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The standard as I learned it is that the flow of current is from positive voltage to negative voltage. The direction of current flow is opposite the direction of electron flow. This is what I learned in school, the assumption made by almost every engineer I've worked with, and the standard in every simulator I've ever seen.

I've encountered two exceptions. One is this textbook, which a colleague has on his shelf from his associates degree training. The other is a pair of former navy personnel I've worked with, both of whom were taught electron flow in the navy and had to unlearn it when they left.

I understand that both are valid mathematical models of the same phenomenon. What I don't understand is why anyone would purposefully and knowingly train people in a fashion contrary to a near-universal standard. (It took a lot of work to make that textbook!) Is the standard as I understand it not as standard as I think it is? Is there some analytical advantage to the electron flow model that I'm not seeing, perhaps in realms of EE I don't visit often?

Why is anyone, anywhere, ever taught that current flows from negative voltage to positive voltage?

Kevin Reid
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Stephen Collings
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  • I've only ever encountered electron flow when deep in semiconductor theory, where there it makes a bit of sense. – whatsisname May 07 '14 at 18:49
  • I use species fluid flow quite a bit in plasma physics (i.e. electron and ion flow). However, there are a lot of simplifications which reduce down to a current density in the "conventional" direction. – helloworld922 May 07 '14 at 19:13
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    I've always assumed that electron current was introduced in the early vacuum tube days to train technicians, as it is very difficult to explain the inner workings of a vacuum tube using conventional current. – Peter Bennett May 07 '14 at 19:18
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    If the Navy teaches it that way (They say there's three ways to do things: the right way, the wrong way, and the Navy way, so no use asking why they would teach it that way) people might write textbooks that way to be able to sell them to the Navy. Why a JC would choose that textbook, I have a harder time explaining. – The Photon May 07 '14 at 21:09
  • Why is electron flow taught in some contexts? Why is the phrase current flow used? Electron flow - yes. Charge flow - yes. Current flow ??? Isn't that a charge (or whatever) flow flow? – Alfred Centauri May 08 '14 at 01:35
  • I have a complete electron flow version of a EE intro textbook (teacher edition freebie). Like Floyd for example. I always wondered if anyone used it for a class. If we all agreed to change at the same time..... – C. Towne Springer May 08 '14 at 03:26

2 Answers2

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Current flows out the positive lead of a power supply and back in thru the negative one. We have arbitrarily decided that electrons have negative charge, so electrons actually flow out the negative lead and back into the power supply via the positive lead. Electrons being negative is a convention, but a universal one.

Current doesn't have to be soley from electrons flowing. It can be due to charged ions physically moving in a solution, for example. In that case, the positively charged ion really do travel in the same direction as what we call the overall current. Of course, negatively charged ions flow the opposite way.

If anyone teaches this differently, they are just plain wrong and doing their students a gross disservice.

However, from the electronics point of view, we don't really deal with individual charges moving. We think in terms of current, and all works out, whether that current is realized by negatively charged particles moving in the opposite direction or not.

Olin Lathrop
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The standard you learned is very standard. I think unless you ask the authors of those books why they taught it that way, you won't find anything except opinion here.

Possible reasons:

  1. Electrons are the things that actually move so it's easier to conceptualize when current flow and the charges themselves are actually moving in the same direction.
  2. They were taught in a non-standard format and so understand it that way and therefore are best able to teach it in that format.
horta
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