The Parallel Plate Capacitor

The parallel plate capacitor is the simplest capacitor. It consists of two parallel plates of surface area A a distance d apart. The plates may be made to store charge by connecting a source of voltage across the plates.

Capacitance is defined via the equationor

To simply the analysis I shall assume:

  1. The electric fieldbetween the plates is uniform. This means I can use the equationor

  2. The charge on the capacitor is stored uniformly on the plates. This means I can use the equationwhereis the surface charge density.

An application of Ampere's Law givesa constant so

is a very useful equation. The capacitance can be increased by use of a dielectric between the plates. A dielectric is made of polar molecules which reduce the electric field, meaning that more charge can be stored.

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