Dielectrics and conductors in an electric field - the theme of the article. The following are the physical processes occurring inside and outside the body. Advised to read the reviews on the topic of electric potential and voltage.
Electricity and Magnetism
Electricity has been known since ancient times, but the other information in addition to recognition of the existence of the phenomenon does not lead. We learned only that the static friction is possible to obtain, and the case stalled. It is difficult to say that publicly before, but geologists believe that magnetism is known to people since at least the V century BC. Findings indicate that the magnetized pieces of rock used for the unknown in modern Turkey.
It is known that the systematization of data on magnetism began earlier. The pioneer was now known, thanks to a single document, Peregrine. In 1269 he wrote a manuscript, which he described and systematized data on magnets, proposed a method for orientation in space travel. From the Latin "Peregrinus", "Pilgrim" - the traveler. Already in the first century AD magnet property is actively exploited by Chinese sailors. Peregrine dissected a number of properties:
- The magnet is always located in the direction from north to south. Therefore, finds the two poles. The same name repel and attract oppositely.
- If the magnet break in half, results in two completely separate piece having the full properties of the original. Get pole individually by simple means will not work.
With regard to electricity, physics give absolute priority to Gilbert. This man created a treatise, where he collected and systematized the available data, a lot of experimenting on their own. Gilbert, coincidentally engaged in comparison of magnetism and electricity. By 1600 no one thought about the relationship of matter and had nothing to prove. Gilbert found that the electricity - in his understanding - it is considered a weak substance: the charge is easily washed off with water, screened and characterized by a small force of interaction. For theory and future generations has made an important observation:
- Magnetic ball from the ore - Gilbert called him Terrell - behaves like a ground with the sense of action on the compass.
- Electrical interaction propagates straight. Consequently, Gilbert was the first to correctly characterized the field lines.
It took two centuries to humanity, to find a similar effect in the wire with current. The above leads to the conclusion that the studies were hampered, in addition to the Inquisition, the lack of electricity generator - there is nothing to carry out experiments. Rub amber hair tedious and inefficient. Hilbert illustration (see. Fig.) prompted researchers to study the structure of the lines of force in the future help to explain the behavior of dielectrics and conductors in a magnetic field.
Gilbert is credited with the first systematization of materials. He was looking for a substance showing the ability to electrification was different lists. In the last class got most metals, the first - dielectrics. Today, it found that the static charge is possible to distribute virtually any body. But friction acquire unusual properties advantageously dielectrics. Thus, Gilbert first systematized materials, although at the time in 1600 was unable to give satisfactory explanations.
It is believed that the first electrostatic generator invented by Otto von Guericke. Sulfur spinning ball rail axis rubbed with the palms observing spark electric discharge. Gericke found redistribution of static electricity on the surfaces of different bodies. Based on the established generator began to experiment, to the middle of the XVIII century materials were divided into classes (conductors and insulators) and the sign of the charge of the resulting friction. There was a resinous (negative) and the glass (positive) electricity.
Further experiments enabled by using the torsion balance (on a thin thread) to establish the law of attraction and repulsion between the charges. It made Charles Coulomb. He described to quantify the interaction force, confirmed the assumption of linearity Hilbert lines of force of electric charges. It took nearly two centuries. Coulomb's Law allowed the scientists to give the first explanation about the behavior of dielectrics and conductors in an electric field. Even then it presents a curious device capable of surprise and a skeptic ...
If the behavior of dielectrics in an electric field for a long time remained unexplored due Metals Volta learned more about electricity and later was able to invent the famous galvanic source power. We are talking about elektroforuse. The device is not very well known in Russia, stirred up the minds of Western scholars, now serves as an indispensable element of the students' activities. The device is now show (and prove), both conductors behave in an electric field.
Elektroforus - static generator with manual reset, metal printing solid size, the best way to demonstrate the static electricity. Imagine that the round substrate of wood glued thinnest rubber sheet. Volta said that a thick piece exhibits inferior properties. But he could not explain the reason. In the ancient times people do not know that the insulators have the ability to store energy of the electric field in the internal structure. The principle is now used in the majority of capacitors.
A thin piece of less field energy absorbed and more left on the surface in the form of charge. Friction rapidly brought up to standard. This fact pointed Volta. Required tire rub. Volta did this good piece of wool for several minutes.
The final stroke design served thin metal disc completely covering rubber. The thickness is chosen less that the properties of the conductor in the electric field appeared brighter. What happened in elektroforuse:
- Operator rubbed rubber to the formation of a dense electron static charge.
- I cleaned wool and dropped on top of the metal disk.
- Conductor electrified influence. Because the surface roughness of the contact points exerted little, bottom disk is positively charged. This is caused by the outflow of electrons ejected top field (see. below).
- Then the operator briefly grounding the upper part of the disc a light touch and break the surface.
- On the bottom side of the metal "printing" static remained free positive charge.
The experience was repeated dozens of times. Witnesses say about the hundreds, and Volta said that "hard to get rid of the fluid rubber" and offered to do it sunlight, candle flame, and other powerful tools. To understand how it works elektroforus, you need to have an understanding of the behavior of a conductor in an electric field.
Behavior conductor in an electric field
Division by conductors, semiconductors and insulators conditional. No clear boundary gradation is carried out by specific substances conductivity. Conductors well conductive, dielectric practically devoid of said quality.
Consider the case of a uniform field with straight and mutually parallel lines of force, as in most physics textbooks. Placed in a constant field metal begins to be charged with static electricity as described above. Meaning: tension lines go in the direction you want to move a positive charge - so decided to Franklin. But the electrons are negative, swim against the current.
As a result, the conductor pattern from the source field accumulates excess carriers with negative sign. A metal end opposite positive. The process is as follows:
- Field penetrates the metal.
- Explorer is full of free charge carriers moving along the field lines.
- Redistribution process goes until proper field electron orbits and free atoms balances the external impact.
- At this constant electric field effect is exhausted.
What happens if the field strength is not constant over time? Let's say, on the surface of the incident electromagnetic wave, causing the alternating motion of the electrons in both directions, causing a response electromagnetic wave. So, the conductor has a shielding properties. Affect only half of it is proved in the theory of the dynamics of propagation. To become a complete shielding effect, it is required to ground metal. What is being done in practice.
dielectric behavior in an electric field
Coherent theory about the behavior of dielectrics in an electric field today do not. Physicists explain what is happening this way: in the thick substances are present dipoles formed by the complex structure of the polymer or amorphous. Size structures lies in the field of nanotechnology. Molecules possess elastic properties, penetrating inside the field directs them accordingly. The positive part is displaced along the direction of the field, and the negative - against.
The dielectric field is able to store energy. It is used in capacitors. It is shown that their capacity is increased in the number of times equal to the permittivity of material placed between the electrodes (air and vacuum value is 1). We will describe what is happening:
- The capacitor is able to charge only up to the level of the applied voltage.
- Between the plates creates a field. Its intensity level is calculated through the difference of electrical potentials.
- The field acts on the insulator. Dipoles inside start to be guided so as to easily loosen the tension field.
- As a result, the voltage across the plates is reduced, the charging process is restarted, until the limit determined by the type of dielectric. We are talking about the permeability of the substance.
Dielectrics in the free state have expressed charge, this effect is called polarization - the creation of the field. The rotation of the dipoles is considered to be a mechanism that manifests itself under external influence. Secondly, the basic charges in addition begin to drift apart. Dipole stretched. elastic forces make contribution to the field of energy storage of the dielectric.
Static charge on the material can not be applied influence. They are well electrified by friction and touch. What engineers are aware of the oil business. Massa takes effort to prevent the electrification of the fuel, resulting in an explosive situation. It is facilitated in that the charge tends to stay on the surface of the substance. And special combs easily performed neutralization. They give it to oil flow path and is removed on the earthing overcharging.