How capacitors work

Electricity is seamlessly integrated into our lives like nothing else. Many do not understand how the many different components operate in order to manipulate electricity into a useful thing. Capacitors are one of these key components that we use to control electricity. To understand how a capacitor works, it is helpful to understand how a battery works.

A battery has two terminals: a positive side and a negative side. The electrical charge in a battery is created by a chemical reaction inside the battery. Negatively charged electrons collect at one end and positively charged electrons collect at the other. When there is a demand on the battery, the negative charge flows through the circuit to the positive side, creating direct current.

A capacitor is a passive component in a circuit. It cannot create a charge like a battery. In common with the battery is that it has positive and negative terminals and can store and release electrons.

At its most basic level the capacitor is two conductive plates, each with a terminal and separated by a non-conductive material called a dielectric. The dielectric can be any non-conductive material that can keep the plates of the capacitor from touching. The size of the plates and the type and size of the material determines the capacitance of the capacitor.

Like the battery, one side of the capacitor stores an electrical charge. Unlike the battery, it discharges instantaneously. This storing and releasing of electrons is the basic function of the capacitor which in turn creates several uses. Most obvious is its ability to rapidly discharge. A good example of this is a camera flash. Stored electrons are instantly released upon demand, creating an immediate and temporary flash.

A less obvious function is the ability to smooth out AC voltage. By absorbing and releasing the electron charge, the bumps and spikes in unstable AC voltage can be eliminated. By using smaller capacitors that can be charged and discharged at a rapid rate, electronic and computer devices are able to abate power spikes and disruptions in sensitive circuits and systems.

The capacitance of a capacitor is measured in farads. A farad is defined as the unit of capacitance in the meter-kilogram-second system equal to the capacitance of a capacitor that has a charge of one coulomb when one volt is applied. It is abbreviated as F. One amp is equal to the rate of flow of one coulomb of electrons per second.

A coulomb is defined as the measure of an electrical charge equal to the charge transferred in one second by a current of one ampere. So, a one amp capacitor holds one amp-second of electrons at one volt. This would actually be a very large capacitor. Capacitors are typically rated in micro-farads or smaller.

The capacitor is one of many different components used in electronic circuits to control electricity. At its most basic level, it is used to store a charge and release the charge instantaneously. Smaller capacitors are used to do this at a rate of thousands of times per second, creating a seamless, smoother AC voltage within a circuit.

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