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I like this explanation of why there's nothing wrong with conventional current being the opposite direction from electron current. It mentions batteries and fluorescent bulbs as two cases where the current is not a flow of electrons. (As well as ion flow in human beings and proton flow in water ice, though those are not electrical components.) What other electrical components involve flows of charge that are not electrons? Does this happen in the electrolyte of electrolytic capacitors?

From the topic electron theory we know that metals emit electrons easily and semi-conductors and electrolytes emit them with great difficulty. The electrons in the electrolyte are in fact not free but are bound in ions. http://www.electronics-tutorials.com/basics/polarization-capacitor.htm

Do holes in semiconductors really count, since they're not physical particles?

Brian Carlton
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endolith
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  • @reemrevnivek, the argument could be made that holes are still a flow of current. – Kortuk Mar 20 '11 at 17:07
  • The only way you can get positive charges to move (instead of the absence of negative charges, if we're going to differentiate that) is through transporting atom nuclei. In a solid or crystal structure this will be *extremely* slow, and possibly damaging. – Nick T Mar 20 '11 at 18:06
  • Er, current in fluorescent bulbs is indeed the flow of electrons ;) – tyblu Mar 20 '11 at 18:13
  • I think you can have holes allowing for flow, without an equal number of electrons. The material is ptype, doped for having holes without (many) electrons. So (not that you necessarily would) but if you doped Si with As or P, you would get a material with extra holes relative to electrons. – ArielP Mar 21 '11 at 12:41
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    @Nick: I don't think that's necessarily true. The moveable charges don't need to be the same material as the solid. The link describes proton flow in water ice, for instance. Most flows of current are "extremely slow". – endolith Mar 21 '11 at 15:10
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    @tyblu: In fluorescent tubes, there is a flow of positive ions. They are operated with AC because DC would cause all the mercury ions to accumulate at one end of the tube. – endolith Mar 21 '11 at 15:18
  • ArielP: But holes places where electrons would be but gone missing. So to have hole current you have to have electrons hopping between these holes. – jpc Mar 21 '11 at 15:40
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    @reemrevnivek : AFAIk, hole flow in semiconductors is not actually flow of positive charges -- it's still electron flow but it's not due to the free electrons (which is also why holes generally have lower mobility) – Alex Mar 21 '11 at 18:40
  • @Alex, I intended to write that in my comment but used the word current. Don't write tired. – Kortuk Mar 24 '11 at 02:52
  • @jpc: "It shall be noted that in the classical view, there are only electrons moving in the same average direction both in the case of electron or hole conductivity. This cannot explain the opposite sign of the Hall effect observed. ... A common source of confusion with the Hall Effect is that holes moving to the left are really electrons moving to the right, so one expects the same sign of the Hall coefficient for both electrons and holes. This confusion, however, can only be resolved by modern quantum mechanical theory of transport in solids." http://en.wikipedia.org/wiki/Hall_effect – endolith May 30 '11 at 01:31
  • @endolith: This is a very interesting point, thanks for the link. :) – jpc May 30 '11 at 13:39
  • See also http://physics.stackexchange.com/a/17131/176 – endolith Dec 16 '11 at 19:27

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Now, this does get confusing when you get to semiconductor theory, and I understand your issue. I can name one very important case. When working with charge pumps in the human body. Many places in biology the charge flow is positive. When taking a biomedical modeling class for EE we often had positive charge flow.

We can get crazier, what if you have cancer? There are many options, sometimes you pick radiation. Photon radiation exists, what about proton radiation? The amount of protons they are sending are measured in Amperes. Why? Positively charged particles per second(enjoy the pun).

The important part here your particle makes an issue of. If electrons were positively charged the issue would be swept under the rug by most people. The fact that they are negatively charged makes people think about what it really means.

If you really get down to the physics it is just a sign convention and is a menial problem. If you would like to assign them positive charge please do so, be internally consistent and do not publish anything and no one will be the wiser.

The most important thing is that if electrons were positively charged we would not have nearly as great of a name for the positron. I personally would not live in a world were the negatron is a particle.

Kortuk
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    I give your answer +2 anti-negatronic votes. – tyblu Mar 20 '11 at 18:35
  • I was really asking about electrical components, though, not the human body. The human body is already covered in the linked article. Batteries, fluorescent tubes, ... – endolith Mar 21 '11 at 18:18
  • @endolith, your electrical cicuits we use every day use electronics. The metals we use are electron flow. There is no way around this, protons form part of the lattice, electrons may move freely. – Kortuk Mar 21 '11 at 20:11
  • A battery is an electrical component, and part of the circuit. In a battery, current consists of positive and negative ions, not electrons. Lone protons and ionized atoms are certainly capable of moving in electric circuits. – endolith Mar 21 '11 at 21:30
  • @endolith, you knew the battery case, and I thought it was the first example your article gave. I put in a few other example of flow. – Kortuk Mar 22 '11 at 01:52
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Neurons! @Kortuk touched this by mentioning biological charge pumps. Charge is transferred in bursts called action potentials, created by a local chemical reaction that increases ion concentration (Na+) and travels along neurons (ok, it's a bit more complicated than that, but I think we all get the idea).

Electroplating! We electronics buffs know a lot about this due to PCB plating (nickel, gold, mixtures, etc.), but it's used in all walks of industry and arts: galvanizing, gold plating, and other metal deposition is done for waterproofing, rust protection, fancy-factor, colouring, anodizing, conductivity, as an intermediate step before other material deposition like polymers, and chemical reactivity changes (other than rust protection). Again, this is the movement of ions. There's also plenty of electrons involved.

Current flow due to ion transfer in piping: for example, in our city drinking water pipes there is an ion concentration (chlorine, fluoride, etc.). As it flows through the pipes it is electricity, the movement of charge, and often creates trouble for sensitive magnetic sensors.

Photons create charge differentials. From radio to gamma rays, we make use of the entire electromagnetic spectrum by turning electrical energy into photons, then back into electrical* at the receiver antenna. Photons excite valence electrons (are absorbed) with enough energy to hit conduction band creating an electron-hole pair. There's other mechanisms, but I'll screw them up if I try to explain them.

Many doohickeys and thingamabobs have a non-neutral charge, and their movement relative to a differentially-charged object creates an electromagnetic field. The channeled, group description of this effect is electricity. Electrons are everywhere and really light -- they're easy -- so we they get abused into doing the grunt electrical work most of the time.

*There is work going on to make entirely photonics-based circuitry, but I'm really not the right person to introduce it.

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tyblu
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  • Where's the current flow in water pipes coming from? Chlorine and fluorine in the water is more oft discussed because that's the "active" part in the additives, but those negative ions usually come attached with some positive ones to make it neutral; sodium, potassium, hydronium (acid), etc. – Nick T Mar 21 '11 at 00:16
  • I am not sure I would count photons, but I always forget electroplating. +1 for finding a way to add electromagnetic spectrum to your post. – Kortuk Mar 21 '11 at 02:45
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    @NickT, group charge does indeed tend to neutralize over time, but is usually non-neutral in water pipes -- at least locally. Personal experience was an undergrad project to map magnetic field over a ~km^2 to get an idea as to what kind of shielding and pipe relocation was needed for some new, fancy nanotech equipment at [NINT](http://www.nrc-cnrc.gc.ca/eng/ibp/nint.html). – tyblu Mar 21 '11 at 21:14
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Yes, I also like the ways William Beaty explains "Which way does the "electricity" really flow?" and the distinction between the flow of charged particles (nearly always very slow) and the flow of electrical energy (nearly always very fast).

(Alas, this isn't really an answer to your question, but a response to some of the responses to it).

The only way you can get positive charges to move (instead of the absence of negative charges, if we're going to differentiate that) is through transporting atom nuclei.

Yes, that is exactly how positive charge does move. In a proton conductor such as ice, you can think of the moving positive charges as hydrogen nuclei.

"In a solid or crystal structure the flow of positive charges will be extremely slow, and possibly damaging"

Yes. Also, the flow of electrons is also surprisingly slow, and often damaging. The charged particles that move through solids are typically very small -- electrons in a metal, protons in a proton conductor.

On the other hand, quite large charged particles -- both positive and negative -- flow through battery electrolyte (liquid) and during electric glow discharge (gas).

fluorescent bulbs

Some people claim that current in fluorescent bulbs is indeed the flow of electrons.

Yes, during the brief fraction of a second when first applying power to a "cold" tube, electrons are the only charged particles available.

When first starting a "cold" tube, the cathode (because it is metal) has plenty of movable "free" electrons available, and yet the tube has a very high resistance.

Later, after striking an electric "arc" (electric glow discharge), during normal operation of a fluorescent bulb or neon light, there are lots of charged ions available. Since the tube has a much lower resistance at that time, (a) fluorescent tubes require ballast, and (b) we are led to conclude that most of current involves charged ions rather than electrons.

When a fluorescent lamp "operated from DC, the starting switch is often arranged to reverse the polarity of the supply to the lamp each time it is started; otherwise, the mercury accumulates at one end of the tube." -- Wikipedia

This is evidence that charged mercury ions physically move in a fluorescent lamp.

davidcary
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  • our protons move quite fast, although they do damage crystalline structures, anything in the way that is electronics does not work so great. – Kortuk Mar 24 '11 at 02:38
  • A contemporary hot topic is: proton flows in "solid electrolyte" and "solid acid" fuel cells. These are proton-conductor solids, designed for large proton currents without any damaging breakdowns required. Car-battery's acid is mostly a proton conductor, since the acid's +H ions have far higher mobility than the equal number of negative sulfate ions also present. But acidic fuel cell electrolytes, if solid, don't have negative ion mobility, since the much larger negative ions are trapped in the solid lattice. – wbeaty Feb 28 '16 at 03:15
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In plasma (used in various technological processes for depositing thin films and etching stuff) both electrons and ions do the conduction. Ion guns as their name implies use ions accelerated in vacuum using a very string electrical field (in a way similar to how cathode ray tube displays work) to etch away material or implant the ions on a very small scale (nano- to micrometer scale).

Holes in semiconductors are just electrons. It is just that there are so many immobile electrons in p-doped semiconductor that the holes stand out and let us do the theory. In reality the electrons (leaving empty holes behind them) are still the moving parts.

jpc
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Depending on the definition of 'flow of charge':

Your wall outlets and anything else involving AC voltage. The electron drift velocity is zero at the macro level, at the micro level electrons wobble back and forth and therefore have a non-zero drift velocity at a particular point in time. Energy is transfered via EM waves in AC circuits. In practice there is always a small DC offset so there is some 'macro scale' electron drift down the wires. However, its not the primary mechanism of current flow and is very slow, like an inch a day depending on the offset. You can, correctly, argue that electrons are still the charge carrier here, but i guess i wouldn't describe this as a flow of charge.

Even thinking about current purely as electron flow under DC voltage isn't a good or accurate way to think of it. Electron drift velocity is very slow, depending on the voltage and of course the material it can be inches per hour. Of course we know that 'electricity' moves much faster than this which is because current is the result of sorta 'bumping' the charge along the conductor rather than requiring a specific electron to 'flow' all the way down the conductor.

In electrolytic capacitors the primary charge carriers are ions.

Mark
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Electrolytic capacitor.

Dielectric has currents "flowing" in it...

Tim Williscroft
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  • Can you elaborate on this? "The electrolyte is usually boric acid or sodium borate in aqueous solution". The metal conductors touch the electrolyte, and then the electrolyte touches the oxide layer? Are the ions negative or positive? When do they flow? – endolith Mar 23 '11 at 16:51
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Aluminum

In the most common process of converting naturally occurring aluminum (fully oxidized AL2O3) to the more useful metallic aluminum, workers drop aluminum oxide into molten cryolite, which produces free Al3+ and O2- ions. Then a voltage across two carbon electrodes attracts the Al3+ ions to the negative electrode (cathode), where it becomes uncharged pure liquid Al and sinks to the bottom, where it is tapped off.

(Aluminum is the most abundant metallic atoms in the Earth's crust. Metallic aluminum is now a common, everyday household material, used in many electrical components, and the process of making aluminum uses a significant fraction of all the electrical energy produced every day. But does this really qualify as an "everyday component"?)

davidcary
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