Talk:Electronvolt

message: 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)
replies: text: Hardy's right, but the standard Kelvin <-> eV conversion is defined to be like it is. - mako 09:49, 19 February 2006 (UTC)
thread_title:  Electronvolts and kinetic energy: Temperature of a particle 

message: 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)
thread_title:  Help! 

message: 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)
thread_title:  Errors in "Electronvolts and time" section 

message: A very brief length of time can be measured with eV. The uncertainty principle gives  {\Delta}E \, \cdot \, {\Delta}t  \ {\ge} \ \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\times10^{-34}\ \mbox{J}\cdot\mbox{s}}{2 \times 1.6022 \times 10^{-19} \mbox{J}} = 3.29101135938 \times10^{-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)
replies: text: 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)
thread_title: Electronvolts and time

message: 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)
replies: text: 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)
thread_title:  How much is 1.0000 kg 

message: Maybe back in 2002, the CODATA value was 1.602 176 53(14) J, but it's 2008 now, and the value is 1.602 176 487(40) J. Some of the equations need to be reworked because of this.
67.171.43.170 (talk) 23:10, 5 September 2008 (UTC)
thread_title:  Obsolete J/eV value used almost throughout 

message: 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)
thread_title:  Aw, awww ... 

message: 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)
thread_title:  Origin of the unit 

message: 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)
thread_title:  Richard Feynman quote 

message: 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)
thread_title:  Energy released by fusion seems wrong... 

message: 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)
thread_title:  As a unit of energy 

message: 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)
thread_title:  Lightbulb 

message: I was trying to find the eV of a terahertz frequency signal.  This led me to the NIST CODATA conversion factor  and several examples   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)
thread_title:  Hertz conversion seems wrong 

message: 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)
replies: text: 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)
replies: text:  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)
replies: text:  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)
thread_title:  Page Move 

message: 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)
thread_title:  Velocity 

message: 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)
replies: text: 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)
replies: text: "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)
thread_title:  The name of the unit 

message: :Feel free to state your position on the renaming proposal by beginning a new line in this section with *Support or *Oppose, then sign your comment with ~~~~. Since polling is not a substitute for discussion, please explain your reasons, taking into account Wikipedia's policy on article titles.
*Oppose – outdated/inapplicable data presented; recent standards bodies overwhelmingly use electronvolt.  — Quondum 19:36, 7 July 2013 (UTC)
thread_title: Survey

message: 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)
thread_title:  Mass-Energy equivalence 

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thread_title:  External links modified 

message: 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)
replies: text: 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)
thread_title:  Silly noob Q 

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thread_title:  External links modified 

message: 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)
thread_title:  Is it an "independent quantity"?  Is it based on "the elementary charge"? 

message: "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)
replies: text: I fixed #4. The other points you raise merit discussion. Dondervogel 2 (talk) 10:10, 20 July 2020 (UTC)
thread_title:  Intro seems muddled 

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