# Why is V the symbol for voltage?

1. Jan 22, 2013

### spareine

I was wondering why V is a common symbol for voltage. The symbol is not named after the unit volt, because it is older than the volt unit, which dates from 1874. Before that, voltage was potential. In 1828 Green used the symbol V for the potential function which he introduced in his essay on electricity. In 1785 Laplace used the symbol V for M/r, in his Théorie des attractions. Laplace used V without giving it a name, but to us it is the gravitational potential except for a constant. In 1788, Lagrange expressed conservation of vis viva (living force, energy) as T+V = const, with T=1/2 m v2. (Méc. analytique)

So now I am wondering if the symbol V is named after vis viva.

2. Jan 22, 2013

### OmCheeto

TLDR
Nickt spreken me Frenchy.
Nickt spreken me Frenchy again.
You are welcome.

3. Jan 22, 2013

### Whovian

I think the OP stated that the symbol V predated the unit "volt." I can't confirm this since I'm quite rusty on my physics history. :tongue2:

4. Jan 22, 2013

### OmCheeto

I cannot confirm that V predated the volt.

Although originally published in 1828, there is no guarantee that subsequent transcriptions didn't replace his symbol for volts, with "v".
Therefore, I would have to view the original work.
Green: 14 July 1793 – 31 May 1841
This is dated: MDCCCXCIV
which translates to 1894.
The "volt" was given its name in 1881. (Encyclopædia Britannica, Volume 12, page 426)
For the same reason as above, "v" may have replaced what Pierre Simon Laplace originally used.
Laplace: 23 March 1749 – 5 March 1827(wiki)
T=1/2 mv2 is the equation for kinetic energy. "v" stands for velocity. So this is a bit of a red herring.
Mec. Analytique dated: 1811
Joseph Louis Lagrange: 25 January 1736 – 10 April 1813
And I still don't speak French.
I'm going to go out on a limb again and say that "V" is named after Alessandro Giuseppe Antonio Anastasio Volta (18 February 1745 – 5 March 1827)

It would make sense to me that after the Volt was given its name, everything published afterwards would use that name, regardless of what was originally used. Imagine the confusion of students if the original symbols were used. Electricity is confusing enough, without having to memorize what every person through history referred to it as.

If Laplace did use "V" for voltage (vis viva), it may have been a happy coincidence.

ps. To the OP, thank you for this question. I should know this stuff. And if you can find the original transcripts of Lagrange and Green, I would very much like to see them. My oldest textbook is only 78 years old.: Introduction to Quantum Mechanics, by Linus Pauling, Cal Tech, and E. Bright Wilson, Harvard. 1935. Fortunately, my math skills are all but gone, so I can't get past page 1.

5. Jan 22, 2013

### eachus

Hmm... In (now old) Electrical Engineering texts I've seen E(electropotential) = IR, W (or P for power) = I^2R, etc. Anyway, the question for me has always been, where did the I for current come from? C is not a good choice, if you are doing integration, but why not A for Ampere?

6. Jan 22, 2013

### cabraham

The German word for "intensity" is what gave birth to "I" for current. I'm not sure if the quantity was called "current" in the 1830's. I believe it was either Ohm or Kirchoff that used the term "intensity". I haven't read up on this issue for a long time, but I do remember that "I" denotes "intensity".

Claude

7. Jan 22, 2013

### OmCheeto

I don't know.

hmmm...

Ah ha! It's those darned French people again...

André-Marie Ampère
Born 20 January 1775 Parish of St. Nizier, Lyon, France
Died 10 June 1836 (aged 61) Marseille, France

8. Jan 22, 2013

### ModusPwnd

Thx for that. Before you posted this I did a google translate for "current to german" but it started with "s".

9. Jan 22, 2013

### the_emi_guy

Its not German, its from French (as OmCheeto pointed out). Ampere was a French physicist.

10. Jan 22, 2013

### spareine

In 1881 the cgs-system was adopted: "The British Association got the happy idea to designate the various units by the names of scholars to whom we owe the major discoveries that have led to modern electricity, you have followed this path, and now the names of Coulomb, Volta, Ampere, Ohm and Faraday remain closely linked to the daily applications of the doctrine which they were the happy creators " http://seaus.free.fr/spip.php?article964 [Broken]

The work of Green and that of Laplace is mathematical, they do not contain units.

Mathematically, gravitational force near a point mass and electrostatic force near a point charge are similar, they obey an inverse square law. Their potentials are similar as well. V=-GM/r and V=(1/4πε)Q/r . Laplace studied gravity, Green studied electricity. The purpose of the links was to illustrate that the symbol V was used for any potential in the 18th and 19th century, and for potential energy (V = const - 1/2 m v2)

Standardization of the units happened late in the 19th century.

Last edited by a moderator: May 6, 2017
11. Jan 23, 2013

### spareine

Actually, Maxwell chose the symbol C for current in his Treatise on Electricity and Magnetism (p.236), and he assigned the I to the Magnetization (M, today). He had assigned the A already to the vector potential.

12. Jan 23, 2013

### DiracPool

Qu'est-que c'est?!