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These are the electrical energy storage devices. They store energy in the electric field between a pair of conductors. However, basically they store electric charge. These devices are commonly used in different types of electric circuits. For instance, they are used to tune the frequency of radio receivers, as filters in power supplies, to eliminate sparking in automobile ignition systems and as energy-storing devices in electronic flash units.
The figure in the right shows capacitors of different size. The size determines the capacity to store the charge or energy.
In its basic form, a capacitor consists of two parallel plates/conductors separated by an insulator. The insulator that separates the conductors is called dielectric. When a voltage is applied to the conducting plates, a current flows charging up the plates so that one plate is positively charged and the other plate is negatively charged. This flow of electrons to the plates is known as the charging current and continues to flow until the voltage across the capacitor is equal to the applied voltage. At this point the capacitor is said to be fully charged.
The simplest form of capacitors is parallel plate capacitor. This type of capacitors consists of the plates made up of metal foil or metal film deposited on an insulating dielectric material. The most common type of dielectric materials are paper, plastic, ceramic, glass and oil etc.
Depending upon the type of dielectric material the modern capacitors can be classified as:
(i) low loss and high stability- mica, polystyrene, low K-ceramic
(ii) medium loss and medium stability- paper, plastic film, high K-ceramic
(iii)polarized capacitors- electrolytic, tantalums
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Electromagnetism