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Voltage at microscopic level

  1. Jan 21, 2008 #1
    Hey,

    I'm posting this because I couldn't find one single tutorial that could really answer my questions...

    My question is, what is voltage, and how does it really work at microscopic level (atoms, electrons, etc)?

    I'm not looking for answers like "it is what pushes the electrons!", the water's analogy, etc, but the electrons motion, kinetic energy, ions, etc.

    I would like, if possible, to be given an explanation regarding a simple circuit composed by a battery, two wires and a bulb.

    Common voltage-related questions I've got are...

    - Why does the battery run out of energy? Because the negative terminal runs out of electrons?

    - Why isn't there current in an open circuit?

    - "An 8V battery provides 8 joules/coulomb"... does it really provide? or does it provide a force that will give each coulomb an 8 joule potential energy?

    - etc...


    With answers like "it is what pushes the electrons!", it's impossible to understand the nature of things.


    PS: I'm sorry for my english. I hope you can understand it.
     
  2. jcsd
  3. Jan 21, 2008 #2

    NoTime

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    Batteries are composed of two chemical compounds, separated so that they can not exchange electrons. When a circuit is connected to the battery electrons are exchanged and the original compounds are changed to different compounds. When most of the original compounds are converted then the battery is dead. Some chemical reactions are reversible, hence rechargeable batteries.

    There is no place for the electrons to flow.
    You might keep in mind that if you change an open circuit there may be current flow for a short time as potentials equalize.
    This topic needs some understanding of capacitance.

    Both. The chemical reaction in the battery supplies the electrons and the energy differential to move them.

    Hope that helps some.
     
  4. Jan 22, 2008 #3

    Andy Resnick

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    Voltage is a source of potential energy for charges, like gravity is a source of potential energy for mass.

    Batteries create mobile charges through chemical reactions (wet cells and dry cells), and these charges move, creating current, in response to voltage. In a battery, the chemical potential energy of the reaction is converted into electrical potential, and when the excess chemical potential goes to zero, the chemicals in the battery are in equilibrium and the reaction stops.

    It's tempting and generally valid to think of current, voltage, resistance, inductance in analogy to fluids. A great book to read along these lines is "There are no electrons", by Kenn Amdahl.
     
  5. Jan 22, 2008 #4

    dst

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    Voltage is more or less a name assigned to how likely something will move from A==>B, just like work, force, etc. Since it's pretty arbitrary, you're free to come up with all sorts of formalisms which will work if they're dimensionally correct and likewise, will be correct experimentally because you've decided so (assuming perfect conditions). And electrons don't exactly flow but they do get transferred, pretty damn slowly (at least if you want your battery to last long). The 'electricity' propagates very fast but it's not a tangible object per se, just as the "ball currently changing its momentum" in say, Newton's cradle is also not tangible. In Newton's cradle, individual balls may or may not move much if at all, but you can obviously see the effects. Voltage is the name assigned to the energy each electron transfers (well, a coloumb anyway) to another. So no, it's not tangible, but neither are phonons - we still work with them.
     
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