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Trouble understanding - to + vs + to - current flow

  1. Nov 29, 2015 #1
    1. The problem statement, all variables and given/known data
    When reading about directions of magnetic flux in relation to current flow on pages 6 to 8 of http://www.free-energy-info.tuks.nl/Non-Ferrous-Magnet.pdf , I found that in figure 11 the current is travelling from + to - terminals, while in figure 12, the current flows from - to + terminals. I am still learning about the basics of circuitry and magnetism, and I want to understand why and how a current can flow in both directions.

    2. Relevant equations
    None that I know of. If there are some I would like to be enlightened.

    3. The attempt at a solution
    After reading this article "http://www.blueraja.com/blog/179/do...tive-to-negative-or-from-negative-to-positive" I found that from a Physics standpoint a current would travel from - to + in reference to electron flow, but in electronics it doesn't matter. Why doesn't it matter? Can a current move both ways or only one?
     

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  3. Nov 29, 2015 #2

    TSny

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    Looks like you caught an error in the text! The two arrows in figure 12 should be reversed so that current will be flowing from + to - in the wires. The directions of the magnetic fields in fig 12 should also be reversed.
     
  4. Nov 29, 2015 #3
    Oh, ok. Does this mean that currents ,in reference to an electrical perspective (as opposed to a Physics perspective), always travel from + to - in DC and AC currents, or are there exceptions?
     
  5. Nov 29, 2015 #4

    TSny

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    As long as you take current to be in the direction that positive charge would flow, then current will always flow in a conductor from higher potential to lower potential. The + and - refer to regions of higher and lower potential respectively. This is true in both DC and AC circuits. In AC, the potentials of the two ends of a conductor are alternating in regard to which end is at the higher potential.

    The usual convention in physics today is to take current to be in the direction that positive charge would flow, therefore opposite to the direction of electron flow. I believe that this is also the usual convention being used in electronics. However,some older texts take the direction of electron flow to define current direction. So, you have to be careful when switching between different books.
     
  6. Nov 30, 2015 #5
    That makes sense. Thanks for setting things straight and informing me of the standard current conventions used today.
     
  7. Nov 30, 2015 #6

    davenn

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    It doesn't matter too much which one you use, as long as you state which and stick to it through out a given discussion when talking generally

    but you need to know and understand that current IS the flow of electrons from negative to positive
    This is because the electrons are the mobile charge carriers ... the positive ions in a wire don't move ! ... they are fixed in the atomic lattice of the conductor and don't go anywhere
    The only real variation to this is when dealing with semiconductors where things get a little more complicated


    Dave
     
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