The dielectric materials are used in capacitors to store electrical energy. Depending upon the type of dielectric used, the capacitor may be ground into the following four categories.
1. Capacitors which use vacuum, air & gases as dielectric: Dielectric losses in these capacitors are very small. The value of these capacitances is not very large. Therefore these are used in radio frequency circuits and in low frequency measuring circuits where precision is highly desirable.
2. Capacitors in which the dielectric is a mineral oil: Dielectric losses are not very small. The values of these capacitors are very large. So these are used in high voltage applications.
3. Capacitors which used a combination of solid and liquid dielectric : Paper, films of materials, glass, mica etc, and mineral oil, castor oil, silicon liquids, etc.are used as dielectrics. This type of capacitors is used for power factor correction on electric power distribution system where precision is not so important but a high value of capacitance is required.
4. Capacitors with only a solid dielectric: Glass, mica, titanium oxide, etc. are used in these capacitors. These type capacitors are used in laboratories as standard capacitors. The dielectric constant of mica does not change much with temperature variation and time. Further it has value dielectric constant and high insulation resistance.
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