After reading the postings on "Conventional Current Flow", I believe some clarifications are in order.

First of all, charged sub-atomic particles sometimes move or flow. When they do, it is called current. Current IS flow or movement of charged particles. Therefore, "current flow" really means charge flow flow, which is redundant and ridiculous. Most of the world has gotten into this bad habit of describing what should be referred to as CHARGE FLOW or simply current.

Next we have conventional charge flow or conventional current; the assumption that positive current direction is from from the positive to the negative terminal in an external circuit. This convention did not come about because Fat Fool Franklin was wrong. It came about because engineers wanted a consistent mathematical method to describe current direction. Now it is true that in metallic conductors, negative electrons are the primary charge carriers. But negative particles are not the only charge carriers in other situations. There are just as many positive charges running around the universe as negative ones. For instance p-type semiconductors have a predominance of positive charges. And quantum theory says that positive holes have just as much physical "reality" as electrons do. Then there are all the positive ions in electolytic chemistry. So while it may be correct to say that electron flow determines direction in a wire, it would also be correct to say that positive ions can determine the current direction in a particular electrochemical reaction. In that case, we truly have "correct" current direction going from positive to negative. Or in a different reaction, the negative ions can 'really' go from negative to positive. And they can both be doing their thing at the same time. As one can see, it is difficult and confusing to base current direction on the "real" movement of the charged particles

Now comes conventional current direction to the rescue. We have positive charges flowing from positive to negative; no problem there. Then we can have negative charges moving from negative to positive. Mathematically speaking, a negative charge moving in one direction is the same as a positive charge moving in the opposite direction. Therefore a negative charge moving from the neg to the pos is the same as a positive charge moving from the pos to neg. By embracing this simple mental doublethink, the engineers and mathematicians have removed the worry and concern about whether a plus or minus charged particle is moving into/from a neg/pos terminal. It all boils down to always ASSUMING that a external flow of positive charges from the pos to the neg terminal of a voltage source always produces a positive current. This causes electron flow to have a MATHEMATICALLY opposite direction with respect its real direction, but it is consistent and correct with respect to positively charged particles. In cases where knowing the real physical particle direction is important, that can be handled on a case by case basis. Most of the time in circuit analysis, the real direction does not matter. So conventional current direction takes away the wonderment of directional dependency of differently charged particles. I hope this clears things up a bit. Ratch
Posted on 2003-04-27 07:39:27 by Ratch
I'm not so sure you cleared this up, but thanks. <grin>

Oh, anyone want to take a crack at a current flow not involving the movement of charged particles?

I know you all have a device that can do this. Lots of em in fact.
Posted on 2003-05-03 03:32:06 by Ernie
What fun!

I almost quit electronics as a hobby when I was a teenager due to the arrows pointing the "wrong way" with no explanation, until I stumbled across the following. I've since seen another explanation, but I don't know which is the urban myth, so I'm sticking with Michael Faraday.

When Faraday caused a current to flow though a solution of silver salt, the negative terminal became heavier with silver plating. Faraday therefore assumed that whatever electricity was, it moved from positive to negative, leaving the silver behind on the terminal. By the time (many years later) it was understood that it was really electrons flowing into the cathode and neuralizing silver ions it had become the convention to draw the arrows depicting current flow from positive to negative, which is why it is called "conventional current"! This also explains why we still measure things in inches and feet instead of centimeters and meters -- conventions die hard. Thank goodness for holes, so after 100 years Michael can rest easy.
Posted on 2005-01-23 02:04:51 by steverose
Here's my theory, if anyone's interested. Hope it doesn't sound too snotty.

Electrons do not travel in any direction. When an electron in the outer shell of an atom receives a photon packet large enough to 'knock' it out of orbit, it disappears so to speak as a particle and becomes a wave, which is nothing more than a phenomenon. Waves moving across the surface of water are not water molecules travelling across the water. Only the phenomenon of the wave travels across the water, the water molecules are moving primarily in a vertical fashion, uniformly and in a time predictable manner creating the illusion of physical horizontal movement.

Likewise, the electron does not travel from point A to point B, or from Negative to Positive as described by the theory of electron current . The electron particle disappears when it encounters a photon, then disappears as a particle and becomes a wave. The wave phenomenon, which is not a particle, then (theoretically) moves at near the speed of light (or instantaneously, depending on which theory one prescribes to) until it has reason to stop being a wave. Practically any known particle in the universe could give this wave a reason to stop being a wave. In a conductive or semi-condictive material, a wave is usually terminated by an atom that desires an additional electron to fullfill it's shell quota. The wave encounters the desiring atom, and ceases to be a wave and becomes a particle. Upon becoming a particle, it is adopted into the atoms outer shell, and emits a photon,

One popular theory today is that particles do not have mass, but only direction and spin, which reduces the electron in it's particulate state to nothing more than another phenomenon. So, by this theory, if the phenomenon of a negative 'charge' moved from point A to point B, then so also did a deducable phenomenon of a 'positive' charge move from point B to point A. Basically the same thing Ratch said, but my version is more likely to put you to sleep.
Posted on 2005-01-28 17:27:33 by gluespill
gluespill,
Basically the same thing Ratch said, but my version is more likely to put you to sleep.

Another jabberwocky joke? Ratch
Posted on 2005-01-31 12:13:39 by Ratch
Not a joke, just my interpretation of current flow. I apologize if you find it upsetting.
Posted on 2005-01-31 17:00:10 by gluespill