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A capacitor is a device used for storing charge. It normally consists of two conducting plates with a dielectric material between them, although an “empty capacitor” – one with a vacuum between the plates – may also be used in some applications.

Each capacitor has a capacitance C, the standard units of which are Farads (F). The capacitance is defined by the relationship Q = C V where Q is the charge on each capacitor plate and V is the voltage between capacitor plates. Therefore 1 F = 1 CV-1.

Diagram of a capacitor

The capacitance is affected by various factors, such as the capacitor geometry, however here we shall only deal with the effect of the dielectric material chosen to occupy the space between the plates.

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Increasing the capacitance in this way is desirable, since it allows a greater electric charge to be stored for a given field strength.

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