Different Types Of Capacitors

By Author: Pierce Brosnan
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Introduction to different types of capacitors:

The simplest and basic form of a capacitor is the parallel plate capacitor . But , for different applications different types of capacitors are used . Some of the types of capacitors are described as :

Variable Capacitor
Multiple Capacitor
Paper Capacitor
Electrolyte Capacitors

Variable Capacitor:

As the name itself indicates, the capacitance of a variable capacitor can be varied gradually . This is achieved by adjusting the effective area included between the plates . The plates are usually made of brass or aluminium and semi circular in shape . Variable capacitors are widely used in circuits in radio and T.V receivers .

As shown in figure (1) a variable capacitor consists of two sets of plates . One set of plates is fixed in position and is called the stator . The other set of plates can be rotated over the stator by rotating the piston . This set is called rotor . During rotation of the motor , the area common to the plates of stator and rotor is varied .

Multiple and Paper Capacitors

Multiple Capacitor

Multiple ...
... Capacitor is a combination of several parallel plate capacitors connected in parallel and is of fixed capacitance . Mica is used as the dielectric between a number of tin foils arranged in parallel as shown in figure (2).

If the capacitance is C between two successive plates , then the capacitance of the multiple capacitor is nC , where 'n' is the number of dielectric plates used . The whole arrangement is sealed in a plastic case . These capacitors are used in high frequency oscillating circuits . The dielectric constant of mica does not change much temperature and hence , these capacitors are used as standard capacitors in the laboratory .

Paper Capacitor

A paper soaked in wax or oil is used as the dielectric in the paper capacitor . In between tin foils that serve as capacitor plates . This is shown in figure (3a) . In order to increase the capacitance to a large extent , waxed paper and strips of metal foils are arranged alternatively as shown in figure (3b) .

Finally , the entire capacitor can be rolled and sealed in a cylinder as shown . As these capacitors , occupy small space and are cheaper in cost , they are widely used in radio circuits and in laboratories .

Electrolyte Capacitor:

An electrolyte is obtained by passing a direct current between two sheets of aluminium foils ( A and C ) with a suitable electrolyte ammonium borate between the foils . Due to electrolysis , a very thin film of thickness of the order of 10-6 cm of aluminium oxide is formed on the anode plate and acts as the dielectric between the two plates . The electrolyte is a good conductor and hence , along with C it forms the cathode . As the dielectric thickness d is very small the capacitance will be very high . Care must be taken to connect this capacitor with proper polarity in a circuit . Otherwise the oxide film will breakdown . For this reason , in an electrolyte capacitor the polarity of terminals will be indicated .
These are widely used when high capacitance are required .Capacitance of the order of 103 `mu`F can be easily obtained with electrolyte capacitors of small volumes .

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