronvolts also being a unit of mass were true, then that would be another matter altogether, but since it doesn't, I believe this section doesn't really add anything to the article. I could be in the minority with this opinion but thought I'd put it out there, since I don't really believe in unnecessary clutter. Ionic1337 (talk) 00:34, 28 July 2015 (UTC)[reply]

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Shouldn't a mol (6.02 × 10²³) of protons weigh about 1g? The units given show 10^-36kg, which is a long way from 10^-23. Or is this one of those "relativistic" things where once the electron joins the party and the proton is now a "nucleus", the mass changes?

Riventree (talk) 16:45, 5 June 2016 (UTC)[reply]

Yes, one mole of protons weighs about 1 gram. But what does an eV/c² have to do with that? Double sharp (talk) 09:01, 24 November 2016 (UTC)[reply]

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energy consumed by a single 100-watt light bulb in one second

If this is what I think it is, in many countries they don't sell those any more, and it's not much of a relatable standard for our youngest readers. — MaxEnt 01:12, 26 May 2018 (UTC)[reply]

Very true. The point has been made before but so far no one has come up with a simple example that younger readers can relate to. Be bold and propose something better. Dondervogel 2 (talk)

Maybe a portable domestic electric heater, or hair-dryer, or toaster. Basically something electrical that heats with a set power usage. An advantage is that — like incandescent light globes — these are sold by power usage (input), not by performance (output), so increases in efficiency won't affect the calculation of power usage. A disadvantage is that typical power ratings for these appliances would vary by country-by-country (depending on the domestic power supply), but it is worth considering.

Young folk will be familiar with things like mobile phones too, but they are not at all suitable because power draw varies depending on the model and how the device is being used at that moment, and because technology for these things is changing much faster/more than for electric heaters & related appliances.

—DIV (1.129.107.117 (talk) 03:53, 30 May 2019 (UTC))[reply]

The article reads: "a unit of energy equal to exactly 1.602176634×10⁻¹⁹ joules (symbol J) in SI units." and "Like the elementary charge on which it is based, it is not an independent quantity".

Is the latter still correct, or only historically correct? J is a derived unit, but based upon N×m, and neither of these depend upon the electron's charge.
—DIV (1.129.107.117 (talk) 03:43, 30 May 2019 (UTC))[reply]

"In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the amount of kinetic energy gained (or lost) by a single electron accelerating from rest through an electric potential difference of one volt in vacuum."

1. Is eV a unit? If so, that's probably the first fact that should be mentioned.

2. Presumably measurements using the unit eV can range over positive or negative values. Hence the unit must have a positive sense. So is the positive sense a gain of energy, or loss of energy? That determination may be complicated by the fact that the electron carries a negative charge. So eV = e x V might well be negative in terms of Joules, when V is positive.

3. Is it only the energy gained(/lost) when the electron is accelerated from rest? Or is it the gain(/loss) when moving through a 1V field, regardless of the starting velocity?

4. If we take the sentence literally to mean only starting from rest, then how does an electron at rest actually lose energy?

"When used as a unit of energy, the numerical value of 1 eV in joules (symbol J) is equivalent to the numerical value of the charge of an electron in coulombs (symbol C). Under the 2019 redefinition of the SI base units, this sets 1 eV equal to 1.602176634×10−19 J."

5. The preceding sentence told us that eV is an amount of energy. So why does this new sentence qualify "when used as a unit of energy". Does this suggest that eV is sometimes not a unit, or sometimes not a unit of energy?

6. Are there any circumstances where 1 eV expressed in Joules is not 1.602...x 10^-19?

7. What is even the point of "the numerical value of 1 eV in joules (symbol J) is equivalent to the numerical value of the charge of an electron in coulombs (symbol C)". That bunch of words is simply a complicated way of saying 1.602 x 10^-19 = 1 x 1.602 x 10^-19. Obviously the numerical value will be the same on both sides of the equation. Gwideman (talk) 08:20, 20 July 2020 (UTC)[reply]

I fixed #4. The other points you raise merit discussion. Dondervogel 2 (talk) 10:10, 20 July 2020 (UTC)[reply]

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