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# Spannung - Voltage - Electric Potential

Kommentar
Hello,
Something seems wrong to me about a text I'm translating. The source I am referring to ougth to be reliable, and that is why I have to ask a better authority on German Physics expressions. The problem is as follows:

The text defines 'Elektrische Spannung' and states:
"Einheit der el. Spannung ist 1 Volt (V)"

I am familiar with Spannung = voltage = electric potential.

But then the text denotes 'Elektrische Spannung' with "U".
The text then goes on to state Ohm's law (Ohmsches Gesetz) as:
"I = U/R".

I am only familiar with Ohm's law as:
"V = IR" or, in this arrangement, "I = V/R".

Why have they taken "U" instead of "V"? If it exists in this relation in Ohm's law, they can only be talking about voltage, right? In that case, can I put "V" without the proofreaders jumping down my throat about "altering the text"?
Verfassermaudie18 Mai 05, 13:12
Kommentar in germany the symbol for "Spannung" is usually "U" (don't ask me where this comes from) and its unit is "V" (for Volt)."v" as a symbol (in lower case) is used for speed / velocity.
Kommentar http://www.elektrotechnik-fachwissen.de/pdf/o...maudie, your source is right, at least as the German side is concerned. 'Spannung' in this formula is signified by 'U', whereas 'V' is the dimension unit (Volt).There seems to be a slight confusion (?) about electronic potential, voltage (V), Electric Motive Force (Emf) as the English terms are concerned.E value in Volts, cf. http://www.woodsbas.demon.co.uk/calcs/ohmslaw.htmEmf = Electro Motive Force (Volts), cf. http://freespace.virgin.net/tommy.sandham/ohm...To me, substituting U by V seems not hazardous, but: since I'm not a Physics expert in English (nor in German), I cannot ultimately tell about English proofreaders' reactions ;-)HTH
Kommentar Maudie, there is nothing wrong about your text. In german - and I guess not only there - the symbol for "Spannung" very often is U (in the english world mostly V - and I know "E" as well). Consequently we write I=U/R to state Ohm's law.The question why they have chosen the U instead of V I cannot answer, but I assume that V was already taken by V_olume and a U isn't too far away :-) I don't think there is a ofiical rule how to denote physical values.Not to confound with the symbol for the UNIT, they are named after their discoververs (Volt; Ampere; Watt; Faraday; Siemens;...).By the way, how many differnt symbols for "energy" do you know? E,U,H...?
Kommentar OK, thanks to all of you. It's good to know the source is at least correct. I would have been very surprised if it hadn't been (being an institute on electromagnetism)!!I think I will make the daring move and change the formula to the familiar (to English speakers) "I = V/R", though. I just never realised before that the denotation changes between languages.Just to clarify: I was not confusing the denotation "U" with the unit "V", I was just wondering if the symbol in German really is different or not. It would have been silly for me to translate Spannung as voltage if they were actually talking about something else.It actually comes down to a "how much of a translation do you want" question. Asking the client is out of the question, because they typically refuse to understand your dilemma, and/or lose faith in your authority as a translator. The forum is a much "safer" place to ask around...
Kommentar Wenn man das Ohmsche Gesetz betrachtet, dann ist es doch mit den anderen Größen (Stromstärke und Widerstand) auch so. Stromstärke hat die Einheit Ampère (A) und wird in Formeln mit I angegeben, der Widerstand hat die Einheit Ohm (griechisches O) und wird in Formeln mit R angegeben. Das hat alles auch so seinen Sinn, R ist ja nur ein "Wirkwiderstand", der bei Gleichstrom messbar ist oder bei Wechselstrom ohne Spulen und Kapazitäten vorhanden ist. Diese kapazitiven oder induktiven Widerstände werden in Formeln mit X angegeben, ihre Einheit ist aber trotzdem Ohm. R und X ergeben dann gemeinsam den Wirkwiderstand Z. Das muss in englischsprachigen Ländern ja auch irgendwie ausgedrückt werden.
Kommentar Du hast zwar recht Katja mit dem was du sagst, dennoch wird international für Spannung oder elektr. Potenzial ein V als Symbol UND als Einheit benutzt. Der einzige Fall, der mir einfällt bei dem da nicht unterschieden wird.
Kommentar @ Katja,That's right, there are different phenomena that have the same unit of measurement, but obviously require a different denotation in a mathematical formula. That is why I did not feel comfortable enough to assume straight away that they were talking about "voltage", even though they said the unit of measurement is the Volt.Given that U is simply not used in English, though, I feel you can't put "let voltage be U", because traditionally it is not so. It has pretty much always been "let voltage be V" where I have learned it (only up to low-level university, I admit). Though, I think I have seen it depicted as E (if memory serves correctly) in Ohms law formulas.@ Markus, there is a kind of official rule, which I have decided to use as an authority: the System Internationale (SI), which also uses V.
Kommentar @Markus: Welche Einheit und welches Formelzeichen wird denn international für die Geschwindigkeit verwendet, das gehört zwar jetzt gerade nicht hierher, interessiert mich aber doch.
Kommentar maudie:Yes, but that's again the UNITS which are described by the SI. Don't mix that up with the letter used in the formula itself!In German Physics books:I = U/R means I[A] = U[V]/R[Ohm] The letter in brackets is the letter for the unit, while the others (I,R,U) are the letters used in the mathematical formula.It seems to be that in English you would write:I[A] = V[V]/R[Ohm] but the use of V for the mathematical symbol as well as for the unit is an exception in this case! In fact, I find it even a bit confusing:V = 220 V ?? Is that how you would write it in English?In German you would write:U = 220 V where - in my opinion - it is clear that V is the unit (Volt) and U means the voltage itself.
Kommentar Katja: Geschwindigkeit ist v [m/s], Spannung U (bzw. V) [V].Man beachte die Gross- und Kleinschreibung!
Kommentar I (electr. eng.) support Anita's last statements. And I suppose that this is the (so far missing) explanation why in Germany voltage is denoted by U - simply to avoid confusion with the unit symbol.In a translation, the symbol should be "translated" to the "common term", too, if possible, because scientists are very accustomed to their usual way of reading formulas.
Kommentar Anita,You're right, of course. This time I _did_ get confused - the SI doesn't specify the letter in the formula, it specifies the unit... oops.but I wasn't confusing that before. As you can see, my exact problem at the beginning of this discussion was a little different: I was just unfamiliar with the use of U for voltage/Spannung.Anyway, the upshot seems to be that it is better to "localise" U into V to denote Voltage in formulas for English-speaking audiences.Ta, everybody.
Kommentar @Anita: Und was ist wenn die Größen zeitlich veränderlich sind, aus dem großen U wird ein kleines u, wenn man bei Wechselspannung den Momentanwert oder den Scheitelwert der Spannung angibt. Wenn man international ein kleines v nimmt, dann könnte man durcheinander kommen. Grundsätzlich ist zwar klar, ob man Spannung oder Geschwindigkeit berechnet, aber Verwechslungen sind nicht ausgeschlossen.

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