Electron flow vs conventional current flow

Discussion in 'Feedback and Suggestions' started by daviddeakin, Jan 7, 2015.

  1. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
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    This is still not correct, and a serious shortcoming of this otherwise outstanding eBook. Electron flow is only the 'physical reality of electricitiy' in metal. Electricity can also flow in gases and liquids, where it is often made up of positive charges!

    The definition of current has nothing to do with the flow of electrons, but with the flow of charge. The definition of current is:
    i = dq/dt

    Hence if you take the notional 'direction of current' as being the same as the electrons, then the 'q' in that equation is negative, because electrons are negative. Hence the current, i, flowing in the direction of the electrons, is negative. Simple math.
    Conversely, if you take the notional 'direction of current' as being against the flow of electrons, then you have two minus signs (one for the negative electrons, one for the fact they are moving against the reference direction). Hence the current, i, flowing against the direction of the electrons, is positive. (Remember, electric current itself does not really 'flow' anywhere; it is just a scalar number, like 'speed'.)

    Both situations are equivalent and equally valid. But you cannot mix the two. If you want to use 'electron current' arrows, then any current you talk about, flowing in that direction, must be called negative. Unless you intend to redefine current with the opposite sign too! i=-dq/dt (And I sure hope not, because a LOT of physics textbooks will then need rewriting!)

    Since the entire world has settled on the fist definition of current, and prefers to use positive numbers where possible (i.e. 'conventional current'), then by adopting the opposite convention you are willfully making 99.9% of all other academic materials appear unintuitive to beginners. Conventional current is no more right or wrong than electron current, it is just more convenient (it's too easy to make algebraic mistakes when dealing with a lot of negative numbers). But your version of electron current being also re-defined as positive is wrong, both mathematically and historically.

    EDIT: Sorry for bringing up this old thread, but the more relevent ones have been locked.
     
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Cedric was reported as last seen in 2009, so I don't think he will be bothered by any new discussion on this subject.

    David, I don't know why you hijacked this thread rather than start one of your own on the subject, but I am not clear about your point.
     
  3. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
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    I was responding to Bill Marsden. He has a forum sticky about this topic, but replies are locked. http://forum.allaboutcircuits.com/threads/conventional-flow-vs-electron-flow.32158/
    Ressurecting this existing thread allows earlier objections to the 'electron flow' notation to be re-read quickly by anyone interested in it. This makes it less likely that people will repeat the same info than if I stared a new thread on the same topic.
     
  4. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    When I first encountered electron flow versus conventional flow, I stopped visualizing the arrows in symbols such as a diode and started visualizing them as a "spray head". Thus, electrons enter at the point and exit at the broad end. Furthermore, the diode symbol's cross bar became a large minus symbol, indicating which end should be connected to negative.

    This small visualization trick has helped me.
     
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  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Read my signature line. I consider the use of Electron Current as used on this web site the biggest shortcoming of the E-books. For that reason, I never refer newbies to this web site for explanations.

    If a student is to ever get anywhere in the Electronics field, they should learn it the way that Science and Engineering does it; not the way Navy Technicians do.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Actually, that was done by consensus of the moderators before I was a moderator. This horse is dead, I'm tired of hitting it, but I learned electron flow and I think in electron flow. Nuff said, you want my arguments they are scattered all through the site,
     
  7. tshuck

    Well-Known Member

    Oct 18, 2012
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    What is it that you think is mobile?

    It's the electrons!

    Even in ion current (not just positive charges as you've claimed), the ion is created through the movement of electrons. The ions may, themselves be mobile, but it is only the movement of electrons (in one direction or another) that is the electric current.
     
  8. #12

    Expert

    Nov 30, 2010
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    The use of electron current might be a big shortcoming, but all the CRTs I know won't work if you wait for a proton to jump off the visible screen at the right time.
     
  9. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
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    Mobility has nothing to do with the definition of current. And the defintion states that you cannot have a movement of negative charges from A to B and say that the current flowing from A to B is positive. Electrons are negative and therefore the current reckoned in the direction of the electrons is also negative (a helpfully intuitive bit of maths for a change!) It is a lot more helpful to use the positive direction of current where possible because it leads to fewer algebraic mistakes, and because the diode arrows helpfully point in this direction!
     
  10. tshuck

    Well-Known Member

    Oct 18, 2012
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    It has everything to do with it. It is a time-varying quantity, is it not?

    The charges that move are the charges that make up the current. If no charges move, no current exists. So, which charges are moving?
     
  11. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
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    Your mental picture of current may involve movement, but the definition, dq/dt, is purely maths; no statement about things moving, or what might be moving. It would still apply if someone discovered a new particle which could spontaneously change its charge without moving! (Indeed, the weirdness of quantum phsysic even allows for this; electrons are clouds of probability, not actual particles). That's the beauty of a mathematical defintion -it is universal.

    You can choose to use current arrows opposite to the conventional choice -there's nothing inherently wrong with this, other than being pointlessly contrary- but you cannot say "1 amp of current flows from the negative terminal of the battery to the positive terminal". You can only say "minus 1 amp of current flows from the negative terminal of the battery to the positive terminal". The electrons are negative, so the current is negative. Unless, that is, you redefine all quantum particles with the opposite charge, or redefine current as -dq/dt...
     
  12. tshuck

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    Oct 18, 2012
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    We are referring to the real, known universe, are we not?

    Being pedantic, you can't say n amps flow anywhere as current is a rate, not an object.

    The minus only comes into play when a direction has been defined and only holds meaning at such time.

    Electrons are not probabilities. That is a useful construct we use when appropriate.
     
  13. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Perhaps Wikipedia puts it best: "The direction of conventional current is arbitrarily defined so that a positive current flows in the same direction as positive charges and vice versa."

    I like to put it that conventional current is simply a definition to support an accounting method. A definition is neither true nor false, rather it is either useful or not useful.

    As the worldwide industry standard fully supports conventional current it makes little sense to follow a different convention.

    [​IMG]
     
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  14. WBahn

    Moderator

    Mar 31, 2012
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    An ampere is the flow of charge past a given point of interest (or through a given area of interest) at the rate of one coulomb per second.

    If you have 6.24x10^18 electrons moving from left to right through a wire each second and that is the direction that you choose as the direction of your current because you want to define your current as flowing in the same directions that the electrons are flowing, then fine. But you do NOT have a current of 1A in that wire since you have a charge of -1 coulomb going in the direction of your defined current -- you have a current of -1A.
     
  15. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    I'm teaching my little girl electricity, electronics and basic field theory. She is being taught the correct physics of charge and fields before explaining electron flow and current as the physical matter effects of electrical energy. I personally think way too much time is spent teaching electricity in terms of electrons as it tends to cloud the issues of energy flow in circuits by making students think about water analogies when that's a blind alley.
     
  16. #12

    Expert

    Nov 30, 2010
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    The definition of, "convention" is a man made agreement, not a law of physics.
     
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  17. WBahn

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    Mar 31, 2012
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    If I have one ampere of current flowing between two initially uncharged and electrically isolated objects, namely from A and to B. What is the charge on the B after ten seconds?

    Simple, right? The net change in charge is the current flowing to B integrated over the time that if flows which, if at a constant rate, is Q = I·t = (1 A)(10 s) = (1 C/s)(10 s) = 10 C

    Hence the ball has a positive charge of 10 C. It doesn't matter how that process took place. It could have been a positively charged molecular beam with the particles traveling physically from A to B or it might have been an electron beam fired from B toward A. Doesn't matter -- the end result is that B has a positive charge of 10 C.

    This is where many proponents of electron current fail to be self-consistent. In the case of an electron beam they will insist that the current is from B to A with a magnitude of 1 A. Okay, but that means that, by their definition, it is Object A that is positively charged since they claim that a current of 1A flowed TO Object A. Of course, they know that A actually becomes negatively charged so, while they will still insist that Q = I·t, they will surreptitiously throw in a minus sign somewhere to make the answer agree with what they know it has to be despite the fact that their math doesn't justify it.

    If you want to use electron current, fine. But be consistent and state that you have a current flowing from B to A of -1A.
     
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