Capacitance is the amount of charge that can be stored at a given voltage by an electrical component called a capacitor. The unit of capacitance is the Farad (F) and a 1F capacitor charged to 1V will hold one Coulomb of charge. A capacitor is a passive electronic component that consists of two conductive plates separated by an insulating material called a dielectric. A voltage applied to the plates creates an electric field across the dielectric, which causes the plates to accumulate a charge. The charge remains after the voltage source is removed, allowing energy to be stored until the capacitor is discharged (allowing the stored energy to perform work).
The size of the conductive plates and the permittivity of the insulating dielectric material determine capacitance.
The larger the capacitance of a capacitor, the longer it takes to charge and discharge. This means it takes more time for voltage to build up (charge) or fall (discharge). This makes capacitance useful for filtering out small voltage variations that last only a short length of time, i.e., high-frequency transients.
Unintended (parasitic) capacitance exists between any two conducting materials – the closer their proximity and size, the greater the value. This must be factored into the design of a circuit as it can affect the speed at which it operates. For example, a large transistor may allow faster switching, but its larger size means a larger parasitic capacitance exists between its terminals and this may slow the speed of the circuit driving it.
Capacitance is measured using a capacitance meter. A 1F capacitor would be quite big – the size of a small bottle. For this reason, capacitance values used in electronic circuits are in the microfarad to nanofarad range.
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