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Any chance of a simple definition? One that a high school student could understand? VoltageX 01:49, 19 November 2006 (UTC)

The Ampere is still a base unit: see the page of the International Bureau of Measurement.

Still? Are you expecting them to change it? -- Tim Starling 13:28, Dec 16, 2003 (UTC)
Yes. Once we are able to reliably count individual electrons, that will be a much more precise way of measuring many electrical quantities. Then I expect the Coulomb to become the base unit -- re-defined as containing some arbitrary number of electrons -- and the Ampere re-defined as one Coulomb per second. --DavidCary 02:41, 15 Jan 2005 (UTC)

Although amp is commonly used, the NIST defines amp as incorrect usage. It should be ampere or the symbol "A". —Preceding unsigned comment added by (talk) 14:38, 19 March 2008 (UTC)

>> The smallest commonly used submultiple of the ampere is the milliampere (mA), which is one thousandth of an ampere.

No way. One might write something like "Commonly used magnitudes range from 40 ampere home wiring down to picoampere bias currents of FET OPamps", but there are no true limits to this definition of 'commonly used'. — How about a table that compares light bulbs, a big CPU, LEDs, US/European home wiring, flashlights, transatlantic power lines, lightning bolts, car stereos, etc. ? It would take up half the space of the current article though (don't you hate that pun). Femto 15:11, 3 Nov 2004 (UTC)
Ironically, given the poster's name, the smallest commonly used unit of current is the femtoampere, not the picoampere. I have some electrometer op-amps with bias currents in the low single-digit fA.Enon (talk) 09:02, 24 December 2010 (UTC)

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From what I can determine from the article, it seems that the ampere and the coulomb are defined in terms of each other. Am I correct in assuming this? Leenewton 3 July 2005 11:55 (UTC)

It appears that way at first, but if you read closer into the article you'll find the actual definition. (Something about two wires of infinite length and 1 newton of force between them.)

As far as the definition, is the sentence, "Although this is the internationally accepted definition, one should realize that it does not actually make sense, either grammatically or mathematically." actually meant seriously. It sounds like a joke (and a good one) so if it is true, it could maybe use some explanation. If it's a joke, I suggest we leave it. 04:48, 7 February 2006 (UTC)

The definition as it stands does not seem to actually define the direction of the current - the force will be in the same direction so long as the currents are parallel rather than anti-parallel, whether the currents are of positive or negative charges. Specifying the conductors to be metallic (electron currents) would seem to give the wrong sign for the direction of conventional (positive-charge) current flow. I can't see any way to fix the definition - it is inherently scalar unless one adds in the electrochemical cell definition of the volt with one terminal defined as positive and the other negative, for example. —Preceding unsigned comment added by Enon (talkcontribs) 23:57, 17 May 2010 (UTC)

Why doesn't somebody add a definition in plain English with an analogy making it simple to understand for us laymen and laywomen who aren't nuclear physicists —Preceding unsigned comment added by (talk) 09:45, 12 March 2009 (UTC)

I added an introduction to the definition that explains the general idea of the definition. Is that better? --Jc3s5h (talk) 13:07, 12 March 2009 (UTC)

How can the electric current possibly be taken as a Base unit Quantity? Electric current is a measure of charge movement over time: it is a derived unit. The base property is electric charge with the unit as the coulomb. The Ampere is NOT a base unit, nor is electric current a Base Property. Is this entire article a big joke because it sounds like it. No offence intended. —Preceding unsigned comment added by (talk) 01:58, 15 January 2011 (UTC)

Any group of units could be declared base units so long as they will force all the other units to take on particlular definitions, and not create any contradictions. Which ones to choose would depend on being able to do experiments to realize the units with as little interaction among the definitons as possible, given the available technology. Jc3s5h (talk) 02:16, 15 January 2011 (UTC)
I might agree with 120 in that I think a more natural base unit is one of dimension electric charge and derive the unit of current from that and from the unit time. But in fact, in the SI system, the ampere is defined first without a reference to time (except in the mechanical quantities). The ampere is the amount of current flowing to get to a certain force per unit length. The from that current and from the second, a unit charge is defined. So it is the base unit from which other electrical units are derived. But I would think it more natural to define base units in time, length, mass, and charge. Although I know why the mole and candela are defined as base units, I really believe they are superfluous. But I cannot deny their status as base units in SI. (talk) 04:54, 15 January 2011 (UTC)

I need more context please, to learn about this subject

I appreciate knowing the technical information about how amperes can be exactly defined. But, it doesn't help me with what I came here to learn. The fact that something has a way in which it is exactly measured doesn't tell me a thing about how the thing is experienced in the real world.

It's like saying a clock second or minute is defined as a certain amount of radiation from caesium-133. A unit of time is something we experience in a certain way in our world, daily. How much can you think in a second or a minute? how much can you speak in that amount of time? How wet will you get in the rain in a minute?

I need to have an explanation about these scientific issues which relates to the context in which they are used and experienced.

What is an ampere? How is that measurement used in electrical circuits? Is an ampere a measurement of how much potential energy is there, or how much kinetic energy is there? To use a syllogism, is an ampere like the bulk of water flowing down a river past any given juncture in it - or is an ampere like the force that water has when it hits the same rock before falling over the waterfall? Rainbird 17:59, 17 August 2005 (UTC)

The definitions do exactly what you ask: relate the unit to a physical phenomenon reproducible in a laboratory. You cannot define the second in human terms because all the measurements you mention are inherently very variable. Rain is not a universally steady phenomenon, for example.
(By the way, the unit of time is defined by the frequency of the radiation of a particular transition of Cs-133, not by the amount of radiation, which would be a measurement of energy)
Getting back to the ampere, it is a quantity of electric charge per unit of time, so the hydraulic analogue would be the quantity of water flowing by per unit of time (cubic metres per second, for example). The force necessary to push the water through depends on the resistance opposed by the river's bed; the electric analogue is electric resistance, and the force required the voltage. These three quantities are related to each other through Ohm's law.
Urhixidur 01:34, 2005 August 18 (UTC)
Well... thank you for your comments, Urhixidur. I very much appreciate you taking a moment to explain this to me. Now, you talk about electricity requiring a force to push itself through a circuit. That would be a different stuff than the force which electricity itself, exerts, when it does it's work. Right? Another thing which I've always been curious about, is that an ampere seems to be something of a relative measurement. An ampere of electrical current would be a different amount, if you are working with 1.5volts of direct current, than if you were working of 115volts of alternating current. Is this correct?
You say the only definition needed here, is one framed up in terms of how the thing exactly can be scientifically calculated. Wikipedia is resource used by the general public, and not only by scientists who work in laboratories. I would say that there is more context needed. Everything in the world around us interacts with everything else. There are always larger contexts to put our observations into. And when we look at the larger picture, we gain a more comprehensive understanding of everything which is involved. For instance, I would like to see this article expanded, in a way which illustrates exactly how electricians, makers of computer equipment, and other technicians think and relate to the idea of amperes. For contrast, it should also be explained where they use measurements of watts, resistance, and voltage. Thus, I still insist that an ampere is a thing, which needs to be described in terms of how it is experienced in the real world; and we shouldn't be content with only a brief description of how it can be exactly measured. Rainbird 21:09, 20 August 2005 (UTC)
« ... electricity requiring a force to push itself through a circuit. That would be different from the force which electricity itself, exerts, when it does its work. Right? »
Nope. Same force. The easiest way (and most frequently used) to get electricity to do work for you is to have it heat stuff (stove tops, space heaters) or give off light (light bulbs). The electricity is forced through a resisting medium, and the resulting energy deposited in the medium radiates away as heat or light (a light bulb works because of a filament heated to white-heat, so its the same mechanism at work).
« ... An ampere of electrical current would be a different amount, if you are working with 1.5 volts of direct current, than if you were working of 115 volts of alternating current. Is this correct? »
Essentially yes. An ampere at low voltage is not the same as an ampere at high voltage. The water analogy would be a litre of water at low pressure versus a litre of water at high pressure. More energy in the latter. For direct current, the power (energy per unit of time) is equal to the voltage times the amperage (with alternating current, it's also true but there is a constant that has to be factored in to account for the time-varying voltage).
For the context you ask for, you are right in a way, but it is not the Ampere article's place; try the more general articles dealing with eletrical theory. Because you cannot compare amperages beyond saying that they represent varying quantities of electric charge per unit of time without specifying the other key factors: the resistance and voltage involved. A lightning bolt delivers a huge amperage (30 to 300 kiloamperes) but over a very short time. About the only other human-scale titbit I can dredge up at this juncture is this one: it's not the voltage of an electric shock that stops your heart (static elctricity sparks you generate by rubbing your feet on carpet is in the kilovolts range, but it can't kill you), its the amperage. It takes about 2 amperes to stop a heart from beating.
Urhixidur 03:09, 2005 August 21 (UTC)
All I see here, in what you say, is that you have a rubber ruler which you're working with. You explain that an ampere, figuratively speaking, is a measurement of volume, which does not indicate the same amount of volume, every time you use the term.
So, is the concept that voltage is a way of compressing energy? Somehow, you're able to have more electricity in any given length of that wire. This would mean it has more potential to spring back, and release the energy which was given to it, originally.
I can tell that you are a person who is fond of mathematics, and of theories which have to do with what mathematics can tell us about something.
I have to again insist, however, that there is a need for the general public to learn what these concepts mean. If you explain amperes with the language of mathematics, only, you have not communicated the definition of that concept to the ears of the public with symbols which they have in their language.
post script - I see that you are fleshing the article out a bit with the electrical safety issue. Good idea. I think the most common place people see the term "ampere" is on fuses in a fuse box.--Rainbird 06:37, 21 August 2005 (UTC)
You're reading me wrong (my mistake in writing just "litre" earlier, when I meant "litre per second"). The hydraulic analogue of amperage is not volume, it is flow rate, that is to say, volume per unit of time. And there is no fluctuation: an ampere is an ampere is an ampere. It's just that amperage, by itself, is not enough to describe unambiguously an electrical phenomenon. Going back to the unavoidable hydraulic analogy, a flow of x litres per second is an incomplete description: that flow going through a one-inch square aperture is under a lot more pressure than the same flow spread over a frontage of one kilometre (and even then one would need to specify the height of the water front to gauge its speed and pressure).
Voltage, in its turn, is not a way of "compressing" energy, it is a measure of the energy associated with the electricity. Specifically, a volt is a joule per coulomb, so it designates a very specific amount of energy attached to each unit of electric charge. Thinking in terms of the "amount of electricity" in a wire is misleading, but the analogy between a loaded spring and the voltage of an electrical supply is not a bad one.
Urhixidur 17:26, 2005 August 21 (UTC)

Why is the letter "I" used in the mathematical formula?

I understand that C is used for specific heat so we couldn't use it for current. But is there a relationship between current and the letter "I"? Is it latin? thanks for help

I've read *somewhere* that "I" was chosen since it stood for "Intensity". As a consequence, electrical engineers use "j" where mathematicians use "i" for the imaginary unit. With only 26 letters, overloading will occur, which is why advanced mathematicians must know English, Greek, Hebrew and other alphabets. ( Oh, and you can sign your posts with --~~~~, or use the signature button in the default editor.) --Wtshymanski 20:44, 29 September 2005 (UTC)
Indeed, it's explained in the electric current article. --Mudd1 (talk) 01:07, 19 January 2014 (UTC)

erroneous definition for Ampere.

just to let you know that i corrected a serious error "Alternate exact definition" that you made to the SI definition of the unit of electric current, Ampere. it's amazing that this error was left uncorrected for more than 18 months. in an article about objective physical convention, please be careful with applying words like "definition" and "exactly". do not apply those terms to things that are neither definitions nor exact. Rbj 01:04, 4 May 2006 (UTC)

I love a good argument. Considering:
1) CIPM, 1988, Recommendation 2 (PV, 56, 45 and Metrologia, 1989, 26, 70) recommends « that 25 812.807 W exactly be adopted as a conventional value, denoted by RK-90, for the von Klitzing constant, RK ».
2) CIPM, 1988, Recommendation 1 (PV, 56, 44 and Metrologia, 1989, 26, 69) recommends « that 483 597.9 GHz/V exactly be adopted as a conventional value, denoted by KJ-90 for the Josephson constant, KJ ».
3) Since KJ = 2he and RK = 1/he², we have e = 2/(RKKJ)
4) Hence the exact value quoted originally (defining the Ampere-second in terms of 1/e = RKKJ with no loss of precision).
It should be understood, however, that this exact value is not endorsed by the CIPM, which was careful to state that « Recommendations 1 (CI-1988) and 2 (CI-1988) do not constitute a redefinition of Sl units. The conventional values KJ-90 and RK-90 cannot be used as bases for defining the volt and the ohm (meaning the present units of electromotive force and electrical resistance in the Système International d’Unités (SI)). To do so would change the status of µ0 from that of a constant having an exactly defined value (and would therefore abrogate the definition of the ampere) and would also produce electrical units which would be incompatible with the definition of the kilogram and units derived from it. »
This "contradiction" holds true only if one keeps the original definition of the ampere, which is why I presented this as an alternate definition. So, you are right in saying it is not a definition --not an official one--, but you are wrong in claiming the value is not exact.
Urhixidur 02:34, 4 May 2006 (UTC)
baloney. the value is not exact because we do not know exactly what the elementary charge, measured in ampere-seconds is. the SI unite called the "ampere" is defined in such a way that the permeability constant is exactly 4 π x 10-7 (in SI units), the ampere together with the definition of the second are combined to define the SI unit of charge, the coulomb. all of these definitions are made without any reference to the elementary charge. the elementary charge plays no role in defining the Ampere nor the Coulomb. given these definitions, then physicists go about to measure the elementary charge and that is published along with their degree of uncertainty. Rbj 03:55, 5 May 2006 (UTC)
You're missing the point. The value is exact because there are no missing decimals. This has nothing to do with whether the value is correct or not. Urhixidur 16:26, 5 May 2006 (UTC)
no, Urhixidur, you missed the point. the values you give for RK-90 KJ-90 are neither exactly the values you state, nor are they exactly known, given how units like the kilogram and ampere are defined. the result, that the elementary charge comes out to be the reciprocal of exactly 6.241 509 629 152 65Template:E in coulombs, is misleading. it implies that the elementary charge is exactly known (and it's a little off from known values). Rbj 17:28, 5 May 2006 (UTC)
i made another fix. Urhixidur, we don't put "definitions" into Wikipedia that are not official definitions. or, at the very least, definitions that are not logically and substantively equivalent to the official definitions. take a look at the kilogram page. they put in these other proposed definitions in another section. if the proposed definition gets adopted by the "governing bodies", whoever they are, then Wikipedia's definition should be changed. not until then.
Nicely done. Urhixidur 16:26, 5 May 2006 (UTC)
BTW, your conventional values for RK-90 KJ-90 do not agree exactly to the current 2002 CODATA values. One is even outside the standard uncertainty. So, now that they have newer revised values for those constants, I highly doubt that even if they adopt this proposed definition for the kilogram that the result of the defined value for the elementary charge will come out to be the reciprocal of exactly 6.241 509 629 152 65Template:E in coulombs. By the currently accepted values for RK-90 KJ-90, that's already too far off. Rbj 04:49, 5 May 2006 (UTC)
Hey, it's not my convention, it is the CIPM's. SI has been moving steadily towards pinning the unit definitions to universal, natural phenomena. Taking the second as a starting point, the speed of light ties it to the metre. This leaves two degrees of freedom: the ampere and the kilogram. If the Josephson and von Klitzing constants (RK-90 and KJ-90) are used, this pins the ampere, and one can preserve the permeability constant by finally defining the kilogram from the force between conductors (as detailed in the kg article). Of course, as the CODATA values make clear, the CIPM conventional values are definitely off, which is another way of saying the "new" ampere and kilogram would be substantially different from their current values. No doubt this is in part what has prevented (and likely will continue to prevent) the new potential definitions from being adopted. The key point to realise is that the definitions of the ampere and the kilogram should go hand in hand, and that nobody disputes that the current kilogram (defined by an arbitrary lump of metal alloy) is a bad choice. Urhixidur 16:26, 5 May 2006 (UTC)
i dunno why you appeal to an 18 year old convention that conflicts with the harmonized 4 year old measurement, that was in fact not adopted an the SI definition, for anything. it's dumb. those values for RK-90 and KJ-90 are not accurate. they have revised values for that today and those revised values do not agree with your values.
really what you're talking about is a redefinition of the kilogram in such a way that preserving the permeablity, μ0 to what it is, will also fix the value of the elementary charge e, to an exact value. but there are two mistakes that you are making. first, they might redefine the kg to fix Planck's constant, h, to an exact value instead (instead of choosing to fix e). i think that is more likely after reading papers from Peter Mohr and Barry Taylor. second, if they change the definition of the kg away from the Paris prototype so such that fixes either h or e, they will do it in such a way so that at the time of the change of definition, there will be no change in the numerical value of the constant they're fixing. as measurements are improved or revised, then the mass of a kilogram (more precise what we believe it to be) will drift away from the mass of the prototype, but the fixed constant will remain. but since we already have a newer and different value for e, given our present base unit definitions, there's less than an ice cube's chance in hell that they will ever redefine a Coulomb to be precisely 6.241 509 629 152 65Template:E elementary charges. that number is crap. it is already outside the std. uncertainty of the known value of e. but in any case, it ain't the definition and to say it is, is misleading. Rbj 17:28, 5 May 2006 (UTC)

okay, Urhixidur, i believe and hope that i came to a revision that is substantively accurate and is acceptable to you. if and when the kg gets redefined in such a manner as to set the elementary charge to be virtually e = 1.602176491612271Template:E C, then your alternative definition of the ampere will be functionally equivalent to the present definition. since they haven't yet done that (and they might not, i would be rooting for them to define the kg to fix h instead), the alternative definition is not functionally equivalent to the official definition, so it isn't yet a definition, but is a proposed definition. actually, since the definition of the ampere need not change from its present definition fixing μ0 = 4 π Template:E H/m, this redefinition of the kg does not change the definition of the ampere, but creates a functionally equivalent alternate definition (that is not in force, presently). i hope these last changes to the ampere and kilogram article meet with your approval. Rbj 01:03, 7 May 2006 (UTC)

Looks good enough for now. I would also like to see a discussion (maybe in the metrology article, but more likely in the SI article) of degrees of freedom of the system of units, and of the continuing drive to tie each unit to known physical phenomenon. It would tie in nicely with the similar discussion already extant about the differences between the CGS esu and emu systems.
Don't think I'm pushing for KJ-90 and RK-90 to become enshrined (like c already is). They're too obscure —compared to Planck's constant, for one.
Urhixidur 02:02, 30 May 2006 (UTC)

RK-90 is just a conventional value. It cant be made exact by redefining the kilogram because the von Klitzing constant equals half the speed of light times the magnetic permeability of free space divided by the fine-structure constant. The speed of light and the permeability of free space are already defined as 299792458 m/s and 4π/10^7 N/A^2 respectively, so we'd need to know the exact value of the fine structure constant to do that. --Army1987 09:33, 2 August 2006 (UTC)

I agree with Army here. Even though the elementary charge can be defined to an exact value (which would result in a valid alternative definition of the Ampere to be a specified number of elementary charges per second passing a boundary) by redefining the kilogram, that doesn't mean it would do it by redefining RK and KJ, but just e. However, I still think it's more likely that they'll redefine the kg to set Planck's constant to a defined value instead. Perhaps we should take out all of the talk of RK-90 and KJ-90 in the alternative definition. r b-j 19:56, 2 August 2006 (UTC)
It's six of one, half a dozen of the other; of h, KJ, RK, and α, you need only pick any two (remember that µ0 ≡ 4πTemplate:E N/A²):
h = h e²·RK e/KJ µ0·c·e²/2·α
RK = h/e² RK 2/e·KJ µ0·c/2·α
KJ = e/h 2/e·RK KJ 4·α/µ0·c·e
α = µ0·c·e²/2·h µ0·c/2·RK µ0·c·e·KJ/4 α
You can also express e in terms of any pair of the others (except RK and α): e = (h/RK)1/2 = h·KJ/2 = 2·h·α/µ0·c = 2/RK·KJ = 4·α/µ0·c·KJ
--Urhixidur 14:58, 7 August 2006 (UTC)
just because there are expressions of RK in terms of h/e² or 2/e·KJ, it doesn't matter. µ0 and c are defined and α is a primary measurement (being that it is dimensionless and we actually measure dimensionless values). so even it it appears you can define RK to be some conventional constant (by redefining the kg to set h and e to some values or to set e and KJ), you can't. if the conventional value for RK puts it outside µ0·c/2·α and α is the only measured quantity and is outside of the standard uncertainty of the what you would get for α resulting from that conventional RK, the that conventional value just cannot be right, given the present state of knowledge. r b-j 17:37, 7 August 2006 (UTC)

Ok, experts - but what is an Ampere?

How does a layman judge amps as a unit of electricity? How can the term be understood by layman? Ill give you an example from an article about diesel-electric locomotives: This 270,000-pound (122,470-kg) locomotive is designed to tow passenger-train cars at speeds of up to 110 miles per hour (177 kph). The diesel engine makes 3,200 horsepower, and the generator can turn this into almost 4,700 amps of electrical current. The four drive motors use this electricity to generate over 64,000 pounds of thrust.

Now, what in the blazes does this term 4,700 amps of electrical current mean? I usually hear of the term "kilowatt". If a reader can't figure it out from the article, it's useless. (The same article goes on to measure another generator as producing kw.)Scott Adler 08:16, 6 August 2006 (UTC)

if the reference to amps in that other article is uninformative, take it out. but the definition here is, i think, physically explicit. amperes is a measure of electric current, how rapidly electrical charge is moving past a boundary of some sort. it is precisely a Coulomb per second, but the ampere is defined first (from this setup with parallel wires and magnetic force) and then the coulomb is defined to be the charge that passes, in 1 second, a boundary of which a 1 ampere is flowing. r b-j 02:54, 7 August 2006 (UTC)
Without specifying the voltage, the amperage figure is useless. --Urhixidur 14:13, 7 August 2006 (UTC)
the ampere figure is useful for telling one how fat the conductors have to be. (the voltage would be useful to determine how much insulation they need on those conductors.) r b-j 17:39, 7 August 2006 (UTC)


Please don't remove multiples, for consistency they are in all seven base SI units.

Definition, Again

The definition is inconsistent. At one point the article says at an ampere is the "amount" of charge, and later it says that an ampere has nothing to do with quantity. This is patently inconsistent. PLEASE CHANGE IMMEDIATELY. 00:23, 1 September 2007 (UTC)

You need to distinguish between the definition and the relationship to charge. The definition is not in terms of charge, but in terms of forces, lengths, and such already defined base units. Charge is defined later as a derived unit. This is not so intuitive, but is the way the SI system is built up. An ampere is indeed an amount of charge displaced per second, but that's not how it is defined. It's not inconsistent. AND WHAT'S THE RUSH? Dicklyon 00:31, 1 September 2007 (UTC)
I re-ordered the section to make it more clear. I hope you find it less contradictory. Dicklyon 00:40, 1 September 2007 (UTC)

Was Ampere originally a unit of charge? This quote seems to say so

Readers of my paper are requested to bear in mind that it was written so long ago that the Ampere was still understood to mean the electromagnetic unit quantity of electricity of the Ohm series. The term is now always applied to the unit current.

Omegatron 18:09, 9 September 2007 (UTC)

What is CA?

This spec sheet: , talks about current in unit of CA. What is CA? Thanks, Daniel.Cardenas 14:46, 4 October 2007 (UTC)

In the battery charging rate 3CA, the A is for Amps and the C is for capacity, made nondimensional. If you have a 1 AmpHour battery, C is 1, and you can charge it at 3 A. Usually the A is omitted and his is referred to as a 3C charge rate, meaning you can charge the battery in not much more than 1/3 hour. Dicklyon 18:38, 4 October 2007 (UTC)

Its a 40 AmpHour battery. Does this mean C is 40 and you can charge it a max of 120 amps? I'm wondering if this kind of information should go into the main article. I don't see how. Thanks! Daniel.Cardenas 23:10, 4 October 2007 (UTC)

Yes that's what it means; no it doesn't belong in the Ampere article. Dicklyon 23:46, 4 October 2007 (UTC)

Plugs in India

What is the difference between a 5 amp plug and a 16 amp plug and for which different electrical appliances these are used. Vivek. —Preceding unsigned comment added by (talk) 06:23, 30 April 2008 (UTC)

I have put a title on this section, based on the IP address being in India. Perhaps someone familiar with electric power in India can answer. --Gerry Ashton (talk) 13:28, 30 April 2008 (UTC)

What is a parameter?

what is aparameter —Preceding unsigned comment added by (talk) 16:07, 27 May 2008 (UTC)

The word "parameter" does not appear in the article, nor on this talk page; where did you see the word? One meaning is an argument to a mathematical function. --Gerry Ashton (talk) 16:12, 27 May 2008 (UTC)

why 2*10^–7?

Why not, you know... 1 newton? --Random832 (contribs) 16:42, 16 June 2008 (UTC)

In the article, under External links, there is a web page, A short history of the SI units in electricity. That gives a good explaination.
My summary of that external link is that the 2 comes from the fact that there are two wires carrying equal current, and the 10-7 is an scale factor that makes the magnitude of the ampere convenient. In particular, this value allows all the electrical and mechanical laws to be consistent; for example, one ampere flowing through one ohm for one second is one joule of energy, also, it requires one joule of energy to move an object a distance of one meter against a force of one newton. --Gerry Ashton (talk) 17:43, 16 June 2008 (UTC)
Right, but an ohm would be a smaller unit if the ampere were larger, so it would still be consistent. And, yeah, this makes the ampere and ohm convenient, but the farad isn't - if the ampere were a larger unit (get rid of the 10^7 and the amp we'd have would be 10^3.5 or ~3162 of what we now call amps), we'd be used to talking in microamps where we use milliamps now. (of course, the farad would be even bigger than it is now) - but mostly I was wondering why 10^-7 and not 10^-6 or 10^-8 - based on that link, though, it looks like the 10^-7 has its origins in the CGS system --Random832 (contribs) 19:36, 16 June 2008 (UTC)
It has its origins in the value of muo in the equation for the force between two current carrying wires. Check out the article on Ampere's Force Law - pretty good explanation there. PhySusie (talk) 00:21, 17 June 2008 (UTC)
You're confusing cause and effect - μ0 has its value because the ampere was set to the size it was, not the reverse. --Random832 (contribs) 02:11, 17 June 2008 (UTC)
A simple answer to the original poster's question: 2 is probably because there are two wires (as mentioned above). 10^-7 is because they originally did these experiments measuring in centimetres and grams. So force was measured in dynes = g cm s^-2 (as opposed to newtons = kg m s^-2) and the distance between the wires in cm (as opposed to m) gives you a factor of 1000 x 100 x 100 = 10^7 (from the kg, and cm twice). (talk) 12:54, 13 April 2011 (UTC)

What is a Yottampere?

Enquiring minds want to know. This page is the target for redirection from "Yottampere" yet there is no mention of what a Yottampere is on this page. I'd add it myself but I don't know what it is. (talk) 06:21, 2 September 2008 (UTC)

A yottaampere is the combination of the SI prefix yotta- with the unit ampere, and means 1024 amperes, or 1,000,000,000,000,000,000,000,000 amperes. If the entire output power of the sun were converted to electicity at a voltage of 120 volts (used for household lights and small appliances in North America) the current would be about 3 yottaamperes (see the yotta- article).--Gerry Ashton (talk) 15:39, 2 September 2008 (UTC)


The dubious numbers in this article appear to come from a fake quote, one nowhere to be found in the cited source. Gene Nygaard (talk) 17:34, 23 December 2008 (UTC)

I've removed the dubious numbers, and revised the "Proposed future definition" section to be more in line with what's in the cited sources, so hopefully this issue is now fixed. Djr32 (talk) 19:25, 8 March 2009 (UTC)


If I am giving 500 'A', what voltage should i maintain and how. Please even show me the calculation on how should I keep the track of voltage according to the Amperes.

( (talk) 07:04, 4 March 2009 (UTC))

What kind of load is the current flowing through? Is the current DC or AC? --Gerry Ashton (talk) 16:29, 4 March 2009 (UTC)


The NIST standards for SI units requires that units be lower case unless the unit is based on a human name. E.g. Hertz or Hz is correct. hz is not. See NIST section 6, 6.1.2 Both Amperes and Coulombs must be capitalized. (talk) 02:34, 29 October 2010 (UTC)

The proceeding paragraph is complete nonsense. Jc3s5h (talk) 03:06, 29 October 2010 (UTC)
Indeed.] Do these guys just not know whatever the hell they be talking about (yet insist on presenting themselves as expert) or are they deliberately trying to screw things up? (talk) 03:45, 29 October 2010 (UTC)

Template:Outdent The source cited on in the above discussion by, NIST Special Publication 811, states

"Unit symbols are printed in lower-case letters except that:

(a) the symbol or the first letter of the symbol is an upper-case letter when the name of the unit is derived from the name of a person;

A different section, section 9 ,Rules and Style Conventions for Spelling Unit Names, states

When spelled out in full, unit names are treated like ordinary English nouns. Thus the names of all units start with a lower-case letter, except at the beginning of a sentence or in capitalized material such as a title.

Emphasis has been added to the preceding quotations.Jc3s5h (talk) 13:06, 29 October 2010 (UTC)

Don't stop the quote there. The very next sentence is:

In keeping with this rule, the correct spelling of the name of the unit °C is “degree Celsius” (the unit “degree” begins with a lowercase “d” and the modifier “Celsius” begins with an uppercase “C” because it is the name of a person). (talk) 15:25, 6 December 2012 (UTC)


Interesting additions: Examples of how many amps various common appliances draw, what ratings are common on fuses and circuit breakers around the world, whether they are different for 120V or 240V countries, etc. -- Beland (talk) 02:46, 24 January 2011 (UTC)

I have added a section "Everyday examples". Does this section have the correct structure? If so, I will collect some references for the various statement made. Also, should we restrict ourselves to everyday examples, or should we look at industrial systems? In either respect, the list should be kept short. Martinvl (talk) 14:10, 25 January 2011 (UTC)
That structure is fine, though as we fill it out it would be helpful to have apples-to-apples comparisons for the U.S. vs. Europe. Thanks for your work on this! -- Beland (talk) 18:40, 25 January 2011 (UTC)

The European examples are based on the usual false premise. There is practically nowhere in Europe that has a 230 volt mains supply. Most of Europe is still 220 volts and the UK is still 240 volts and there is (at present) no intention of changing this. All that has happened is that the whole of Europe has been made nominally 230 volts with a voltage tolerance (± 10%) that encompases both the 220 volt areas and the 240 volt areas (and also the few 250 volt areas that remain in the UK). Most European domestic appliances are specified to run from 230 ± 10% volts and will thus operate anywhere in Europe. The most notable exception is filament light bulbs which are manufactured only in 220 and 240 volt versions for their respective markets. (talk) 12:10, 7 November 2012 (UTC)

"nowhere in Europe that has a 230 volt ...?" Not true. Germany, Switzerland, Austria and the Czech Republic is where I measured 230 V (± 5 Volts) most of the time. Own research... Even the light bulbs are frequently made for 230 V, meaning they deliver the specified power at this voltage. Of course they will work within ± 10%, only the light output and life expectancy is affected.

I think we should make this section "Examples" or "Examples of Amperage" and include some higher amps like the current flow in the plasma of tokamak reactors ~ 3 million amps. --JohnTsams (talk) 21:31, 29 July 2013 (UTC)

Charge passing a point, per unit time

Physicists definition would refer to charge penetrating a Gaussian surface per unit time, not passing a point. Only in one-dimensional conductors would current be the charge rate passing a point. I've added "passing a point in a circuit," although there might be a better resolution somewhere between a physicist's version and a non-scientific version. (talk) 02:41, 1 June 2011 (UTC)

How about something to the effect, "passing through a cross-section of a conductor"? Such terminology informally describes a surface that (effectively) completely traverses the path of all the charge carriers, is compatible with the Gaussian surface concept, and neatly allows for the fact that nearly all charge carriers travel on the surface of conductors (see Hall Effect). Also, (based on my experience as an EE) this kind of phrase is commonly used in texts that address basic electric theory. -- (talk) 19:19, 5 June 2011 (UTC)
I have reworded the lede, removing one of the occurences of the word "point". The other occurence is qualified as being a "point of an electric circuit". I am not convinced that all currents travel on the surface of conductors - what are the mechanics of current conduction in lightning or in plasmas. (This is not a rhetorical questions - I do not know). Martinvl (talk) 20:28, 5 June 2011 (UTC)

Revocation of 19 November 2011

Please discuss these changes at Wikipedia talk:WikiProject Measurement#Changes to the ledes of many SI-related articles. Martinvl (talk) 18:26, 19 November 2011 (UTC)

Revocations of 3 October 2012

I reverted recent changes made by User:Hgrosser on 3 October 2012. The reasoning was:

  • (S)He removed a number of "hard" spaces in the text. It is usual to include a "hard" space ( ) when writing something like "3 A" as this ensures that there is no line break between the "3" and the "A". This is in accordance with WP:MOSNUM and also international standards.
  • I reinstated the the original values of current drawn by various domestic appliances. I notice that Hgrosser appears to be American - I am British and I was writing about European appliances. I took the values from appliances around my own home. BTW, in the UK, an "Immersion heater" is an electical hot water supply. The type of immersion heater shown in the picture in Wikipedia is illegal in the UK as it is regarded as a fire risk. Martinvl (talk) 06:06, 3 October 2012 (UTC)
That would be original research then. There is no European mains supply at 230 volts (see above). What makes you think that the type of immersion heater illustrated is illegal in the UK? I can buy one in almost any hardware or electrical supplier. In any case: so what? It is an immersion heater and that is what that article is about. (talk) 12:18, 7 November 2012 (UTC)