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