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How can a conductive surface be held at a desired potential?

  1. Aug 7, 2013 #1
    I was reviewing some things relating to electric fields around conducting surfaces, and the book I was using (Purcell) mentioned that a conducting surface can be held at any arbitrary electric potential (within reason). My question is, how would this actually be done in practice? Purcell mentioned something about using a battery, but my circuitry intuition is weak, so I don't see how this can establish a desired potential starting from a neutral surface.
  2. jcsd
  3. Aug 7, 2013 #2
    For example, attach the positive end of an 8 V battery to the metallic surface, and earth the negative end. Now all parts of your surface are "floating" at a potential of +8 V relative to earth.

    Batteries in series are good to use for this purpose because they provide a stable ripple-free potential. For high voltages you'd have to use a power supply similarly connected to the surface and to earth.

    Edit: A variable resistor can be used to generate a particular potential.
    Last edited: Aug 7, 2013
  4. Aug 7, 2013 #3
    Please excuse my ignorance, but I'm not sure how a battery works. If each end is connected to a conductive surface (without completing the circuit), will electrons flow through the battery until the two surfaces reach the correct potential difference? Also, what is driving the electrons? I realize it's some kind of chemical reaction in the battery, but doesn't the circuit need to be complete for the battery to provide work?
  5. Aug 8, 2013 #4
    There will be a momentary flow of electrons (too rapid and too small to detect using conventional means), but this will stop once the potential has been established. The set-up described is not a circuit and can't be analysed using conventional electronics ideas.
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