direction of current flow in a circuit

Discussion in 'General Electronics Chat' started by opeets, Mar 20, 2015.

  1. opeets

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    Mar 16, 2015
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    I'm a bit confused here when it comes to direction of current flow in a basic circuit. Some schematics show the direction of current flow with arrows pointing from the positive terminal of DC battery source through a resistor, through an LED, and back to the negative terminal of the battery. In other schematics I have seen the arrows point from negative to positive. Which is correct or does it depend on the context?
     
  2. MaxHeadRoom

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    Probabally one method is using Electron flow, the other conventional flow, the 'true' one is electron flow, but most schematics now are drawn using conventional flow, pos to neg.
    Max.
     
  3. alfacliff

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    where do you find schematics with arrows for direction of current flow? I have never seen them.
     
  4. tshuck

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  5. nsaspook

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  6. MikeML

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    And guess which convention Real Electrical Engineers use??? ( read my sig line...)
     
  7. MaxHeadRoom

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    Although I don't really deal with anything tube based any more, but whenever I do even now, I still hark back to my basic teachings when tube technology was the norm.
    And I intuitively follow the circuit from cathode to anode direction.
    Max.
     
  8. WBahn

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    The diagrams showing current as flowing from positive to negative is "conventional flow" and the one showing it flowing from negative to positive is "electron flow". You can work with either one and you can even do so with mathematical rigor, but I've only seen electron flow done with rigor a few times. In almost all cases, including in the E-book on this site, the users of electron flow are very sloppy and employ magical mystery minus signs when needed in order to make things work out. If done rigorously, the two are identical since the values for the currents the electron flow folks should use are negative. The overwhelming majority of electron flow users are not talking about the flow of charge but rather the flow of charge carriers and they ignore the fact that the electron is negatively charged.

    Conventional current, on the other hand, IS charge flow and is mathematically consistent without the need for magical mystery minus signs and that is why it is used by the overwhelming majority of engineers.
     
  9. alfacliff

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    or you can just get over it, and try to understand how it really works. bias on tubes, or solid state devices, phasing of transformer windings, and such, not some non existent arrows.
     
  10. nsaspook

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    Trick question. What type of flow is this diagram using?

    Slightly edited the diagram to make it clearer.
     
    Last edited: Mar 21, 2015
  11. WBahn

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    Definitely a trick question -- since the image won't display. :D
     
  12. WBahn

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    Not that simple. He has to learn how to communicate ideas to and from others.
     
  13. nsaspook

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    Classic! Attached a file to the question.
     
  14. ErnieM

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    Here's his image:

    [​IMG]
     
  15. ErnieM

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    When you wish to describe a phenomena called "current" and wish to quantify your meaning you use a term called "Ampere."

    Now the Ampere turns out to have a well establish international meaning. As Wikipedia puts it "(t)he International System of Units (French: Système International d'Unités, SI) is the modern form of the metric system and is the world's most widely used system of measurement, used in both commerce and science. It comprises a coherent system of units of measurement built around seven base units, twenty-two named and many more unnamed."

    Also "(i)n practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time, with an equivalent charge to 6.241×1018 charge carriers (or one coulomb) per second constituting one ampere.[6] Amperes are a measure of flow rate of electric charge." Do note that "one coulomb" is a positive number.

    That is the "convention" as used in science and engineering.Thus one coulomb of positive charge moving from A to B constitutes a current of 1 Ampere. Also, one coulomb of negative charge moving from B to A also constitutes a current of 1 Ampere as the signs cancel.

    Thus, to be consistent with international standards one would use conventional current flow.
     
  16. nsaspook

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    Exactly. That's why I posted my twisty little arrows diagram with positive (+ions) and negative (electrons) charge carriers. Simply looking at a current arrow on a wire tells you little about what's happening in real world circuits that deal with physical processes. Knowing what's happening 'inside the box' in terms of field energy flow that causes charge movements is what matters when you need to see the whole system picture. The 'direction of current flow' from the standpoint of the energy flow of 'electricity' seems important even in steady state DC at first but most finally see that the physical 'current' direction at one point is dependent on the physical properties of the system at that point and could change direction several times in a typical circuit.

    Conventions are important but just like a volume knob CW/CCW turning direction, it works just as well both ways if it's consistent even if its consistently backwards.
     
    Last edited: Mar 21, 2015
  17. MCU88

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    You've got tickets on yourself Mike.

    It is rather confusing since my teacher told me that current flows from positive to negative, and current is (n) quantity of electrons. However electrons travel from negative to positive. I don't ponder on theory such as this anymore and just accept it for as 'whatever' and concentrate on the kinetic side of things.
     
  18. ErnieM

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    Don't ever just accept something someone told you: keep at it till it makes complete sense, then move on.

    (Mostly) True:"current flows from positive to negative"

    Better :"current is defined as flowing from positive to negative"

    True: "electrons travel from negative to positive"

    Now if you notice that traveling from negative to positive is a negative direction (or a negative current) but of a negative charge you have -1 * -1 = +1 for the sign of the current.
     
  19. KL7AJ

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    And of course, this was all Ben Franklin's fault, when he defined current flow as being the flow of material in an electroplating solution as being the flow of material...which we NOW know to be ions. Ions flow the opposite direction of electrons (if indeed they can flow). Well, we can forgive old Ben for not knowing too much about electrons. :)
     
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  20. MCU88

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    Yes. At University level this is what they want. They want you to have an mind of your own and question everything. However, you cannot question anything in academia without support for your argument. Now we speak of current (an invisible entity) -- how do we support an argument around this other than to reference to existing literature in textbooks written by (n) qualified people. These books are all going to say the same thing. My teacher was an diploma qualified professional preaching the words of these books.
     
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