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Capacitance of point charge electrode

  1. May 7, 2008 #1
    Consider a capacitor which is just like a plate capacitor, but instead of the upper electrode being a plate it is a point charge Q. the lower plate is held at a fixed potential V=0.

    how could you calculate the capacitance of the system?

    when trying to calculate - it looks like it will be 0 since the potential near the point charge is inifinite and so is the potential difference between the two electrodes, and the C=Q/V is 0...
  2. jcsd
  3. May 7, 2008 #2
    The energy of a capacitor is based on force between point charges. The physical structure that holds the charges is called a capacitor. As point charges are added to a capacitor, voltage increases (V=Q/C).

    A point charge is neither a conductor, nor an insulator. A magnetic field cannot add kinetic energy to a point charge, but a (changing) magnetic field can add magnetism to a conductor. The electron environment makes a difference.

    In other words, a point charge near a conductive plate is not a capacitor.
  4. May 7, 2008 #3
    OK thanks.
    I was asked to calculate the capacitance of such a system...
    so you're saying that the question is problematic right?
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