Conventional Current in a circuit

  • #1

Main Question or Discussion Point

Alas, another one of my conceptual struggles in regards to current. In regards to a circuit in which a solid metal conductor is used to connect the positive and negative terminals of a battery, I do not understand the idea of conventional current.

I understand the way negative charges (carried by electrons) move- in the opposite direction of the electric field. I am under the impression that only negative charges move in such a circuit. I do not see why there would be a "convential current" (positive charge flow) in the opposite direction of the electron flow. And if there were such a positive flow in the opposite direction of the electron flow, how would the two flows manage to get through the conductor? Wouldn't they just attract each other and get "mixed up" for lack of a better term? Is there even positive flow in such a wire?
 
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Answers and Replies

  • #2
jtbell
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There is no actual positive charge flow in such a situation. "Conventional current" is a historical artifact. Blame Benjamin Franklin for the confusion!

Basically, Franklin originated the idea of objects being positively and negatively charged, in his "single fluid" theory of electricity around 1750. In his theory, positively charged objects had an excess of "electric fluid" and negatively charged objects had a deficit. Electric fluid tended to flow (as an electric current) from positively-charged objects to negatively-charged ones, in order to distribute itself more evenly. Franklin could not actually see the direction the electric fluid flows, so he had to guess which objects were positively charged and which ones were negatively charged (and therefore also the direction of current flow).

Now we know that there are actually two kinds of electric charge (positive and negative), but in most everyday electrical phenomena, it is electrons that flow from one object to another, and that they actually flow from Franklin's negatively-charged objects to positively-charged ones.

But by the time people realized this, Franklin's assignment of positive and negative charge, and the corresponding direction of current flow, was so well established and used by everyone, that it would have been too confusing to make everyone change their terminology. So, we still speak of current flowing from positive to negative ("conventional current") even though the electrons flow in the opposite direction, and we call electrons "negatively charged" to make the same objects positively and negatively charged, as before.
 
  • #3
Thank you very much for that! I knew there was something that just wasn't right. I appreciate your response, thanks again
 
  • #4
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I know for a fact that electric current flow has nothing to do with the flow of electrons. They stay right where they are - inside the atoms. The 'flow' of electrons does not exist. What flows is charge. Electrons can be induced to flow - as in tv's ect - but that is a secondary response to the primary 'flow' of charge. And they then need to be collected in an amalgam - before they can respond to this charge. Electrons - within the atoms of conductive wiring - simply do not flow. They stay put. The 'flow' of electric current still needs a definition.
 
  • #5
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Convensional current is far more useful in circuit analysis and design for the simple reason that NPN transistors have better characteristics than PNP, and now, as well, N channel FETs are better than P channel FETs.
 
  • #6
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I know for a fact that electric current flow has nothing to do with the flow of electrons. They stay right where they are - inside the atoms. The 'flow' of electrons does not exist. What flows is charge. Electrons can be induced to flow - as in tv's ect - but that is a secondary response to the primary 'flow' of charge. And they then need to be collected in an amalgam - before they can respond to this charge. Electrons - within the atoms of conductive wiring - simply do not flow. They stay put. The 'flow' of electric current still needs a definition.
This is not a fact. It is nonsensical. If you combine your two claims that no electrons flow in a conductor, but will flow in a beam, then you will obtain an imbalance of charge per electron. You will end up with a bunch of naked electrons on the surface of the anode.

This is a physics forum, not a personal-theory forum (sorta).
 
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  • #7
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Point taken. I'm suitably reprimanded. But here's my confusion. Current flows through a resistor - pd great enough to spark a fire. Extreme reaction. The fire entirely disintegrates the resistor leaving behind some disassociated iron and carbon atoms. Their number precisely corresponds to the number that initially fromed that resistor. But they are now disassociated. A puddle of powder. All atoms have the same atomic structure as before - including their electrons. Yet something burned up. What was that?
 
  • #8
chroot
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All atoms have the same atomic structure as before - including their electrons. Yet something burned up. What was that?
"Fire" is the combination of oxygen with other compounds. In the case of a burning resistor, the binders, enamels, etc. combine with oxygen and become, as you say, "dissociated." This burning process will continue, and the resistance will go up, until the power dissipated by the resistor is no longer capable of achieving those temperatures.

- Warren
 
  • #9
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We have fire in suns that have zero oxygen. My point is that energy was stored in the resistor during its manufacture. This was 'liberated' due to properties of current flow. Result being to dismantle the original manufactured resistor from its identifiable amalgam. But those properties have nothing to do with a flow of electrons. In any event Pauli's exclusion principle would forbid the flow of electrons on a shared path - as required by this image of current flow. The 'flow' of electrons is only something to hold in the mind's eye. I know it is a widely held concept. But whether or not it is correct is still an open question.
 
  • #10
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We have fire in suns that have zero oxygen. My point is that energy was stored in the resistor during its manufacture. This was 'liberated' due to properties of current flow.
What happens is that the current through the resistor would be high enough to heat it up hot enough to cause a fire. The flow of electrons is responsible for the heating up, but not the burning. Now, when electrons flow in a solid, they replace other electrons, so that almost all of the electrons are right next to positively charged nuclei. Electrons replace other electrons, but none are "used up" in the heating up or the fire.

I think you may be confusing the flow of electrons with the flow of electrical power. Electrons travel down a wire pretty slowly, but when one electron is nudged forward, it pushes another, which pushes another, and so forth, and so no electron has to move far for a force to be felt far down the wire.
 
  • #11
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I think that the flaw in this explanation is that one electron nudges another. Electrons will not 'nudge' up against each other any more than like poles on a bar magnet can 'nudge' together. Then too, the time taken for these 'series' of interactions exceeds the time of actual flow of current which is known to be instantaneous. The fact is that engineers use the concept of 'the flow of electrons'. But it has very little to do with known proven fact. But nor is there an explanation of current flow. That's my point. It's the mystery of energy which is still out there. A really big question. Another big question is 'what is fire'? Also no real explanation.
 
  • #12
chroot
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We have fire in suns that have zero oxygen.
Whoa! Watch out here, this is one of the most basic misconceptions possible. The Sun is not "on fire." It has no oxygen, and no chemical reactions are taking place within it. Instead, nuclear fusion is operating in its core, fusing hydrogen into helium. This process liberates energy, but has nothing to do with fire. The surface of the Sun appears the color of flame simply because it is roughly the same temperature as a flame.

The 'flow' of electrons is only something to hold in the mind's eye. I know it is a widely held concept. But whether or not it is correct is still an open question.
Actually, this is by no means an "open question." The vast preponderance of evidence is all around you. The behavior of electric currents (of both negative and positive charges) is at the very heart of the science that made possible the microprocessor in the computer you used to type this message. Everything we can do with electricity is made possible by our very, very deep understanding of its microscopic behavior. The largest branch of physics is called consended-matter physics, and one of its largest concerns is the movement of charged particles through matter of various sorts. The number of people and experiments involved in the study of the microscopic behavior of electricity is absolutely immense. We have incredibly good models of the conduction of electricity. Ironically, you are attacking the very most solid branch of physics there is.

- Warren
 
  • #13
chroot
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I think that the flaw in this explanation is that one electron nudges another. Electrons will not 'nudge' up against each other any more than like poles on a bar magnet can 'nudge' together.
This is a strawman argument. No physical theory contends that electrons move through conductors by being nudged in turn, so your argument is moot.

Another big question is 'what is fire'? Also no real explanation.
Another big question is whether or not you're simply trolling...

- Warren
 
  • #14
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Warren, I seem to have offended you. I apologise. I know that the field of electrodynamics is extraordinary. What is 'trolling'.
 
  • #15
Matterwave
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Rosie: You state a lot of things as if they are scientific fact when in fact they are just plain wrong. Where do you get your information? Have you been reading a lot of VERY old (>200 years) textbooks? I mean, the phenomenon of fire has been explained for quite a while now...
 
  • #16
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Matterwave - I know there's a classical explanation for fire - but it does nothing to explain the thing itself. What, for instance is the difference between fire on earth and fire in our sun. They both burn. And to explain it as some interaction requiring oxygen also does not explain it. I'm stuck at the fundamentals. I was hoping that by joining this forum I'd get an explanation for these questions. Another question - what is gravity. Another what is the strong and weak nuclear force. I don't mean it's measurment. I mean the thing itself. That I have a mathematical equation to measure it does not explain it. And I am not alone in defying the current flow as a movement of electrons. I have good authorities in profound physicists. But I grant you it is not popular thinking. Either way - can we not agree to disagree. I am in awe of quantum electrodynamics. It's amazing. But because it is so exquistely useable does not explain it. I'm struggling here.
 
  • #17
chroot
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Matterwave - I know there's a classical explanation for fire - but it does nothing to explain the thing itself. What, for instance is the difference between fire on earth and fire in our sun. They both burn. And to explain it as some interaction requiring oxygen also does not explain it. I'm stuck at the fundamentals. I was hoping that by joining this forum I'd get an explanation for these questions.
As I've already said, "fire" is the chemical reaction of oxygen with other compounds, which releases energy as heat. The heat causes ionization and glowing, which we call a "flame."

The Sun does not "burn," and contains no "fire." It fuses hydrogen into helium -- a nuclear, not chemical process -- which releases energy. The heat causes ionization and glowing, which is why the Sun is yellow and bright.

Is this explanation unacceptable? If so, why?

The reason you're getting such gruff answers is that you are stating falsehoods as if they were fact. In fact, you're stating falsehoods that could easily be cleared up by reading a few Wikipedia pages, or *gasp* a freshman-level physics textbook. You haven't made the slightest effort to understand physics, yet appear to believe it is beneath you, and that is deeply offensive.

Another question - what is gravity.
The force that occurs between two massive objects.

Another what is the strong and weak nuclear force.
The forces which occur between certain subatomic particles.

I don't mean it's measurment. I mean the thing itself. That I have a mathematical equation to measure it does not explain it.
Your position is unfortunately extremely common. Science seeks knowledge, and does so by the continual refinement of a model, guided by experimental evidence. The model is used to predict the outcome of experiments, but you feel the model is "just a model," and does not speak of what "really happens" inside atoms. People in your position are often uncomfortable with physical theories unless they involve familiar agents -- billiard balls, ramps, and other macroscopic things.

Perhaps unfortunately, atoms and subatomic particles do not behave in a way that is describable with such macroscopic concepts, and many experiments have proven so. It has been proven that there is no way to extend the human concepts of "sight" and "touch" down to the subatomic level, so scientists do not try. We strive to make models which accurately predict the results of all experiments, and believe the model is therefore a commentary on what happens inside atoms. This is the very best one can do, in fact.

And I am not alone in defying the current flow as a movement of electrons. I have good authorities in profound physicists. But I grant you it is not popular thinking. Either way - can we not agree to disagree. I am in awe of quantum electrodynamics. It's amazing. But because it is so exquistely useable does not explain it. I'm struggling here.
You are most certainly alone in defying the flow of electrons. Your position is literally incompatible with hundreds and hundreds of years of scientific exploration and technological progress. Again, it is paradoxical that you use a computer, yet deny the very understanding that allowed a human being to build it.

The plain truth is this: if you wish to learn physics, perhaps you should begin typing less and reading more.

- Warren
 
  • #18
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Warren - This has been a remarkably ascerbic attack. I have very restricted vision and am obliged to use all kinds of sight aids. Possibly why I do not read enough. But, for my age, I believe I am extremely well read. And there is nothing wrong with my reasoning nor my education in physics which I admit is ongoing. That's why I joined the forum.

However to get back to the point. Could you please reconcile Pauli's exclusion principle with the 'flow of electrons' through your standard electric circuit?

As I understand it electrons belong to the Lepton family. They are charged. They have mutually exclusive orbits around a nucleus. How then do they 'follow each other' however it's done - through electric circuitry? This could only be done if they simultaneously 'lost their charge'.

Regarding your explanation of 'fire'. A 'chemical reaction' that somehow requires oxygen to enable it does nothing to explain the thing itself. All the molecules and all the atoms that go into that 'event' come out in tact. Not even bruised - and not one atom more nor less. Some may float away as gases - some may be trapped by gravity - some may even recombine with other atoms to form new exotic molecules. But all of them are basically and exactly as they were before the fire. So I ask you again - what then is fire? What burned? I propose that it may be their 'bound state' that changed. Just a thought. Because then the energy that was stored was then expended. It balances. But I'm more than likely wrong. I'd just like to know.

if this forum is simply based on a system of 'you ask the question and I'll give the answer' then I have lost the plot. I was rather hoping that we could explore complex questions. They keep me awake. It would help if I could find others who also ask these questions?

But I did not mean to antagonise you. I am just looking to find answers.

That 'fire' in the sun is the result of a nuclear reaction is exactly the same as saying that the fire on the circuit was a chemical reaction. It says nothing about the nature of 'fire'. Is it photons? Is it pure energy? What?
 
  • #19
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sorry - I meant to add - those who disagree with the movement of electrons comprising the flow of current. I'll provide that list tomorrow. I've got to search through my books and it takes ages because - as mentioned - I'm blind as a bat.
 
  • #20
chroot
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Warren - This has been a remarkably ascerbic attack. I have very restricted vision and am obliged to use all kinds of sight aids. Possibly why I do not read enough. But, for my age, I believe I am extremely well read. And there is nothing wrong with my reasoning nor my education in physics which I admit is ongoing. That's why I joined the forum.
You appear to have very little interest in education; instead, the bulk of your posts are strawmen and attacks against them. You seem eager to find flaws in a model that you clearly do not understand at all.

However to get back to the point. Could you please reconcile Pauli's exclusion principle with the 'flow of electrons' through your standard electric circuit?
Reconcile? What does the Pauli exclusion principle have to do with the movement of electrons through a conductor in the first place?

As I understand it electrons belong to the Lepton family. They are charged. They have mutually exclusive orbits around a nucleus. How then do they 'follow each other' however it's done - through electric circuitry? This could only be done if they simultaneously 'lost their charge'.
In a conductor, some electrons have energies sufficient to allow them to move freely throughout. The electrons in a conductor can be modeled reasonably well as a gas of free electrons. The electrons are not entirely free, of course, since they do interact with the atoms, but the effect is small.

If you apply an electric field, these mobile electrons will feel a force, and will begin moving. Their thermal energies are relatively high, though. They bounce around randomly inside the conductor with speeds approaching a million miles an hour, but the electric field biases them to travel a little more easily in one direction than the other. Over time, that bias causes them to slowly move through conductor. The speed at which they move through the conductor, the bias, is called the "drift velocity." This speed is on the order of centimeters per hour in normal situations. That's right, an individual electron's progress through a wire is slower than that of a snail.

Regarding your explanation of 'fire'. A 'chemical reaction' that somehow requires oxygen to enable it does nothing to explain the thing itself. All the molecules and all the atoms that go into that 'event' come out in tact.
When you burn something, you modify its molecules. You combine carbon atoms with oxygen atoms, say, and produce carbon dioxide. The atoms are the same, but they have been rearranged. That rearrangement liberates energy.

In the same way, a book on the edge of a table is one valid arrangement of books and tables. If the book falls off, energy will be released. The book might then end up under the table. That's also a valid arrangement, but it has less energy than the previous arrangement. Neither the book nor the table has changed in the process, but their arrangement is different, and energy has been released.

if this forum is simply based on a system of 'you ask the question and I'll give the answer' then I have lost the plot. I was rather hoping that we could explore complex questions. They keep me awake. It would help if I could find others who also ask these questions?
You are more than welcome to ask questions. You are absolutely not welcome to propose your own theories and tout them as being better than those of accepted, mainstream science. That's particularly troublesome when you make it clear that you don't even understand what accepted, mainstream science says in the first place.

That 'fire' in the sun is the result of a nuclear reaction is exactly the same as saying that the fire on the circuit was a chemical reaction. It says nothing about the nature of 'fire'. Is it photons? Is it pure energy? What?
"Fire" is a common name for any chemical reaction involving oxygen. It has no deeper physical meaning.

- Warren
 
  • #21
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I think that the flaw in this explanation is that one electron nudges another. Electrons will not 'nudge' up against each other any more than like poles on a bar magnet can 'nudge' together. Then too, the time taken for these 'series' of interactions exceeds the time of actual flow of current which is known to be instantaneous.
This is a strawman argument. No physical theory contends that electrons move through conductors by being nudged in turn, so your argument is moot.
Maybe I should've used a better word than "nudge". I did not mean to imply that electrons bounce into each other like billiard balls, or line up behind each other one-by-one, but rather that:

  1. when you apply an electric field to a small portion of a wire loop, the electrons will move in the opposite direction (since they're negatively charged), and this will cause the charge density to change from 0 everywhere to positive in one direction of the portion of wire and negative in the other direction;
  2. the electrostatic force ensures that any charge density created will push forward more electrons, which will in turn create a new charge density change; and
  3. this means that a charge density wave will propagate around the wire.

This example shows how electrical power can be transmitted down a wire. You can imagine a similar example with water in a loop of pipes, where you would only have to move the water a little bit to get all of the rest of the water to move a little bit.

I don't claim that this is exactly what happens; for example, I didn't mention drag, I didn't mention the random thermal motions the electrons were doing before any electric field was applied, and in the long term (over the time it would take to get the electric field to full strength) the electron motion would be less wavey and more uniform throughout the wire, but I hope I've made myself clearer.

I know for a fact that electric current flow has nothing to do with the flow of electrons. They stay right where they are - inside the atoms.
In a metal, not all electrons are stuck to atoms. The higher-energy electrons (the "conduction electrons") can travel almost freely within the metal.

It's difficult to explain why the Pauli exclusion principle does not prevent electrons from traveling through a metal. One explanation is this: When an electron is in an atom, it is in a quantum state (or a superposition of them), and when an electron is a conduction electron, it is also in a quantum state, in this case one which is spread out among the entire metal...I think. (I posted a question about this a little while ago, but got no replies.) Anyway, conduction electrons move in conduction electron states, and thus don't have to worry about using the atomic states which would be forbidden under the Pauli exclusion principle.

That 'fire' in the sun is the result of a nuclear reaction is exactly the same as saying that the fire on the circuit was a chemical reaction. It says nothing about the nature of 'fire'. Is it photons? Is it pure energy? What?
"Fire" is a process. It is a chemical reaction. Maybe you're thinking about "what is a flame?", in which case I can tell you it's very hot gases which glow. They are hot because the chemical reaction releases a lot of energy. I don't know if they glow from being so hot (i.e., I don't know if thermal radiation is strong enough at visual frequencies at the temperature of a fire to explain its glow), or if they glow due to chemical reactions which are occurring within the gas or the particles in the flame.
 
  • #22
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Ok. Here's the situation. I have a simple flyback switching circuit with a load in series with an inductor. A diode is placed in parallel to both resistor and inductor and returns to the battery. The switch is opeated with a 555 powering a MOSFET. The MOSFET has a protection body diode so that current is enabled during the off and on period of each switching cycle. I can arrange the frequency of the switch to operate at, say, 100KHz. The apparatus is powered by a battery. I generate a voltage across the load resistor and through my scope meter can see that the waveform is above zero for say, 90% of each cycle which corresponds to the on period of the duty cycle. Then the switch opens - the fields in the inductor collapse and the waveform moves in a sharp voltage spike before returning to zero. That spike goes way below zero. and this energy, from collapsing fields in the inductor can be seen to cause a small but measurable increase in the voltage across my battery showing that it is partially recharging the battery. Bear in mind that the circuit integrity is retained during the off period of the duty cycle by virtue of the MOSFET's protection body diode. This is well known. Nothing new. Not hypothetical.

It has to be due to the 'negative' voltage causing this fractional recharge in the battery - which implies that there is a definite negative curent flow. The v squared over r analysis of the wattage at the resistor corresponds to both cycles including that sharp spike. In other words the resistor gets hot.

Now. Electrons first 'flowed' to establish the positive current flow which resulted in the voltage across the resistor above zero. Then they 'flowed' to establish the negative current flow back through the resistor and then to the battery. As mentioned, the battery is seen to partially recharge. But the electron cannot be responsible for both a negative and a positive current flow. So it must be something other than the electron that managed the second half of that flow.

Then. If the flow of 'loose electrons' in metal stuctures determine a postive current flow do 'loose protons' then allow for a negative current flow? To the best of my knowledge there are no loose protons or electrons in either. Just speculatively there may be. But that's not scientific.

That's another reason that I question conventional models.
 
  • #23
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JoAuSc - I have just seen your post. The above was meant for Warren regarding the properties of current flow. It's so nice to get a thoughtful reply. Thanks for that. I'll study it tomorrow. Right now I'm tired and feeling a bit bruised.

Rosie
 
  • #24
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Warren - by the way, I've actually done that experiment. I think it's called a flyback circuit used for powering battery operated drills and such like. The point is that if you put the diode to a second battery connected to the supply battery only through the negative rail - you can actually see the recharge cycle in process. I think it's used - partially - in that drill system - but am not sure. The point is that when you use it precisely for generating heat - then there's a marginal increase in efficiency.
 
  • #25
chroot
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If electrons travel one direction, you're free to call that "positive current." If the electrons travel in the opposite direction, you're free to call that "negative current." Both are still due to the movement of electrons.

- Warren
 

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