Plate capacitor

Flat capacitor - physical simplification, has taken the beginning of the early studies of electricity, which is a structure where the electrode surfaces are in uniform at any point are parallel.


People are looking for formulas describing the capacity of a plane capacitor. Read below interesting and little known facts, dry mathematical signs are also important.

First identified capacity flat capacitor Volta. In his possession was not yet the value - the potential difference, called voltage, but intuitively correct scientist explained the phenomenon. The magnitude of the number of charges, interpreted as the amount of electric fluid atmosphere - not quite right, but it seems to be true. According voiced outlook capacity flat capacitor is the ratio of volume of accumulated electric fluid to the difference of atmospheric potentials:

C = q / U.

The formula is applicable to any capacitor, regardless of structure. Recognized as universal. Specially designed for flat capacitors formula capacity, expressed in terms of properties of the dielectric material and the geometrical dimensions:

In this formula, S denotes electrodes through the area, which is calculated as the product of the parties, and d - indicates the distance between the electrodes. Other symbols - dielectric constant (8,854 pF / m) and the dielectric constant of the dielectric material. Electrolytic capacitors have such a large capacity for good reason: the solution is separated from the conductive metal oxide layer is extremely thin. Hence, d is the minimum. The only negative - polar electrolytic capacitors, they can not be connected to the AC circuit. For this purpose, on the anode or cathode, are marked with a plus or minus sign.

Flat capacitors are rare today, it is mostly microscopic Membrane technology, said race surfaces is considered dominant. All passive and active elements are formed through a screen to form a kind of film. Flat inductors, resistors and capacitors are applied in the form of conductive pastes.

Material depends on the dielectric capacitance, each own structure. It is believed that the amorphous material is of non-oriented dipoles, the elastically fortified in their places. When an external electric field are reversibly guided along the lines of weakening tension. As a result, charge is accumulated until the process stops. As the power output of electrodes dipoles return to place, making it possible a new working cycle. So it is operating a flat electric capacitor.

Capacitor for lessons

Capacitor for lessons

From the history

First began to explore the great accumulation of charge Alessandro Volta. The report of the Royal Society in 1782 for the first time voiced the word capacitor. In understanding Volts elektroforus representing two parallel plates, pumped from ether electrical fluid.

In ancient times, all the knowledge came down to the opinion of scientists, if the Earth's atmosphere contains something that is not defined devices. Attended elementary electroscopes able to determine the sign of the charge and its existence does not give an indication of the amount. Scientists simply rubbed with fur body surface and a tray for research in the area of ​​influence of the device. Gilbert showed that the electrical and magnetic interactions become weaker with distance. Scientists roughly knew what to do, but studies have not progressed.

The hypothesis of atmospheric electricity suggested by Benjamin Franklin. He actively investigated lightning and came to the conclusion that these are manifestations of the same united force. Launching a kite in the sky, he put together a toy silk thread to the ground and watched the arc. It's dangerous experiments, and Benjamin repeatedly risked his life for the sake of science. Silk thread conducts static electricity - it is proved by Stephen Gray, first gathered in 1732 an electrical circuit.

In 20 years (1752), Benjamin Franklin proposed the construction of the first lightning rod, lightning protection carried out the nearby buildings. Just think about it! - first of all I expected the house burns from accidental impact. Benjamin Franklin proposed one type called positive charge (glass) and the second negative (resin). So physicists were misled as to the true direction of electron motion. But where will undertake a different opinion, when in 1802, based on the experience of Russians Petrova saw that the anode is formed fossa? Consequently, the positive charge particles are transferred to the cathode, but in reality it proved air plasma ions.

By the beginning of the study volt electrical phenomena already known, static charges and the fact that they have the two characters. People stubbornly believed that the "fluid" is taken from the air. This idea prompted experiments with rubbing amber hair, not reproducible under water. Consequently, it became logical to assume that the electricity may occur solely from the Earth's atmosphere, which, of course, is not true. For example, many solutions investigated Humphrey Davy, conduct electric current.

The reason therefore is different - by rubbing amber underwater frictional force decreased in the tens or hundreds of times, and the charge is dissipated by the volume of liquid. Therefore, only the process ineffective. Today, every miner knows that oil is electrified by friction against the pipe without air. Consequently, the atmosphere for the "fluid" is not considered a compulsory component.

The largest plate capacitor in the world

Such a systematic, but is fundamentally wrong interpretations have not stopped Volta on the research path. He studied hard elektroforus as perfect generator of the time. The second was a ball of sulfur Otto von Guericke invented a century earlier (1663). Its design has changed little, but after the discovery of Stephen Gray charge began to take off with the help of guides. For example, in the electrostatic machine metal comb-converters are used.

For a long time scientists were swinging. Electrostatic machine 1880 has the right to be considered the first powerful discharge generator allows you to get an arc, but the true power of the electrons reached in the Van de Graaff (1929), where the potential difference of the unit megavolt. For comparison - the storm cloud, according to Wikipedia, it detects potential relative to the earth in gigavolt units (three orders of magnitude higher than in the human machine).

In summary, with a certain degree of certainty say that natural processes are used as principle action electrification by friction, impact and other types, and powerful cyclone is the largest of the known flat capacitors. Lightning shows what happens when the dielectric (the atmosphere) can not withstand the applied potential difference and breaks. Exactly similar is happening in a flat capacitor, created by man, if the voltage is excessive. Breakdown irreversible solid dielectric, and an electric arc is often the cause of melting electrodes and machine breakdown.


So, Volta took up the study of models of natural processes. Elektroforus first appeared in 1762, designed by Johann Karl Wilcke. A truly popular device becomes after reports Volta Royal Society (mid-70s of the XVIII century). Volta has given the instrument the current name.

View elektroforusa

View elektroforusa

Elektroforus capable of accumulating an electrostatic charge formed by the friction coat rubber piece. It consists of two plane, mutually parallel electrodes:

  • The bottom is a thin piece of rubber. The thickness chosen for reasons of efficiency of the device. If we choose a piece of solid, significant part of the energy will be accumulated in the dielectric on the orientation of its molecules. That is celebrated in the modern flat capacitor where the dielectric is placed to increase elektroomkosti.
  • The upper plate of thin steel is laid on top, when the charge already accumulated friction. Due to the influence of excess negative charge is formed on the top surface are removed on the earthing switch, so that when two plates undocking not occurred mutual compensation.

The operating principle of parallel-plate capacitor is already clear. An operator rubs rubber coat, leaving a negative charge. Top piece of metal is put. Due to the large surface roughness are not in contact but are spaced apart from each other. As a result, the influence of the electrified metal. The electrons are repelled rubber surface charge and go to the external plane, where the operator removes them through earthing slight momentary touch.

The bottom of the metal plate remains positively charged. When undocking the two surfaces, this effect is retained in the material is observed deficiency of electrons. And much spark, if you touch a metal plate. This experience allowed on a single charge rubber prodelyvat hundreds of times, its surface static resistance is extremely large. It does not allow the charge to flow. Demonstrating described experiment, Volta attracted the attention of the scientific world, but studies have not moved forward, with the exception of the discoveries of Charles Coulomb.

In 1800, Alessandro gives impetus to the development of research in the field of electricity, invented the famous voltaic power source.

The design of the flat capacitor

Elektroforus is constructed from first planar capacitors. His plates are capable of storing only a static charge, otherwise it is impossible to electrify the rubber. Surface extremely long stores electrons. Volta even suggested to remove them through a candle flame ionized air or ultraviolet radiation from the sun. Today, every schoolchild knows that the phenomenon is done with water. However, elektroforus then need to dry.

In today's world, the bottom plate was coated with Teflon or plastic. They are well gaining static charge. Dielectric becomes air. To go to the construction of a modern condenser, it is necessary both to make metal plates. Then, in the event of one charge electrification spread to the second, and if the other terminal is grounded, the stored energy is stored a certain time.

Design details

Design details

Margin electrons depends on the dielectric material. For example, are found among modern capacitors:

  1. Mica.
  2. Air.
  3. Electrolytic (oxide).
  4. Ceramic.

In the name laid dielectric material. The composition depends directly on the capacity that can be increased many times over. Role dielectrics explained above, their parameters are determined directly the structure of matter. However, many materials with high performance, fail to use because of their unfitness. For example, water has a high dielectric constant.

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