Archive for November 2015
A capacitor is made up of two electrical conductors called plates separated by an insulator called the dielectric. The two plates within a capacitor are each wired to two electrical connections on the outside called terminals, which can be hooked into an electric circuit. The point of capacitors is to store and release electrical energy; its two plates hold opposite charges and their separation creates an electric field, allowing for electric energy to be stored. To store additional electrical energy in a capacitor is called charging, while releasing that energy is called discharging.
A capacitor is distinct from a battery in that while a battery uses chemicals to store electrical energy and release it through a circuit at a slow, measured pace, a capacitor generally releases its energy much more rapidly. A capacitor would be used, for example, to generate the energy necessary to light a flash bulb on your camera. It may charge up using energy from your camera’s batteries before the flash goes off, but the devices are interconnected, yet not one in the same.
A capacitor can be charged simply by wiring it up to an electric circuit; when you turn on the power, the electric charge gradually builds up on the plates. If you disconnect the electric circuit and the capacitor, the charge will be stored on the plates (though it will likely leak some charge over time). If you keep them connected and then hook the capacitor up to an electric engine or a flash bulb, the charge will flow through the capacitor to the motor until the capacitor’s plates are all out of charge.
The amount of electrical energy that a single capacitor can store is called its capacitance. Capacitance is measured in farads (F). Because one farad is so large, most capacitors’ capacitance is measured in fractions of a farad. To increase a capacitor’s capacitance, its plate size can be increased, its plates can be placed closer together, and its dialectric can be replaced with an even more powerful insulator. Dialectrics can be composed of a variety of insulators, from normal air to ceramics to plastic.
Capacitors may only really store energy, but the way that they do so makes them very useful. Because they generally take a very precise, predictable amount of time to charge, they can be used as timing devices. They also can smooth voltage in circuits, help people to tune into particular radio and TV stations, and, in the form of larger supercapacitors, they can be used in place of batteries.
If the physics is still confusing you, imagine all of these elements in the context of a large cloud during a lightning storm: Ice particles flying around in the cloud rub against the air and gain static electrical charges. Lighter, positively charged particles move to the top of the cloud while negatively charged particles move to the bottom. The polarity of the cloud’s charges turn it into somewhat of a capacitor; the more static electricity builds, the more polar the cloud becomes and the more electrical potential is being stored in this growing storm. Once the voltage reaches a certain level, the air in the cloud converts from an insulator to a conductor, allowing for all of the energy to be released at once in the form of lightning.