Alternating current is a type of current whose flow direction is continuously changing. It becomes possible due to the presence of potential difference, obeying the law. In everyday understanding, the form of alternating current resembles a sine wave. The constant is able to vary in amplitude, the direction is the same. Otherwise we get alternating current. The treatment of radio technicians is opposite to the school one. Pupils are told - a constant current of one amplitude.
How alternating current is formed
The beginning of alternating current was laid by Michael Faraday, readers will find out more in the text below. Shown: electric and magnetic fields are connected. The current becomes a consequence of the interaction. Modern generators work by changing the magnitude of the magnetic flux through the area covered by the contour of the copper wire. Explorer can be any. Copper is selected from the criteria of maximum suitability at minimum cost.
Static charge is predominantly formed by friction( not the only way), alternating current occurs as a result of processes invisible to the eye. The value is proportional to the rate of change of the magnetic flux through the area covered by the contour.
The history of the discovery of alternating current
For the first time, alternating currents began to pay attention to the commercial value after the birth of inventions created by Nikola Tesla. The material conflict with Edison marked the strong imprint of the fate of both. When an American entrepreneur took back promises to Nikola Tesla, he lost a lot of profit. The eminent scientist did not like free circulation, a Serb invented an industrial-type AC motor( the invention was made much earlier).Enterprises used exclusively permanent. Edison promoted this view.
Tesla showed for the first time: by using alternating voltage, much better results can be achieved. Especially when energy has to be transmitted over long distances. The use of transformers easily allows you to increase the voltage, dramatically reducing losses on active resistance. Receiving side parameters again returns to the original. Not bad save on the thickness of the wires.
Today it is shown: the transfer of direct current is more economical. Tesla changed the course of history. Think of a scientist DC converters, the world would look different.
The beginning of the active use of alternating current put Nikola Tesla, creating a two-phase motor. Experiments on the transmission of energy over considerable distances placed the facts in their places: it is inconvenient to transfer production to the Niagara Falls area, it is much easier to lay a line to the destination.
The alternating current demonstrates a number of properties that distinguish the phenomenon from the direct current. First we turn to the history of the discovery of the phenomenon. The ancestor of alternating current in everyday life of mankind is considered Otto von Gerike. The first to notice: charges of natural two signs. The current can flow in a different direction. Regarding Tesla, the engineer was more interested in the practical part, the author's lectures mention two experimenters of British origin:
- William Spottyswood is deprived of the page of the Russian-language Wikipedia, the national part is silent about work with alternating current. Like Georg Omu, a scientist - a talented mathematician, it remains to be regretted that it is difficult to find out exactly what the husband of science was doing.
- James Edward Henry Gordon is much closer to the practical part of using electricity. He experimented a lot with generators, developed a device of his own design with a capacity of 350 kW.He paid a lot of attention to lighting, energy supply of plants and factories.
It is believed that the first alternators were created in the 30s of the XIX century. Michael Faraday experimentally investigated magnetic fields. The experiments caused jealousy of Sir Humphry Davy, who criticized the student for plagiarism. It is difficult for descendants to find out the rightness, the fact remains: the alternating current existed for half a century unclaimed. In the first half of the 19th century, an electric motor was invented( authored by Michael Faraday).Worked powered by direct current.
Nikola Tesla first guessed to implement the theory of Arago about a rotating magnetic field. It took two phases of alternating current( 90 degree shift).In passing, Tesla noted: more complex configurations are possible( the text of the patent).Later, the inventor of the three-phase motor, Dolivo-Dobrovolsky, vainly tried to patent the brainchild of a fruitful mind.
For a long time the alternating current remained unclaimed. Edison resisted the introduction of phenomena in everyday life. The industrialist was afraid of major financial losses.
Why alternating current is used more often than constant
Scientists have recently proved: it is more profitable to transmit direct current. Line radiation losses are reduced. Nikola Tesla turned the tide of history, truth triumphed.
Nikola Tesla: Safety and Efficiency Issues
Nikola Tesla visited a competing company from Edison, promoting a new phenomenon. I got carried away, often set up experiments on myself. In contrast to Sir Humphry Davy, who shortened his life by breathing in various gases, Tesla achieved considerable success: he had conquered the milestone for 86 years. The scientist discovered that changing the direction of current flow at a speed higher than 700 times per second makes the process safe for humans.
During the lectures, Tesla took a light bulb with a platinum filament with his hands, showed the device glowing, passing high-frequency currents through his own body. He claimed: the phenomenon is harmless, even benefits health. The current flowing over the surface of the skin simultaneously cleans. Tesla said, the experimenters of previous days( see above) missed surprising phenomena for the reasons given:
- Imperfect mechanical type generators. The rotating field was used in the literal sense: the rotor was unwound with the help of the engine. Such a principle is powerless to issue high frequency currents. Today it is problematic, despite the current level of technology development.
- In the simplest case, manual breakers were used. There is nothing to talk about high frequencies.
Tesla himself used the phenomenon of charge and discharge of a capacitor. We imply RC-chain. Being charged to a certain level, the capacitor begins to discharge through the resistance. The parameters of the elements determine the speed of the process proceeding according to the exponential law. Tesla is deprived of the opportunity to use the methods of control circuits semiconductor keys. Thermionic diodes were known. We venture to suggest that Tesla could use products, imitating zener diodes, operating with reversible breakdown.
However, security issues lack an honorable first place. The frequency of 60 Hz( generally accepted by the USA) was suggested by Nikola Tesla, as optimal for the operation of engines of its own design. Very different from the safe range. Easier to design the generator. AC in both senses wins over DC.
Over the Air
Continue unsuccessfully disputes regarding the discoverer of the radio. The passage of the wave through the ether was discovered by Hertz, describing the laws of motion, showing an optical affinity. Today it is known: a variable field furrows space. The phenomenon Popov( 1895) used, transmitting the first Earth message "Heinrich Hertz".
We see that pundits are friendly with each other. How much respect is shown by the first message. The date remains controversial, each state wants to assign the championship unchallenged. Alternating current creates a field propagating through the ether.
Today broadcasting ranges, windows, walls of the atmosphere, various media( water, gases) are well known. An important place is given to the frequency. It is established that each signal can be represented as a sum of elementary oscillations of sinusoids( according to the Fourier theorems).Spectral analysis operates with the simplest harmonics. The total effect is considered as the resultant of the elementary components. Arbitrary signal decomposed by Fourier transform.
Atmospheric windows are defined in the same way. We will see the frequencies passing through the thickness of the good and bad. The latter does not always turn out to be a negative effect. Microwave ovens use 2.4 GHz frequencies, shock absorbed by water vapor. For communication, the waves are useless, but they are good culinary abilities!
Novices are concerned about the issue of wave propagation through the air. We will discuss in more detail the riddle unresolved by scientists today.
Hertz Vibrator, Ether, Electromagnetic Wave
The relationship of electric, magnetic fields was first demonstrated in 1821 by Michael Faraday. A little later showed: the capacitor is suitable for creating oscillations. It cannot be said that the connection between the two events is immediately recognized. Felix Savary discharged the Leyden jar through a choke, the core of which was a steel needle.
It is not known for certain what the astronomer was seeking, the result was curious. Sometimes the needle was magnetized in one direction, sometimes the opposite. Generator current single sign. The scientist correctly concluded: a damped oscillatory process. Not really knowing inductive, capacitive reactances.
Process theory let down later. The experiments were repeated by Joseph Henry, William Thompson, who determined the resonant frequency: where the process lasted the maximum period of time. The phenomenon allowed to quantitatively describe the dependence of the characteristics of the circuit on the elements of the components( inductance and capacitance).In 1861, Maxwell derived the famous equations, one consequence is especially important: "An alternating electric field generates a magnetic field and vice versa."
A wave arises, the induction vectors are mutually perpendicular. Spatially repeat the form of the spawned process. Wave surf the air. The phenomenon used Heinrich Hertz, turning the capacitor plates in space, the plane became emitters. Popov guessed to lay the information in the electromagnetic wave( modulate), which is used everywhere today. And on the air and inside semiconductor technology.
Where alternating current is used
Alternating current underlies the principle of operation of the majority of devices known today. It is easier to say where constant is applied, readers will conclude:
- Direct current is used in batteries. Variable generates movement - can not be stored with modern devices. Then in the device electricity is converted to the desired form.
- higher efficiency collector DC motors. For this reason, it is advantageous to apply these varieties.
- With the help of direct current magnets act. For example, intercoms.
- Constant voltage applied by electronics. Current consumption varies within certain limits. The industry is called permanent.
- Constant voltage is applied by kinescopes to create potential, increase cathode emission. Cases are called analogues of power supplies for semiconductor technology, although sometimes the difference is significant.
In other cases, alternating current shows a significant advantage. Transformers - an integral part of technology. Even in welding, direct current does not always dominate, but there is an inverter in any modern equipment of this type. So much easier and more convenient to get decent technical specifications.
Although historically the first static charges were received. Recall wool and amber, with which Thales of Miletus worked.