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Electrons and batteries

  1. Apr 1, 2003 #1
    Two questions here that I hope you can help with.

    1) If an electrical current flows because of the attraction and repulsion between electrons and the terminals, do the electrons actually go though the battery? 2) I know that the battery does not put electrons into the circuit so, if the electrons don't go through the battery is there a build up of charge at the terminals?
     
  2. jcsd
  3. Apr 1, 2003 #2

    russ_watters

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    Staff: Mentor

    Electricity is acutally just the FLOW of electrons that are already there. So yes, the electrons in the battery flow through the wire and back to the battery. Ever see one of those self-contained garden waterfalls? Same thing. The water is there whether the pump is on or off, but the pump makes it move around. The battery is the pump.
     
  4. Apr 1, 2003 #3
    I'm no electrician, but I thought about this before. It seems to me that it could not really be a complete, closed loop circuit with a battery. As you pointed out, the charge differential causes the flow. It seems to me that electrons would distribute from the negatively-charged end to the positive until all electrons are rather evenly distributed. Electrons that were once in the wire are now in the + side, electrons that were once in the - side are now in the wire and the + side, and some are still in the - side. As long as the positivity of the + side is about equal to the negativity of the - side, the total number of electrons in the wire should remain about the same.

    Because, really, if it was a complete circuit, the charge would even out rather quickly (a short circuit). Actually, the charge would flow backwards through the battery (the + side is more positive than the wire, so electricity would flow from the - to the + within the batttery), I would think.
     
  5. Apr 1, 2003 #4

    russ_watters

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    Staff: Mentor

    The voltage is caused by the chemical reaction inside the battery. Thats why it isn't a short circuit and thats why it can drive electrons around the loop. Eventually though, Dan, it DOES get depleted similar to the way you suggest.
     
  6. Apr 2, 2003 #5
    It is a closed loop, but there is an internal resistance in any power supply. Resistance doesn't mean that their isn't a path, just that the path isn't superconducting.

    The number of electrons in the wire do remain about the same. It's just that they are moving. When you have a particle with a velocity it inherently contains momentum. So even though the + terminal of the battery attracts the electrons, the imparted motion gives them enough momentum to go right past the + terminal instead of sticking to it.
    Kind of like the way the earth keeps moving around the sun even though the sun keeps pulling the earth towards it; when the earth reaches it's closest point to the sun it has gained enough velocity/momentum to swing back around instead of fall into the sun.

    A short circuit is not an even distribution of charge, but rather an unimpeded path for the charges to move. Really it is simply a low resistance which means a larger current or more charge moving per unit of time. Also, keep in mind that a battery isn't simply a box with a lot of electrons on one end and a lack of them on the other, it is a collection of smaller "cells" so that it looks more like this:
    -+-+-+-+-+-+-+-+-+-+-+-+
    than this:
    ------------++++++++++++
    so that the net effect is one side is more positive than the other.
     
  7. Apr 8, 2003 #6
    waitamin...so let me get this straight...1)the total no. of electrons in wire and battery are the same and will always remain the same
    2)the battery is the pump and the electrons are the stuff that get pumped...
    so how does the battery pump the electrons in a closed circuit?
     
  8. Apr 8, 2003 #7

    FZ+

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    1. Pretty much.

    2.By applying an emf (voltage) between the junctions of the cell. This pushes and pulls the electrons along.
     
  9. Apr 8, 2003 #8
    I wouldn't use the phrases "are the same" and "will always remain the same". Because of oxidation, molecular permeability, etc. I like how FZ said "pretty much" better. Get's the point across without being absolute. Notice, even I said "remain about the same".
    I think that nit has been successfully picked. :wink:
     
  10. Apr 9, 2003 #9
    so how does the emf drag or push the electrons?
     
  11. Apr 9, 2003 #10
    emf stands for electro-motive force.
    A force is always required to make an unmoving object move or change it's velocity - called acceleration. (See Newton's Laws.)

    The negative charge of the battery (battery is the "emf source") pushes the electrons away from that part of the battery because that is what happens when an electron (negatively charged) is close to a negative charge - the fundamental nature of charge - Like charges repel, opposite charges attract. A negative charge attracts (force) a positive charge, but a negative charge pushes (force) another negative charge.

    The positive charge of the battery pulls the electrons towards it for the very same reason, the very same way - by force.
     
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