Talk:Coulomb

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.

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.

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)

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)

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)

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)