It consists of a pair of surfaces that are conductive, usually in the form of sheets or plates, in a position to influence the total (i.e. the electric field of all the field lines that start from one electric device and connect to another) field separated by a medium that is dielectric or vacuum. These plates, subjected to a potential difference, acquire a given electric charge, one positive and the other negative, with the total charge of zero variation.
Although from the physical point of view a capacitor stores no charge or power, but simply mechanical energy that is latent; when introduced into a circuit it behaves in practice as an element that is able to store the electrical energy it receives during the charging period, the same energy yield during the period after discharge. Due to this particular characteristic, capacitors are widely used in the field of electronics to boost the capacity of electrical devices. There are a wide variety of capacitors available in the market and they are used for commercial as well as domestic purposes.
The different types of capacitors are as follows:
Variable capacitor – These capacitors typically consist of a dielectric parallel plate and encapsulated in glass. As their electric permittivity is unity, they have a very small capacity. They are used in radio and aviation radars because of which they are regarded as very important in the field of aviation.
Mica capacitors – The mica capacitors have several properties that make them suitable for things that require a dielectric capacitor. They suffer low losses, can be wrapped in thin sheets, withstands high temperatures and are not degraded by oxidation or moisture. Aluminum is deposited on one side of the mica capacitors, forming an armature. Several of these sheets are stacked alternately by welding the ends to each of the terminals. These capacitors work well at high frequencies and high voltages, but are expensive and are gradually being replaced by other types.
Paper capacitors – These capacitors consist of waxed paper dielectric, and are subjected to any other treatment that reduces their hygroscopic and increases isolation. They are made of two strips of paper that help to prevent the pores that may arise. They are very useful in devices that require handling high voltage electricity. The paper capacitors have applications in industrial environments.
Metalized film capacitors – They are also known as self-healing capacitors. When they are faced with an overload that exceeds the dielectric strength of the capacitor, the paper tears at some point, causing a short circuit between the plates, but this short causes high current density in the torn area. This current melts the thin aluminum layer surrounding the circuit, restoring the insulation between the plates.
Electrolytic capacitors – It is a type of capacitor that uses an electrolyte, which acts as a cathode. With proper tension, the electrolyte deposits an insulating layer (which is generally a very thin layer of aluminum oxide) on the second armature or anode, thus achieving very high capacities. They cannot be operated with AC power.
Varying dielectric capacitor – These types of capacitors have a movable armature which rotates about an axis. The profile of the armature is normally such that the capacitance change is proportional to the logarithm of the rotating angle. They are used in different industrial devices that require a lot of electricity.
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