Ohms law question.

[CreoNic]

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*I

In Swedish/European:
U=R*I

None of us express Ohms law with the unit we measure in.
V= ?*A
We 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?

[c4757p]

Hmm.... we use U at my school sometimes, but it's not consistent. I am curious too

[AndyC_772]

I've never, ever seen the symbol U used for potential difference.

V=IR. The end.

[Metalcrowe]

We only use U for voltage in Switzerland.

[IanB]

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.

[Wytnucls]

U is also used in Belgium and France, as in U=IR

[AndyC_772]

OK, I've learned something. What does the U stand for?

[Kromag]

What does the U stand for?

As Metalcrowe wrote - U is for voltage...

[Wytnucls]

U is for 'tension', V is for volt, the unit of measurement of 'tension'

[AndyC_772]

So it's not a word that actually starts with a 'U', then... just an arbitrary choice of letter?

[nanofrog]

Seen "E" used to represent voltage here in the US as well.

[alm]

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.

I'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.

[IanB]

"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 - IR

to express the relationship between the internal voltage potential and the actual output voltage allowing for internal resistance.

(Edit: simulpost with alm)

[maros]

Seen "E" used to represent voltage here in the US as well.

I think that "E" may come from electromotive 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.

[con-f-use]

I have studied Physics, build circuits for 10 years and bought 4 oscilloscopes without ever seeing V=R I once.

[IanB]

I'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.

Well, 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

[Dave]

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.

[madires]

We use U too. One of multiple explanations is that the U is based on the Latin verb "urgere".

[ddavidebor]

also sometimes "e" is used for potential

[Bored@Work]

So it's not a word that actually starts with a 'U', then... just an arbitrary choice of letter?

Nop, Latin ugero - (among many other things) meaning to press, push, force, drive.

[SAI_Peregrinus]

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.

[nanofrog]

Physicists happily use F for free energy and EE textbooks often use E for electric potential.

"E" is often used to represent potential

I figured as much, but what I tend to think of is the front cover of Ugly's Electrical Safety Handbooks due to the formula wheel printed on it (http://www.amazon.com/Uglys-Electrical-Safety-NFPA-Edition/dp/1449642411/ref=pd_sim_b_2#_). 

[Dave]

People who use E for voltage, which symbol do you use for electric field?

[c4757p]

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.

[AndrejaKo]

Here in Serbia we use several popular combinations:

U is used for constant tensions and effective tensions, U is 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, E is 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.