Electron Flow versus Current Flow

Discussion in 'Electronics Resources' started by Jsw123, Mar 7, 2013.

  1. Jsw123

    Jsw123 Thread Starter Active Member

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    Today, while reading some information about batteries, I ran across an article that described that while electron current flow was negative to positive, conventional current flow is positive to negative. I have always understood that current flow is negative to positive.

    In my search for clarity, I found many articles, such as the one in the link below, which suggest that "conventional current flow" is based off some misconceptions from the time in history that scientists believed electricity was a fluid. This suggests to me there is no actual physical difference between electron current flow and conventional current and there is no scientific reasoning to explain the two types of current flow because conventional current flow is a theory that is actually proven wrong.

    Am I correct on this?

    If so, for electrical components in DC circuitry that may be marked with current direction, rather than marked positive and negative markings (I am thinking of the schematic of a diode for an example), is this flow marking based on electron or conventional current flow?

    Link showing electron vs conventional current flows:

    http://web.engr.oregonstate.edu/~traylor/ece112/lectures/elect_flow_vs_conv_I.pdf
  2. wmodavis

    wmodavis Active Member

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    It is an interesting theoretical discussion for some people but IMO of no practical significance. Using either you can do circuit mesh and node analysis. It is more important to concentrate on other things if your goal is to be a good technician or engineer. Therefore my sugestion is to pick one and consistently use it and focus on learning about controlling the current flow to do useful things. The arrows on some components, rightly or wrongly point in the direction of conventional current so If I were you I'd learn to work with that rather then electron flow. But it's your choice. They both are useful.
  3. Jsw123

    Jsw123 Thread Starter Active Member

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    So, to confirm, will current flow (and not be blocked by the diode) in the attached diagram, since arrows on devices indicate conventional current flow?

    My previous knowledge would lead me to believe current in this circuit would be blocked, but if all symbols use conventional flow rather than actual flow, that would not be the case.

    Attached Files:

  4. wmodavis

    wmodavis Active Member

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    Blocked.
    For current to flow the battery + must be connected to the anode of the diode. The arrow of the diode symbol indicates the direction of conventional current flow. + voltage to anode forward biases the diode allowing current flow in direction of arrow or electron flow opposite direction.
  5. Jsw123

    Jsw123 Thread Starter Active Member

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    Thanks for the clarity. My training on reading the diode symbol (coming from a book called "Electricity 1-7") taught me to read the diode symbol showing that if current was flowing in the direction of the arrow, it would be blocked. I was taught that was what the solid line in front of the point of the arrow was supposed to communicate.

    Is this conventional current rule applicable for transistors as well?
  6. MrChips

    MrChips Moderator Staff Member

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    It depends on where you first got your training in electricity and electronics.
    I was always taught conventional current flow and that works fine for me because it matches the symbols in circuit diagrams.
  7. WBahn

    WBahn AAC Fanatic!

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    The origin of the diode symbol comes from the notion of "cathode rays", which are really electrons. Think of a CRT display -- the CRT is a "cathode ray tube" but we know that the "rays" are really streams of electrons.

    The line on the symbol represents the cathode of a vacuum tube and the triangle represents a spray of "cathode rays" coming off of it and going to the other terminal (the anode).

    Therefore, with that understanding, you know that for "cathode rays" to flow, the anode has to be more positive than the cathode in order to attrach electrons at the cathode toward the anode.

    It is merely a very useful coincidence that the symbolic representation chose to represent cathode rays looks like an arrow pointing in the other direction and, hence, an arrow pointing in the direction of conventional current flow.

    As others have said, as long as you are consistent it doesn't matter which you use. There are some situations, particularly when dealing with semiconductor physics or ion beams or such, when it is reasonably important to think in terms of the actual charge carrying "things" that are moving around. But for most circuit analysis you can think of it either way. The reason that conventional current rules the day in engineering is because it allows for a consistent mathematical convention that naturally carries the polarity information through the computations.
  8. wmodavis

    wmodavis Active Member

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    I would like to read the exact text in that book (which by the way I taught from in my career) because I believe you simply misinterpreted what it was saying. That is/was a fairly reputable electronics text and that is such a basic electronic component and idea my guess, cuz I do not actually remember that far back, is that is not what it said. I could be wrong but..... show me the text.
  9. atferrari

    atferrari AAC Fanatic!

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    The aftermath of this, for you, is that when discussing anything related with currents you should make clear what convention you use and be ready for a lot of confusion.

    Have you ever tried to drive on the wrong side of a street? Not easy (really not) and even rsiky.
  10. crutschow

    crutschow AAC Fanatic!

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    Current flow direction was originally designated when they didn't actually know the polarity of the charge carriers and assumed they were positive. When the charge was determined to be negative it was realized that the charge flow was opposite to the assigned current flow.

    I like current flow since, with the commonly used positive supply voltage in a circuit, the current flows from the top to the bottom of a typically schematic. Also the current flow in semiconductor components, such as transistors and diodes, is in the direction of the arrow.

    The only time you need to really think about electron flow is when looking at semiconductor physics or the inner working of vacuum tubes (valves).
  11. WBahn

    WBahn AAC Fanatic!

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    I think it dates back even further than that. Benjamin Franklin, in working with static electricity, noted that the attraction and repulsion of charged objects behaved in a way that could be completely explained by the presence of just two types of charge. If you rub certain materials together you charge both of them up and they are always oppositely charged. He called the type of charge on one "positive" and the other "negative". Over the course of the next century that arbitrary choice became the standard and once it was discovered that the charge transfer occured by the transfer of particles from the (soon to be) positively charged material to the (soon to be) negatively charged material it was far to late to change the name assignment.

    So it's not that Franklin guessed wrong, it's that he simply made an arbitrary naming choice when faced with what were indistinquishable possibilities and it ended up having some unfortunate inconveniences down the road. But, had he chosen the other way, there would have still be some inconveniences because sometimes it is positive charge carriers that move.
  12. ErnieM

    ErnieM AAC Fanatic!

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    I'm always amused by these discussions about "conventional current flow" and some other type. One thing always missed is the word "convention."

    From Wikipedia: "A convention is a set of agreed, stipulated, or generally accepted standards, norms, social norms, or criteria, often taking the form of a custom."

    "General acceptance" means it's what everybody else does. In the US "by convention" we drive on the right side of the road. Now I could "announce" my intent to follow a different convention by flashing my lights and honking my horn but sooner or later I'm going to cause an accident.

    Always always use conventional current when discussing electronics with anyone else. If it makes you feel special or smart to believe it is wrong that's fine, I'm sure I have my silly ideas too.

    Convention: it's the convention!
    justtrying and #12 like this.
  13. MrChips

    MrChips Moderator Staff Member

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    The problem with this is that sometime in the past someone decided that the AAC tutorials will use the electron flow model in describing and explaining how circuits function.
  14. WBahn

    WBahn AAC Fanatic!

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    The problem is that the convention is nowhere near universal. Many people, particularly coming up through the traditional trades paths, are taught electron flow for years and have it thoroughly engrained before they get to a point that they have to deal with the more widely used conventional current flow.

    The AAC textbook specifically states that it is committed to using electron flow, which is why I don't have any plans of contributing anything to it that would involve currents. I believe that having to work in a world where a positive voltage difference results in a negative current flow is just inviting mistakes.
  15. MrChips

    MrChips Moderator Staff Member

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    I teach electronics. The first thing I do is explain that current flow is quantified by magnitude, direction and the sign of charge. Once you multiply the sign with the direction I can drop the subject and move on to describing circuit behaviour using positive current flow.
  16. edwardholmes91

    edwardholmes91 Member

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    In my schooling, I was always taught "conventional current flow". It wasn't until I was studying at high school level when I learnt about electron flow. I think in most instances current flow is fine, as long as you are clear of the two and indeed there differences. ErnieM... your post about flashing your lights and honking your horn made me laugh! I think not only might you cause an accident... you might also be in trouble with the law! :p
  17. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    Sounds good, until you enter the world of sputtering machines, electronic flame offs, and vacuum tubes. Then you are back to explaining real physics and real particles.

    I may be a minority, but I agree with the author, it matters. Too many electronic processes care.
  18. thatoneguy

    thatoneguy AAC Fanatic!

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    They do it in movies all the time!

    I see it both ways, but generally use conventional current when explaining to people new to the hobby. Otherwise, the confusion level increases, since they've generally been taught at some level in grade school that "electricity" flows from positive to negative.

    Trying to switch their worldview at the same time as teaching, essentially physics, to a person can make the task very difficult, and far from "fun" for them.
  19. WBahn

    WBahn AAC Fanatic!

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    The problem with using electron flow is that it is almost always done only part way. Instead of using a current of positive charge flowing from left to right, they say that it is a current of electrons flowing from right to left.

    But a current is a measure of the amount of charge flowing past a given point per unit time, or I = dQ/dt = Q/T (in steady state terms). If the "conventional current" guys say that there is a current of positive charge from left to right, then the "electron current" guys say that there is a current of negative charge from right to left. But, they forget about the "negative charge" part of it. So they have a current from right to left that is negative because Q is negative. Hence, they also have a positive current from left to right.

    So if they want to put the direction of their current arrow such that it shows a current flowing from the negative terminal of the 12V battery through the 10Ω resistor to the positive terminal, that's fine. But they better then compute that the current in the resistor is -1.2A since there is a charge of -1.2C/s flowing in the direction they have indicated.

    But the "electron current" guys are almost universally sloppy on that point. They want to go on and on about how the physical charge carriers actually go from negative to positive but then completely ignore that the physical charge carries are negatively charged.
  20. ErnieM

    ErnieM AAC Fanatic!

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    That a particular convention is not universally accepted says nothing about it's truth nor it's usefulness. If 999,999 cars on the road drive on the right side it is not an issue of the convention when some drunk drives on the left side.

    Good habbits lead to good results. Using a different convention can lead to confusion, or it may be so completely transparent you don't even notice it is there.

    WTF am I talking about? Have you even used a digital logic chip? It has long been the convention in logic chips to denote current into the device as positive, and current out of the device as negative. Simple, clean, seems to make sense too, right?

    But what about the outputs? Check sheet 5, "recommended operating conditions." You will note that the device (a simple inverter) is spec'ed to source Ioh of -0.4mA, and sink Iol of 16 mA.

    Now before you electron flow guys start jumping up and down, do note these are both spec'ed as MAX values. So one may be lead to believe the output MUST always drive that -0.4 mA OR MORE, since -10A is less then the MAX of -0.4mA, right?

    Nope... somewhere in the general spec for TTL it's stated currents are evaluated using their magnitude only, so the sign disappears. (While checking a 74C04 data sheet it seems this absolute value convention has since been dropped.)

    You may be onto something there. Electron flow guys just don't get something, least they would stop saying us conventional current guys don't get something. I've never been sure what that something is, I definitely lean towards it not being some physics misunderstanding but something psychological.
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