2.7. DISCOVERY OF ELECTROMAGNETIC INDUCTION
A great contribution to modern electrical engineering was made by the English scientist Michael Faraday, whose works, in turn, were prepared by previous work on the study of electrical and magnetic phenomena.
There is something symbolic in the fact that in the year of M. Faraday’s birth (1791), Luigi Galvani’s treatise was published with the first description of a new physical phenomenon - electric current, and in the year of his death (1867) a “dynamo” was invented - a self-exciting DC generator, i.e. a reliable, economical and easy-to-use source of electrical energy has appeared. The life of the great scientist and his unique activity in its methods, content and significance not only opened a new chapter in physics, but also played a decisive role in the birth of new branches of technology: electrical engineering and radio engineering.
For more than a hundred years, many generations of students have learned in physics lessons and from numerous books the story of the remarkable life of one of the most famous scientists, a member of 68 scientific societies and academies. Usually the name of M. Faraday is associated with the most significant and therefore most famous discovery- the phenomenon of electromagnetic induction, made by him in 1831. But a year before that, in 1830, for research in the field of chemistry and electromagnetism, M. Faraday was elected an honorary member of the St. Petersburg Academy of Sciences, and a member of the Royal Society of London (British Academy of Sciences) he was elected back in 1824. Since 1816, when the first scientific work of M. Faraday, dedicated to chemical analysis Tuscan lime, and until 1831, when the famous scientific diary “ Experimental studies on Electricity,” M. Faraday published over 60 scientific papers.
Great hard work, thirst for knowledge, innate intelligence and observation allowed M. Faraday to achieve outstanding results in all those areas scientific research, to which the scientist addressed. The recognized “king of experimenters” liked to repeat: “The art of the experimenter is to be able to ask nature questions and understand its answers.”
Each study of M. Faraday was distinguished by such thoroughness and was so consistent with previous results that among his contemporaries there were almost no critics of his work.
If we exclude from consideration the chemical research of M. Faraday, which in its field also constituted an era (it is enough to recall the experiments of liquefying gases, the discovery of benzene, butylene), then all his other works, at first glance sometimes scattered, like strokes on an artist’s canvas, taken together, form an amazing picture of a comprehensive study of two problems: interconversion various forms energy and physical content of the environment.
Rice. 2.11. Diagram of “electromagnetic rotations” (based on Faraday’s drawing)
1, 2 - bowls with mercury; 3 - moving magnet; 4 - stationary magnet; 5, 6 - wires going to the battery of galvanic cells; 7 - copper rod; 8 - fixed conductor; 9 - movable conductor
M. Faraday's work in the field of electricity began with the study of so-called electromagnetic rotations. From a series of experiments by Oersted, Arago, Ampere, Biot, Savart, carried out in 1820, it became known not only about electromagnetism, but also about the uniqueness of the interactions between current and magnet: here, as already noted, central forces that were not familiar to classical mechanics acted, and other forces sought to establish the magnetic needle perpendicular to the conductor. M. Faraday posed the question: does the magnet tend to move continuously around the conductor as a drain? The experiment confirmed the hypothesis. In 1821, M. Faraday described a physical device, schematically presented in Fig. 2.11. In the left vessel with mercury there was a permanent bar magnet, hinged at the bottom. When the current was turned on, its upper part rotated around a stationary conductor. In the right vessel, the magnet rod was motionless, and the current-carrying conductor, freely suspended on a bracket, slid along the mercury, rotating around the pole of the magnet. Since this experiment featured for the first time a magnetoelectric device with continuous motion, it is quite legitimate to begin the history of electric machines in general and the electric motor in particular with this device. Let us also pay attention to the mercury contact, which subsequently found application in electromechanics.
It was from this moment, apparently, that M. Faraday began to develop ideas about the universal “interconvertibility of forces.” Having obtained continuous mechanical movement with the help of electromagnetism, he sets himself the task of reversing the phenomenon or, in the terminology of M. Faraday, converting magnetism into electricity.
Only absolute conviction in the validity of the hypothesis of “interconvertibility” can explain the determination and perseverance, thousands of experiments and 10 years of hard work spent on solving the formulated problem. In August 1831, a decisive experiment was made, and on November 24, at a meeting at the Royal Society, the essence of the phenomenon of electromagnetic induction was outlined.
Rice. 2.12. Illustration of Arago's experiment ("rotation magnetism")
1 - conductive non-magnetic disk; 2 - glass base for mounting the disk axis
As an example characterizing the scientist’s train of thought and the formation of his ideas about the electromagnetic field, let us consider M. Faraday’s study of the phenomenon that was then called “rotational magnetism.” Many years before the work of M. Faraday, navigators noticed the braking effect of the copper compass body on the oscillations of the magnetic needle. In 1824 D.F. Arago (see § 2.5) described the phenomenon of “rotation magnetism,” which neither he nor other physicists could satisfactorily explain. The essence of the phenomenon was as follows (Fig. 2.12). A horseshoe magnet could rotate around a vertical axis, and above its poles there was an aluminum or copper disk, which could also rotate on an axis, the direction of rotation of which coincided with the direction of rotation of the magnet's axis. At rest, no interactions were observed between the disk and the magnet. But as soon as the magnet began to rotate, the disk rushed after it and vice versa. To eliminate the possibility of the disk being entrained by air currents, the magnet and the disk were separated by glass.
The discovery of electromagnetic induction helped M. Faraday explain the phenomenon of D.F. Arago and at the very beginning of the study write down: “I hoped to make a new source of electricity from Mr. Arago’s experience.”
Almost simultaneously with M. Faraday, electromagnetic induction was observed by the outstanding American physicist Joseph Henry (1797–1878). It is not difficult to imagine the experiences of the scientist, the future president of the American National Academy of Sciences, when, about to publish his observations, he learned about the publication of M. Faraday. A year later, D. Henry discovered the phenomenon of self-induction and extra-current, and also established the dependence of the circuit inductance on the properties of the material and the configuration of the coil cores. In 1838, D. Henry studied "currents higher order", i.e. currents induced by other induced currents. In 1842, the continuation of these studies led D. Henry to the discovery of the oscillatory nature of the capacitor discharge (later, in 1847, this discovery was repeated by the outstanding German physicist Hermann Helmholtz) (1821–1894).
Let us turn to the main experiments of M. Faraday. The first series of experiments ended with an experiment demonstrating the phenomenon of “voltaic-electric” (in the terminology of M. Faraday) induction (Fig. 2.13, A- G). Having detected the occurrence of current in the secondary circuit 2 when closing or opening the primary 1 or during mutual movement of the primary and secondary circuits (Fig. 2.13, V), M. Faraday set up an experiment to determine the properties of the induced current: inside the spiral b, included in the secondary circuit, a steel needle 7 was placed (Fig. 2.13, b), which was magnetized by an induced current. The result indicated that the induced current was similar to the current obtained directly from a galvanic battery 3.
Rice. 2.13. Schemes of the main experiments that led to the discovery of electromagnetic induction
Replacing the wooden or cardboard drum 4, on which the primary and secondary windings were wound with a steel ring (Fig. 2.13, d), M. Faraday discovered a more intense deflection of the galvanometer needle 5. This experience indicated the significant role of the environment in electromagnetic processes. Here M. Faraday first uses a device that can be called a transformer prototype.
The second series of experiments illustrated the phenomenon of electromagnetic induction that occurred in the absence of a voltage source in the primary circuit. Based on the fact that a coil flown by current is identical to a magnet, M. Faraday replaced the voltage source with two permanent magnets (Fig. 2.13, d) and observed the current in the secondary winding when the magnetic circuit closed and opened. He called this phenomenon “magnetoelectric induction”; Later he noted that there is no fundamental difference between “voltaic-electric” and “magnetoelectric” induction. Subsequently, both of these phenomena were united by the term “electromagnetic induction.” In the final experiments (Fig. 2.13, e, g) the appearance of an induced current during movement was demonstrated permanent magnet or coils with current inside the solenoid. It was this experiment that more clearly demonstrated the possibility of converting “magnetism into electricity” or, more precisely, mechanical energy into electrical energy.
Based on new ideas, M. Faraday gave an explanation of the physical side of the experiment with the disk of D.F. Arago. Briefly the course of his reasoning can be summarized as follows. An aluminum (or any other conductive but non-magnetic) disk can be thought of as a wheel with infinite a large number spokes - radial conductors. With the relative motion of the magnet and the disk, these spoke-conductors “cut the magnetic curves” (Faraday's terminology), and an induced current arises in the conductors. The interaction of current with a magnet was already known. In M. Faraday’s interpretation, the terminology and method of explaining the phenomenon attracts attention. To determine the direction of the induced current, he introduces the rule of a knife cutting the lines of force. This is not E.H.'s law yet. Lenz, who is characterized by the universality of the characteristics of the phenomenon, but only attempts each time by detailed descriptions determine whether current will flow from the handle to the tip of the blade or vice versa. But the fundamental picture is important here: M. Faraday, in contrast to supporters of the theory of long-range action, fills the space in which various forces act with a material medium, ether, developing the ethereal theory of L. Euler, who, in turn, was influenced by the ideas of M.V. Lomonosov.
M. Faraday gave magnetic, and then in the study of dielectrics and electric lines of force, physical reality, endowed them with the property of elasticity and found very plausible explanations for a wide variety of electromagnetic phenomena, using the idea of these elastic lines, similar to rubber threads.
More than a century and a half have passed, and we still have not found a more visual way and scheme for explaining phenomena associated with induction and electromechanical actions than the famous concept of Faraday lines, which to this day seem to us to be tangible.
From the disc by D.F. Arago M. Faraday actually made a new source of electricity. Having forced an aluminum or copper disk to rotate between the poles of the magnet, M. Faraday placed brushes on the axis of the disk and on its periphery.
In this way, an electric machine was designed, which later received the name unipolar generator.
When analyzing the works of M. Faraday, the general idea that was developed by the great scientist throughout his creative life clearly emerges. Reading M. Faraday, it is difficult to get rid of the impression that he dealt with only one problem of the interconversion of various forms of energy, and all his discoveries were made casually and served only to illustrate the main idea. He explores different kinds electricity (animal, galvanic, magnetic, thermoelectricity) and, proving their qualitative identity, discovers the law of electrolysis. At the same time, electrolysis, like the twitching of the muscles of a dissected frog, initially served only as proof that all types of electricity manifest themselves in the same actions.
Research on static electricity and the phenomenon of electrostatic induction led M. Faraday to the formation of ideas about dielectrics, to a final break with the theory of long-range action, to remarkable studies of discharge in gases (the discovery of Faraday's dark space). Further research interactions and interconversions of forces led him to the discovery of magnetic rotation of the plane of polarization of light, to the discovery of diamagnetism and paramagnetism. The conviction of the universality of mutual transformations forced M. Faraday to even turn to the study of the connection between magnetism and electricity, on the one hand, and gravity, on the other. True, Faraday's ingenious experiments did not give positive result, but this did not shake his confidence in the existence of a connection between these phenomena.
Biographers of M. Faraday like to emphasize the fact that M. Faraday avoided using mathematics, that there is not a single mathematical formula in the many hundreds of pages of his Experimental Studies in Electricity. In this regard, it is appropriate to cite the statement of M. Faraday’s compatriot, the great physicist James Clark Maxwell (1831–1879): “Having begun to study Faraday’s work, I found that his method of understanding phenomena was also mathematical, although not presented in the form of ordinary mathematical symbols. I also found that this method could be expressed in ordinary mathematical form and thus be compared with the methods of professional mathematicians."
The “mathematical nature” of Faraday’s thinking can be illustrated by his laws of electrolysis or, for example, by the formulation of the law of electromagnetic induction: the amount of electricity set in motion is directly proportional to the number of lines of force crossed. It is enough to imagine the last formulation in the form of mathematical symbols, and we immediately obtain a formula from which the famous d?/dt very quickly follows, where? - magnetic flux linkage.
D.K. Maxwell, who was born in the year of the discovery of the phenomenon of electromagnetic induction, very modestly assessed his services to science, emphasizing that he only developed and put into mathematical form the ideas of M. Faraday. Maxwell's theory electromagnetic field was appreciated by scientists of the late 19th and early 20th centuries, when radio engineering began to develop based on the ideas of Faraday and Maxwell.
To characterize the insight of M. Faraday, his ability to penetrate into the depths of the most complex physical phenomena, it is important to recall here that back in 1832, the brilliant scientist ventured to suggest that electromagnetic processes are of a wave nature, with magnetic oscillations and electrical induction propagating at a finite speed.
At the end of 1938, a sealed letter from M. Faraday, dated March 12, 1832, was discovered in the archives of the Royal Society of London. It lay in obscurity for more than 100 years, and it contained the following lines:
“Some research results... led me to the conclusion that the propagation of magnetic influence takes time, i.e. When one magnet acts on another distant magnet or piece of iron, the influencing cause (which I will allow myself to call magnetism) spreads gradually from the magnetic bodies and requires a certain time for its propagation, which, obviously, will turn out to be very insignificant.
I also believe that electrical induction travels in exactly the same way. I believe that the propagation of magnetic forces from the magnetic pole is similar to the vibrations of a disturbed water surface, or to sound vibrations air particles, i.e. I intend to apply the theory of oscillations to magnetic phenomena, as is done in relation to sound, and is the most probable explanation of light phenomena.
By analogy, I believe it is possible to apply the theory of oscillations to the propagation of electrical induction. I want to test these views experimentally, but since my time is occupied with official duties, which may cause the experiments to be prolonged... I want, by transferring this letter for safekeeping to the Royal Society, to assign the discovery to myself by a certain date...".
Since these ideas of M. Faraday remained unknown, there is no reason to refuse his great compatriot D.K. Maxwell in the discovery of these same ideas, to which he gave a strict physical and mathematical form and fundamental significance.
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So far we have considered electric and magnetic fields that do not change over time. It was found that the electric field is created by electric charges, and the magnetic field by moving charges, i.e., electric current. Let's move on to getting acquainted with electrical and magnetic fields, which change over time.
Most important fact, which was discovered, is the closest relationship between electric and magnetic fields. A time-varying magnetic field generates an electric field, and a changing electric field generates a magnetic field. Without this connection between fields, the variety of manifestations of electromagnetic forces would not be as extensive as they actually are. There would be no radio waves or light.
It is no coincidence that the first decisive step In the discovery of new properties of electromagnetic interactions, Faraday became the founder of the concept of the electromagnetic field. Faraday was confident in the unified nature of electrical and magnetic phenomena. Thanks to this, he made a discovery, which subsequently formed the basis for the design of generators for all power plants in the world, converting mechanical energy into electrical energy. (Other sources: galvanic cells, batteries, etc. - provide an insignificant share of the generated energy.)
An electric current, Faraday reasoned, can magnetize a piece of iron. Couldn't a magnet, in turn, cause an electric current?
For a long time this connection could not be detected. It was difficult to figure out the main thing, namely: only a moving magnet or a time-varying magnetic field can excite electricity in a reel.
The following fact shows what kind of accidents could have prevented the discovery. Almost simultaneously with Faraday, the Swiss physicist Colladon tried to produce an electric current in a coil using a magnet. When working, he used a galvanometer, the light magnetic needle of which was placed inside the coil of the device. So that the magnet did not have a direct effect on the needle, the ends of the coil into which Colladon pushed the magnet, hoping to receive a current in it, were brought into the next room and there connected to a galvanometer. Having inserted the magnet into the coil, Colladon walked into the next room and, with chagrin,
I made sure that the galvanometer did not show any current. If he had only to watch the galvanometer all the time and ask someone to work on the magnet, a remarkable discovery would have been made. But this did not happen. A magnet at rest relative to the coil does not generate current in it.
The phenomenon of electromagnetic induction consists in the occurrence of an electric current in a conducting circuit, which is either at rest in a time-varying magnetic field or moves in a constant magnetic field in such a way that the number of magnetic induction lines penetrating the circuit changes. It was discovered on August 29, 1831. It is a rare case when the date of a new remarkable discovery is known so accurately. Here is a description of the first experiment given by Faraday himself:
“A copper wire 203 feet long was wound on a wide wooden spool, and between its turns was wound a wire of the same length, but insulated from the first with a cotton thread. One of these spirals was connected to a galvanometer, and the other to a strong battery consisting of 100 pairs of plates... When the circuit was closed, a sudden but extremely weak action was noticed on the galvanometer, and the same was noticed when the current stopped. With the continuous passage of current through one of the spirals, it was not possible to notice either an effect on the galvanometer, or at all any inductive effect on the other spiral, despite the fact that the heating of the entire spiral connected to the battery and the brightness of the spark jumping between the coals indicated battery power" (Faraday M. "Experimental Research in Electricity", 1st series).
So, initially, induction was discovered in conductors that are motionless relative to each other when closing and opening a circuit. Then, clearly understanding that bringing current-carrying conductors closer or further away should lead to the same result as closing and opening a circuit, Faraday proved through experiments that current arises when the coils move each other.
regarding a friend. Familiar with the works of Ampere, Faraday understood that a magnet is a collection of small currents circulating in molecules. On October 17, as recorded in his laboratory notebook, an induced current was detected in the coil while the magnet was being pushed in (or pulled out). Within one month, Faraday experimentally discovered all the essential features of the phenomenon of electromagnetic induction.
Currently, everyone can repeat Faraday's experiments. To do this, you need to have two coils, a magnet, a battery of elements and a fairly sensitive galvanometer.
In the installation shown in Figure 238, an induced current occurs in one of the coils when closing or opening electrical circuit another coil, stationary relative to the first. In the installation in Figure 239, the current strength in one of the coils is changed using a rheostat. In Figure 240, a, the induction current appears when the coils move relative to each other, and in Figure 240, b - when a permanent magnet moves relative to the coil.
Faraday himself already grasped the general thing on which the appearance of an induction current depends in experiments that outwardly look different.
In a closed conducting circuit, a current arises when the number of magnetic induction lines piercing the area limited by this circuit changes. And the faster the number of magnetic induction lines changes, the greater the resulting induction current. In this case, the reason for the change in the number of magnetic induction lines is completely indifferent. This may be a change in the number of magnetic induction lines penetrating the area of a stationary conducting circuit due to a change in the current strength in the adjacent coil (Fig. 238), or a change in the number of induction lines due to the movement of the circuit in a non-uniform magnetic field, the density of the lines of which varies in space (Fig. 241).
After the discoveries of Oersted and Ampere, it became clear that electricity has magnetic force. Now it was necessary to confirm the influence of magnetic phenomena on electrical ones. Faraday brilliantly solved this problem.
Michael Faraday (1791-1867) was born in London, in one of its poorest parts. His father was a blacksmith, and his mother was the daughter of a tenant farmer. When Faraday reached school age, he was sent to elementary school. The course Faraday took here was very narrow and was limited only to learning to read, write and begin to count.
A few steps from the house in which the Faraday family lived, there was a bookshop, which was also a bookbinding establishment. This is where Faraday ended up after completing his course primary school, when the question arose about choosing a profession for him. Michael was only 13 years old at this time. Already in his youth, when Faraday was just beginning his self-education, he sought to rely exclusively on facts and verify the messages of others with his own experiences.
These aspirations dominated him all his life as the main features of his scientific activity Faraday began performing physical and chemical experiments as a boy at his first acquaintance with physics and chemistry. One day Michael attended one of the lectures of Humphry Davy, the great English physicist.
Faraday made a detailed note of the lecture, bound it and sent it to Davy. He was so impressed that he invited Faraday to work with him as a secretary. Soon Davy went on a trip to Europe and took Faraday with him. Over the course of two years, they visited the largest European universities.
Returning to London in 1815, Faraday began working as an assistant in one of the laboratories of the Royal Institution in London. At that time it was one of the best physics laboratories in the world. From 1816 to 1818, Faraday published a number of small notes and short memoirs on chemistry. Faraday's first work on physics dates back to 1818.
Based on the experiences of his predecessors and combining several of his own experiences, by September 1821 Michael published “The History of the Advances of Electromagnetism.” Already at this time, he formed a completely correct concept of the essence of the phenomenon of deflection of a magnetic needle under the influence of current.
Having achieved this success, Faraday left his studies in the field of electricity for ten years, devoting himself to the study of a number of subjects of a different kind. In 1823, Faraday made one of the most important discoveries in the field of physics - he was the first to liquefy gas, and at the same time established a simple but effective method for converting gases into liquid. In 1824, Faraday made several discoveries in the field of physics.
Among other things, he established the fact that light affects the color of glass, changing it. IN next year Faraday again turned from physics to chemistry, and the result of his work in this area was the discovery of gasoline and sulfur-naphthalene acid.
In 1831, Faraday published a treatise “On a Special Kind of Optical Illusion,” which served as the basis for an excellent and curious optical projectile called the “chromotrope.” In the same year, another treatise by the scientist, “On Vibrating Plates,” was published. Many of these works could themselves immortalize the name of their author. But the most important of scientific works Faraday's research is in the fields of electromagnetism and electrical induction.
Strictly speaking, important department physics, which interprets the phenomena of electromagnetism and inductive electricity, and which is currently of such enormous importance for technology, was created by Faraday out of nothing.
By the time Faraday finally devoted himself to research in the field of electricity, it was established that under ordinary conditions the presence of an electrified body is sufficient for its influence to excite electricity in any other body. At the same time, it was known that a wire through which current passes and which also represents an electrified body does not have any effect on other wires placed nearby.
What caused this exception? This is the question that interested Faraday and the solution of which led him to the most important discoveries in the field of induction electricity. As was his custom, Faraday began a series of experiments designed to clarify the essence of the matter.
Faraday wound two insulated wires parallel to each other on the same wooden rolling pin. He connected the ends of one wire to a battery of ten cells, and the ends of the other to a sensitive galvanometer. When current was passed through the first wire,
Faraday turned all his attention to the galvanometer, expecting to notice from its vibrations the appearance of a current in the second wire. However, nothing of the kind happened: the galvanometer remained calm. Faraday decided to increase the current strength and introduced 120 galvanic elements into the circuit. The result was the same. Faraday repeated this experiment dozens of times and still with the same success.
Anyone else in his place would have left the experiments convinced that the current passing through a wire has no effect on the neighboring wire. But Faraday always tried to extract from his experiments and observations everything that they could give, and therefore, not receiving a direct effect on the wire connected to the galvanometer, he began to look for side effects.
He immediately noticed that the galvanometer, remaining completely calm during the entire passage of current, begins to oscillate when the circuit itself is closed and when it is opened. It turned out that at the moment when a current is passed into the first wire, and also when this transmission stops, at the second wire is also excited by a current, which in the first case has the opposite direction to the first current and the same with it in the second case and lasts only one instant.
These secondary instantaneous currents, caused by the influence of the primary ones, were called inductive by Faraday, and this name has remained with them to this day. Being instantaneous, instantly disappearing after their appearance, inductive currents would have no practical significance if Faraday had not found a way, with the help of an ingenious device (a commutator), to constantly interrupt and again conduct the primary current coming from the battery along the first wire, thanks to which the second wire is continuously excited by more and more new inductive currents, thus becoming constant. Thus, a new source of electrical energy was found, in addition to the previously known ones (friction and chemical processes), - induction, and the new kind This energy is inductive electricity.
Continuing his experiments, Faraday further discovered that simply bringing a wire twisted into a closed curve close to another through which a galvanic current flows is sufficient to excite an inductive current in the neutral wire in the direction opposite to the galvanic current, and that removing the neutral wire again excites an inductive current in it. the current is already in the same direction as the galvanic current flowing along a stationary wire, and that, finally, these inductive currents are excited only during the approach and removal of the wire to the conductor of the galvanic current, and without this movement the currents are not excited, no matter how close the wires are to each other .
Thus, a new phenomenon was discovered, similar to the above-described phenomenon of induction when the galvanic current closes and stops. These discoveries in turn gave rise to new ones. If it is possible to cause an inductive current by short-circuiting and stopping the galvanic current, then wouldn’t the same result be obtained by magnetizing and demagnetizing iron?
The work of Oersted and Ampere had already established the relationship between magnetism and electricity. It was known that iron becomes a magnet when an insulated wire is wound around it and a galvanic current passes through the latter, and that magnetic properties of this iron stop as soon as the current stops.
Based on this, Faraday came up with this kind of experiment: two insulated wires were wound around an iron ring; with one wire wrapped around one half of the ring, and the other around the other. Current from a galvanic battery was passed through one wire, and the ends of the other were connected to a galvanometer. And so, when the current closed or stopped and when, consequently, the iron ring was magnetized or demagnetized, the galvanometer needle quickly oscillated and then quickly stopped, that is, the same instantaneous inductive currents were excited in the neutral wire - this time: already under the influence of magnetism.
Thus, here for the first time magnetism was converted into electricity. Having received these results, Faraday decided to diversify his experiments. Instead of an iron ring, he began to use an iron strip. Instead of exciting magnetism in iron by galvanic current, he magnetized the iron by touching it to a permanent steel magnet. The result was the same: always in the wire wrapped around the iron! a current was excited at the moment of magnetization and demagnetization of iron.
Then Faraday introduced a steel magnet into the wire spiral - the approach and removal of the latter caused induced currents in the wire. In a word, magnetism, in the sense of exciting induction currents, acted in exactly the same way as galvanic current.
At that time, physicists were intensely interested in one mysterious phenomenon, discovered in 1824 by Arago and which could not be explained, despite; the fact that this explanation was intensely sought by such outstanding scientists of the time as Arago himself, Ampère, Poisson, Babage and Herschel.
The point was as follows. A magnetic needle, hanging freely, quickly comes to rest if a circle of non-magnetic metal is placed under it; if then the circle is brought into rotational movement, the magnetic needle begins to move behind it.
IN calm state it was impossible to discover the slightest attraction or repulsion between the circle and the arrow, while the same circle, in motion, pulled behind it not only a light arrow, but also a heavy magnet. This truly miraculous phenomenon seemed to the scientists of that time a mysterious mystery, something beyond the limits of the natural.
Faraday, based on the above data, made the assumption that a circle of non-magnetic metal, under the influence of a magnet, during rotation is run around by inductive currents, which affect the magnetic needle and drag it along the magnet.
And indeed, by introducing the edge of a circle between the poles of a large horseshoe magnet and connecting the center and edge of the circle with a galvanometer with a wire, Faraday obtained a constant electric current when the circle rotated.
Following this, Faraday focused on another phenomenon that was then arousing general curiosity. As you know, if you sprinkle iron filings on a magnet, they group along certain lines called magnetic curves. Faraday, drawing attention to this phenomenon, gave the basis in 1831 to magnetic curves the name “lines of magnetic force,” which then came into general use.
The study of these “lines” led Faraday to a new discovery; it turned out that in order to excite induced currents, the source’s approach and distance from the magnetic pole are not necessary. To excite currents, it is enough to cross the lines of magnetic force in a known manner.
Faraday's further work in the mentioned direction acquired, from a contemporary point of view, the character of something absolutely miraculous. At the beginning of 1832, he demonstrated a device in which inductive currents were excited without the help of a magnet or galvanic current.
The device consisted of an iron strip placed in a wire coil. This device, under ordinary conditions, did not give the slightest sign of the appearance of currents in it; but as soon as it was given a direction corresponding to the direction of the magnetic needle, a current was excited in the wire.
Then Faraday gave the position of the magnetic needle to one coil and then introduced an iron strip into it: the current was again excited. The reason that caused the current in these cases was earthly magnetism, which caused inductive currents like an ordinary magnet or galvanic current. To more clearly show and prove this, Faraday undertook another experiment, which fully confirmed his considerations.
He reasoned that if a circle of non-magnetic metal, such as copper, rotating in a position in which it intersects the lines of magnetic force of an adjacent magnet, produces an inductive current, then the same circle, rotating in the absence of a magnet, but in a position in which the circle will cross the lines of earthly magnetism, must also give an inductive current.
And indeed, a copper circle rotated in a horizontal plane produced an inductive current that produced a noticeable deflection of the galvanometer needle. Faraday ended his series of studies in the field of electrical induction with the discovery, made in 1835, of the “inductive influence of current on itself.”
He found out that when a galvanic current is closed or opened, instantaneous inductive currents are excited in the wire itself, which serves as a conductor for this current.
Russian physicist Emil Khristoforovich Lenz (1804-1861) gave a rule for determining the direction of induction current. “The induction current is always directed in such a way that the magnetic field it creates complicates or inhibits the movement causing induction,” notes A.A. Korobko-Stefanov in his article on electromagnetic induction. - For example, when a coil approaches a magnet, the resulting induced current has such a direction that the magnetic field it creates will be opposite to the magnetic field of the magnet. As a result, repulsive forces arise between the coil and the magnet.
Lenz's rule follows from the law of conservation and transformation of energy. If induced currents accelerated the motion that caused them, then work would be created out of nothing. The coil itself, after a slight push, would rush towards the magnet, and at the same time the induction current would release heat in it. In reality, the induced current is created due to the work of bringing the magnet and the coil closer together.
Why does induced current occur? A deep explanation of the phenomenon of electromagnetic induction was given by the English physicist James Clerk Maxwell, the creator of a complete mathematical theory of the electromagnetic field.
To better understand the essence of the matter, consider a very simple experiment. Let the coil consist of one turn of wire and be penetrated by an alternating magnetic field perpendicular to the plane of the turn. An induced current naturally arises in the coil. Maxwell interpreted this experiment exceptionally boldly and unexpectedly.
When a magnetic field changes in space, according to Maxwell, a process arises for which the presence of a wire coil has no significance. The main thing here is the emergence of closed ring lines electric field, covering a changing magnetic field. Under the influence of the resulting electric field, electrons begin to move, and an electric current arises in the coil. A coil is simply a device that detects an electric field.
The essence of the phenomenon of electromagnetic induction is that an alternating magnetic field always generates an electric field with closed lines of force in the surrounding space. Such a field is called a vortex field.”
Research in the field of induction produced by terrestrial magnetism gave Faraday the opportunity to express the idea of a telegraph back in 1832, which then formed the basis of this invention. In general, the discovery of electromagnetic induction is not without reason considered one of the most outstanding discoveries XIX century - the work of millions of electric motors and electric current generators all over the world is based on this phenomenon...
Source of information: Samin D.K. “One Hundred Great Scientific Discoveries.”, M.: “Veche”, 2002.
After the discoveries of Oersted and Ampere, it became clear that electricity has magnetic force. Now it was necessary to confirm the influence of magnetic phenomena on electrical ones. Faraday brilliantly solved this problem.
Michael Faraday (1791-1867) was born in London, in one of its poorest parts. His father was a blacksmith, and his mother was the daughter of a tenant farmer. When Faraday reached school age, he was sent to primary school. The course Faraday took here was very narrow and was limited only to learning to read, write and begin to count.
A few steps from the house in which the Faraday family lived, there was a bookshop, which was also a bookbinding establishment. This is where Faraday ended up, having completed his primary school course, when the question arose about choosing a profession for him. Michael was only 13 years old at this time.
Already in his youth, when Faraday was just beginning his self-education, he sought to rely exclusively on facts and verify the messages of others with his own experiences. These aspirations dominated him all his life as the main features of his scientific activity.
Faraday began to carry out physical and chemical experiments as a boy at his first acquaintance with physics and chemistry. One day Michael attended one of the lectures of Humphry Davy, the great English physicist. Faraday made a detailed note of the lecture, bound it and sent it to Davy. He was so impressed that he invited Faraday to work with him as a secretary. Soon Davy went on a trip to Europe and took Faraday with him. Over the course of two years, they visited the largest European universities.
Returning to London in 1815, Faraday began working as an assistant in one of the laboratories of the Royal Institution in London. At that time it was one of the best physics laboratories in the world. From 1816 to 1818, Faraday published a number of small notes and short memoirs on chemistry. Faraday's first work on physics dates back to 1818.
Based on the experiences of his predecessors and combining several of his own experiences, by September 1821 Michael published “The History of the Advances of Electromagnetism.” Already at this time, he formed a completely correct concept of the essence of the phenomenon of deflection of a magnetic needle under the influence of current. Having achieved this success, Faraday left his studies in the field of electricity for ten years, devoting himself to the study of a number of subjects of a different kind.
In 1823, Faraday made one of the most important discoveries in the field of physics - he was the first to liquefy gas, and at the same time established a simple but effective method for converting gases into liquid.
In 1824, Faraday made several discoveries in the field of physics. Among other things, he established the fact that light affects the color of glass, changing it.
The following year, Faraday again turned from physics to chemistry, and the result of his work in this area was the discovery of gasoline and sulfur-naphthalene acid.In 1831, Faraday published a treatise on “A Special Kind of Optical Illusion,” which served as the basis for an excellent and curious optical projectile called the “chromotrope.” In the same year, another treatise by the scientist, “On Vibrating Plates,” was published.
Many of these works could themselves immortalize the name of their author. But the most important of Faraday's scientific works are his studies in the field of electromagnetism and electrical induction. Strictly speaking, an important branch of physics that treats the phenomena of electromagnetism and inductive electricity, and which is currently of such enormous importance for technology, was created by Faraday out of nothing.
By the time Faraday finally devoted himself to research in the field of electricity, it was established that under ordinary conditions the presence of an electrified body is sufficient for its influence to excite electricity in any other body.
At the same time, it was known that a wire through which current passes and which also represents an electrified body does not have any effect on other wires placed nearby. What caused this exception? This is the question that interested Faraday and the solution of which led him to the most important discoveries in the field of induction electricity.
As was his custom, Faraday began a series of experiments designed to clarify the essence of the matter. Faraday wound two insulated wires parallel to each other on the same wooden rolling pin. He connected the ends of one wire to a battery of ten cells, and the ends of the other to a sensitive galvanometer. When a current was passed through the first wire, Faraday turned all his attention to the galvanometer, expecting to notice by its vibrations the appearance of a current in the second wire. However, nothing of the kind happened: the galvanometer remained calm. Faraday decided to increase the current strength and introduced 120 galvanic elements into the circuit. The result was the same. Faraday repeated this experiment dozens of times and still with the same success. Anyone else in his place would have left the experiments convinced that the current passing through a wire has no effect on the neighboring wire. But Faraday always tried to extract from his experiments and observations everything that they could give, and therefore, not receiving a direct effect on the wire connected to the galvanometer, he began to look for side effects.
He immediately noticed that the galvanometer, remaining completely calm during the entire passage of current, began to oscillate when the circuit itself was closed and when it was opened. It turned out that at the moment when a current is passed into the first wire, and also when this transmission stops, a current is also excited in the second wire, which in the first case has the opposite direction to the first current and the same with it in the second case and lasts only one instant. Secondary instantaneous currents caused by the influence of primary ones were called inductive by Faraday, and this name has remained with them to this day.
Being instantaneous, instantly disappearing after their appearance, inductive currents would have no practical significance if Faraday had not found a way, with the help of an ingenious device (a commutator), to constantly interrupt and again conduct the primary current coming from the battery along the first wire, thanks to which the second wire is continuously excited by more and more new inductive currents, thus becoming constant. Thus, a new source of electrical energy was found, in addition to the previously known ones (friction and chemical processes), - induction, and a new type of this energy - inductive electricity.
Continuing his experiments, Faraday further discovered that simply bringing a wire twisted into a closed curve close to another through which a galvanic current flows is sufficient to excite an inductive current in the neutral wire in the direction opposite to the galvanic current, and that removing the neutral wire again excites an inductive current in it. the current is already in the same direction as the galvanic current flowing along a stationary wire, and that, finally, these inductive currents are excited only during the approach and removal of the wire to the conductor of the galvanic current, and without this movement the currents are not excited, no matter how close the wires are to each other . Thus, a new phenomenon was discovered, similar to the above-described phenomenon of induction when the galvanic current closes and stops.
These discoveries in turn gave rise to new ones. If it is possible to cause an inductive current by short-circuiting and stopping the galvanic current, then wouldn’t the same result be obtained by magnetizing and demagnetizing iron? The work of Oersted and Ampere had already established the relationship between magnetism and electricity. It was known that iron becomes a magnet when an insulated wire is wound around it and a galvanic current passes through it, and that the magnetic properties of this iron cease as soon as the current stops. Based on this, Faraday came up with this kind of experiment: two insulated wires were wound around an iron ring; with one wire wrapped around one half of the ring, and the other around the other.
Current from a galvanic battery was passed through one wire, and the ends of the other were connected to a galvanometer. And so, when the current closed or stopped and when, consequently, the iron ring was magnetized or demagnetized, the galvanometer needle quickly oscillated and then quickly stopped, that is, the same instantaneous inductive currents were excited in the neutral wire - this time: already under the influence of magnetism. Thus, here for the first time magnetism was converted into electricity.Having received these results, Faraday decided to diversify his experiments. Instead of an iron ring, he began to use an iron strip. Instead of exciting magnetism in iron by galvanic current, he magnetized the iron by touching it to a permanent steel magnet. The result was the same: always in the wire wrapped around the iron! a current was excited at the moment of magnetization and demagnetization of iron. Then Faraday introduced a steel magnet into the wire spiral - the approach and removal of the latter caused induced currents in the wire. In a word, magnetism, in the sense of exciting induction currents, acted in exactly the same way as galvanic current.
At that time, physicists were intensely interested in one mysterious phenomenon, discovered in 1824 by Arago and which could not be explained, despite; the fact that this explanation was intensely sought by such outstanding scientists of the time as Arago himself, Ampère, Poisson, Babage and Herschel. Case I was as follows. A magnetic needle, hanging freely, quickly comes to rest if a circle of non-magnetic metal is placed under it; If the circle is then put into rotation, the magnetic needle begins to move behind it. In a calm state, it was impossible to discover the slightest attraction or repulsion between the 5th circle and the arrow, while the same circle, in motion, pulled behind it not only a light arrow, but also a heavy magnet. This truly miraculous phenomenon seemed to the scientists of that time a mysterious mystery, something beyond the limits of the natural. Faraday, based on the above data, made the assumption that a circle of non-magnetic metal, under the influence of a magnet, during rotation is run around by inductive currents, which affect the magnetic needle and drag it along the magnet. And indeed, by introducing the edge of a circle between the poles of a large horseshoe magnet and connecting the center and edge of the circle with a galvanometer with a wire, Faraday obtained a constant electric current when the circle rotated.
Following this, Faraday focused on another phenomenon that was then arousing general curiosity. As you know, if you sprinkle iron filings on a magnet, they group along certain lines called magnetic curves. Faraday, drawing attention to this phenomenon, gave magnetic curves the name “lines of magnetic force” in 1831, which later came into general use. The study of these “lines” led Faraday to a new discovery; it turned out that in order to excite induced currents, the source’s approach and distance from the magnetic pole are not necessary. To excite currents, it is enough to cross the lines of magnetic force in a known manner.
Faraday's further work in the mentioned direction acquired, from a contemporary point of view, the character of something absolutely miraculous. At the beginning of 1832, he demonstrated a device in which inductive currents were excited without the help of a magnet or galvanic current.
The device consisted of an iron strip placed in a wire coil.
This device, under ordinary conditions, did not give the slightest sign of the appearance of currents in it; but as soon as it was given a direction corresponding to the direction of the magnetic needle, a current was excited in the wire. Then Faraday gave the position of the magnetic needle to one coil and then introduced an iron strip into it: the current was again excited. The reason that caused the current in these cases was earthly magnetism, which caused inductive currents like an ordinary magnet or galvanic current. To more clearly show and prove this, Faraday undertook another experiment, which fully confirmed his considerations. He reasoned that if a circle of non-magnetic metal, such as copper, rotating in a position in which it intersects the lines of magnetic force of an adjacent magnet, produces an inductive current, then the same circle, rotating in the absence of a magnet, but in a position in which the circle will cross the lines of earthly magnetism, must also give an inductive current. And indeed, a copper circle rotated in a horizontal plane produced an inductive current that produced a noticeable deflection of the galvanometer needle.Faraday ended his series of studies in the field of electrical induction with the discovery, made in 1835, of the “inductive influence of current on itself.” He found out that when a galvanic current is closed or opened, instantaneous inductive currents are excited in the wire itself, which serves as a conductor for this current.
Russian physicist Emil Khristoforovich Lenz (1804-1861) gave a rule for determining the direction of induction current.
“The induction current is always directed in such a way that the magnetic field it creates complicates or inhibits the movement causing induction,” notes A.A. Korobko-Stefanov in his article on electromagnetic induction. - For example, when a coil approaches a magnet, the resulting induced current has such a direction that the magnetic field it creates will be opposite to the magnetic field of the magnet. As a result, repulsive forces arise between the coil and the magnet.
Lenz's rule follows from the law of conservation and transformation of energy. If induced currents accelerated the motion that caused them, then work would be created out of nothing. The coil itself, after a slight push, would rush towards the magnet, and at the same time the induction current would release heat in it. In reality, the induced current is created due to the work of bringing the magnet and the coil closer together.
Why does induced current occur? A profound explanation of the phenomenon of electromagnetic induction was given by the English physicist James Clerk Maxwell, the creator of a complete mathematical theory of the electromagnetic field.
To better understand the essence of the matter, consider a very simple experiment. Let the coil consist of one turn of wire and be penetrated by an alternating magnetic field perpendicular to the plane of the turn. An induced current naturally arises in the coil. Maxwell interpreted this experiment exceptionally boldly and unexpectedly. When a magnetic field changes in space, according to Maxwell, a process arises for which the presence of a wire coil has no significance. The main thing here is the emergence of closed annular electric field lines, covering a changing magnetic field.
Under the influence of the resulting electric field, electrons begin to move, and an electric current arises in the coil. A coil is simply a device that detects an electric field. The essence of the phenomenon of electromagnetic induction is that an alternating magnetic field always generates an electric field with closed lines of force in the surrounding space. Such a field is called a vortex field.”
Research in the field of induction produced by terrestrial magnetism gave Faraday the opportunity to express the idea of a telegraph back in 1832, which then formed the basis of this invention.
In general, the discovery of electromagnetic induction is not without reason considered one of the most outstanding discoveries of the 19th century - the work of millions of electric motors and electric current generators all over the world is based on this phenomenon...
>> Discovery of electromagnetic induction
Chapter 2. ELECTROMAGNETIC INDUCTION
So far we have considered electric and magnetic fields that do not change over time. It was found that the electrostatic field is created by stationary charged particles, and the magnetic field by moving ones, i.e. electric current. Now let's get acquainted with electric and magnetic fields, which change over time.
The most important fact that was discovered is the close relationship between electric and magnetic fields. It turned out that a time-varying magnetic field generates an electric field, and a changing electric field generates a magnetic field. Without this connection between fields, the variety of manifestations of electromagnetic forces would not be as extensive as they actually are. There would be no radio waves or light.
§ 8 DISCOVERY OF ELECTROMAGNETIC INDUCTION
In 1821, M. Faraday wrote in his diary: “Convert magnetism into electricity.” After 10 years, he solved this problem.
It is no coincidence that the first, decisive step in the discovery of new properties of electromagnetic interactions was made by the founder of the concept of the electromagnetic field, M. Faraday, who was confident in the unified nature of electrical and magnetic phenomena. Thanks to this, he made a discovery that became the basis for the design of generators in all power plants in the world, converting mechanical energy into electrical energy. (Sources operating on other principles: galvanic cells, batteries, etc., provide an insignificant share of the generated electrical energy.)
Electric current, M. Faraday reasoned, is capable of magnetizing a piece of iron. Couldn't a magnet, in turn, cause an electric current? For a long time this connection could not be discovered. It was difficult to figure out the main thing, namely: a moving magnet, or a time-varying magnetic field, can excite an electric current in a coil.
The following fact shows what kind of accidents could have prevented the discovery. Almost simultaneously with Faraday, the Swiss physicist Colladon tried to obtain an electric current in a coil using a magnet. During his work, he used a galvanometer, the light magnetic needle of which was placed inside the coil of the device. To prevent the magnet from directly influencing the needle, the ends of the coil into which Colladon inserted the magnet, hoping to generate current in it, were taken to the next room and there connected to a galvanometer. Having inserted the magnet into the coil, Colladon went into the next room and was disappointed to see that the galvanometer did not show any current. If he had only to watch the galvanometer all the time and ask someone to work on the magnet, a remarkable discovery would have been made. But this did not happen. A magnet at rest relative to the coil does not generate current in it.
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