# Who (and Why) started the “electrons are negative, protons are positive” convention? [duplicate]

For some reason everyone labels electrons using a minus sign and protons using a positive sign, even though the opposite seems more intuitive:

Who started the convention that electrons should be "negative" and protons should be "positive"?

What's the reason for choosing so?

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## marked as duplicate by Ben Crowell, Qmechanic♦Jun 18 '13 at 19:11

I think it was Ben Franklin. He called electrons negative as a guess. 50/50 chance and he got it wrong – Jim Jun 18 '13 at 16:32
@Jim, since he knew that there are more electrons in one place and less electrons in the other place, Why guess minus-sign should designate the place with more electrons when the other option seems more reasonable? – Pacerier Jun 18 '13 at 16:37
– Alfred Centauri Jun 18 '13 at 17:11
voting to close as a duplicate of physics.stackexchange.com/q/17109 – Ben Crowell Jun 18 '13 at 17:49
There is a letter written by Benjamin Franklin in which he explains this to some degree. It's at books.google.de/… on page 8. But I don't think that's the first letter he wrote about that. There should be one where he proposes the positive/negative convention and explains why. I just can't find it. – SpiderPig Jun 18 '13 at 23:43

The wording of the question suggests that the electrons were the first objects or particles whose charge required the people to establish the sign convention. But that's obviously not the case.

The electron was discovered by J. J. Thomson in 1897 but for much more than a century before that moment, people had already been studying electric (and magnetic) phenomena, even quantitatively, and they had already fixed some convention which charged objects or sides of a battery are positive and which of them are negative.

Because this convention was already established, there was absolutely no freedom in the decision about the sign of the electron's charge. It was simply measured in the cathode rays etc. and it turned out to be negative.

Historically, the first man to decide about a sign convention for the electric charge was probably Benjamin Franklin in the 18th century. His model of electricity assumed that charged objects contain some fluid – it's the electric charge of a continuous type (the similarity with phlogiston, the fluid that was believed to personify heat, can't be overlooked). If there's too much of this fluid, which is naturally identified with the plus sign, he would talk about the positive electric charge and vice versa.

Up to the moment when the elementary particles were being discovered, there was no way to prove that one of the two sign conventions was better than others. In fact, even today, it's not true that the opposite sign convention would be "better" in any sense. Electrons could carry a positive charge in the opposite convention but protons and nuclei (and up quarks) that are equally important (and, in the case of up quarks, equally fundamental) would be negatively charged while they're nicely positively charged in the world around us.

Once a convention is fixed for the electric charge, a natural convention emerges for the sign of the current, voltage, and many other electric observables, too. It just happens that in the circuits, the arrows for the current have the opposite direction than the velocities of the electrons but this discrepancy only became visible once people knew that the currents was composed of the negatively charged electrons which was a long time – a century – after Benjamin Franklin's setting of the convention. This apparent discrepancy causes no problems as long as we carefully follow it and realize (and, when necessary, emphasize) that the arrows represent the current according to the established conventions and not the electrons' velocity.

One should also point out that there exist conductors where the conductivity is guaranteed by positively charged carriers (or both), for example in solutions (positively charged ions) or semiconductors (holes). In those conductors, the signs of the current agree with the sign of the velocity of the (positively charged) carriers.

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Great answer! I think symbols help on the argument that the other sign convention would not be "better": the (local) current can be written as $\vec{I} = nq\vec{v}A$, where $n$ is the (local) carrier density, $q$ the carrier charge, $\vec{v}$ the (instantaneous, net) carrier velocity and $A$ the surface perpendicular to $\vec{v}$. – Wouter Jun 18 '13 at 18:11
Since it's called "electricity", it seems more sensible for "electrons" to be defined to have a positive charge. I guess alternatively we could start calling it "protonity"... but isn't it the flow of electrons from nucleus to nucleus that creates the electric current? – intuited Aug 27 '13 at 21:44
An anonymous user tried to edit the post to add a comment. I'll post the comment here: In the second to last and last paragraph, where "electron velocity" is mentioned, the author's may mean to say "the arrows for the current are drawn in the opposite direction than the movement of the electrons", though neither that sentence nor the one he uses make sense, because there is only one "sign" for velocity, as there is no such thing as a "negative velocity". I believe the author should correctly establish what he means to say, edit his entry, then delete this first paragraph. – glS Feb 6 '15 at 11:06
continues: Secondly, "positively charged carriers" is a confusing term, where the correct term is "positive charge-carriers". And in the case of semiconductors, "holes" are not capable of traveling by themselves; it is an electron-hole pair that is a referred to as the charge carrier in this case, i.e. when an electron is excited from the valence band into the conduction band, – glS Feb 6 '15 at 11:07
continues: charge separation takes place, and the absence of that electron leaves a net positive charge in the valance band. This hole in the valance band and the electron now in the conduction band remain separated (unless recombination occurs), and they essentially travel alongside one another as a charge-carrier. – glS Feb 6 '15 at 11:08