Talk:Coulomb

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Does coulomb imply positive or negative charge? Since the ampere per second is conventional current, would it technically be 6.24×1018 times the charge on a proton? - Omegatron 16:36, May 26, 2004 (UTC)

I think you're probably right. However, I think it probably also makes sense to say "1 coulomb of electrons", knowing that this is the same as -1 coulomb of conventional charge. -- Anon
Er ... I think "does coulomb imply positive or negative charge?" is as meaningful a question as is "does meter imply positive or negative distance?" (or rather, displacement, so that we can actually allow negative values). A unit in itself has no sense of direction, positive or otherwise; it's just a measure of the magnitude.
The charge of the electron is defined to be negative and the Coulomb is the SI derived unit for electrical charge, therefore a charge of 1 C cannot be from an excess of electrons. (See the definition of elementary charge.) Treating electrons as positively charged is a definitional error which could lead students consulting this article seriously astray. I have changed the references to electrons to protons where appropriate in the article to correct this, and added a reference supporting the correct view. Enon (talk) 23:12, 17 May 2010 (UTC)

put number of electrons / coulomb on top

thats what people look for when they get to this page, now they first have to skim through not so important numbers (Explanation, Faraday...) before they get to number of eletrons —Preceding unsigned comment added by 209.221.240.47 (talk) 18:52, 30 October 2007 (UTC)

Yes! I have to agree: all the physics niceties are very nice, but ISTM that for most people the most helpful definition of a C is as a number of electrons. That number per second gives an Amp and so on, and the whole of basic electrics becomes as easy to comprehend as water in a pipe.
Maybe my electronics background is biasing me, but the idea of 'a number of fundamental electric charges' can easily be derived from that definition. And what, after all, is the "fundamental unit of charge"? The one-third electron charges found in quarks? Planck Charge? --Cdavis999 (talk) 09:59, 20 September 2008 (UTC)

no need for a list of binary prefixes. avogadro's number is a common misconception

thank you but i don't understand!

Discussion moved to Talk:Units of measurement

Kilogram

<-n00b says : . . . . Kilogram ?!? Please clarify how the kilogram applies.

I don't see how the kilogram note is relevant to this article. Being that it lacks an explanation, it's just an odd little statement.
I see how one can make that statement, but I'm not sure how to fit it into an encyclopedic article, not a physics homework. Anyways, this is how: the definition of ampere states, 1 A is the current such that if 2 parallel wires (at distance 1 m) have 1 A through it, there will be 2e-7 N/m of force on wires. Defining C on its own gives an alternate definition of ampere as 1 C/s, and once ampere is defined that way, we can define newton in terms of ampere, and since newton = m*kg*m/s^2, now we can define kg in terms of newton .... which is defined in terms of ampere and meter, which is defined in terms of coulomb and meter and second.
Interesting, but why mention the kg here at all? —Preceding unsigned comment added by 207.189.230.42 (talk) 08:50, 28 October 2007 (UTC)
Presently, the kilogram is an artifact, there is a platinum iridium cylinder in France somewheres, and the kilogram is defined as the amount of mass equal to the mass of that cylinder. obviously, that's kind of untidy, physicists would much rather have the kilogram based on a universal constant. personally, I can't see why they don't just count out one thousand moles of protons. —Preceding unsigned comment added by 207.216.24.138 (talk) 08:00, 3 December 2007 (UTC)
Yes, but the article is supposed to be about the coulomb. 207.189.230.42 (talk) 09:09, 15 December 2007 (UTC)
I agree, the kilogram paragraph is confusing.
It is given top-level "explanation status", but it is really an esoteric proposal that has apparently not been adopted by the physics community and doesn't make anything clearer to the novice. Could this be put at the end?
I came to this page looking for an explanation and was hoping to find something about the idea that a charge can be accumulated in a space or device (e.g. capacitor), and just how large 1 coulomb of charge is (e.g. a 10,000 uF capacitor charged to 100V stores 1 Coulomb). And intuitively, why are Coulombs of charge, which can be stored in a capacitor, different from Joules of energy, which can also be stored in a capacitor (or battery)? -Paul —Preceding unsigned comment added by 68.122.32.141 (talk) 15:53, 13 February 2008 (UTC)

Historical Note re derived unit

"The Ampere is in fact a derived unit..." but not according to the Wikipedia entry for Ampere, where it says, "Because it is a base unit, the definition of the ampere is not tied to any other electrical unit."

Given the definition for the Ampere as given in the Ampere entry, I'm inclined to believe that the Ampere is in fact the base unit and the Coulomb is the derived unit, despite the relationship 1 A = 1 C/s.

Correct. The current SI standard defines the ampere as a base unit, for practical reasons. (It is more intuitive to think of the charge on one electron as fundamental unit on which to base the definition of the Coulomb and then base the Ampere upon the Coulomb, but that's not how things are defined in current SI.)
I am suspicious of the article section: "The ampere was historically a derived unit - being defined as 1 coulomb per second. Therefore the coulomb, rather than the ampere was the SI base electrical unit," because what I have read of the history of electrical units did not say that the ampere was figured from coulombs. Here are pages about the history of electrical units:
http://alpha.montclair.edu/~kowalskiL/SI/SI_PAGE.HTML
http://www.sizes.com/units/ampHist.htm

If no one has any good reference that contradicts those references, I shall in time remove or replace the sentences. Nicknicknickandnick 08:54, 28 October 2007 (UTC)

I removed the reference in the article. I wasn't logged in, so the edit is under an IP address. I thought I'd document my findings, and why I removed it.

The first definition of the coulomb was by the 1st international Congress of Electrical Engineers in 1881, and clearly indicates that the coulomb is derived from the ampere. Resolution 6 of that Congress states: "A quantity of electricity given by ampere in a second is to be called a coulomb." - source IEC The ampere was derived from the volt and ohm, but it was NOT derived from the coulomb.

"The international ampere adopted at a meeting of the British Association in Edinburgh (1892) was the current that would deposit silver from a silver nitrate solution at a rate of 0.001118 g/s under specified conditions, using a silver “voltameter”" - source NIST This is the first reference I could find where the ampere first becomes a base electrical unit (i.e. defined in terms of mass and time, but not in terms of other electrical units).

The 9th CGPM (1948) adopted the ampere for the unit of electric current, following a definition proposed by the CIPM (1946, Resolution 2), the equivalent definition which is used in the modern SI: "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 x 10–7 newton per metre of length."source BIPM

I can find no authoritative reference for the coulomb ever having been considered a base unit. (the reference in the article was to a $$ journal article, written by someone from Montclair State College).

Msauve (talk) 23:10, 5 April 2009 (UTC)

The coulomb is not an SI unit! There are only 7 SI units, (http://en.wikipedia.org/wiki/International_System_of_Units) and the Ampere is one of them, not coulomb. Someone please change the first sentance of this article which describes the coulomb as the SI unit for electric charge.

I believe the coulomb USED to be the SI unit, but it has been changed to the Ampere. —Preceding unsigned comment added by 211.28.52.64 (talk) 07:01, 4 July 2009 (UTC)
No, the Coulomb *is* the SI unit for charge. The NIST literature specifically states that SI units include both the base units and the derived units. (And anyhow, if Coulomb isn't an SI, unit, then what is the SI unit for charge? Faradays? Abcoulombs? Nooo.) Coulomb is an SI unit. But it's not measured directly as in the day when charge was standardized to a certain gram-ionic weight of monovalent ions (where one Faraday of charge passed through a molten-salt NaCl cell will deposit one mole or 23 grams of Sodium on an electrode.128.95.172.173 (talk) 01:56, 29 October 2010 (UTC)

Constant vandalism

Oh grow up! N^O^el (talk) 06:45, 5 March 2008 (UTC)


Real-world example

It would be nice to have a real-world explanation of how much energy 1 Coulomb is.N^O^el (talk) 06:47, 5 March 2008 (UTC)

Charge is not energy. However, inside copper metal, one coulomb of mobile charge occupies a cubic volume 0.42mm on a side. When coulombs are flowing through wires, each Coulomb is a little blob about 1/64" across. This immediately makes you suspect that one Ampere, or a Coulomb per second, is a very slow flow. After all, most wires are lots wider than 1/64" in diameter. 128.95.172.173 (talk) 02:11, 29 October 2010 (UTC)
Cool. I never thought of it that way. This is my "What I learned on Wikipedia this week" item for the week. If you had a reference for this, I'd love to have it in the article; this sort of vivid physical example helps a lot. (Running the arithmetic myself shows that it's correct, asssuming one conductin band electron per copper atom...but I daren't post my calculations because the OR bigots will be on me.) --Wtshymanski (talk) 13:57, 29 October 2010 (UTC)

Yes indeed it would be an awesome idea --can some expert educated us. --69.235.4.174 (talk) 08:47, 31 May 2008 (UTC)

Zero. A coulomb is a measurement of charge, not energy. But it would be useful to know how much charge it is (e.g. how much charge your common or garden AA cell holds; that sort of thing). 212.137.63.86 (talk) 12:14, 6 August 2008 (UTC)
Isn't charge a measure of stored (potential) energy? The stored energy in a battery is converted to kinetic energy (amperage) which does actual work (turns on a light) Tocksin (talk) 12:30, 27 March 2009 (UTC)
No, charge has nothing to do with energy, and if you know the amount of charge, you cannot calculate the amount of energy. Analogy: charge is like water. Water can be stored behind a dam, or water can flow in a hydraulic system. But water isn't a kind of energy; water isn't measured in KWH or Joules! Neither is charge. But if you know the water pressure and flow rate, you can measure the amount of work being done or the amount of hydraulic energy stored or transferred. Same with charge: if you know the PD in volts and the total amount of Coulombs of charge transferred, then you can calculate the amount of work that was done or the amount of electrical energy stored or transferred. But if the charge was transferred at zero volts, then no energy was transferred, only charge.128.95.172.173 (talk) 02:11, 29 October 2010 (UTC)

I added an "everyday charges" section. --Steve (talk) 21:31, 29 January 2011 (UTC)

Better Definition?

According to Teach Yourself Electricity and Electronics Third Ed 1 coulomb = ~6.24 x 1018 electrons or holes. A current of 1 coulomb/1 sec = 1 amp. I find this definition a lot easier than the current one though it seems less precise. Could someone with more knowledge edit this page to include the definition that I've included, or explain why this definition was not included?. --69.235.4.174 (talk) 08:47, 31 May 2008 (UTC)

It's not included because it's not the definition. JIMp talk·cont 08:33, 8 February 2010 (UTC)

Unit Symbol

I would like to propose adding the Q=It equation found on the Ampere page on this page, as Q also represents Coulombs. I feel that this would help clear some confusion I personally experienced initially, which was why there where two different symbols (C and Q) for the coulomb. Or is there some reason why its not there? 209.129.16.5 (talk) 04:17, 3 February 2009 (UTC)

The symbol for coulomb is C. Q is used in that equation as a symbol for charge - which is measured in coulombs. A variable in an equation is (hardly ever) symbolized by the abbreviation for the SI unit for measuring that variable. Anyway, Q=It is a special case where the current is constant. --Wtshymanski (talk) 15:30, 3 February 2009 (UTC)

zeptocoulomb and yoctocoulomb?

Why are zeptocoulomb (10^-21) and yoctocoulomb (10^-24) listed when a single electron has a charge of about 1.602 x 10^-19 coulombs and the smallest quark charge is 1/3 of this? Is there something I'm missing here? -- B.D.Mills  (T, C) 10:37, 2 March 2009 (UTC)

Because some editors think that every SI prefix *must* be attached to every SI unit, disregarding actual usage, common sense or physical realizability to anyone other than astronomers or string theorists. I burnt on on this one about 2 years ago, but you're definitely on the right side on this one, in my opinion. --Wtshymanski (talk) 14:27, 2 March 2009 (UTC)

I agree with both of you - I'm deleting zeptocoulomb and yoctocoulomb. If somebody has a reference for those actually being used, feel free to put them back in. Enon (talk) 21:25, 17 May 2010 (UTC)

The table is automatically generated by a template, Template:SI multiples which made it difficult to edit. The best I could do was to note zeptocoulomb and yoctocoulomb as "not used". A note on when fractions of a esu are meaningful (fractional quantum hall effect, quarks etc. might be helpful or it might be off-topic. Enon (talk) 22:10, 17 May 2010 (UTC)

Zeptocoulomb is used in the article on Zepto- [[1]]. Xakepxakep (talk) 20:13, 18 March 2011 (UTC)

units

In principle, the coulomb could be defined in terms of the charge of an electron or elementary charge. ... . A coulomb is then equal to exactly 6.241 509 629 152 65 × 1018 elementary charges.

Elementary_charge It has a measured value of approximately 1.602176487(40)×10−19 coulombs.[2]

???????????// —Preceding unsigned comment added by 123.24.118.155 (talk) 03:07, 18 November 2009 (UTC)

I rewrote this part, I hope it's clearer now. The quote before was inaccurate, no one to my knowledge has proposed "6.241 509 629 152 65 × 1018 elementary charges" as a redefinition (unlike a different numerical expression which has been proposed, it's a ratio of two exact numbers). I also tried to clarify that the discussion concerns different unit systems. --Steve (talk) 21:30, 29 January 2011 (UTC)

Negative number of electrons?

"-6.24151×1018 electrons"

Since it makes no sense to have a negative number of electrons, and units are typically treated as magnitudes, not vectors, shouldn't this be positive? 71.55.0.14 (talk) 05:34, 29 January 2011 (UTC)

Hope it's OK now (thanks Wtshymanski‎). --Steve (talk) 21:30, 29 January 2011 (UTC)

It does actually make sense to have a negative number of electrons. In semi-conductor talk, these are holes. If you have a material, and you remove 10 electrons, you get charge on that material. That'd be a value of -10 electrons, or 10 holes. -John —Preceding unsigned comment added by 50.88.51.181 (talk) 21:31, 11 May 2011 (UTC)

"Not the way the coulomb is defined"?

Hi Wtshymanski,

I made this edit, which you undid here. The explanation was "not the way the coulomb is defined". Can you say more specifically what it is that I wrote that is wrong? Are you disagreeing with my "Definition" section, or my "Relation to elementary charge and "conventional Coulomb"" section, or both? Whichever it is I will be happy to supply references, I don't believe I wrote anything that isn't standard and universally accepted.

Also, you put in a template, "This section does not cite any references or sources," in a section that cites two sources! In the future I suggest the {{citation needed}} template would be a better choice. Or do you think the current citations are invalid? I can see that the battery capacity claim should have a citation, but I don't think the Coulomb's law claim needs one, it's a straightforward calculation that anyone can check. (BTW right now that example is in the article twice! You restored it without re-deleting it from the other place.) --Steve (talk) 22:43, 29 January 2011 (UTC)

UPDATE: I restored my version, now with a footnote source for almost every sentence I added. If you think something is incorrect or unclear please let me know. --Steve (talk) 19:05, 30 January 2011 (UTC)

1C = 1A x 1s? (Confusing lead paragraph)

Something is amiss and entirely confusing. Comparing the Coulomb article: "1C = 1A x 1s" with the Ampere article: "one coulomb per second constituting one ampere" leads me to believe, substituting for 1A, that 1C = (1C x 1s) x 1s which leads to my confusion.

As I understand it by reviewing information in the Coulomb and Electric Current articles: a Coulomb is the charge of ~ 6 x 10^18 electrons or protons and an Ampere is the current of that charge flowing for one second.

From the point of view of someone trying to learn and understand this, I'm utterly confused and/or thinking an error could have been made. If none of the articles are technically wrong, having such seemingly contradictory information in the lead paragraph should either be briefly explained or deferred to the body of the article.

I'm not qualified to make or suggest what the changes should be. From my point of view, it's confusing and frustrating when you're learning and something is self-defined. I may be wrong if I arrived at 1C = (1C x 1s) x 1s but I wish it were clearer instead of seeming similar to reading "canine" defined as "something in the the canine family". --70.90.174.173 (talk) 22:47, 12 February 2012 (UTC) — Preceding unsigned comment added by 70.90.174.173 (talk) 22:37, 12 February 2012 (UTC)

You might want to review your algebra; it's not helping you at this point. One coulomb per second is one ampere. 1 C/s = 1A. A steady current of one ampere transfers one coulomb of charge: 1 C/s * 1 s = 1 C. The seconds cancel. Thus physics was saved. --Wtshymanski (talk) 00:59, 13 February 2012 (UTC)
Thanks, thanks a lot. I think in the heat of trying to learn I was reading "one coulomb per second constituting one ampere" as 1C * 1s = 1A. So, 1. - it wasn't this article but the Ampere article which confused me, and 2. - there's nothing inherently wrong with that article.
I was confused nonetheless, so not to criticize but to show the UN-clarity that happens when one's learning: I missed the key word per in the spelled out equation after reading it over and over. I think I was thrown off by the equation being written in "reverse" and using the word "constituting". A symbolic(?) equation later in Ampere () uses a mix of longhand and shorthand forms by showing the implied 1s but reducing 1C/1s to - which I know is mathematically correct, but I was thinking in terms of the simplest longhand. I'm not suggesting any changes are (or aren't) warranted to the Ampere article, I just wanted to document the thought process of a lost reader in hopes it might somehow, some way, help out some future contributor: showing a reader at their thickest moment. Someday I'll learn to state things with more brevity, but 'till then, thanks again for saving physics for all and getting my brain out of an infinite loop... and thanks to all the other contributors who spend so much of their time and effort on these articles. — Preceding unsigned comment added by 24.7.92.109 (talk) 09:20, 13 February 2012 (UTC)

I don't think Wtshymanski is correct. The s's only cancel out if the later s doesn't have a value > 1. Coulomb has 2 meanings. One is its basic unit value of number of electron charges. Its other use is accumulative. 3 Amps for 10 seconds doesnt equal 3 coulomb. It equals 30 coulomb. And that's the value you would need to use if you use it with joules say to find voltage. That is a large confusion with that stuff, and related to the fact that 1sec is often left off of these formulas. — Preceding unsigned comment added by bobpaul1 (talk) 00:56, 27 November 2013 (UTC)