Current Flow - John Dunn, Consultant, Ambertec, P.E., P.C.

There may still be sounds reverberating at this place where I once heard a really HOT argument going on over the question "Which way does current flow, from positive to negative or negative to positive?". The opposing sides came from different industries in which the conventions of current flow seemed to be opposites of each other and each side was absolutely certain of being in possession of absolute, divine and irrefutable truth.

It may be an apocryphal story, I really don't know, but I once read that we should blame Benjamin Franklin for this problem. The story was that when he charged up his Leyden jar during his lightning experiment, he arbitrarily chose to call one post of the jar "positive" and the other one "negative" and he thereby set the precedent which was that as the Leyden jar was discharged, current flowed out of the positive post and into the negative post. Had he known what electrons were, he might have set the precedent the other way.

Of course, there were some points that the arguing parties missed. One was that current flow does not have to be achieved only by means of electron travel. Alpha particles have electric charge also, a +2 as opposed to an electron's -1, so if you get of stream of alpha particles moving along, you have an electric current that way too.

Also, we are told how a vacuum tube's cathode gives off electrons that travel to the tube's plate, yet we still speak colloquially of a tube as drawing plate current FROM a positive B+ supply. Oddly, that dichotomy didn't seem to bother anyone that day.

Then there's the concept of hole current. One shout was "What do you mean the movement of the absence of something????". I'm afraid that the following sketch was simply beyond that poor fellow:

 

Comments

[DavidP]

Well, to truly get down to brass tacks, in a metal the electrons move and the neutrons and protons don't, much, or you have electrogalvanic corrosion, but then as the electrons move, there is an equal and opposite motion in the "fixed" portion, just very minimal due to mass ratios. Now, much of that motion may be absorbed in the soft, elastic mechanical response of the fixed portion or the crystal itself, especially if the impulse is small and cyclic.