Electron flow direction: Convention VS what's exactly happening

  • #1
Femme_physics
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Main Question or Discussion Point

[I meant "what's actually happening"]


The convention is that the electrons flow from + to -
But in reality they flow from - to +


I don't get it. Why don't we just mark it like it happens in reality? Why decided to do it otherwise? Isn't it just confusing, esp. to new students?
 

Answers and Replies

  • #2
Femme_physics
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Oh, and also, isn't it vital to know the REAL direction they're flowing in when we design circuits? In that case, why do we delusionally live in opposite world?
 
  • #3
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I don't get it. Why don't we just mark it like it happens in reality? Why decided to do it otherwise? Isn't it just confusing, esp. to new students?
When people first started studying electricity they initially thought that electrons went from positive to negative because given the nomenclature it just seemed to make sense. Why they convention has remained, I don't know.


Oh, and also, isn't it vital to know the REAL direction they're flowing in when we design circuits? In that case, why do we delusionally live in opposite world?
When designing circuits, no not really. When dealing with electrochemistry and physics, absolutely.
 
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  • #4
Femme_physics
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I see. I also read an explanation in another forum that

When we say "current flows from + to -", we do NOT mean electron flow. We mean conventional current flow or "hole" flow. Do you know the concept of electrons and holes? We know positive charges come from protons and negative charges come from electrons. But we also know that protons do not flow since the proton is stuck in the nucleus, therefore positive charges do not physically flow. Electrons on the other hand, do flow since they can jump from atom to atom so negative charges can flow. But when the negative charge jumps, it leaves behind a "hole" of positive charge that originates from the proton in the nucleus which no longer has it's charge cancelled to zero because the electrons isn't there anymore. As the electrons move in one direction and leave behind holes, it will appear as though the holes flow in the opposite direction. This hole flow is conventional current.

I got confused though-- current flow is from + to -. Electrons flow is from - to +.
 
  • #5
jambaugh
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It was Ben Franklin who established the + vs - charge convention based on his experiments. Given the plus ---> minus, minus--->plus symmetry the choice was arbitrary and I guess established by some baseline phenomenon, i.e. rubbing a glass rod with wool established one as + charged and the other as - charged.

Given the established convention, I believe it was Thompson who discovered the electron as the principle charge carrier and "oops!" it turns out to be the opposite of the + charge convention. So electrons ended up with negative charge and the direction of charge flow is opposite the direction of electron flow.

(Does that mean WE are the ones in the antimatter universe and them other guys are in the matter universe?:wink:)
 
  • #6
dlgoff
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I can't explain it better than this:

Although it is electrons which are the mobile charge carriers which are responsible for electric current in conductors such as wires, it has long been the convention to take the direction of electric current as if it were the positive charges which are moving. Some texts reverse this convention and take electric current direction as the direction the electrons move, an obviously more physically realistic direction, but the vast majority of references use the conventional current direction...
I added the bold type.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecur.html#c3"
 
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  • #7
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If you studied electric fields in your EE class, you should know that electric lines go from plus to minus. Yes convention could have been changed but, think about it... All these circuits in school books all over the world have this embedded.

Personally i found it irritating too, but later you will find out that it really doesn't matter in circuit analysis in which direction current starts from.

If you find this confusing, think about why is electron given negative charge and proton positive charge. Why is left-left, and why is right-right. Some thing you have to set. Franklin did this and too much effort would be invested to change current situation and the results wouldn't be of much significance.
 
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  • #8
Femme_physics
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If you studied electric fields in your EE class, you should know that electric lines go from plus to minus.
We're starting on basic electricity/electronics, lots of newbie questions naturally.

Personally i found it irritating too, but later you will find out that it really doesn't matter in circuit analysis in which direction current starts from.

If you find this confusing, think about why is electron given negative charge and proton positive charge. Why is left-left, and why is right-right. Some thing you have to set. Franklin did this and too much effort would be invested to change current situation and the results wouldn't be of much significance.
Fair enough :)
 
  • #10
sophiecentaur
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Most of Electrical Theory was sorted out well before 'they' discovered electrons. It doesn't matter a toss what particles are moving where in Classical electrical theory. All you need to think of is Charge etc.
The very fact that it was all largely sorted out without needing to know about electrons proves that which-way-what is going is not relevant. If you were in another part of a universe in which the majority of matter happened to be antimatter, there would be antiprotons in nuclei of antimetals with positrons in clouds around them. Whatever, the electrical theory would be just the same. Once you have settled on it, the 'sign' is immaterial.

If I had been given £1 for every kid who tried to tell me 'they got it wrong', I'd be a rich man. But they didn't 'get it wrong'. It doesn't matter, one way or another to anyone who understands the system.
Particles have their place, of course, but that place isn't in a problem about Ohm's Law or how an Antenna manages to radiate.
 
  • #11
I hate this too...It gets really confusing when I look at schematics, sometimes it looks like + to - sometimes it looks like - to + and sometimes I don't know WHAT the heck it's saying to me...
 
  • #12
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I hate this too...It gets really confusing when I look at schematics, sometimes it looks like + to - sometimes it looks like - to + and sometimes I don't know WHAT the heck it's saying to me...
Its always from plus to minus in schematics, maybe in theory explaining some certain process, like EMF in batteries its other way
 
  • #13
sophiecentaur
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There's nothing to hate. Current flows from the + on the source emf to the -. Forget whether it's electrons, positrons or pork sausages on the move - that is quite irrelevant. The rule is followed without exception because (positive, naturally) charges will flow from a high potential to a low potential (on a scale from +∞ to -∞). Schematic diagrams, when drawn correctly, need not be confusing. In some circuits it may require actual calculation to tell which of two points in a circuit is at a higher potential but it can be done.
 
  • #14
sophiecentaur
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Its always from plus to minus in schematics, maybe in theory explaining some certain process, like EMF in batteries its other way
Even in that case there will be, somewhere in the 'equivalent circuit' an emf with a + and - sign on it. In a power source, there is always an emf which causes charges to flow out of the +, in which case, it is made quite clear so there need be no confusion.
Don't go looking for trouble because you won't come across this, as a beginner / student.
 
  • #15
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Even in that case there will be, somewhere in the 'equivalent circuit' an emf with a + and - sign on it. In a power source, there is always an emf which causes charges to flow out of the +, in which case, it is made quite clear so there need be no confusion.
Don't go looking for trouble because you won't come across this, as a beginner / student.
When you explain a car battery with sulfuric acid solution and electrodes, you get that desired electron flow in the wire from - to +, but yes current is still from + to -. Some book even mark this. They say, electron flow is in this direction and current by convention goes in opposite direction. Sometimes electron flow is important, don't neglect that.
 
  • #16
Integral
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I have never seen a schematic which specifies the current carrier. You can take your pick when analysing. It does not make a bit of difference which you choose to use, either +iv current or -iv, the final result will be the same. The only difference is the direction your finger moves along the lines. I am aware that SophieC. does not like electron flow, but it is indeed every bit as valid, and more physical, than +iv current flow.
 
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  • #17
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I have never seen a schematic which specifies the current carrier. You can take your pick when analysing. It does not make a bit of difference which you choose to use, either +iv current or -iv, the final result will be the same. The only difference is the direction your finger moves along the lines. I am aware that SophieC. does not like electron flow, but it is indeed every bit as valid, and more physical, than +iv current flow.
Bottom line, in engineering you take from + to - current flow. If arrows point the other way, an explanation must be given somewhere.
 
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  • #18
sophiecentaur
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Of course electron flow is relevant in many circumstances. It's hard to discuss Cathode Ray Tubes without being aware. BUT, and this is a big but, once you start on circuit behaviour you need to stick to conventional current. Has anyone ever seen an Ammeter with "Electrons per second" in it's scale? Why not? It's because, at that level, it is irrelevant and confusing. It is for the same reason that we use g when discussing gravitational potential on and near the Earth's surface and why we use Newton's Laws of motion rather than Special or General Relativity in our everyday mechanics. The world is a series of 'shells' of understanding and looking outside one shell when it isn't necessary makes life needlessly hard. Anyone would think that bringing up the movement of charge carriers actually helped in understanding circuit theory. As I have mentioned before, all that stuff was done and dusted before the electron was discovered. Maxwell doesn't care about electrons yet the Equations work amazingly well in pretty well all cases.
Why try to imply that 'they got it wrong' when they didn't.
 
  • #19
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Of course electron flow is relevant in many circumstances. It's hard to discuss Cathode Ray Tubes without being aware. BUT, and this is a big but, once you start on circuit behaviour you need to stick to conventional current. Has anyone ever seen an Ammeter with "Electrons per second" in it's scale? Why not? It's because, at that level, it is irrelevant and confusing. It is for the same reason that we use g when discussing gravitational potential on and near the Earth's surface and why we use Newton's Laws of motion rather than Special or General Relativity in our everyday mechanics. The world is a series of 'shells' of understanding and looking outside one shell when it isn't necessary makes life needlessly hard. Anyone would think that bringing up the movement of charge carriers actually helped in understanding circuit theory. As I have mentioned before, all that stuff was done and dusted before the electron was discovered. Maxwell doesn't care about electrons yet the Equations work amazingly well in pretty well all cases.
Why try to imply that 'they got it wrong' when they didn't.
Now you statement is full, and I agree. In engineering when you design a cell phone or what have you, you don't have to worry about things like current direction. Question "What is really going on" I and i think everybody else asked because, maybe they feel like its a rudiment.

I would feel illiterate and uneducated to study electrical engineering and not know what is really going on. If you understand what is the point of all this, current direction shouldn't confuse you. If you cross the line too much with "what is really going on", in my opinion that not engineering anymore that is physics, solid state physics. You should have an average knowledge of such manner, just to keep your tingling curiosity at rest.

I bet the fellow was just curious, and I think asked the same question not so long ago.
 
  • #20
sophiecentaur
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"What is really going on" is not a valid question to ask of any Science. The best we can hope for is to ask how well a particular model accounts for what we see.

I may be a bit touchy on the topic of electron flow and current but I have heard so many students obsessing about what they see as an 'error' in Science in an attempt to avoid getting to grips with stuff and just 'Learning' a few things and 'getting on with it'. I believe in No Pain No Gain and some things are just Hard!
 
  • #21
AlephZero
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Getting back to the OP's question, you might not have learned yet that not all "current flow" is the result of "electrons moving". Sure, free electrons are the current carriers in metal wires, but not for what happens inside batteries, or in many semiconductor devices (diodes, transistors, etc).

If you have a complete circuit as simple as a battery, a resistor, and an LED lamp, you really don't want to have to keep track of all the chemistry and quantum physics that is going on, just to apply Ohm's law to find the current.

Of course if you want to understand in detail how a battery of a transistor works, then you DO need to get involved with the "physical" current carriers, how the different ones interact with each other and are created and destroyed, etc.
 
  • #22
sophiecentaur
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Well put.
 
  • #23
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Charge carriers make a difference in the Hall effect and in microelectronics where half the time the charge carriers are positive.
 
  • #24
sophiecentaur
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Yes, naturally. And. of course, they are not always electrons. Also, a meter. connected in circuit wouldn't 'know' what the carriers were.
 
  • #25
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There is more to the comments by AZ than meets the eye.

Consider a simple loop consisting of a battery and a resistor. Let us call the resistor and wiring the external part of the circuit and the internal space between the battery terminals (within the battery) the internal part of the circuit.

In the external circuit the charge carriers are moving from the negative terminal towards the positive, whether by each bumping the neighbour along a bit or as a steady stream or whatever.

The $64,000 question is "In what direction are the charge carriers moving within the battery ie in the internal circuit"

Well if the curent is moving in a complete loop then they must be moving from positive to negative.

This is unavoidable if you divide a loop into two parts by imposing two terminals on it.

So no matter which way you chose as your conventional direction you will have an apparantly contradictory flow.

As AZ said, conventionally we avoid this by not considering what happens inside the battery.
 

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