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Conventional Current Versus Electron Flow?

  1. Feb 17, 2012 #1
    I've been trying to get involved in electronics for some time now, but I can't seem to manage to wrap my head around conventional current versus electron flow. I understand that electrons do the movement, but does that mean that electricity flows from the negative to positive side? Or the other way around?

    Could someone explain this to me in the simplest possible terms?
     
  2. jcsd
  3. Feb 17, 2012 #2

    Bobbywhy

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    Plozen, Welcome to Physics Forums! This is a place where real scientists, engineers, and other highly experienced people contribute to your understanding of science, technology, engineering, and mathematics.

    I will give you an example of how "current flow" was taught by the US Navy Electronics School fifty years ago. It worked quite well in those days, but be advised, this is only part of the answer to your question.

    The simplest vacuum tube amplifier is a triode, meaning it has three electrodes: cathode, anode (plate), and control grid. The cathode was most negative and had a heating element that glowed red-hot. This caused electrons to "boil off" and be attracted by the anode, which was at a high positive voltage...typically +250 volts. The control grid was a screen between the anode and cathode which controlled the flow of electrons. This triode could amplify a small signal placed on the control grid. We said: "Current flows from the cathode to the anode". Our rule was "current flows from negative to positive", which made sense to us, since we knew electrons had a negative charge. We used the terms "current flow" and "electron flow" interchangeably.

    Now, that is only one part of your answer. I defer to other (younger) contributers here to explain the rest of the story!
     
    Last edited: Feb 17, 2012
  4. Feb 17, 2012 #3
    In metals electricity flows by the movement of negative electrons.
    In semiconductors it is possible to have negative electrons and positive 'holes' contributing to the current
    In liquids the electric current can be due to the flow of negative electrons and/ or positive ions.
    So this is not a simple story!!
    One thing is essential to know......conventional current is taken to be the direction in which + charges would flow. This is the direction shown by the arrow on circuit diagrams.
    It is the convention used to determine the rules of magnetic forces which includes the direction electric motors will turn etc
    Conventional current flows from the + terminal of a battery.
     
  5. Feb 17, 2012 #4

    AlephZero

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    There are two different issues here. If you want to understand how electronic components "work", you need to consider the what is actuallly "carrying" the current, and as #3 said this is not necessarily electrons. For semiconductor devices, you often need to consider quantum mechanics as well, which makes the whole concept of "particles flowing" rather too simple minded.

    On the other hand for analysing complete circuits, most of the time you can ignore the detail of how the components actually "work" and treat them as "black boxes" that carry out some function. For that purpose, everybody takes the direction of "current flow" to be from positive to negative voltage, and the fact the "electrons really travel the other way" is irrelevant, even when the current is being carried by electrons and not by something else.

    This site might show you some other things you were taught about electricity that you need to "unlearn": http://amasci.com/miscon/elect.html
     
  6. Feb 17, 2012 #5

    jim hardy

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    When you take your class in circuits you will learn to write equations using Kirchoff's Laws of voltage and current.

    It makes absolutely NO DIFFERENCE whether you think in negative or conventional current.

    Try it - draw green arrows for negative current and red ones for positive and write KVL around the loop.
    You get the same answer.
    Conventional current leaves source from positive terminal, negative current from negative.
    Conventional current enters a load at positive terminal, negative at negative.
    Make your signs in green and red and you'll see they're same.
    So when you write the loop equations you get same result.

    I taught a course in toubleshooting instrument current loops to a mix of engineers and Navy Nukes.
    I did the above exercise then asked the class which current they preferred, and conducted each class in their preferred current.

    If you're to succeed in industry you need to be able to flip back and forth.
    So develop that skill. Else you'll have to endure much teasing about "Engineer's Current".
    It's easier than you think.

    And, when in Rome..........
     
  7. Feb 17, 2012 #6
    My path to PROPERLY understanding this stuff involved this mental picture:

    A 2d cross section of a crystal lattice at the atomic level. Lets say for example a crystal of copper, a popular conductive metal. Electrons are occupying the orbitals of these constituent atoms. Now suppose some magical entity swoops down and removes ONE electron from some random atom's orbital in this perfect crystal arrangement. There will be a hole left around that atom which the electron had been occupying. Other electrons from adjacent atoms in this lattice slide into the gap that was created while creating their own gap on their former home atom. This kind of behavior leads to electrons shifting around and having the "hole" transferred to all the different atom sites in this rigid lattice where only electrons have mobility. This is kind of a crude way of putting it but I hope you get the picture. In real circuits you would have directionality where the hole would slide over in a specific direction around the loop, leading to "conventional current"
     
  8. Feb 17, 2012 #7

    Integral

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    How about making that Many , not everybody uses positive current flow. I am Navy trained and really like electron flow in normal circiuts. As has been said above it does not make any difference as long as you are consistent in any given application.
     
  9. Feb 17, 2012 #8
    Also of note: if you plan on later expanding your understanding to how semiconductors work in terms of N and P doped silicon, thinking in terms of conventional current provides somewhat of an advantage in my opinion.
     
  10. Feb 18, 2012 #9
    It is wrong to think that electrons in metals leave behind a positive hole that needs to be filled.
    Electrons in metals are 'free' at all temperatures and form a sea of free electrons
    In semiconductors (intrinsic) electrons are not free unless the temp is increased. In this way every 'free' electron does leave behind a positive hole. As temp rises intrinsic conduction increases
    Dopants in semiconductors do release ( or accept!) electrons easily so these electrons ( or holes) are free in the same sense as electrons in a metal.
    The details of these mechanisms requires some consideration of the energy band structure in metals and semiconductors
     
  11. Apr 24, 2012 #10
    Conventional current and electron flow are different ways of describing exactly the same physical phenomena in a circuit. Electron flow is the correct model of reality, but both can be used. In some professions such as electrical engineering, conventional current is still the standard. If you think of electricity as water traveling through a pipe from the negative terminal to positive terminal, electron flow is correct. If you pretend the electricity is traveling in the opposite direction, all the math and circuit analysis will still yield the same results. It is only important to stick with one method, to realize which method a book or course on electricity or circuits is using, and to realized which way a diode and magnetic field are oriented in relation to the model of current flow you are using. I actually found a really straightforward explanation of this at http://www.infobarrel.com/Conventional_Current_vs_Electron_Flow
     
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