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I've been told to use the term ampere in exams and class (I'm in high school), instead of amp as it's not a valid unit, although I've been using the amp for years along with all of my friends who do electronics.

Is this technically invalid or acceptable as far as the scientific consensus goes, and what would you think if you saw it used in a scientific paper?

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  • $\begingroup$ Whatever the answer, your teacher has evidently done the right thing since he's got you thinking about the potential issues relating. $\endgroup$ – Lightness Races in Orbit Aug 11 '14 at 11:11
  • $\begingroup$ @baharini It's entirely up to you (no pressure), but alemi's answer is now far more official and complete than mine so you may consider changing the accepted answer. $\endgroup$ – user10851 Aug 11 '14 at 18:29
  • $\begingroup$ Thanks Chris, I've changed it, hopefully someone else will find it useful. Thanks for your answer anyway ;) $\endgroup$ – baharini Aug 11 '14 at 18:33
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Technically, apparently, your teacher is correct.

BIPM and NIST

In the official brochure from the Bureau international des poids et mesures (BIPM, the keepers of SI units) in §5.1 Unit symbols we find:

It is not permissible to use abbreviations for unit symbols or unit names, such as sec (for either s or second), sq. mm (for either mm2 or square millimetre), cc (for either cm3 or cubic centimetre), or mps (for either m/s or metre per second). The use of the correct symbols for SI units, and for units in general, as listed in earlier chapters of this Brochure, is mandatory. In this way ambiguities and misunderstandings in the values of quantities are avoided.

In NIST's official SI guide, §6.1.8 we find (thanks to Emilio):

6.1.8 Unacceptability of abbreviations for units

Because acceptable units generally have internationally recognized symbols and names, it is not permissible to use abbreviations for their unit symbols or names, such as sec (for either s or second), sq. mm (for either mm2 or square millimeter), cc (for either cm3 or cubic centimeter), mins (for either min or minutes), hrs (for either h or hours), lit (for either L or liter), amps (for either A or amperes), AMU (for either u or unified atomic mass unit), or mps (for either m/s or meter per second). Although the values of quantities are normally expressed using symbols for numbers and symbols for units (see Sec. 7.6), if for some reason the name of a unit is more appropriate than the unit symbol (see Sec. 7.6, note 3), the name of the unit should be spelled out in full.

Both sources agree that when printed, the unit's name should appear as the lowercase, non-italic: "ampere" and its symbol should be the uppercase roman script letter: $\mathrm{A}$.

When spoken, people regularly use "amp" as short for "ampere" (which never causes confusion), though it would appear, according to official recommendations, in printed material the full name should always be used.

IEEE

For engineers (specifically the IEEE) the policy seems more lax, though in an amusing way.

Specifically in IEEE Std. 260-1 [doi] we find in footnote 1:

The unit names ampere and second have sometimes been abbreviated amp and sec, respectively, but this usage is now deprecated. The standard unit symbols for ampere and second are A and s, respectively

But then in 2014 IEEE Standard's Style Manual [pdf], regarding footnotes in §16.2 Footnotes we find:

Mandatory requirements shall not be included in text footnotes because these footnotes are not officially part of the standard.

so it would appear IEEE members are unbound from the deprecation mentioned.

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    $\begingroup$ Note that the NIST guide (§6.1.8) specifically rules out the abbreviation 'amp' in printed material. $\endgroup$ – Emilio Pisanty Aug 11 '14 at 10:32
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    $\begingroup$ @EmilioPisanty Thank you. I had been visually and algorithmically searching for 'amp', and somehow completely missed that occurrence of 'amps'. And that section title for that matter. I should sleep more. $\endgroup$ – alemi Aug 11 '14 at 12:26
  • $\begingroup$ Would upvote again if I could. I was also surprised to find that the name of the unit is simply 'ampere', without the capital A or the accented è. Go figure. $\endgroup$ – Emilio Pisanty Aug 11 '14 at 13:10
  • $\begingroup$ @EmilioPisanty The drop of the accent is complicated. The BIPM goes out of its way to say that the English translation of the standard is not to be considered official in the Notes at the top of the brochure: "Readers should note that the official record is always that of the French text." In the french it appears as "ampère", but not knowing french I don't know if they specifically refer to unaccented versions in the french guide. $\endgroup$ – alemi Aug 11 '14 at 13:18
  • $\begingroup$ Huh, I'll be darned. My French is pretty limited, but as far as I can tell they completely gloss over the matter. My guess is that the name is 'ampère' in French and 'ampere' in English, particularly comparing the lists (ampère, mètre, kilogramme) vs. (ampere, metre, kilogram) (§2.1.2). Thus you'd use the unaccented version unless you also felt compelled to translate kilogram into French. Or something. $\endgroup$ – Emilio Pisanty Aug 11 '14 at 13:28
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If I saw the word "amp" written as such in a paper in my field (astrophysics) it would strike me as a bit informal. I would expect to see the full "ampere" written.

That said, it is rare to actually write out the full name of a unit; usually it follows a number and is given its standard abbreviation. When abbreviated to e.g. "$5\ \mathrm{A}$", I would pronounce the quantity as "five amps" even when giving a formal presentation. I just wouldn't write "amp." (Similar to how I would use contractions while giving a formal presentation, but I wouldn't write them in a journal paper.)

Customs may vary from one field to another, however. Most scientific journals have very detailed style guides for authors that cover things like this. And even if you ignore their requests they often fix up such usages to standardize them before the article goes to print.

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    $\begingroup$ As an engineer, seeing "ampere" in a paper is a bit jarring. I usually see "amps" or simply the symbol "A". It's weird how we insist on using Ampere's full name for the unit but simply only the first four letters of Volta's name. $\endgroup$ – slebetman Aug 11 '14 at 4:40
  • $\begingroup$ Check out the IEEE journal online for an example of a journal where you'd find more mention of "amps" than "amperes". $\endgroup$ – slebetman Aug 11 '14 at 4:47
  • $\begingroup$ I feel it's a science vs. engineering thing? $\endgroup$ – Mehrdad Aug 11 '14 at 4:54
  • $\begingroup$ How many times do amps come into play in astrophysics anyways? $\endgroup$ – Nick T Aug 11 '14 at 5:58
  • $\begingroup$ @slebetman the IEEE officially appears unbound against restrictions against the use of "amps", but in a slightly amusing way, for details see my answer below. $\endgroup$ – alemi Aug 11 '14 at 13:05
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According to the Wikipedia page, amp is acceptable, but is not a correct SI unit. I think your instructor is being thorough and making certain that you know the correct term to use.

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For me in my own field (optics, where one most often comes across it in engineering considerations), "amps" is common spoken usage, particularly for compound words such as milliamp or microamp.

For written usage, I'm afraid I like to see the full name - it is, after all, recalling a very great man of science André-Marie Ampère. Even so, curiously, the SI convention I believe is only to use the upper case "A" in the abbreviation, and the lower case for the full name (even thought it is someone's name); thus one writes "5 A" but "5 ampere" (note that one doesn't use the plural form in SI, either).

If you think of "amp" as a kind of "diminutive" name, you won't go far wrong. My passport and other documents have my full forename in them, my friends simply call me "Rod"; likewise everyone calls my little son "Sascha" whereas his name on all documents is "Alexander".

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    $\begingroup$ One doesn't write "ampères" — the unit is called "ampere" in English, without that "è" thing. $\endgroup$ – Ruslan Aug 11 '14 at 11:32
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    $\begingroup$ @Ruslan BTW you're right about the lack of accent: I didn't know this, and it's never been picked up in any paper I've written. $\endgroup$ – WetSavannaAnimal Aug 11 '14 at 11:58
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Well, amp is also used as a short form of "amplifier". I highly suggest to use the full name of the unit or its symbol, i.e. Ampere or A. :)

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    $\begingroup$ Are you suggesting that using 'amp' for 'ampere' will indeed lead to confusion with 'amplifier' on real-world cases? It would be helpful to back this up with examples. $\endgroup$ – Emilio Pisanty Aug 11 '14 at 10:27

protected by Qmechanic♦ Aug 11 '14 at 10:48

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