Talk: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 R_K-90, for the von Klitzing constant, R_K ».

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 K_J-90 for the Josephson constant, K_J ».

3) Since K_J = 2he and R_K = 1/he², we have e = 2/(R_KK_J)

4) Hence the exact value quoted originally (defining the Ampere-second in terms of 1/e = R_KK_J 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 R_K-90 K_J-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 65×10¹⁸ 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 R_K-90 K_J-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 65×10¹⁸ in coulombs. By the currently accepted values for R_K-90 K_J-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 (R_K-90 and K_J-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 R_K-90 and K_J-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 65×10¹⁸ 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 = 1.602176491612271×10⁻¹⁹ 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 ×10⁻⁷ 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)

Seems that the current (ha ha) proposal is for e=1.60217×10⁻¹⁹ C.^[1]

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 R_K and K_J, 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 R_K-90 and K_J-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, K_J, R_K, and α, you need only pick any two (remember that µ₀ ≡ 4π×10⁻⁷ N/A²):

You can also express e in terms of any pair of the others (except R_K and α): e = (h/R_K)^1/2 = h·K_J/2 = 2·h·α/µ₀·c = 2/R_K·K_J = 4·α/µ₀·c·K_J

--Urhixidur 14:58, 7 August 2006 (UTC)

just because there are expressions of R_K in terms of h/e² or 2/e·K_J, 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 R_K to be some conventional constant (by redefining the kg to set h and e to some values or to set e and K_J), you can't. if the conventional value for R_K 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 R_K, the that conventional value just cannot be right, given the present state of knowledge. r b-j 17:37, 7 August 2006 (UTC)

The statement is correct but confusing. It can be defined as stated, but currently isn't defined that way. In many standards, some words have specific meanings, such as shall. Others don't, even if they would in English. One result is that may and may not are synonyms. Gah4 (talk) 05:20, 27 April 2018 (UTC)

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)

Hebert Peró (talk) 22:09, 11 March 2014 (UTC)Just to help clarify, the person who referred to Amps in that locomotive knew that an engineer could make the connection of power and current, so (s)he gave the power in hp and current in amps. The missing number is the efficiency of the generator, but it is a precision number that does not matter in that context. Anyway, in a machine of that power, one could use η of 98% and be very close to the real number. So I judge it adequate, because it is not a definition, but simply an illustration. If it is a consensus, I can revise it.

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

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. 76.24.28.237 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)

This spec sheet: http://www.thunder-sky.com/pdf/200725164258.pdf , 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)

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 124.253.3.21 (talk) 06:23, 30 April 2008 (UTC)

I have put a title on this section, based on the IP address 124.253.3.21 being in India. Perhaps someone familiar with electric power in India can answer. --Gerry Ashton (talk) 13:28, 30 April 2008 (UTC)

what is aparameter —Preceding unsigned comment added by 196.0.25.118 (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 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)

There is no cause and effect -- the ampere was defined from use of an equation that, when solved for current, will depend on the specific value of μ₀ existing already. So simultaneously we get the size of the ampere and and we get the specific defined value of μ₀ that is considered as a fixed value in the SI system, not subject to refinement by experiment. At the time I write, there is the proposal to make the elementary charge value fixed instead and defining the ampere in terms of that, which would then make μ₀ become unfixed and then subject to refinement. (Also about the below comment, the prior use of cm and such doesn't matter -- the ampere was sized for convenience regardless.) Nicknicknickandnick (talk) 05:03, 27 April 2018 (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). 132.165.76.2 (talk) 12:54, 13 April 2011 (UTC)

The 2 comes from Ampère's force law, which comes from the integrals in the Biot-Savart law. The power of 10 to make a nice sized unit. Gah4 (talk) 05:32, 27 April 2018 (UTC)

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.220.237.63.219 (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.

(122.167.235.238 (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.128.95.172.173 (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? 70.109.176.87 (talk) 03:45, 29 October 2010 (UTC)

The source cited on in the above discussion by 128.95.172.173, 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).

188.192.109.185 (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. 86.159.159.194 (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)

Yes only life and light output change, but by large enough factors that the difference is significant. In the US, it is common to use 130V lamps in industrial environments where lamp changing cost is large enough to shift the optimum, compared to 120V for home use. I suspect in 220V countries, 240V lamps could be used the same way. You would not want to use 220V lamps at 240V for normal use. The efficiency of induction motors can be significantly different. Switching power supplies for electrical equipment can run over a wide voltage range. Gah4 (talk) 05:40, 27 April 2018 (UTC)

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. 128.95.172.173 (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. --69.255.17.51 (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)

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)

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. 86.159.159.194 (talk) 12:18, 7 November 2012 (UTC)

Hebert Peró (talk) 23:17, 11 March 2014 (UTC) Maybe we could create this section to clarify the use of Amp as a "Power-like" unit. Something like:

It is common the misuse of Ampere to refer to power, instead of current.

The main reason is the tendency of the standardization of the voltages in general. As Power (watt) is the product of Voltage (Volts) and Current (Amps), and the voltage is standardized in an application, the current becomes indication of power.

For example, cars use 12 Volt batteries, but the advertisement may say: "10 Amps more power than...". If the voltage is fixed in 12 volts, then a battery with 10 Amps more, means that it has 120 watts more power than others.

The same occur with home appliances, industry components etc. The idea is that you can easily calculate the real number by the information given, i.e. calculate watts using Amps.

As an illustration, think about asking the seller, in a car battery store, for a 12 Volt battery. S(he) will ask immediately: "how many Amps?" or, understanding that the question is really "As I need a new battery, and I don´t know it, can you sell me the correct one for my car?", s(he) will ask: "what is your car model and year?", and look up the "Amps" in a catalog.

This is tricky. Vacuum cleaners are commonly advertised in amps, but given the power factor for inductive loads, that isn't very useful. Gah4 (talk) 05:43, 27 April 2018 (UTC)

What blithering crap. Leave physics to physicists. An amp is a couloumb per second. DOne, — Preceding unsigned comment added by 165.201.140.130 (talk) 20:13, 13 May 2014 (UTC)

And what then is a coulomb? — Preceding unsigned comment added by 94.196.243.2 (talk) 11:42, 13 March 2016 (UTC)

All batteries I know of are rated in Amp-hours (big ones) or mA H (small ones), not in C or mC. The article suggests that they are in C. Gah4 (talk) 14:20, 25 October 2015 (UTC)

The definition really should point out that (a) the current definition also fixes the value of the permeability of free space, and (b) in effect, the current definition in effect defines the Amp by defining the permeability of free space as a fixed value (the theoretical experiment involving parallel wires really just being a rather convoluted way of getting permeability involved) — Preceding unsigned comment added by 94.196.243.2 (talk) 11:45, 13 March 2016 (UTC)

I had thought that the US NEC limited the current for usual (type A) plugs from 15A outlets to 12A. I was going to change the values, but it seems that there are 1800W (15A) toasters. I believe it is 12A for hair dryers, though. You can watch them get closer, and finally reaching 1440W. I don't have a current NEC to look it up. Gah4 (talk) 08:48, 1 April 2016 (UTC)

How should we fix it?

Actually it's hard to say which is worse, the fact that the new definition makes the page out of date, or the wording of the new definition itself, which contains undefined terms like A and ∆ν. (The latter refers to the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, namely 9192631770 Hz, but a casual reader of this Wikipedia article might not immediately recognize it as such.) In my case I came to this article because I needed the exact definition of the ampere, which I had to go elsewhere to find since this clearly was not it.

Since elementary charge (that of a proton) is so fundamental, I don't understand why the coulomb was not defined as a certain number of elementary charges and an ampere as one coulomb per second. All I can think is that the electronvolt should be a certain number of joules, namely ${\displaystyle 1.602176634\times 10^{-19}}$ joules exactly, and that this relationship for some reason takes precedence over the number of electrons in a coulomb. Had the latter been used it would have been natural to make it an integer, as with the Avogadro number. In fact the reciprocal, 6241509074460762607.77624098... is not quite an integer, falling short by about 9/40 of an electron, .223759... to be more precise. Vaughan Pratt (talk) 19:21, 11 July 2019 (UTC)

The new definitions are all in 2019_redefinition_of_the_SI_base_units. It doesn't explain the reasoning behind the definition of the charge of the electron, though. Some are to make the uncertainties come out small enough, and in the right places. I was wondering not so long ago, why Avogadro's number was not a multiple of 12, such that an integer number of C-12 atoms would be in a gram. Again, I didn't try to follow the math. Since coul/electron is used in calculations more often that electrons/coul, maybe that is the reason. Gah4 (talk) 21:37, 11 July 2019 (UTC)

To improve consistency, shouldn't the title be "Ampere (unit)"? — Preceding unsigned comment added by Davidhaugs (talk • contribs) 13:01, 6 February 2021 (UTC)

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