Ohms law question. - Page 1
Forum section: electronics / beginners

author: CreoNic
author_rank: Newbie
timestamp: October 07, 2013, 08:26:03 pm
content: I'm not a beginner but all of a sudden I just realized that I don’t know the history behind the difference between the European/Swedish Voltage naming and American/English voltage naming.Ohm law in American/English:V=R*IIn Swedish/European:U=R*INone of us express Ohms law with the unit we measure in.V= ?*AWe don’t want to mix in the measurement units in calculations.So, the Swedish/European way to use U instead of V seams consistent.But V=R*I seams to be the most frequent used in the world.Is there anyone here that know some history behind this difference?

author: c4757p
author_rank: Super Contributor
timestamp: October 07, 2013, 08:27:15 pm
content: Hmm.... we use U at my school sometimes, but it's not consistent. I am curious too

author: AndyC_772
author_rank: Super Contributor
timestamp: October 07, 2013, 08:31:01 pm
content: I've never, ever seen the symbol U used for potential difference.V=IR. The end.

author: Metalcrowe
author_rank: Contributor
timestamp: October 07, 2013, 08:32:57 pm
content: We only use U for voltage in Switzerland.

author: IanB
author_rank: Super Contributor
timestamp: October 07, 2013, 08:35:53 pm
content: There is often a choice for what letter or symbol to use to represent different quantities in physics.We can say fairly readily that "V" is for voltage, and "R" is for resistance. It would be difficult to use "C" for current since "C" is already used for capacitance. I believe the use of "I" comes from intensity (of current flow).In the English speaking world we don't use "U" for voltage since U already is used for internal energy (in thermodynamics). Although it is sometimes unavoidable to have the same symbol standing for two or more different things, it is best to avoid this where possible.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 07, 2013, 08:54:41 pm
content: U is also used in Belgium and France, as in U=IR

author: AndyC_772
author_rank: Super Contributor
timestamp: October 07, 2013, 08:56:03 pm
content: OK, I've learned something. What does the U stand for?

author: Kromag
author_rank: Contributor
timestamp: October 07, 2013, 08:57:14 pm
content: Quote from: AndyC_772 on October 07, 2013, 08:56:03 pmAsMetalcrowewrote - U is for voltage...

author: Wytnucls
author_rank: Super Contributor
timestamp: October 07, 2013, 09:04:37 pm
content: U is for 'tension', V is for volt, the unit of measurement of 'tension'

author: AndyC_772
author_rank: Super Contributor
timestamp: October 07, 2013, 09:06:17 pm
content: So it's not a word that actually starts with a 'U', then... just an arbitrary choice of letter?

author: nanofrog
author_rank: Super Contributor
timestamp: October 07, 2013, 09:08:25 pm
content: Seen "E" used to represent voltage here in the US as well.

author: Unknown
author_rank: Unknown
timestamp: October 07, 2013, 09:12:21 pm
content: Quote from: IanB on October 07, 2013, 08:35:53 pmI'm not convinced that any attempt is made to avoid conflicting use of symbols. Physicists happily use F for free energy and EE textbooks often use E for electric potential. Physicists often use V instead of U for potential energy, so I guess in a high-school physics textbook it makes sense to pick U for voltage to avoid confusion (voltage is potential energy per unit of charge, not potential energy).I guess the use of both U and V for voltage is because both are used for potential energy, and voltage is closely related to potential energy. No idea why potential energy would be indicated by U and V.

author: IanB
author_rank: Super Contributor
timestamp: October 07, 2013, 09:14:53 pm
content: "E" is often used to represent potential, as in the EMF of a voltage source, whereas "V" is the measured voltage. Thus we might write:V = E - IRto express the relationship between the internal voltage potential and the actual output voltage allowing for internal resistance.(Edit: simulpost with alm)

author: maros
author_rank: Contributor
timestamp: October 07, 2013, 09:20:05 pm
content: Quote from: nanofrog on October 07, 2013, 09:08:25 pmI think that "E" may come fromelectromotive force. As for "U" used for describing voltage unlike "V", this is because "V" is for voltage units, like Greek omega for resistance and (A) Ampere for current.

author: con-f-use
author_rank: Unknown
timestamp: October 07, 2013, 09:20:19 pm
content: I have studied Physics, build circuits for 10 years and bought 4 oscilloscopes without ever seeing V=R I once.

author: IanB
author_rank: Super Contributor
timestamp: October 07, 2013, 09:24:55 pm
content: Quote from: alm on October 07, 2013, 09:12:21 pmWell, yes, there aren't enough letters in the alphabet, even when including Greek letters.When it comes to free energy we can also find G for Gibbs free energy and A (or F) for Helmholtz free energy. It has to be "A" and not "H" for the Helmholtz energy because H was already taken for enthalpy. (And as noted above U is used for internal energy.)There just aren't enough letters to go around, and different letters get used for the same quantity depending on the tradition (e.g. physicists may use different symbols from thermodynamicists for the exact same thing.)Link:http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/helmholtz.html

author: Dave
author_rank: Super Contributor
timestamp: October 07, 2013, 09:25:53 pm
content: We use U for voltage (potential difference) and V for potential here in Slovenia. Makes sense to have a symbol for voltage that's different to the unit.

author: madires
author_rank: Super Contributor
timestamp: October 07, 2013, 09:28:21 pm
content: We use U too. One of multiple explanations is that the U is based on the Latin verb "urgere".

author: ddavidebor
author_rank: Super Contributor
timestamp: October 07, 2013, 09:30:04 pm
content: also sometimes "e" is used for potential

author: Bored@Work
author_rank: Super Contributor
timestamp: October 07, 2013, 09:34:32 pm
content: Quote from: AndyC_772 on October 07, 2013, 09:06:17 pmNop, Latin ugero - (among many other things) meaning to press, push, force, drive.

author: SAI_Peregrinus
author_rank: Contributor
timestamp: October 07, 2013, 09:38:04 pm
content: The worst single-character variable overloading has to be the computer engineers building robots and such.i, j, and k are common variable names for loops. EG "For i = 1 to 100" etc.i, j, and k are unit vectors for the X, Y, and Z axes. The mechanics of your robot or other physical system will use this.I is current.i is the imaginary unit for mathematicians, and j is the imaginary unit for EE/CEs.So i can have four possible meanings (possibly more) depending on case/font/vector notation, j can have three, and k two. Context becomes very important.

author: nanofrog
author_rank: Super Contributor
timestamp: October 07, 2013, 09:57:17 pm
content: Quote from: alm on October 07, 2013, 09:12:21 pmQuote from: IanB on October 07, 2013, 09:14:53 pmI figured as much, but what I tend to think of is the front cover ofUgly's Electrical SafetyHandbooks due to the formula wheel printed on it (http://www.amazon.com/Uglys-Electrical-Safety-NFPA-Edition/dp/1449642411/ref=pd_sim_b_2#_).

author: Dave
author_rank: Super Contributor
timestamp: October 07, 2013, 11:07:58 pm
content: People who use E for voltage, which symbol do you use for electric field?

author: c4757p
author_rank: Super Contributor
timestamp: October 07, 2013, 11:11:28 pm
content: I've only seen E used for potential in situations where a symbol for electric field is not needed. I've seen E for potential in my Circuits class, but in Physics we used U, and E for field.

author: AndrejaKo
author_rank: Frequent Contributor
timestamp: October 07, 2013, 11:37:32 pm
content: Here in Serbia we use several popular combinations:U is used for constant tensions and effective tensions,Uis for complex tensions, Um (or just sometimes U) is for maximum amplitude of time-variant tension and u is for time-varaint tension as in u=Um*cos(omega*t).E is used for constant electromotive force source and for effective values of electromotive force,Eis used for complex values of electromotive force, Em (or just sometimes E) is used for maximum amplitude of time-variant electromotive force and e is used for time-variant electromotive force as in e=Em*cos(omega*t). Often used for ideal voltage sources (or ideal voltage generators as we call them). E is also used to represent electrical field.Then there's also variations such as Ucc, Udd and so on.On the other hand, we use V and phi for electrical potential, so you can find for example U12=V1-V2. We also don't have problems explaining the difference between tension and electrical potential, since they're two different words here.Also "effective value" is term used for what mathematicians call root of mean square and for some strange reason English is losing the use of word tension in favor of "voltage" (what's next? Being careful not to exceed your kilometrage per hourage?), but I still see that high-tension supply and high-tension lines are alive and well.

author: c4757p
author_rank: Super Contributor
timestamp: October 07, 2013, 11:53:27 pm
content: Quote from: AndrejaKo on October 07, 2013, 11:37:32 pmWe 'mericans have "mileage"........ that one's hard to place its exact usage. Sometimes it's distance per unit fuel volume, other times just distance.

author: IanB
author_rank: Super Contributor
timestamp: October 08, 2013, 12:00:42 am
content: Quote from: AndrejaKo on October 07, 2013, 11:37:32 pmIt's a long time since tension was routinely used to refer to voltage. But I recently heard "pressure" used in an archive film from years passed (as in "the electricity is delivered at a pressure of 22 000 volts"). H.T. lives on as an abbreviation long after the origin of these initials has faded into history.You can use amperage in English as an alternative to current if you wish.

author: Dave
author_rank: Super Contributor
timestamp: October 08, 2013, 12:16:36 am
content: Quote from: c4757p on October 07, 2013, 11:53:27 pmDon't you usually call that "gas mileage"?It's one thing when you have different symbols in different countries, but I had to deal with different symbols in different classes, now that was something. Our physics prof in high school insisted on using 'e' for electric charge, while our EE prof demanded we used 'Q', as it should be. Pretty freaking stupid and somewhat confusing at first, but you do get used to it eventually.

author: c4757p
author_rank: Super Contributor
timestamp: October 08, 2013, 12:31:36 am
content: Yes, we do call it "gas mileage", but we also like to abbreviate everything to a ridiculous extent, and then insist that the abbreviations are "correct". Therefore there are a lot of people who call it "mileage".

author: Unknown
author_rank: Unknown
timestamp: October 08, 2013, 12:36:59 am
content: Quote from: Dave on October 08, 2013, 12:16:36 amThis is good preparation for the real world, where as shown in this thread multiple, conflicting symbols are used for the same quantity. You're often expected to figure out from context what the symbol refers to.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 08, 2013, 12:40:18 am
content: When I first stared out in Electronics,all the texts,whether from Australia,The UK,or USA used I=E/RAs English speakers we didn't use European texts.Later on,there was a gradual change to I=V/R.I think it was mainly to prevent confusion,as E referred to "Electromotive Force",which had gone out of fashion.In English,& perhaps other languages there has been a confusion between "V" & "U"over many years.Old inscriptions often use "V" where modern usage requires "U".A classic is the letter "W"(" double U"),which is actually written as a "double V".I always assumed that European use of "U" for voltage came from this,so I just make the mental adjustment & it doesn't bother me.

author: AndyC_772
author_rank: Super Contributor
timestamp: October 08, 2013, 06:27:24 am
content: The only time I recall seeing E used for EMF was at school, in the context of a battery with internal resistance - modelled as an ideal voltage source in series with a resistor. The EMF of the battery was defined as the potential difference across the voltage source, as distinct from the voltage which would ever actually be measured in a real circuit where current is being drawn.I think in that instance it was more important to emphasize to students that there were two different quantities which needed to be considered. Giving them different symbols was a way to help get across the point that there was an unknown quantity ('E') which couldn't be directly measured in a real circuit, and the symbol V was used for potentials that could actually be measured with a meter.Since then, it's always been V.

author: ivaylo
author_rank: Frequent Contributor
timestamp: October 08, 2013, 06:53:25 am
content: Yup, never seen V=IR until I came to the states. U is voltage, E is potential and have always been at least in four Euro languages I've seen electronics books and magazines in.Time to bring upversusI guess...

author: con-f-use
author_rank: Unknown
timestamp: October 08, 2013, 08:22:24 am
content: Euro resistance symbol is easier to draw and looks more like a resistor (both through hole and smd). The other one could be confused with an inductor. Fairly easy to say what's betterNow it's time for a flame war!

author: vk6zgo
author_rank: Super Contributor
timestamp: October 08, 2013, 10:46:57 am
content: Quote from: con-f-use on October 08, 2013, 08:22:24 am*Only by Europeans!

author: olsenn
author_rank: Frequent Contributor
timestamp: October 08, 2013, 10:59:08 am
content: U is sometimes used to represent "potential" energy. Perhaps they are broading it to be voltage potential as well.

author: c4757p
author_rank: Super Contributor
timestamp: October 08, 2013, 11:08:13 am
content: I remember seeing a schematic which used both resistor symbols: the zigzag symbol for power resistors (I assume because it looks like a wirewound?). Can't remember where I saw it, though.

author: filip_cro
author_rank: Regular Contributor
timestamp: October 08, 2013, 11:23:30 am
content: In Croatia I use:U - voltageI - currentR - resistanceE - EMF? (phi) - potential? (epsilon) - electrical fieldu - signal voltage (exempje voltage going into amplifier)i - signal current

author: tazelikechickn
author_rank: Regular Contributor
timestamp: October 08, 2013, 01:22:44 pm
content: As an Automotive lecturer in Australia, I have been using the formulaV = A x ?as this is what is shown on mulitmeters and is easily understood by mechanics who use these symbols everyday.Not saying that isthecorrect way - just different and easier to identify.The picture is a poster I have made for students in class.Hope this helps

author: amyk
author_rank: Super Contributor
timestamp: October 08, 2013, 01:43:31 pm
content: Quote from: IanB on October 08, 2013, 12:00:42 amYou'll also see "pressure" often in Chinese products' mistranslations, as apparently their character for "voltage" also means "pressure".

author: tmammela
author_rank: Contributor
timestamp: October 08, 2013, 05:50:53 pm
content: Quote from: ivaylo on October 08, 2013, 06:53:25 amI'm having hard time when voltage is V, because here we have a word "puimuri" which is used to remember P = UI and U=RI. M is for mellan which is Swedish for "in between" and because they are our neighbors we know some of that language. Puimuri is Finnish for "harvester".Quote from: ivaylo on October 08, 2013, 06:53:25 amHere we use the left one but I don't like it, fuse looks almost the same.

author: ablacon64
author_rank: Frequent Contributor
timestamp: October 08, 2013, 06:56:41 pm
content: In Brazil we use V = IR but most books I've seen use E = IR. Don't remember seeing "U".

author: smashedProton
author_rank: Frequent Contributor
timestamp: October 08, 2013, 07:01:39 pm
content: V is velocity not emf...

author: AndrejaKo
author_rank: Frequent Contributor
timestamp: October 08, 2013, 07:42:55 pm
content: Here we use v for velocity.Anyway, about the resistors: Both type of resistors are used in Serbia, but it seems that there's some sort of holy war going on between various "expert" groups. Some people here argue that it's better to use american symbol for pure resistance and the IEC for complex impedance, non-ideal resistors and so on, while others claim that resistor is a resistor and needs to have only one symbol, which is the box. I've also seen different variations of the IEC resistor symbol with various types of black triangles covering one half of the box. Apparently, they used to mean different types of resistors, but I was unable to find any explanation which type of resistor was associated with which symbol.Also I've lost the count of how many times I drew a fuse when I was intending to draw a resistor.

author: JackOfVA
author_rank: Unknown
timestamp: October 09, 2013, 01:09:14 am
content: Received my electrical engineering undergrad degree in 1968 (from a university in the USA) and it was E=IR, E standing for electromotive force.