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Current return path: Why does current return to its source

  1. Jun 6, 2017 #1
    Hi, I've looked through some of the replies regarding this topic on this forum, but I'm still a bit hazy on the topic.

    So this is my problem, why do current try to return to its source?
    I'm trying to understand this problem with the premise that as long as there is a potential difference, current will flow(which I consider a quite fundamental phenomena used to describe current flow).
    Does it mean that if I were to provide something that would have created a larger potential difference compared to the difference between the source, the current would not return to its source?

    ps: I was thinking about neutral grounding resistors in power transformers when this thought came up.
     
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  3. Jun 6, 2017 #2

    anorlunda

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    Current is the flow of electric charge. If the current does not return to the source, then charge builds up someplace. There will be an excess + charge someplace and excess - charge elsewhere. That unbalance would cause potential differences tending to make the current want to flow backward.

    If we say (a) that the net flow of charge in and out of every node every component in a circuit is zero, then that implies (b) that current must return to its source. Think about it for a while. (a) implies (b) no matter what the circuit.
     
  4. Jun 6, 2017 #3

    tech99

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    I think you might have in your mind the question of how does the current in an Earth-return circuit know how to find the Earth electrode at the sending end.
    The reason is that it is attracted to the wire all the way back. And this works right across the Atlantic.
    In more strict terms, if we send an impulse, applied between the wire and Earth, it travels away from the sending end with opposite polarity on each conductor. They are 180 degrees out of phase. As the two conductors involved are of opposite polarity there is an attraction, the electric field between them taking the shortest route and guiding the Earth current to be close to the wire..
     
  5. Jun 6, 2017 #4

    jim hardy

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    Anorlunda gave a good answer,
    let me paraphrase it -
    When you take charge out of something and don't put it back, it creates an electric field that'll try to put it back for you.
    You see it every time you pull a styrofoam cup out of a stack . A few charges rub off one cup and stick to the other.
    That leaves the two cups oppositely charged so they attract. That's Mother Nature trying to get the charges back where they came from.


    Now that's everyday static electricity. It takes only a tiny bit of charge to make an enormous static electric field with thousands of volts.

    In circuits we don't often deal with such tiny amounts of charge or such enormous fields. So we consider any source of charge as having to be continually replenished.
    That's what Kirchoff is telling you - charge must get back to where it came from. Even static electricity is trying to.



    Find a copy of the "IEEE Green Book", standard for grounding of power systems. It explains grounding clearly in easy to understand language.
     
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