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What Are Fixed Capacitors?

Benjamin Franklin is credited with making the first flat capacitor.
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  • Written By: W. Joyner
  • Edited By: A. Joseph
  • Last Modified Date: 15 April 2014
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Practically every electronic device uses a capacitor in some manner. Capacitors are available as fixed capacitors or variable capacitors. Fixed capacitors are those that maintain a constant and unchanging value of capacitance, its ability to hold an electrical charge. Variable capacitors are characterized by the fact that their value of capacitance can be adjusted or varied.

Capacitance usually is measured in terms of farads or microfarads. Capacitors are available in a wide variety of shapes, sizes and, most importantly, capacitance ratings. In some applications, fixed capacitors are linked together in series to form what is known as a fixed capacitor bank.

Fixed capacitors often are found in timing circuits. Though frequently used in tandem with a resistor to create a timer, fixed capacitors and fixed capacitor banks also are used to supply a continuous supply of level current, which serves to even out the flow of the current. This helps to avoid spikes and surges that might occur in the power supply of an electrical circuit.

There are various types of capacitors. They generally are categorized by the type of dielectric material used. Basically, a dielectric is a material that does not conduct electricity. The dielectric is used in the fixed capacitor to insulate or separate the materials that do conduct electricity.

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The capacitor is constructed with the dielectric sandwiched between the two conducting plates. In this way, each plate is capable of being charged with electrical current and has the ability to hold the charge. The difference in the charge levels of the conductive plates allows an electric field to exist in the dielectric.

A variety of materials are available for use as dielectrics, including paper, plastic, ceramic and others. It also is possible to use air as the insulating layer between the conducting plates. Such is the theory behind vacuum tubes.

The capacitance rating of a fixed capacitor also is affected by the thickness of the dielectric. Additionally, the type of material used for the conducting plates is of vital importance, because some materials have a far greater rate of conductivity than others.

The history of capacitors can be traced to the 18th century. Peter van Musschenbroek of the University of Leyden in the Netherlands developed what came to be known as the Leyden jar, an early form of a capacitor. Benjamin Franklin is credited with later producing the first flat capacitor.

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