Capacitance of point charge electrode

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SUMMARY

The discussion centers on the calculation of capacitance for a system where one electrode is a point charge Q and the other is a conductive plate held at a fixed potential of V=0. It concludes that the capacitance C=Q/V approaches zero due to the infinite potential near the point charge, rendering the concept of capacitance inapplicable in this scenario. The conversation emphasizes that a point charge does not constitute a capacitor, as capacitance relies on the force between point charges and the physical structure that holds them.

PREREQUISITES
  • Understanding of basic capacitor theory and definitions.
  • Familiarity with electric potential and capacitance calculations.
  • Knowledge of point charge behavior in electric fields.
  • Concepts of conductors and insulators in electrostatics.
NEXT STEPS
  • Research the mathematical derivation of capacitance for parallel plate capacitors.
  • Explore the implications of point charges in electrostatic systems.
  • Study the relationship between electric potential and capacitance in various configurations.
  • Investigate the role of magnetic fields in influencing conductive materials.
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Students of physics, electrical engineers, and anyone interested in advanced electrostatics and capacitor design.

shomey
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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...
 
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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.
 
pzlded said:
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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