From the course of physics, everyone knows that electric current means directed ordered movement of particles carrying a charge. To obtain it, an electric field is formed in the conductor. The same is necessary in order for the electric current to continue to exist for a long time.
Sources of electric current can be:
- static
- chemical;
- mechanical;
- semiconductor.
In each of them, work is carried out where differently charged particles are separated, that is, an electric field of the current source is created. Separated, they accumulate at the poles, in the places where the conductors are connected. When the poles are connected by a conductor, particles with a charge begin to move, and an electric current is formed.
Sources of electric current: the invention of the electric machine
Until the middle of the seventeenth century, it took a lot of effort to get an electric current. At the same time, the number of scientists dealing with this issue was growing. And here Otto von Guericke invented the world's first electric car. In one of the experiments with sulfur, it, melted inside a hollow ball of glass, hardened and broke the glass. Guericke strengthened the ball so that it could be twisted. Rotating it and pressing a piece of leather, he received a spark. This friction markedly facilitated the short-term generation of electricity. But more difficult problems were solved only with the further development of science.
The problem was that Guericke’s charges quickly disappeared. To increase the duration of the charge, the bodies were placed in closed vessels (glass bottles), and water with a nail acted as an electrified material. The experiment was optimized when the bottle was coated on both sides with a conductive material (foil sheets, for example). As a result, they realized that it was possible to do without water.
Frog legs as a current source
Another way to generate electricity was first discovered by Luigi Galvani. As a biologist, he worked in a laboratory where he experimented with electricity. He saw how a dead frog's foot contracted when it was excited by a spark from a car. But once the same effect was achieved by accident when the scientist touched it with a steel scalpel.
He began to look for the reasons where the electric current came from. The sources of electric current, according to its final conclusion, were in the frog's tissues.
Another Italian, Alessandro Volto, proved the failure of the "frog" nature of the occurrence of current. It was noted that the largest current occurred when copper and zinc were added to the sulfuric acid solution. This combination is called a galvanic or chemical element.
But the use of such a tool to obtain EMF would be too costly. Therefore, scientists worked on another, mechanical, method of producing electrical energy.
How is a regular generator arranged?
At the beginning of the nineteenth century G.Kh. Oersted discovered that when a current passed through a conductor, a field of magnetic origin arose. A little later, Faraday discovered that when crossing the lines of force of this field, an EMF is induced in the conductor, which causes a current. EMF varies depending on the speed of movement and the conductors themselves, as well as on the field strength. When crossing one hundred million power lines per second, the induced EMF became equal to one Volt. It is clear that manual conduct in a magnetic field is not able to give a large electric current. Sources of electric current of this kind have shown themselves much more efficiently by winding wires onto a large coil or by producing it in the form of a drum. A coil was mounted on the shaft between the magnet and the rotating water or steam. Such a mechanical current source is inherent in conventional generators.
Great Tesla
A brilliant scientist from Serbia Nikola Tesla, having devoted his life to electricity, made many discoveries that we use today. Multiphase electric machines, asynchronous electric motors, energy transfer through multiphase alternating current - this is not the whole list of inventions of the great scientist.
Many are sure that the phenomenon in Siberia, called the Tunguska meteorite, was actually caused precisely by Tesla. But, probably, one of the most mysterious inventions is a transformer capable of receiving voltage up to fifteen million volts. Unusual is both its structure and calculations that are not amenable to known laws. But in those days they began to develop a vacuum technique in which there were no ambiguities. Therefore, the scientist’s invention was forgotten for a while.
But today, with the advent of theoretical physics, interest in his work has renewed interest. The air was recognized as a gas, to which all the laws of gas mechanics apply. It was from there that the great Tesla scooped up energy. It is worth noting that the ether theory was very common in the past among many scientists. It was only with the advent of SRT — Einstein's special theory of relativity, in which he refuted the existence of the ether — that they were forgotten, although the general theory formulated later did not dispute him as such.
But for now, let us dwell in more detail on electric current and devices that are ubiquitous today.
Development of technical devices - current sources
Such devices are used to convert various energy into electrical energy. Despite the fact that the physical and chemical methods of generating electrical energy were discovered long ago, they became ubiquitous only in the second half of the twentieth century, when radio electronics began to develop rapidly. The initial five galvanic couples replenished with another 25 types. And theoretically galvanic pairs can be several thousand, since free energy can be realized on any oxidizing agent and reducing agent.
Physical current sources
Physical current sources began to develop a little later. Modern technology made increasingly stringent requirements, and industrial thermo- and thermionic generators successfully cope with the growing tasks. Physical current sources are devices where the thermal, electromagnetic, mechanical, and energy of radiation and nuclear decay are converted into electrical energy. In addition to the above, they also include electric machine, MHD generators, as well as employees for the conversion of solar radiation and atomic decay.
In order for the electric current in the conductor not to disappear, an external source is needed to maintain the potential difference at the ends of the conductor. For this, energy sources are used which have some electromotive force to create and maintain a potential difference. The EMF of an electric current source is measured by the work performed during the transfer of a positive charge throughout the entire closed circuit.
The resistance inside the current source quantitatively characterizes it, determining the amount of energy loss when passing through the source.
Power and efficiency are equal to the ratio of voltage in the external electric circuit to the EMF.
Chemical current sources
The chemical current source in the electric circuit of the EMF is a device where the energy of chemical reactions is converted into electrical energy.
It is based on two electrodes: a negatively charged reducing agent and a positively charged oxidizing agent, which are in contact with the electrolyte. Between the electrodes there is a potential difference, EMF.
In modern devices are often used:
- as a reducing agent, lead, cadmium, zinc and others;
- oxidizing agent - nickel hydroxide, lead oxide, manganese and others;
- electrolyte - solutions of acids, alkalis or salts.
Dry elements made of zinc and manganese are widely used. Take a vessel of zinc (with a negative electrode). A positive electrode is placed inside with a mixture of manganese dioxide with carbon or graphite powder, which reduces resistance. The electrolyte is paste from ammonia, starch and other components.
An acid lead battery is most often a secondary chemical current source in an electrical circuit, which has high power, stable operation and low cost. Batteries of this kind are used in a variety of areas. They are often preferred for starter batteries, which are especially valuable for cars where they are generally monopolists.
Another common battery consists of iron (anode), nickel oxide hydrate (cathode) and electrolyte - an aqueous solution of potassium or sodium. The active material is placed in steel nickel-plated tubes.
The use of this species has declined after a fire at the Edison plant in 1914. However, if we compare the characteristics of the first and second type of batteries, it turns out that the operation of iron-nickel can be several times longer than lead-acid.
AC and DC generators
Generators are devices that are designed to convert mechanical energy into electrical energy.
The simplest DC generator can be represented in the form of a conductor frame, which was placed between the magnetic poles, and the ends were connected to insulated half rings (collector). For the device to work, it is necessary to ensure rotation of the frame with the collector. Then an electric current will be induced in it, changing its direction under the influence of magnetic lines of force. In the external circuit, he will go in a single direction. It turns out that the collector will rectify the alternating current that is generated by the frame. To achieve direct current, the collector is made of thirty-six or more plates, and the conductor consists of many frames in the form of an armature winding.
Consider what the purpose of the current source in the electrical circuit is. We find out what other sources of current exist.
Electric circuit: electric current, current strength, current source
An electric circuit consists of a current source, which, together with other objects, creates a path for current. And the concepts of EMF, current and voltage reveal the electromagnetic processes taking place at the same time.
The simplest electrical circuit consists of a current source (battery, galvanic cell, generator, etc.), energy consumers (electric heaters, electric motors, etc.), as well as wires connecting the terminals of the voltage source and the consumer.
The electric circuit has an internal (source of electricity) and external (wires, switches and circuit breakers, measuring instruments) parts.
It will work and have a positive value only if a closed circuit is provided. Any rupture causes the current to cease to flow.
An electric circuit consists of a current source in the form of galvanic cells, electroaccumulators, electromechanical and thermoelectric generators, solar cells, and so on.
The electric receivers are electric motors that convert energy into mechanical, lighting and heating devices, electrolysis plants, and so on.
Ancillary equipment are devices that serve to turn on and off, measuring instruments and protective mechanisms.
All components are divided into:
- active (where the electric circuit consists of an EMF current source, electric motors, batteries, and so on);
- passive (which include electrical receivers and connecting wiring).
The chain may also be:
- linear, where the resistance of an element is always characterized by a straight line;
- non-linear, where the resistance depends on voltage or current.
Here is the simplest circuit, where a current source, a key, an electric lamp, a rheostat are included in the circuit.
Despite the widespread widespread use of such technical devices, especially recently, people are increasingly asking questions about installing alternative energy sources.
