Capacitance of point charge electrode

  • Thread starter shomey
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Main Question or Discussion Point

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...
 

Answers and Replies

  • #2
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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.
 
  • #3
30
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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.
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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