The history of electricity
What is electricity?
Electricity is a form of energy caused by the movement of matter particles (electrons)
Electric current is the directional movement of electrically charged particles. The motion of charged particles itself occurs under the influence of an electromagnetic field, one of the fundamental physical interactions. It is divided into:
Direct current is a constant motion of charged particles directed in one direction.
Alternating current is a current in which the direction of motion of particles changes over time.
Pulsating current is a periodic current, the average value for the period of which is different from zero.
The power of the electric current is determined by Ohm's law: I = U/R (current = voltage/resistance). If two values are known, then it is easy to determine the third, since if I = U/R, then R = U/I, and U = I x R. This can be remembered using a diagram:
Voltage is a scalar physical quantity, the value of which is equal to the work of the effective electric field (including third—party fields) performed when transferring a single test electric charge from point A to point B. Simply put, this is the difference in potential values between two points, which causes energy to move.
Resistance is a physical quantity that characterizes the property of a conductor to prevent the passage of electric current and is equal to the ratio of the voltage at the ends of the conductor to the current flowing through it.
The vast majority of electricity produced or generated in the world falls on alternating current. This is due to the fact that it is much easier to transform from a lower voltage to a higher voltage and vice versa. Thus, it is much easier to transmit over long-distance transmission lines. Also, with the help of alternating current, it is possible to implement a multiphase system with which electric machines, in particular asynchronous motors, can be set in motion. Or, if necessary, further increase the efficiency of the power supply system, since fewer wires will be required to transmit electricity of similar power, and three-phase transformers are significantly less than single-phase transformers of similar power.
Multiphase electric circuits are circuits in which equivalent sinusoidal EMF of the same frequency «shifted» relative to each other in time, created by a common source.
Sinusoids of currents in a three-phase circuit
Electromotive force (EMF) is a scalar quantity characterizing the ability of external forces to create a greater or lesser potential difference at the poles of a current source.
The main disadvantages of alternating current are the presence of reactive power and the skin effect. Because of the first, part of the energy is pointlessly spent during circulation between the generator and the load, and because of the second, it does not flow along the entire cross-section of the wire, but only closer to its surface, which leads to an increase in the resistance of the conductor and an additional loss of power.
The various pulsating currents differ from each other in shape (if the voltage never decreases to zero), as well as in the duration and frequency of the pulses (if there is no current in some periods of time) and depends on how it was obtained from an alternating current, or from a constant on the inverter.
Pulsating current is used in amplifiers, rectifiers, radios, generators, televisions, as well as in carbon microphones, telegraph machines and many other devices.
Also, since the current sine wave can be of different shapes and shifted in time, there are power supplies that have two output channels whose voltages are equal, but have the opposite polarity relative to the common point. This is called bipolar voltage.
This bipolar method of powering devices is often used in various kinds of electronics. For example, in amplifiers, this is the best way to improve the quality of the outgoing signal, and in measuring technology, many signals that need to be measured and processed themselves have both a plus and a minus, that is, they are bipolar.
Where electricity occurs in nature
In everything that surrounds us, there are negative and positive electric charges. If 2 objects have strong opposite charges, then they tend to balance them and attract. If unipolar charges are repelled
Friction is a force that occurs between two bodies and prevents one object from sliding on the surface of another. And since some materials, roughly speaking, find it easier to tear off excess electrons from another, static electricity arises with it — a phenomenon in which the negative charge of one atom transitions into another, with a more positive charge. Back in ancient Greece, it was discovered that when amber is rubbed with sheep's wool, amber begins to attract light small objects such as sawdust or hair. This is precisely due to the fact that a small charge of static electricity has accumulated in it.
Lightning is an electrical discharge that occurs when the charge difference between clouds and the earth is high. Due to the friction between the descending water droplets and the rising ice particles inside the cloud, ionization occurs — a process in which electrons are detached from the molecules of a substance, resulting in a pair of a positively charged molecule with a missing electron and a negatively charged one with a «bonus» electron.
A negative charge accumulates in the lower part of the cloud and when the charge difference with the earth becomes large enough, a discharge occurs. If an object acting as a conductor (for example, a temple spire, a tree or a power line pole) is located next to the discharge point, sticking out above the surface of the earth, then lightning will go into the ground along the path of least resistance, thus the lightning rod works.
St. Elmo's lights are a glow that appears on the pointed ends of objects (for example, on rocks in the mountains, spires of cathedrals and masts of ships). They, like lightning, are formed at a high level of ionization of the environment and often precede a thunderstorm or blizzard. When an excessive negative charge «flows down» the spire, acting as a lightning rod, the electrification of the atmosphere decreases, and energy is spent on glow.
Also, living beings actively use electricity, including the nervous system in the human body. Striking examples of this will be electric ramps, which have special organs and an electricity-based method of self-defense, an accurate description of which was compiled by anatomists John Walsh and John Hunter in 1773.
A potential difference is maintained between the inner and outer sides of the cell membrane due to the unequal concentration of ions inside and outside the cell. The «electric» fish have cells-electrocytes (1), collected in columns (2). A nerve ending (3) fits to each, forming a synapse (4), which occupies one of the sides of the cell.
And also the famous experiment of Luigi Galvani in 1791, in which a frog's foot cut off from the body begins to twitch when stimulated by a nerve current, which causes muscle contraction.
Luigi Galvani 1737 — 1798
The first generators
Based on the experience with friction and amber, many experimenters assumed that it was possible to increase the object and the intensity of friction in order to obtain a charge of greater force.
So in 1663, Otto Von Guericke invented one of the first generators that produced a friction charge. The device consisted of a large ball made of sulfur mounted on a rotating axis. When rubbing against a dry hand, the ball became electrified and, as in the case of amber, other bodies with a charge stuck to it or repelled it, and besides, it crackled and emitted a faint and inconspicuous glow in the dark, but nevertheless, which was later called electroluminescent.
Otto Von Guericke 1602 — 1686
In 1706, Francis Hawksby created his own generator, in which he used not sulfur, as with earlier devices from other experimenters, but a glass ball from which air was pumped out using a pump. When rubbing during rotation, a more noticeable glow appeared inside the glass ball, highlighting the contours of a person's hand touching it, after which it continued to move along the inner surface of the ball by itself for some time. And although it was possible to «collect» a charge with the help of the first capacitors, the device was usually used to demonstrate electrical phenomena noticeable to the naked eye to the public.
Francis Hawksby 1666 — 1713
The Hawksby Electric Car
More advanced generators include the electrophoretic machine, also known as the Wimshert generator, which was developed in the early 1880s by the British inventor James Wimshert. It already uses electromagnetic induction — the phenomenon of the occurrence of an electric field or electric current when the magnetic field changes, when the charge difference tends to balance.
This device consists of two insulated disks rotating in opposite directions to each other, on which conductive sectors — plates are applied. Despite the fact that the universe tends to electromagnetic equilibrium, there is a charge difference every now and then. Therefore, when the discs rotate, the charge from one plate will remove the charge from the opposite one, it can immediately be removed with a metal brush, after which it is stored at the poles of the machine, presented in the form of Leyden cans, in which opposite electric charges accumulate.
James Wimshert 1832 — 1903
Electrophoretic Machine
Electromagnetic induction was discovered by Michael Faraday in 1831, and a unipolar Faraday generator was created to demonstrate it. It has long been clear that magnetism and current are related, but in fact they are manifestations of the same phenomenon. Therefore, if you take a magnet and rotate it next to the wire winding, then current begins to flow there.
This generator contained a spinning conductive disk exposed to a constant magnetic field. At the same time, a current was generated, and a significant amount of it.
Another Faraday invention is a transformer, a device by electromagnetic induction that converts an alternating current of one magnitude into an alternating current of another magnitude, greater or lesser.
Michael Faraday 1791 — 1867
The Faraday Generator
A few decades later, in 1856, a direct current generator similar in properties to modern ones was created by German engineer and industrialist Werner Siemens, also known as a dynamo. In it, instead of a permanent magnet, some of the electricity went to electromagnets, which made the magnetic field and, consequently, the outgoing current much stronger. Soon, due to its electrodynamic properties, the dynamo became the first generator to be used in industry. Simmens also sold the rights to his generator to American industrialist George Westenhaus.
Werner Siemens 1816 — 1896
The breakthrough associated with the appearance of the dynamo cannot be underestimated. It has become possible to generate a current of any strength in a cheap and convenient way wherever there is free mechanical energy. 12 years later, when the dynamo was introduced, electricity gradually began to be used everywhere, so in 1879 the first electric railway appeared, in 1880 the first electric lift, and in 1881 the first electric tram line in Berlin.
Dynamo machine
The first asynchronous AC motor, as well as a three-phase current system, was invented in 1889 by Mikhail Dolivo-Dobrovolsky. The design of the asynchronous motor developed at that time turned out to be so efficient that it has not undergone any changes to date.
The main feature of the Dolivo-Dobrovolsky asynchronous motor is a rotor with a winding in the form of a «squirrel cage». The principle of operation of an asynchronous motor is that the current in the stator windings creates a rotating magnetic field, which in turn induces current in the rotor. The magnetic fields begin to interact, and the rotor is set in motion, as the fields relative to each other tend to become mutually stationary.
Mikhail Osipovich Dolivo-Dobrovolsky 1862 — 1919
The first batteries
The first device capable of storing an electric charge as a capacitor was partly discovered by chance. At the time of the mid-eighteenth century, Hawksby and the people before him had found ways to produce electricity, but they had to find a way to save it. Peter Muschenbrook, who conducted experiments in the Dutch city of Leiden, assumed that electricity is fluid, having the same nature as liquid. This means that it can be placed in a vessel.
Muschenbrook took a glass jar, poured some water into it and put it on an insulating material, which was supposed to keep the electricity in the jar, after which he plunged inside the end of the wire connected to the Hawksby electric machine, which was the source of the charge. But no matter how hard he tried, the charge in the jar was not noticeable to the eye.
After many attempts, he forgot to put the jar on the insulator, instead holding it in his hand while it was charging. As a result, it turned out that the scientist touched the top of the jar with his other hand, receiving an extremely powerful electric shock. So in 1746, it was experimentally found out that such a jar could be a device for storing a charge. This bank was named after Muschenbrook's hometown, the Leiden Bank. By the way, later he drew attention to the fact that the physiological effect of the charge is similar to the impact of stingrays, which he was the first to call «electric».
Peter Van Muschenbroek 1692 — 1761
Leiden Bank
Due to the fact that the phenomenon of the Leiden jar was discovered by accident, no one had a clear idea exactly how it worked. But less than 10 years after this discovery, Benjamin Franklin proposed a famous experiment that proved for the first time the electrical nature of lightning.
The first to successfully conduct this experiment were French scientists Georges-Louis Leclerc de Buffon and Thomas-Francois Dalibard. In 1752, inspired by Franklin's 1750 publication, they installed a 12-meter metal pole, the lower edge of which led into an empty bottle, in which the charge was supposed to remain on the same principle as in the Leiden jar. The experiment was successful and there was a charge left in the bottle.
After that, Franklin was the first to suggest that electricity has the nature of certain positively and negatively charged fields, different in nature from a liquid or gas, and present in each object, striving to balance each other. Therefore, the negative «fluids» of the charge are trapped due to the walls of the jar acting as an insulator. But since not only the negative charge tends to equilibrium, then as the charge inside the jar increases, the positive one begins to grow outside.
That is why when a person holding a jar by the insulated outer part touches the upper, non-insulated part, a circuit is closed along which opposite charges begin to flow to each other.
Benjamin Franklin 1706 — 1790
Another important discovery in 1792-1794 was made by Alessandro Volta. At this time, Galvani's theory of «animal electricity» was popular. In his experiments, the legs of a freshly prepared frog suspended on copper hooks contracted when a steel rod touched a nerve. He considered this phenomenon to be something unique, setting in motion the body of «animal electricity» a unique process that differs from other types of energy.
Volta thought otherwise, he perceived the results of Galvani's experiments as another manifestation of ordinary electricity, and muscle movement is just an indicator, which means «animal electricity» can be recreated without animals. After some time, he came to the conclusion that it arises in a closed circuit of dissimilar metals and liquids.
Alessandro Giuseppe Antonio Anastasio Volta 1745 — 1827
Later, he discovered that if you place cloth soaked in dilute acid between metal and copper plates, and then create a bridge between them, you can feel an electric charge. Moreover, not the only discharge, as it was with the Leiden jar, but a constant stream flowing out of the column. It was then that the «Volt element» was invented — the first galvanic cell, and the term «electric current» was born.
A galvanic cell is a chemical source of electric current based on the interaction of two substances, when during the redox reaction in the electrolyte, excess electrons «flow» from the anode to the cathode.
Galvanic cell
When the principle of obtaining current from such an element was finalized, a voltaic column appeared, consisting of Voltaic cells with copper and zinc plates, which is actually the first battery.
Voltov Pole
The first electric lighting
Arc lamps are lamps in which the light source is an electric arc that occurs between two carbon electrodes or electrodes made of refractory metal.
The idea of using electric glow as artificial lighting suggested itself and many conducted research in this area and tried to bring the idea to life. The phenomenon of the electric arc was discovered independently by Russian academician V. V. Petrov and British researchers Humphrey Davy (1778-1829) and William Petrie (1821-1908). However, at that time there were no suitable stable power sources, and the serial production of William Petrie arc lamps turned into a financial disaster, so as it was too expensive, and the lamps themselves were flammable.
It was only by the end of 1876 that Pavel Yablochkov demonstrated and patented an «Electric arc lamp» with parallel electrodes, which became widespread in many cities around the world.
Pavel Nikolaevich Yablochkov 1847 — 1894
Yablochkov arc lamp (without glass cover)
Incandescent lamps are lamps in which the light source is a carbon filament located in an inert medium, incandescent under the action of resistance to passing electric current, or a filament made of a refractory metal (usually tungsten).
There were a large number of inventors who came up with the idea to use not the electric arc itself for lighting, but a substance heated by an electric current. The very first person to invent such a device was Warren de la Rue in 1940. His invention used a platinum thread placed in a glass cylinder in the form of a spiral.
Warren de la Rue 1815 — 1889
Thomas Edison created one of the first commercially successful versions of an incandescent lamp in 1879. Based on the experiments of other researchers from different countries, he and his team created a lamp with carbon fiber and a lifetime of 40 hours. In the future, with further experiments on the selection of the filament material, it was possible to slightly increase the operating time, although the first lamps still had a short service life. In total, Edison conducted about 1,500 tests of various materials and about 6,000 more experiments on carbonation of various plants. Also, along with the lamp design, he refined the principles of the lighting and power supply system, so that, together with lower cost and fire hazard than arc lamps and gas lighting, Edison lamps became very popular.
Thomas Alva Edison 1847 — 1931
Electricity transmission and the «War of Currents»
At a certain point in time, people realized that batteries alone would not provide electricity properly. Thomas Edison, while promoting his method of electric lighting, also thought about supplying electricity to the consumer. He proposed using a large number of power plants with DC generators to supply lighting electricity, so that densely populated areas with well-off customers could be successfully illuminated. But such a method could not pay for the construction of expensive power plants everywhere, since the longer the wire between the DC generator and the consumer, the more energy is lost, since the cable has its own resistance.
Another method that solves the problem of supplying electricity over long distances was invented by inventor Nikola Tesla, who had worked for Edison for some time before. In order to provide electricity from one station to not one street, but entire cities, compensating for the problem of resistance, he proposed to increase the voltage in the common cable by reducing it in the consumer's cable, which was impossible to do with direct current. But it could be implemented using alternating current and inductors of the aforementioned transformer.
Nikola Tesla 1856 — 1943
The achievement was huge, but he still had to convince the world of the superiority of this method, since Edison, who built power plants all over New York, believed that his idea with direct current was better and involved fewer risks. At this point, Tesla met George Westenhaus, to whom he sold his Siemens generator, which allowed him to experiment with alternating current. Westenhaus offered to buy Tesla's patents, after which their open commercial confrontation with Edison began, nicknamed the «war of currents».
George Westenhaus 1846 — 1914
Obviously, both camps were trying to outbid the opponent's prices and the like, but there was another point. Touching a low-voltage DC cable was painful, but relatively harmless. While Tesla's AC cables, which had a huge voltage, were significantly more life-threatening. Edison emphasized exactly this, telling the public about fires caused by short circuits and accidents with Tesla and Westenhaus workers.
Also, the fact that alternating current acts much faster was tried to demonstrate by engineer Harold Brown, whose experiments on experimental animals demonstrated the lethal effects of direct and alternating currents on the body of large mammals. Such experiments have led to unexpected results. American politicians have become convinced that the most humane method of execution is the use of alternating current. So in 1890, the first execution was carried out on the infamous «electric chair».
In turn, Nikola Tesla, sincerely fascinated by how current is transmitted in various media and lightning occurs, came up with various spectacular demonstrations and performances in the apposition, many of which seemed to the public to be something magical. For example, he developed a method for producing very high frequency currents. High frequencies of the order above 20 kilohertz are no longer noticed by the human nervous system, because weak alternating currents of very high frequency do not heat the tissues of the body, and do not cause pain at all. Without protection, he could hold a lamp powered by electricity passing through his body. The main purpose of such demonstrations was to show that, when used correctly, alternating current is no more dangerous than direct current.
As a result, Tesla and Westenhaus won the «war of currents», since their method was more economically profitable. If the world had followed Edison's approach, there would have been space-consuming generators everywhere, and in many residential areas there was basically no electricity supply. It is easier to run a high-voltage cable from a power plant to a residential area by installing separating transformers, because this method is still used.