why does 'conventional flow' still exists?

Discussion in 'General Electronics Chat' started by drk, Mar 3, 2010.

  1. drk

    Thread Starter Active Member

    Mar 8, 2008
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    Hello, I'm currently taking a course in electronics, and there's something that isn't making any sense for me. Why do we have conventional and electron flow?
    If i understood this correctly, the right flow of electrons is the electron flow, so shouldn't we like, remove the other one?
    If we proved one flow as the actual way, we should adapt the teaching to accommodate that. I don't understand why some people are taught with the conventional flow (myself included), and some are with the electron one.
     
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    If you are just in electronics you might get by with electron flow, but is is not the only current flow. There is also current due to positive charges and ions. There is also a current with no charge carriers called displacement current. All of the equations of Physics ( like maxwell's ) are written in terms of conventional current. I think using electron flow as defininging the + direction is a mistake, considering the rest of science, at best for beginners.
     
  3. iulian28ti

    Member

    Dec 4, 2009
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    Me, i go with the conventional flow.
    No pun intended.

    Electron flow messes up my brains. Who cares the electron is negatively charged ?
    +/- and CF/EF are some relative concepts. So.... just go with the flow :D
     
  4. hobbyist

    Distinguished Member

    Aug 10, 2008
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    Electron flow is good for analyzing passive circuits, where you can use ohms law to calculate Vdrops, current (electron flow) times resistance. It may be helpful.

    But conventional is a lot more easier to understand it's use when dealing with (SIGNAL) flow.

    Signals being referenced to negative ground,
    are positive going and it makes it more easier to follow a signal path using this method. (conventional flow).
     
  5. jgessling

    Active Member

    Jul 31, 2009
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    Because that's the way the arrow in diode and transistor symbols points.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    I had a career in electronics design for 38 years (I retired early). I never thought of current direction. I just learned that an NPN transistor is turned on when its base is positive with resect to its emitter and a PNP transistor is the opposite. It is obvious what turns on a diode.

    Mosfets have the arrow in reverse to a bjt but I simply learned it.
    An N-channel Jfet was the same as a vacuum tube. A P-channel was the opposite.

    When I thought very deeply (not very often) then I thought about the real electron flow, never "conventional flow".
     
  7. drk

    Thread Starter Active Member

    Mar 8, 2008
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    I'm not talking about if its easier one way or the other. Or if its 'the way it has always been done'.
    I just think we should go for the one that is right. Just seems strange to me that something like this exists.
     
  8. steveb

    Senior Member

    Jul 3, 2008
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    We have "conventional current flow" and "electron flow" defined in opposite directions because of our hero, Ben Franklin. He did not know the detailed physics of charges and did not know that something called an electron was flowing in a particular direction. In the absence of this knowledge he arbitrarily defined a direction of current and said that a positive charge is flowing and when it moves in a positive direction, that is defined as the direction of positive current. It turned out that, in his experiments, it was actually an opposite charge (the electron) flowing in the opposite direction, but by the time this was well understood, the convention was already established and it was too difficult to change. Note that negative charge going backward is effectively the same as positive charge going forward, for many observable effects, because multiplying two minus signs gives you a positive value.

    It's important to be able to think in terms of electron flow because if you want to think about what is physically happening, you will want to pay attention to the actual charge of the carrier and the actual direction of its flow. And, most of the time, in practice, you will be dealing with electrons flowing, but not always.

    It's also important to be able to think in terms of conventional current direction because all of physics and engineering use this definition for theory. This theory is so firmly established that you don't want to try and make your own equations in terms of electron flow, although you could do so if you choose too. As mentioned above, every text book on Maxwell's equations defines charge flow (actually current density which is a vector with a direction implied) to be in the direction of a positive charge with positive velocity. This implies that a negative charge flowing in a positive velocity direction has charge flow (current) in the negative (or opposite) direction. Again, negative charge flowing in a negative direction will be interpreted as a positive current density (or positive current).

    Basically, current direction can be arbitrary and is defined in the way we use it by convention. Electron flow is not arbitrary and is positive in the direction that electrons flow, by definition.

    The Ebooks here at AAC use electron flow and clearly disclose that fact, so there is no problem with a breaking of convention because electron flow is an accepted convention. The books use a clearly defined concept in a clearly defined manner. Likewise, (most) standard physics and engineering texts use current flow and (usually) clearly disclose the fact that the definition is an agreed upon convention.
     
    Last edited: Mar 3, 2010
  9. Wendy

    Moderator

    Mar 24, 2008
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    Tradition is tough to beat, and this one has 150 years (with all the R&D behind it) to become enshrined.
     
  10. drk

    Thread Starter Active Member

    Mar 8, 2008
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    why did he defined arbitrarily? this is suppose to be science... like prove things and such :) probably got over-confident or something..

    anyway, i understand its something that is a tradition, so it's difficult to do differently, but don't you agree, that the more time passes, the more difficult it will be to change a thing like that.
    if it was too difficult to change 100 years ago, even more it is now, and much more will be in the future.
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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    One assumes you refer to Mr. Franklin. He was free to be completely arbitrary as test equipment had about 100 years to go before being invented, and the idea that charge carriers existed did not get thoroughly investigated until 1907 or so.

    I'm not sure that tradition can really affect what goes on in a wire.

    As to the weight of tradition, you have only to look at systems of measurement. There are few countries still using non-metric systems. Thanks to a bit of fudging with the definition of a meter, it is somewhat more difficult to feel the necessity to abandon inches, feet, yards, and miles.
     
  12. eblc1388

    Senior Member

    Nov 28, 2008
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    Those are not as bad as using "stone" as weight measurement.

    Suitable for those still living in the Stone Age.
     
  13. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    No need to change it. You just need a consistent set of equations and an understanding of how the equations map to reality. "Tree" is a arbitrary term, not wrong, no need to change, but does need to be learned. Switch to french if you wish. Different not wrong or right. Most of science uses convent. current. But in general use the language of the group you wish to communicate with.
     
  14. Audioguru

    New Member

    Dec 20, 2007
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    Some countries measure weight in "stones" and still "weigh" their money. Their currency is in Pounds. They drive on the wrong side of the road etc.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    Ben Franklin created his concepts around the year 1780 or so (18th century), the basic concept of matter (how it is arranged) did not exist until the 20th century. Ben made truly remarkable discoveries, this can not be belittled. Some of his theories just needed a little tweaking, and it took over 100 years for science to catch up.

    A lot of text books were published in that time, and a lot of scientists lived and died with the sure knowledge of how it worked.
     
  16. studiot

    AAC Fanatic!

    Nov 9, 2007
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    This debate seems to regularly exercise this and other forums.

    Most proponents of either side forget that electricity is not about electrons. It is about charge and/or electric fields. Electrons happen to be charge carriers but charge and electrons are distinct entities in their own respective rights.

    There is such a thing as displacement current, which has nothing to do with electrons. What is the correct direction for this?

    Current direction is merely a book-keeping sign convention for certain procedures. Accept it, use it and forget about it.
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    And if you are using an arc, or a vacuum tube (AKA valves)? There is a reason for the debate. There are many applications where it doesn't matter, but there are some applications where it does. This being the case why have two standards?

    While exceptions exist in chemistry or chemical processes you would be hard put to find where it isn't electrons, be it wires or human flesh. A conservative estimate would be 99.99% of all electric current is electrons, and the percentage is probably much higher. I have already seen basic misunderstandings on the exceptions, because of the basic insistence that conventional is as good. A theory in science breaks down where obvious exceptions exist, this is such a case.
     
  18. steveb

    Senior Member

    Jul 3, 2008
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    It is very difficult to change, whether now or anytime in the future. Consider that the simplest way to change is to redefine an electron to have positive charge and for a proton to have negative charge. You would then need to rewrite all known physics equations to be consistant with this convention, which isn't too hard to do. This would then allow beginning students to better think about what is happening physically and associated it with the convention. It would also be a little more convenient for dealing with physical situations involving electrons as the charge carrier, which in a more common occurance in physics. Note that it is only marginally more convenient, because you will just be avoiding a few minus signs when you write equations.

    However, imagine how much confusion this would create in the period of converting the standard. This is like trying to tell the world that from now on, the word "yes" means "no", and the word "no" means "yes". And, you must nod your head up and down when you mean "no" and move in left and right when you mean "yes". Or, it's like telling everyone that "right" means "left" and "left" means "right" from now on.

    Why would we create all this confusion over a simple matter of a sign convention? Just understand that positive current is defined as positive charge going in the positive direction and negative charge going in the negative direction. Likewise, negative current is defined as positive charge going in the negative direction, and negative charge going in the positive direction. It's not really that hard to do, and there are plenty of much more difficult concepts to master when learning physics.
     
  19. andrew24

    Active Member

    Aug 20, 2008
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    For me, when analysing circuits is a lot easyer to think that current goes from + to ground. Analogy in nature- rain, or water also goes from something higher to the ground, not the other way around.
     
  20. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Why do I always seem to be the one tasked with asking the akward question?

    How many electrons have you seen passing through a capacitor, on their way from -ve to +ve?
     
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