IN electrical circuit, which includes a current source and a consumer of electricity, an electric current arises. But in what direction does this current flow? It is traditionally believed that in an external circuit the current has a direction from the plus of the source to minus, while inside the power source it is from minus to plus.
Indeed, an electric current is an ordered movement of electrically charged particles. If the conductor is made of metal, such particles are electrons - negatively charged particles. However, in the external circuit, electrons move precisely from minus (negative pole) to plus (positive pole), and not from plus to minus.
If included in an external circuit, it will become clear that the current is possible only when the diode is connected with the cathode in the negative direction. From this it follows that the direction electric current in the chain take the direction opposite to the real movement of electrons.
If we trace the history of the formation of electrical engineering as an independent science, we can understand where such a paradoxical approach came from.
The American researcher Benjamin Franklin put forward at one time a unitary (unified) theory of electricity. According to this theory, electrical matter is a weightless liquid that can flow from some bodies, while accumulating in others.
According to Franklin, there is an electric fluid in all bodies, but bodies become electrified only when there is an excess or lack of electric fluid (electric fluid) in them. The lack of electric fluid (according to Franklin) meant negative electrification, and the excess - positive.
This was the beginning of the concepts of positive charge and negative charge. At the moment of connection of positively charged bodies with negatively charged bodies, the electric fluid flows from the body with big amount electric fluid to bodies with a reduced amount of it. It looks like a system of communicating vessels. The stable concept of electric current, the movement of electric charges, has entered science.
This hypothesis of Franklin anticipated the electronic theory of conduction, but it turned out to be far from flawless. The French physicist Charles Dufay discovered that in reality there are two types of electricity that individually obey Franklin's theory, but when they come into contact they cancel each other out. A new dualistic (dual) theory of electricity has appeared, put forward by the naturalist Robert Simmer on the basis of the experiments of Charles Dufay.
When rubbing, for the purpose of electrifying, electrified bodies, not only the rubbed body becomes charged, but also the rubbing one. The dualistic theory asserted that in the ordinary state bodies contain two kinds of electric fluid and in different quantities, which neutralize each other. Electrification was explained by a change in the ratio of negative and positive electricity in electrified bodies.
Both the Franklin hypothesis and the Simmer hypothesis successfully explained electrostatic phenomena and even competed with each other.
The volt column invented in 1799 and the discovery led to the conclusion that during the electrolysis of solutions and liquids, two charges opposite in direction of movement are observed in them - negative and positive. This was the triumph of the dualistic theory, because during the decomposition of water it was now possible to observe how oxygen bubbles were released on the positive electrode, while hydrogen bubbles were released on the negative electrode.
But not everything was smooth here. The amount of gases released was different. Hydrogen was released twice as much as oxygen. This baffled physicists. At that time, chemists did not yet have an idea that there are two hydrogen atoms and only one oxygen atom in a water molecule.
These theories were not understood by everyone.
But in 1820, André-Marie Ampère, in a paper presented to members of the Paris Academy of Sciences, first decides to choose one of the directions of the currents as the main one, but then gives a rule according to which the effect of magnets on electric currents can be accurately determined.
In order not to talk all the time about two currents of both electricity opposite in direction, in order to avoid unnecessary repetitions, Ampère decided to strictly take the direction of movement of positive electricity as the direction of the electric current. So, for the first time, Ampere introduced the hitherto generally accepted rule for the direction of electric current.
This position was later adhered to by Maxwell himself, who came up with the “gimlet” rule, which determines the direction magnetic field coils. But the question of the true direction of the electric current remained open. Faraday wrote that this state of affairs is only conditional, it is convenient for scientists, and helps them to clearly determine the directions of currents. But this is just a convenience.
After the discovery by Faraday electromagnetic induction, it became necessary to determine the direction of the induced current. The Russian physicist Lenz gave a rule: if a metal conductor moves near a current or a magnet, then a galvanic current arises in it. And the direction of the emerging current is such that a fixed wire would come from its action into a movement opposite to the original movement. Simple, easy to understand rule.
Even after the discovery of the electron, this convention has existed for more than a century and a half. With the invention of such a device as the vacuum tube, with the widespread introduction of semiconductors, difficulties began to arise. But electrical engineering, as before, operates with old definitions. This sometimes causes real confusion. But making adjustments will cause more inconvenience.
- In Europe, now no one plays the piano,
play with electricity.
- You can’t play on electricity - it will kill you with an electric shock.
-And they play in rubber gloves...
-E! You can wear rubber gloves!
"Mimino"
Strange... They play on electricity, but for some reason it kills with some kind of current... Where does the current come from in electricity? And what is this current? Hello dear! Let's figure it out.
Well, firstly, let's start with why it is still possible to play on electricity in rubber gloves, but, for example, in iron or lead - it is impossible, although metal ones are stronger? The thing is that rubber does not conduct electricity, but iron and lead do, and therefore will shock. Stop-stop... We are going in the wrong direction, let's turn around... Yeah... You need to start with the fact that everything in our Universe consists of the smallest particles - atoms. These particles are so small that, for example, a human hair is several million times thicker than the smallest hydrogen atom. An atom consists (see Figure 1.1) of two main parts - a positively charged nucleus, which in turn consists of neutrons and protons and electrons rotating in certain orbits around the nucleus.
Figure 1.1 - The structure of the electron
The total electric charge of an atom is always (!) zero, that is, the atom is electrically neutral. Electrons have a fairly strong bond with atomic nucleus, however, if you apply some force and “pull out” one or more electrons from the atom (by heating or friction, for example), then the atom will turn into a positively charged ion, since the value of the positive charge of its nucleus will be greater than the value of the negative total charge of the remaining electrons. And vice versa - if one or more electrons are added to the atom in any way (but not by cooling ...), then the atom will turn into a negatively charged ion.
The electrons that make up the atoms of any element are absolutely identical in their characteristics: charge, size, mass.
Now, if you look at the internal composition of any element, you can see that not the entire volume of the element is occupied by atoms. Always, in any material, both negatively charged and positively charged ions are also present, and the process of converting "negatively charged ion-atom-positively charged ion" occurs constantly. In the process of this transformation, so-called free electrons are formed - electrons that are not associated with any of the atoms or ions. It turns out that different substances have different numbers of these free electrons.
It is also known from the course of physics that around any charged body (even as negligible as an electron) there is a so-called invisible electric field, the main characteristics of which are strength and direction. It is conditionally accepted that the field is always directed from the point of positive charge to the point of negative charge. Such a field arises, for example, when rubbing an ebonite or glass rod on wool, while in the process one can hear a characteristic crack, the phenomenon of which we will consider later. Moreover, a positive charge will form on a glass rod, and a negative charge on an ebonite one. This will just mean the transition of free electrons of one substance to another (from a glass rod to wool and from wool to an ebonite rod). The transfer of electrons means a change in charge. To assess this phenomenon, there is a special physical quantity- the amount of electricity, called the pendant, and 1Cl \u003d 6.24 10 18 electrons. Based on this ratio, the charge of one electron (or it is otherwise called the elementary electric charge) is equal to: 
So what does all these electrons and atoms have to do with it... But what does it have to do with it. If you take a material with a high content of free electrons and place it in an electric field, then all free electrons will move in the direction of the positive point of the field, and ions - since they have strong interatomic (interionic) bonds - remain inside the material, although in theory they should move to that point of the field, the charge of which is opposite to the charge of the ion. This has been proven with a simple experiment.
Two different materials (silver and gold) were connected to each other and placed in an electric field for several months. If the movement of ions between materials was observed, then a diffusion process should have occurred at the point of contact and gold would form in the narrow zone of silver, and silver would form in the narrow zone of gold, but this did not happen, which proved the immobility of "heavy" ions. Figure 2.1 shows the movement of positive and negative particles in an electric field: negatively charged electrons move against the direction of the field, and positively charged particles move in the direction of the field. However, this is true only for particles that are not included in the crystal lattice any material and are not interconnected by interatomic bonds. 
Figure 1.2 - Movement of a point charge in an electric field
The movement occurs in this way, because like charges repel, and opposite charges attract: two forces always act on a particle: an attractive force and a repulsive force.
So, it is the ordered movement of charged particles that is called electric current. There is a funny fact: it was initially believed (before the discovery of the electron) that the electric current was generated precisely by positive particles, so the direction of the current corresponded to the movement of positive particles from “plus” to “minus”, but later the opposite was discovered, but it was decided to leave the direction of the current the same, and this tradition has remained in modern electrical engineering. So it's actually the other way around! 
Figure 1.3 - The structure of the atom
An electric field can, although it is characterized by the magnitude of the intensity, but is created around any charged body. For example, if all the same glass and ebonite sticks are rubbed against wool, then an electric field will arise around them. An electric field exists near any object and affects other objects, no matter how far they are located. However, with increasing distance between them, the field strength decreases and its value can be neglected, so that two people standing side by side and having some charge, although they create electric field, and an electric current flows between them, but it is so small that it is difficult to fix its value even with special devices.
So, it’s time to talk more about what kind of characteristic it is - tension electric field. It all starts with the fact that in 1785 the French military engineer Charles Augustin de Coulomb, distracted from drawing military maps, deduced a law describing the interaction of two point charges:
The module of the interaction force of two point charges in vacuum is directly proportional to the product of the modules of these charges and inversely proportional to the square of the distance between them.
We will not delve into why this is so, we will simply take the word of Mr. Coulomb and introduce some conditions for compliance with this law:
- point charges - that is, the distance between charged bodies is much greater than their size - however, it can be proved that the force of interaction of two volumetrically distributed charges with spherically symmetric non-intersecting spatial distributions is equal to the force of interaction of two equivalent point charges located at the centers of spherical symmetry;
- their immobility. Otherwise, additional effects come into force: the magnetic field of the moving charge and the corresponding additional Lorentz force acting on another moving charge;
- interaction in a vacuum.
Mathematically, the law is written as follows: 
where q 1, q 2 are the values of interacting point charges,
r is the distance between these charges,
k is some coefficient describing the influence of the environment.
The figure below shows a graphical explanation of Coulomb's law. 
Figure 1.4 - Interaction of point charges. Coulomb's Law
Thus, the force of interaction between two point charges increases with an increase in these charges and decreases with an increase in the distance between the charges, and an increase in the distance by a factor of two leads to a decrease in the force by a factor of four. However, such a force arises not only between two charges, but also between a charge and a field (and again an electric current!). It would be logical to assume that the same field has a different effect on different charges. So the ratio of the force of interaction between the field and the charge to the magnitude of this charge is called the strength of the electric field. Provided that the charge and field are stationary and do not change their characteristics over time. 
where F is the force of interaction,
q is the charge.
Moreover, as mentioned earlier, the field has a direction, and this arises precisely from the fact that the interaction force has a direction (it is a vector quantity: charges of the same name attract, opposite charges repel).
After I wrote this tutorial, I asked my friend to read it, rate it, so to speak. In addition, I asked him one interesting question in my opinion just on the topic of this material. Imagine my surprise when he answered incorrectly. Try to answer this question too (it is placed in the tasks section at the end of the lesson) and argue your point of view in the comments.
And finally, since the field can move a charge from one point in space to another, it has energy, and therefore can do work. This fact will be useful to us in the future when considering the operation of electric current.
This concludes the first lesson, but we still have an unanswered question, why, in rubber gloves, the current will not kill. Let's leave it as an intrigue for the next lesson. Thank you for your attention, see you soon!
- Suppose that in the hero city of Moscow there is a certain outlet, the most common outlet that you have at home. Let's also assume that we stretched the wires from Moscow to Vladivostok and connected a light bulb in Vladivostok (again, the lamp is completely ordinary, the same one now illuminates the room for me and for you). In total, what we have: a light bulb connected to the ends of two wires in Vladivostok and an outlet in Moscow. Now let's insert the "Moscow" wires into the outlet. If we do not take into account a lot of all sorts of conditions and just assume that the light bulb in Vladivostok caught fire, then try to guess whether the electrons that are in this moment are in a socket in Moscow in the filament of a light bulb in Vladivostok? What happens if we connect the light bulb not to the socket, but to the battery?
This is the ordered movement of certain charged particles. In order to competently use the full potential of electricity, it is necessary to clearly understand all the principles of the device and the operation of electric current. So, let's figure out what work and current power are.
Where does electrical current come from?
Despite the apparent simplicity of the question, few are able to give an intelligible answer to it. Of course, nowadays, when technology is developing at an incredible speed, a person does not particularly think about such elementary things as the principle of operation of an electric current. Where does electricity come from? Surely many will answer "Well, from the socket, of course" or simply shrug their shoulders. Meanwhile, it is very important to understand how the current works. This should be known not only to scientists, but also to people who are in no way connected with the world of sciences, for their general versatile development. But to be able to correctly use the principle of current operation is not for everyone.
So, for starters, you should understand that electricity does not arise from nowhere: it is produced by special generators that are located at various power plants. Thanks to the work of rotating the blades of turbines, steam obtained as a result of heating water with coals or oil generates energy, which is subsequently converted into electricity with the help of a generator. The generator is very simple: in the center of the device is a huge and very strong magnet, which causes electric charges to move along copper wires.
How does electricity reach our homes?
After a certain amount of electric current has been obtained with the help of energy (thermal or nuclear), it can be supplied to people. Such a supply of electricity works as follows: in order for electricity to successfully reach all apartments and enterprises, it must be “pushed”. And for this you need to increase the force that will do it. It is called the voltage of the electric current. The principle of operation is as follows: the current passes through the transformer, which increases its voltage. Further, the electric current flows through cables installed deep underground or at a height (because the voltage sometimes reaches 10,000 volts, which is deadly for humans). When the current reaches its destination, it must again pass through the transformer, which will now reduce its voltage. It then passes through wires to installed shields in apartment buildings or other buildings.
The electricity carried through the wires can be used thanks to the system of sockets, connecting household appliances to them. Additional wires are carried in the walls, through which electric current flows, and thanks to it, the lighting and all the appliances in the house work.
What is current work?
The energy that an electric current carries in itself is converted over time into light or heat. For example, when we turn on the lamp, electric view energy is converted into light.
Speaking in an accessible language, the work of the current is the action that electricity itself produced. Moreover, it can be very easily calculated by the formula. Based on the law of conservation of energy, we can conclude that electrical energy has not disappeared, it has completely or partially changed into another form, while giving off a certain amount of heat. This heat is the work of the current when it passes through the conductor and heats it (heat exchange occurs). This is how the Joule-Lenz formula looks like: A \u003d Q \u003d U * I * t (work is equal to the amount of heat or the product of the current power and the time during which it flowed through the conductor).
What does direct current mean?
Electric current is of two types: alternating and direct. They differ in that the latter does not change its direction, it has two clamps (positive "+" and negative "-") and always starts its movement from "+". And alternating current has two terminals - phase and zero. It is because of the presence of one phase at the end of the conductor that it is also called single-phase.
The principles of the device of single-phase alternating and direct electric current are completely different: unlike direct, the alternating current changes both its direction (forming a flow both from the phase towards zero, and from zero towards the phase), and its magnitude. For example, alternating current periodically changes the value of its charge. It turns out that at a frequency of 50 Hz (50 oscillations per second), the electrons change the direction of their movement exactly 100 times.
Where is direct current used?
Direct electric current has some features. Due to the fact that it flows strictly in one direction, it is more difficult to transform it. The following elements can be considered as sources of direct current:
- batteries (both alkaline and acid);
- conventional batteries used in small appliances;
- as well as various devices such as converters.
DC operation
What are its main characteristics? These are work and current power, and both of these concepts are very closely related to each other. Power means the speed of work per unit time (per 1 s). According to the Joule-Lenz law, we find that the work of a direct electric current is equal to the product of the strength of the current itself, the voltage and the time during which the work of the electric field was completed to transfer charges along the conductor.
This is how the formula for finding the work of the current, taking into account Ohm's law of resistance in conductors, looks like: A \u003d I 2 * R * t (work is equal to the square of the current strength multiplied by the value of the resistance of the conductor and once again multiplied by the value of the time for which the work was done).
Few people think about when electricity appeared. And its history is quite interesting. Electricity makes life more comfortable. Thanks to him, television, the Internet and much more became available. AND modern life without electricity it is already impossible to imagine. It greatly accelerated the development of mankind.
History of electricity
If you start to understand when electricity appeared, then you need to remember the Greek philosopher Thales. It was he who first drew attention to this phenomenon in 700 BC. e. Falles discovered that when amber is rubbed against wool, the stone begins to attract light objects to itself.
What year was electricity introduced? After the Greek philosopher, no one investigated this phenomenon for a long time. And knowledge in this area did not increase until 1600. In this year, William Gilbert coined the term "electricity" by examining magnets and their properties. Since that time, this phenomenon began to be intensively studied by scientists.
First discoveries
When did electricity appear, used in technical solutions? In 1663, the first electric machine was created, which made it possible to observe the effects of repulsion and attraction. In 1729, the English scientist Stephen Gray made the first experiment when electricity was transmitted at a distance. Four years later, the French scientist C. Dufay discovered that electricity has 2 types of charge: resin and glass. In 1745, the first electric capacitor appeared - the Leiden Bank.
In 1747, Benjamin Franklin created the first theory to explain this phenomenon. Electricity appeared in 1785 and was studied for a long time by Galvani and Volt. A treatise was written on the action of this phenomenon during muscular movement, and a galvanic object was invented. And the Russian scientist V. Petrov became the discoverer
Lighting
When did electricity appear in houses and apartments? For many, this phenomenon is primarily associated with lighting. Therefore, it should be considered when the first light bulb was invented. This happened in 1809. The Englishman Delarue became the inventor. A little later, spiral-shaped light bulbs appeared, which were filled with an inert gas. They began to be produced in 1909.
The advent of electricity in Russia
Some time after the introduction of the term "electricity", this phenomenon began to be investigated in many countries. The beginning of change can be considered the appearance of lighting. In what year did electricity appear in Russia? According to this date - 1879. It was then that electrification with the help of lamps was first carried out in St. Petersburg.
But a year earlier in Kyiv, in one of the railway workshops, electric lights were installed. Therefore, the date of the appearance of electricity in Russia is a somewhat controversial issue. But since this event was left without attention, the lighting of the Liteiny Bridge can be considered the official date.
But there is another version, when electricity appeared in Russia. From a legal point of view, this date is the thirtieth of January 1880. On this day, the first electrical department appeared in the Russian Technical Society. His duties were charged with supervising the introduction of electricity in everyday life. In 1881, Tsarskoye Selo became the first European city to be fully illuminated.
Another significant date is May 15, 1883. On this day, the Kremlin was illuminated for the first time. The event was timed to coincide with the accession to the Russian throne Alexander III. To illuminate the Kremlin, a small power plant was installed by electricians. After this event, lighting first appeared on the main street of St. Petersburg, and then in the Winter Palace.
In the summer of 1886, the "Electric Lighting Society" was established by decree of the emperor. It was engaged in the electrification of the whole of St. Petersburg and Moscow. And in 1888, the first power plants began to be built in largest cities. In the summer of 1892, a debut electric tram was launched in Russia. And in 1895 it appeared. It was built in St. Petersburg, on the river. Big Ohta.
And in Moscow, the first power plant appeared in 1897. It was built on the Raushskaya embankment. The power plant produced three-phase alternating current. And this made it possible to transmit electricity over long distances without a significant loss of power. Other cities began to build at the dawn of the twentieth century, before the First World War.
