A capacitor is a fundamental electronic component (along with a resistor and an inductor) for storing electrical energy. The best analogy for its operation would be a comparison with a battery. However, the device of the latter is based on reversible chemical reactions, and the accumulation of charge on the capacitor plates is of an exclusively electrical nature.
Content
- Device and principle of operation
- Capacity, charge and voltage
- Dielectric value
Device and principle of operation
In its simplest form the structure consists of two electrodes in the form of conductive plates (called plates), separated by a dielectric, the thickness of which is negligible compared to the dimensions of the plates. Practically used electronic components contain many layers of dielectric and electrodes. As a designation for a capacitor in the diagram, two parallel segments with a space between them are used. They symbolize the metal plates of the plates of the physical device, electrically separated from each other.
Michael Faraday is considered by many to be the inventor of the invention, but in reality this is not the case. But he did the main thing - he demonstrated the first practical examples and methods of using this device for storing an electric charge in his experiments. Thanks to Faraday, humanity received a way to measure the ability to accumulate charge. This quantity is called capacity and is measured in Farads.
The operation of the capacitor can be illustrated by the example of the events that take place in the flash of a digital camera during the time interval between the pressing of the button and the moment when the flash goes out. The electronic circuitry of this lighting device is based on a capacitor, in which the following happens:
- Charger. After pressing the button, the flow of electrons enters the capacitor and stops on one of its plates due to the dielectric. This flow is called charging current.
- Accumulation. Since, under the action of the electromotive force, more and more electrons will enter the plate and be distributed over it, the negative charge of the plate can grow until the accumulated potential repels the incoming excess flow electrons. The second plate, due to the lack of electrons, acquires a positive charge, equal in magnitude to the negative one on the first. The charging current will flow until the voltage on both plates equals the applied one. The strength or speed of the charging current will be at its maximum level when the plates completely discharged, and will approach zero at the moment when the voltage on the plates and the source will be are equal.
- Preservation. Since the plates are oppositely charged, ions and electrons will be attracted to each other, but will not be able to connect due to the dielectric layer, creating an electrostatic field. Thanks to this field, the capacitor holds and stores the charge.
- Discharge. If it becomes possible for electrons to flow in a different way in the circuit, then the voltage accumulated between positive and negative charges of the plates, is instantly realized into an electric current, the pulse of which in the flash lamp is converted into light energy.
Thus, the flash realizes the ability of the capacitor to store the energy from the battery for the pulse. The camera battery is also a storage device, but due to the chemical nature of storage, it generates and releases energy slowly.
Capacity, charge and voltage
The property of a capacitor to retain charge on the plates in the form of an electrostatic field is called capacity. The larger the area of the plates and the smaller the distance between them, the more charge they are able to accumulate and, accordingly, have a greater capacity. When voltage is applied to the capacitor, the ratio of the charge Q to the voltage V will give the value of the capacitance C. 
The capacitor charge formula will look like this:
Q = C * V.
The measure of electrical capacity is farad (F). This unit is always positive and has no negative values. 1 F is equal to the capacity of a capacitor, which is capable of storing a charge of 1 coulomb on plates with a voltage of 1 volt.
Farad is a very large unit of measurement for ease of use apply mainly its fractional measures:
- Microfarad (μF): 1μF = 1 / 1,000,000 F.
- Nanofarad (nF): 1nF = 1 / 1,000,000,000 F.
- Picofarad (pF): 1pF = 1/000000000000 F.
Dielectric value
In addition to the overall size of the plates and the distance between them, there is another parameter that affects the capacity - the type of insulator used. The factor by which the ability of a dielectric to increase the capacity of a capacitor in comparison with a vacuum is determined is called dielectric constant and is described for different materials by a constant value from 1 to infinity (in theory):
- vacuum: 1.0000;
- air: 1,0006;
- paper: 2.5-3.5;
- glass: 3-10;
- metal oxides 6-20;
- electrical ceramics: up to 80.
In addition to solid dielectric capacitors (ceramic, paper, film) there are also electrolytic. The latter use aluminum or tantalum plates with an oxide insulating layer as one electrode and an electrolyte solution as the other.
The main features of this design are that it allows the accumulation of a relatively impressive charge in a small size and is a polar electrical storage. That is, it is included in the electrical circuit with respect to the polarity.
The energy that most capacitors are able to store is usually small - no more than hundreds of joules. In addition, it does not last long due to the inevitable charge leakage. Therefore, capacitors cannot replace, for example, batteries as a power source. And although they are able to effectively perform only one job (conservation of charge), their application is very diverse in electrical circuits. Capacitors are used as filters, for line voltage smoothing, as synchronization devices and for other purposes.
