Discovery of the phenomenon of electromagnetic induction magnetic flux. Faraday

Lesson topic:

Opening electromagnetic induction. magnetic flux.

Target: introduce students to the phenomenon of electromagnetic induction.

During the classes

I. Organizational moment

II. Knowledge update.

1. Frontal survey.

What is Ampère's hypothesis?
What is magnetic permeability?
What substances are called para- and diamagnets?
What are ferrites?
Where are ferrites used?
How do you know that there is a magnetic field around the Earth?
Where are the North and South magnetic poles of the Earth?
What processes take place in the Earth's magnetosphere?
What is the reason for existence magnetic field at the earth?

2. Analysis of experiments.

Experiment 1

The magnetic needle on the stand was brought to the lower and then to the upper end of the tripod. Why does the arrow turn to the lower end of the tripod from either side with the south pole, and to the upper end - the north end?(All iron objects are in the Earth's magnetic field. Under the influence of this field, they are magnetized, and the lower part of the object detects the north magnetic pole, and the top - the south.)

Experiment 2

In a large cork stopper, make a small groove for a piece of wire. Lower the cork into the water, and put the wire on top, placing it along the parallel. In this case, the wire, together with the cork, is rotated and installed along the meridian. Why?(The wire has been magnetized and is set in the Earth's field like a magnetic needle.)

III. Learning new material

Between moving electric charges magnetic forces act. Magnetic interactions are described based on the concept of a magnetic field that exists around moving electric charges. Electric and magnetic fields are generated by the same sources - electric charges. It can be assumed that there is a connection between them.

In 1831, M. Faraday confirmed this experimentally. He discovered the phenomenon of electromagnetic induction (slides 1.2).

Experiment 1

We connect the galvanometer to the coil, and we will put forward a permanent magnet from it. We observe the deviation of the galvanometer needle, a current (induction) has appeared (slide 3).

The current in the conductor occurs when the conductor is in the area of \u200b\u200bthe alternating magnetic field (slide 4-7).

Faraday represented an alternating magnetic field as a change in the number of lines of force penetrating the surface bounded by a given contour. This number depends on the induction AT magnetic field, from the contour area S and its orientation in the given field.

F \u003d BS cos a - magnetic flux.

F [Wb] Weber (slide 8)

The induction current can have different directions, which depend on whether the magnetic flux penetrating the circuit decreases or increases. The rule for determining the direction of the induced current was formulated in 1833. E. X. Lenz.

Experiment 2

We slide a permanent magnet into a light aluminum ring. The ring is repelled from it, and when extended, it is attracted to the magnet.

The result does not depend on the polarity of the magnet. Repulsion and attraction is explained by the appearance of an induction current in it.

When the magnet is pushed in, the magnetic flux through the ring increases: the repulsion of the ring at the same time shows that the induction current in it has such a direction in which the induction vector of its magnetic field is opposite in direction to the induction vector of the external magnetic field.

Lenz's rule:

The induction current always has such a direction that its magnetic field prevents any changes in the magnetic flux, causing appearance induction current(slide 9).

IV. Conducting laboratory work

Laboratory work on the topic "Experimental verification of the Lenz rule"

Devices and materials:milliammeter, coil-coil, arcuate magnet.

Working process

Prepare a table.

The magnetic induction vector \(~\vec B\) characterizes the magnetic field at each point in space. Let us introduce one more quantity that depends on the value of the magnetic induction vector not at one point, but at all points of an arbitrarily chosen surface. This quantity is called the flux of the magnetic induction vector, or magnetic flux.

Let us isolate in the magnetic field such a small surface element with area Δ S so that the magnetic induction at all its points can be considered the same. Let \(~\vec n\) be the normal to the element forming the angle α with the direction of the magnetic induction vector (Fig. 1).

The flux of the magnetic induction vector through the surface area Δ S call the value equal to the product of the modulus of the magnetic induction vector \(~\vec B\) and the area Δ S and the cosine of the angle α between the vectors \(~\vec B\) and \(~\vec n\) (normal to the surface):

\(~\Delta \Phi = B \cdot \Delta S \cdot \cos \alpha\) .

Work B cos α = AT n is the projection of the magnetic induction vector onto the normal to the element. So

\(~\Delta \Phi = B_n \cdot \Delta S\) .

The flow can be either positive or negative depending on the value of the angle α .

If the magnetic field is uniform, then the flux through a flat surface with area S equals:

\(~\Phi = B \cdot S \cdot \cos \alpha\) .

The flux of magnetic induction can be clearly interpreted as a quantity proportional to the number of lines of the vector \(~\vec B\) penetrating a given area of the surface.

Generally speaking, the surface can be closed. In this case, the number of induction lines entering the inside of the surface is equal to the number of lines leaving it (Fig. 2). If the surface is closed, then the outer normal is considered to be the positive normal to the surface.

The lines of magnetic induction are closed, which means that the flux of magnetic induction through a closed surface is equal to zero. (Lines leaving the surface give a positive flux, and lines entering a negative one.) This fundamental property of a magnetic field is due to the absence of magnetic charges. If there were no electric charges, then the electric flux through a closed surface would be zero.

Electromagnetic induction

Discovery of electromagnetic induction

In 1821, Michael Faraday wrote in his diary: "Turn magnetism into electricity." After 10 years, this problem was solved by him.

M. Faraday was confident in the unified nature of electrical and magnetic phenomena, but for a long time the relationship between these phenomena could not be detected. It was hard to think of the main point: only a time-varying magnetic field can excite an electric current in a fixed coil, or the coil itself must move in a magnetic field.

The discovery of electromagnetic induction, as Faraday called this phenomenon, was made on August 29, 1831. Here short description first experience given by Faraday himself. “A copper wire 203 feet long (a foot equals 304.8 mm) was wound on a wide wooden coil, and a wire of the same length was wound between its turns, but isolated from the first 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, it was possible to notice a sudden, but extremely weak effect on the galvanometer, and the same was noticed when the current stopped. With the continuous passage of current through one of the coils, it was not possible to note any effect on the galvanometer, or in general any inductive effect on the other coil, despite the fact that the heating of the entire coil connected to the battery, and the brightness of the spark jumping between the coals, testified about battery power.

So, initially, induction was discovered in conductors that were motionless relative to each other during the closing and opening of the circuit. Then, clearly understanding that the approach or removal of conductors with current should lead to the same result as closing and opening the circuit, Faraday proved through experiments that current arises when the coils move relative to each other (Fig. 3).

Familiar with the works of Ampère, Faraday understood that a magnet is a collection of small currents circulating in molecules. On October 17, as recorded in his laboratory journal, an induction current was detected in the coil during the pushing in (or pulling out) of the magnet (Fig. 4).

Within one month, Faraday experimentally discovered all the essential features of the phenomenon of electromagnetic induction. It only remained to give the law a strict quantitative form and fully reveal the physical nature of the phenomenon. Faraday himself already grasped the common thing that determines the appearance of an induction current in experiments that look different outwardly.

In a closed conducting circuit, a current arises when the number of magnetic induction lines penetrating the surface bounded by this circuit changes. This phenomenon is called electromagnetic induction.

And the faster the number of lines of magnetic induction changes, the greater the resulting current. In this case, the reason for the change in the number of lines of magnetic induction is completely indifferent. This can be a change in the number of lines of magnetic induction penetrating a fixed conductor due to a change in the current strength in an adjacent coil, and a change in the number of lines due to the movement of the circuit in an inhomogeneous magnetic field, the density of lines of which varies in space (Fig. 5).

Lenz's rule

The inductive current that has arisen in the conductor immediately begins to interact with the current or magnet that generated it. If a magnet (or a coil with current) is brought closer to a closed conductor, then the emerging induction current with its magnetic field necessarily repels the magnet (coil). Work must be done to bring the magnet and coil closer together. When the magnet is removed, attraction occurs. This rule is strictly followed. Imagine if things were different: you pushed the magnet towards the coil, and it would rush into it by itself. This would violate the law of conservation of energy. After all, the mechanical energy of the magnet would increase and at the same time a current would arise, which in itself requires the expenditure of energy, because the current can also do work. The electric current induced in the generator armature, interacting with the magnetic field of the stator, slows down the rotation of the armature. Only therefore, to rotate the armature, it is necessary to do work, the greater, the greater the current strength. Due to this work, an induction current arises. It is interesting to note that if the magnetic field of our planet were very large and highly inhomogeneous, then fast movements of conducting bodies on its surface and in the atmosphere would be impossible due to the intense interaction of the current induced in the body with this field. The bodies would move as in a dense viscous medium and at the same time would be strongly heated. Neither airplanes nor rockets could fly. A person could not quickly move either his arms or legs, since human body- a good conductor.

If the coil in which the current is induced is stationary relative to the neighboring coil with alternating current, as, for example, in a transformer, then in this case the direction of the induction current is dictated by the law of conservation of energy. This current is always directed in such a way that the magnetic field it creates tends to reduce current variations in the primary.

The repulsion or attraction of a magnet by a coil depends on the direction of the induction current in it. Therefore, the law of conservation of energy allows us to formulate a rule that determines the direction of the induction current. What is the difference between the two experiments: the approach of the magnet to the coil and its removal? In the first case, the magnetic flux (or the number of magnetic induction lines penetrating the turns of the coil) increases (Fig. 6, a), and in the second case it decreases (Fig. 6, b). Moreover, in the first case, the lines of induction AT’ of the magnetic field created by the induction current that has arisen in the coil, exit from the upper end of the coil, since the coil repels the magnet, and in the second case, on the contrary, enter this end. These lines of magnetic induction in Figure 6 are shown with a stroke.

Rice. 6

Now we have come to the main point: with an increase in the magnetic flux through the turns of the coil, the induction current has such a direction that the magnetic field it creates prevents the growth of the magnetic flux through the turns of the coil. After all, the induction vector \ (~ \ vec B "\) of this field is directed against the induction vector \ (~ \ vec B \) of the field, the change of which generates an electric current. If the magnetic flux through the coil weakens, then the induction current creates a magnetic field with induction \(~\vec B"\) , which increases the magnetic flux through the turns of the coil.

This is the essence general rule determining the direction of the inductive current, which is applicable in all cases. This rule was established by the Russian physicist E. X. Lenz (1804-1865).

According to Lenz's rule

the induction current arising in a closed circuit has such a direction that the magnetic flux created by it through the surface bounded by the circuit tends to prevent the change in the flux that generates this current.

the inductive current has such a direction that it prevents the cause causing it.

In the case of superconductors, the compensation for changes in the external magnetic flux will be complete. The flux of magnetic induction through a surface bounded by a superconducting circuit does not change at all with time under any conditions.

Law of electromagnetic induction

Faraday's experiments showed that the strength of the induced current I i in a conducting circuit is proportional to the rate of change in the number of magnetic induction lines \(~\vec B\) penetrating the surface bounded by this circuit. More precisely, this statement can be formulated using the concept of magnetic flux.

The magnetic flux is clearly interpreted as the number of lines of magnetic induction penetrating a surface with an area S. Therefore, the rate of change of this number is nothing but the rate of change of the magnetic flux. If in a short time Δ t magnetic flux changes to Δ F, then the rate of change of the magnetic flux is \(~\frac(\Delta \Phi)(\Delta t)\) .

Therefore, a statement that follows directly from experience can be formulated as follows:

the strength of the induction current is proportional to the rate of change of the magnetic flux through the surface bounded by the contour:

\(~I_i \sim \frac(\Delta \Phi)(\Delta t)\) .

It is known that an electric current arises in the circuit when external forces act on free charges. The work of these forces when moving a single positive charge along a closed circuit is called the electromotive force. Therefore, when the magnetic flux changes through the surface bounded by the contour, external forces appear in it, the action of which is characterized by an EMF, called the induction EMF. Let's denote it with the letter E i .

The law of electromagnetic induction is formulated specifically for EMF, and not for current strength. With this formulation, the law expresses the essence of the phenomenon, which does not depend on the properties of the conductors in which the induction current occurs.

According to the law of electromagnetic induction (EMR)

The induction emf in a closed loop is equal in absolute value to the rate of change of the magnetic flux through the surface bounded by the loop:

\(~|E_i| = |\frac(\Delta \Phi)(\Delta t)|\) .

How to take into account the direction of the induction current (or the sign of the induction EMF) in the law of electromagnetic induction in accordance with the Lenz rule?

Figure 7 shows a closed loop. We will consider positive the direction of bypassing the contour counterclockwise. The normal to the contour \(~\vec n\) forms a right screw with the bypass direction. The sign of the EMF, i.e., specific work, depends on the direction of external forces with respect to the direction of bypassing the circuit. If these directions coincide, then E i > 0 and, accordingly, I i > 0. Otherwise, the EMF and current strength are negative.

Let the magnetic induction \(~\vec B\) of the external magnetic field be directed along the normal to the contour and increase with time. Then F> 0 and \(~\frac(\Delta \Phi)(\Delta t)\) > 0. According to Lenz's rule, the induction current creates a magnetic flux F’ < 0. Линии индукции B’ of the magnetic field of the induction current are shown in Figure 7 with a dash. Therefore, the induction current I i is directed clockwise (against the positive bypass direction) and the induction emf is negative. Therefore, in the law of electromagnetic induction, there must be a minus sign:

\(~E_i = - \frac(\Delta \Phi)(\Delta t)\) .

AT international system units, the law of electromagnetic induction is used to establish the unit of magnetic flux. This unit is called the weber (Wb).

Since the EMF of induction E i is expressed in volts, and time is in seconds, then from the Weber EMP law can be determined as follows:

the magnetic flux through the surface bounded by a closed loop is equal to 1 Wb, if, with a uniform decrease in this flux to zero in 1 s, an induction emf equal to 1 V occurs in the loop:

1 Wb \u003d 1 V ∙ 1 s.

Vortex field

Changing in time, the magnetic field generates an electric field. J. Maxwell was the first to come to this conclusion.

Now the phenomenon of electromagnetic induction appears before us in a new light. The main thing in it is the process of generating an electric field by a magnetic field. In this case, the presence of a conductive circuit, such as a coil, does not change the essence of the matter. A conductor with a supply of free electrons (or other particles) only helps to detect the emerging electric field. The field sets the electrons in motion in the conductor and thereby reveals itself. The essence of the phenomenon of electromagnetic induction in a fixed conductor is not so much in the appearance of an induction current, but in the occurrence electric field that drives electric charges.

The electric field that occurs when the magnetic field changes has a completely different structure than the electrostatic one. It is not connected directly with electric charges, and its lines of tension cannot begin and end on them. They generally do not begin or end anywhere, but are closed lines, similar to the lines of magnetic field induction. This so-called vortex electric field. The question may arise: why, in fact, is this field called electric? After all, it has a different origin and a different configuration than the static electric field. The answer is simple: the vortex field acts on the charge q in the same way as the electrostatic one, and we considered and still consider this the main property of the field. The force acting on the charge is still \(~\vec F = q \vec E\) , where \(~\vec E\) is the intensity of the vortex field. If the magnetic flux is created by a uniform magnetic field concentrated in a long narrow cylindrical tube with a radius r 0 (Fig. 8), it is obvious from symmetry considerations that the lines of electric field strength lie in planes perpendicular to the lines \(~\vec B\) and are circles. In accordance with the Lenz rule, as the magnetic induction \(~\left (\frac(\Delta B)(\Delta t) > 0 \right)\) increases, the field lines \(~\vec E\) form a left screw with the direction of the magnetic induction \(~\vec B\) .

Unlike a static or stationary electric field, the work of a vortex field on a closed path is not equal to zero. Indeed, when a charge moves along closed line electric field strength, the work on all sections of the path has the same sign, since the force and displacement coincide in direction. A vortex electric field, like a magnetic field, is not potential.

The work of the vortex electric field in moving a single positive charge along a closed fixed conductor is numerically equal to the induction EMF in this conductor.

So, an alternating magnetic field generates a vortex electric field. But don't you think that one statement is not enough here? I would like to know what is the mechanism of this process. Is it possible to explain how this connection of fields is realized in nature? And this is where your natural curiosity cannot be satisfied. There is simply no mechanism here. The law of electromagnetic induction is a fundamental law of nature, which means it is basic, primary. Many phenomena can be explained by its action, but it itself remains inexplicable simply for the reason that there are no deeper laws from which it would follow as a consequence. In any case, such laws are currently unknown. These are all the basic laws: the law of gravity, Coulomb's law, etc.

Of course, we are free to put any questions before nature, but not all of them make sense. Thus, for example, it is possible and necessary to investigate the causes of various phenomena, but it is useless to try to find out why causality exists at all. Such is the nature of things, such is the world in which we live.

Literature

Zhilko V.V. Physics: Proc. allowance for the 10th grade. general education school from Russian lang. training / V.V. Zhilko, A.V. Lavrinenko, L.G. Markovich. - Mn.: Nar. Asveta, 2001. - 319 p.
Myakishev, G.Ya. Physics: Electrodynamics. 10-11 cells. : studies. for in-depth study of physics / G.Ya. Myakishev, A.3. Sinyakov, V.A. Slobodskov. – M.: Bustard, 2005. – 476 p.

Answer:

The next important step in the development of electrodynamics after Ampère's experiments was the discovery of the phenomenon of electromagnetic induction. The English physicist Michael Faraday (1791 - 1867) discovered the phenomenon of electromagnetic induction.

Faraday, still a young scientist, like Oersted, thought that all the forces of nature are interconnected and, moreover, that they are capable of transforming into each other. It is interesting that Faraday expressed this idea even before the establishment of the law of conservation and transformation of energy. Faraday knew about the discovery of Ampere, that he, figuratively speaking, turned electricity into magnetism. Reflecting on this discovery, Faraday came to the conclusion that if "electricity creates magnetism", then vice versa, "magnetism must create electricity." And back in 1823, he wrote in his diary: "Turn magnetism into electricity." For eight years, Faraday worked on solving the problem. Long time he was pursued by failures, and, finally, in 1831 he solved it - he discovered the phenomenon of electromagnetic induction.

First, Faraday discovered the phenomenon of electromagnetic induction for the case when the coils are wound on the same drum. If an electric current arises or disappears in one coil as a result of a galvanic battery being connected to or disconnected from it, then a short-term current appears in the other coil at that moment. This current is detected by a galvanometer which is connected to the second coil.

Then Faraday also established the presence of an induction current in the coil when a coil was approached or moved away from it, in which an electric current flowed.

finally, the third case of electromagnetic induction, which Faraday discovered, was that a current appeared in the coil when a magnet was inserted or removed from it.

Faraday's discovery attracted the attention of many physicists, who also began to study the features of the phenomenon of electromagnetic induction. The next task was to establish the general law of electromagnetic induction. It was necessary to find out how and on what the strength of the induction current in the conductor depends or on what the value of the electromotive force of induction in the conductor in which the electric current is induced depends.

This task proved difficult. It was completely solved by Faraday and Maxwell later in the framework of the doctrine they developed about the electromagnetic field. But physicists also tried to solve it, who adhered to the long-range theory common for that time in the doctrine of electrical and magnetic phenomena.

Something these scientists managed to do. At the same time, they were helped by the rule discovered by the St. Petersburg academician Emil Khristianovich Lenz (1804 - 1865) for finding the direction of the induction current in different occasions electromagnetic induction. Lenz formulated it as follows: “If a metal conductor moves near a galvanic current or a magnet, then a galvanic current is excited in it in such a direction that if this conductor were stationary, then the current could cause it to move in the opposite direction; it is assumed that the conductor at rest can only move in the direction of motion or in the opposite direction.

This rule is very convenient for determining the direction of the inductive current. We use it even now, only now it is formulated a little differently, with the burial of the concept of electromagnetic induction, which Lenz did not use.

But historically, the main significance of Lenz's rule was that it prompted the idea of how to approach finding the law of electromagnetic induction. The fact is that in the atom rule a connection is established between electromagnetic induction and the phenomenon of the interaction of currents. The question of the interaction of currents was already solved by Ampère. Therefore, the establishment of this connection at first made it possible to determine the expression for the electromotive force of induction in a conductor for a number of special cases.

AT general view the law of electromagnetic induction, as we have said about it, was established by Faraday and Maxwell.

Electromagnetic induction - the phenomenon of occurrence electric current in a closed circuit with a change in the magnetic flux passing through it.

Electromagnetic induction was discovered by Michael Faraday on August 29, 1831. He found that the electromotive force that occurs in a closed conducting circuit is proportional to the rate of change of the magnetic flux through the surface bounded by this circuit. The magnitude of the electromotive force (EMF) does not depend on what causes the change in the flux - a change in the magnetic field itself or the movement of a circuit (or part of it) in a magnetic field. The electric current caused by this EMF is called the induction current.

Self-induction - the occurrence of an EMF of induction in a closed conducting circuit when the current flowing through the circuit changes.

When the current in the circuit changes, the magnetic flux through the surface bounded by this circuit also changes proportionally. A change in this magnetic flux, due to the law of electromagnetic induction, leads to the excitation of an inductive EMF in this circuit.

This phenomenon is called self-induction. (The concept is related to the concept of mutual induction, being, as it were, its special case).

Direction EMF self-induction it always turns out to be such that when the current in the circuit increases, the EMF of self-induction prevents this increase (directed against the current), and when the current decreases, it decreases (co-directed with the current). With this property, the self-induction EMF is similar to the force of inertia.

The creation of the first relay was preceded by the invention in 1824 by the Englishman Sturgeon of an electromagnet - a device that converts the input electric current of a wire coil wound on an iron core into a magnetic field generated inside and outside this core. The magnetic field was fixed (detected) by its effect on a ferromagnetic material located near the core. This material was attracted to the core of the electromagnet.

Subsequently, the effect of converting the energy of an electric current into mechanical energy of a meaningful movement of an external ferromagnetic material (armature) formed the basis of various electromechanical telecommunication devices (telegraphy and telephony), electrical engineering, and the electric power industry. One of the first such devices was an electromagnetic relay, invented by the American J. Henry in 1831.

FARADEUS. DISCOVERY OF ELECTROMAGNETIC INDUCTION

Obsessed with ideas about the inseparable connection and interaction of the forces of nature, Faraday tried to prove that just as Ampère could create magnets with electricity, so it is possible to create electricity with the help of magnets.

Its logic was simple: mechanical work easily turns into heat; Conversely, heat can be converted into mechanical work(let's say in steam engine). In general, among the forces of nature, the following relationship most often occurs: if A gives birth to B, then B gives birth to A.

If by means of electricity Ampère obtained magnets, then, apparently, it is possible to "obtain electricity from ordinary magnetism." Arago and Ampère set themselves the same task in Paris, Colladon in Geneva.

Faraday puts on a lot of experiments, keeps pedantic notes. He devotes a paragraph to each small study in his laboratory notes (published in London in full in 1931 under the title "Faraday's Diary"). At least the fact that the last paragraph of the Diary is marked with the number 16041 speaks of Faraday's efficiency.

In addition to an intuitive conviction in the universal connection of phenomena, nothing, in fact, supported him in his search for "electricity from magnetism". In addition, he, like his teacher Devi, relied more on his own experiments than on mental constructions. Davy taught him:

A good experiment is of more value than the thoughtfulness of a genius like Newton.

Nevertheless, it was Faraday who was destined for great discoveries. A great realist, he spontaneously tore the fetters of empiricism, once imposed on him by Devi, and in those moments a great insight dawned on him - he acquired the ability for the deepest generalizations.

The first glimmer of luck appeared only on August 29, 1831. On this day, Faraday was testing a simple device in the laboratory: an iron ring about six inches in diameter, wrapped around two pieces of insulated wire. When Faraday connected a battery to the terminals of one winding, his assistant, artillery sergeant Andersen, saw the needle of a galvanometer connected to the other winding twitch.

Twitched and calmed though D.C. continued to flow through the first winding. Faraday carefully reviewed all the details of this simple installation - everything was in order.

But the galvanometer needle stubbornly stood at zero. Out of annoyance, Faraday decided to turn off the current, and then a miracle happened - during the opening of the circuit, the galvanometer needle swung again and again froze at zero!

Faraday was at a loss: first, why does the needle behave so strangely? Secondly, are the bursts he noticed related to the phenomenon he was looking for?

It was then that Ampère's great ideas, the connection between electric current and magnetism, were revealed in all clarity to Faraday. After all, the first winding into which he applied current immediately became a magnet. If we consider it as a magnet, then the experiment on August 29 showed that magnetism seemed to give rise to electricity. Only two things remained strange in this case: why did the surge of electricity when the electromagnet was turned on quickly fade away? And moreover, why does the surge appear when the magnet is turned off?

The next day, August 30, - new series experiments. The effect is clearly expressed, but nevertheless completely incomprehensible.

Faraday feels that the opening is somewhere nearby.

“I am now again engaged in electromagnetism and I think that I have attacked a successful thing, but I cannot yet confirm this. It may very well be that after all my labors, I will eventually pull out seaweed instead of fish.

By the next morning, September 24, Faraday had prepared a lot various devices, in which the main elements were no longer windings with electric current, but permanent magnets. And there was an effect too! The arrow deviated and immediately rushed into place. This slight movement occurred during the most unexpected manipulations with the magnet, sometimes, it seemed, by chance.

The next experiment is October 1st. Faraday decides to return to the very beginning - to two windings: one with current, the other connected to a galvanometer. The difference with the first experiment is the absence of a steel ring - the core. The splash is almost imperceptible. The result is trivial. It is clear that a magnet without a core is much weaker than a magnet with a core. Therefore, the effect is less pronounced.

Faraday is disappointed. For two weeks he does not approach the instruments, thinking about the reasons for the failure.

Faraday knows in advance how it will be. The experience works out brilliantly.

"I took a cylindrical magnetic bar (3/4" in diameter and 8 1/4" long) and inserted one end of it into a spiral of copper wire(220 feet long) connected to a galvanometer. Then, with a quick movement, I pushed the magnet into the entire length of the spiral, and the needle of the galvanometer experienced a shock. Then I just as quickly pulled the magnet out of the spiral, and the needle swung again, but in the opposite direction. These swings of the needle were repeated each time the magnet was pushed in or out."

The secret is in the movement of the magnet! The impulse of electricity is determined not by the position of the magnet, but by the movement!

This means that "an electric wave arises only when the magnet moves, and not due to the properties inherent in it at rest."

This idea is remarkably fruitful. If the movement of a magnet relative to a conductor creates electricity, then, apparently, the movement of a conductor relative to a magnet must also generate electricity! Moreover, this "electric wave" will not disappear as long as the mutual movement of the conductor and the magnet continues. This means that it is possible to create an electric current generator that operates for an arbitrarily long time, as long as the mutual movement of the wire and the magnet continues!

On October 28, Faraday installed a rotating copper disk between the poles of a horseshoe magnet, from which, with the help of sliding contacts (one on the axis, the other on the periphery of the disk), it was possible to remove electrical voltage. It was the first electrical generator created by human hands.

After the "electromagnetic epic" Faraday was forced to stop his scientific work for several years - his nervous system was so exhausted ...

Experiments similar to Faraday's, as already mentioned, were carried out in France and Switzerland. Colladon, a professor at the Geneva Academy, was a sophisticated experimenter (he, for example, produced on Lake Geneva accurate measurements speed of sound in water). Perhaps, fearing the shaking of the instruments, he, like Faraday, removed the galvanometer as far as possible from the rest of the installation. Many claimed that Colladon observed the same fleeting movements of the arrow as Faraday, but, expecting a more stable, lasting effect, did not attach due importance to these “random” bursts ...

Indeed, the opinion of most scientists of that time was that the reverse effect of "creating electricity from magnetism" should, apparently, have the same stationary character as the "direct" effect - "forming magnetism" due to electric current. The unexpected "transience" of this effect baffled many, including Colladon, and these many paid for their prejudice.

Faraday, too, was at first embarrassed by the transience of the effect, but he trusted facts more than theories, and eventually came to the law of electromagnetic induction. This law then seemed to physicists flawed, ugly, strange, devoid of internal logic.

Why is the current excited only during the movement of the magnet or the change in current in the winding?

Nobody understood this. Even Faraday himself. Seventeen years later, the twenty-six-year-old army surgeon of the provincial garrison in Potsdam, Hermann Helmholtz, understood this. In the classic article "On the Conservation of Force", he, formulating his law of conservation of energy, proved for the first time that electromagnetic induction must exist in this "ugly" form.

Maxwell's older friend, William Thomson, also came to this independently. He also obtained Faraday's electromagnetic induction from Ampère's law, taking into account the law of conservation of energy.

So the "fleeting" electromagnetic induction acquired the rights of citizenship and was recognized by physicists.

But it did not fit into the concepts and analogies of Maxwell's article "On Faraday lines of force". And this was a serious shortcoming of the article. In practice, its significance was reduced to illustrating the fact that the theories of short-range and long-range interactions represent different mathematical descriptions of the same experimental data, that Faraday's lines of force do not contradict common sense. And it's all. Everything, although it was already a lot.

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After discoveries Oersted and Ampere it became clear that electricity has a magnetic force. Now it was necessary to confirm the influence of magnetic phenomena on electrical ones. This problem was brilliantly solved by Faraday.

Michael Faraday (1791-1867) was born in London, one of the poorest parts of it. 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 taken by Faraday here was very narrow and limited only to teaching reading, writing, and the beginning of counting.

A few steps from the house where the Faraday family lived, there was a bookstore, which was also a bookbinding establishment. This is where Faraday got to, having completed the course elementary school when the question arose about choosing a profession for him. Michael at that time was only 13 years old. Already in his youth, when Faraday had just begun his self-education, he strove to rely solely on facts and verify the reports of others with his own experiences.

These aspirations dominated him all his life as the main features of his scientific activity. chemical experiments Faraday began to do it as a boy at the first acquaintance with physics and chemistry. Once Michael attended one of the lectures Humphrey 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 offered Faraday to work with him as a secretary. Soon Davy went on a trip to Europe and took Faraday with him. For 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 physical laboratories in the world. From 1816 to 1818 Faraday published a number of small notes and small memoirs on chemistry. Faraday's first work on physics dates back to 1818.

Based on the experiences of their predecessors and combining several own experiences, by September 1821 Michael had typed "The success story of electromagnetism". Already at that time, he made up a completely correct concept of the essence of the phenomenon of deflection of a magnetic needle under the action of a 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 first achieved the liquefaction of a gas, and at the same time established a simple but valid method for converting gases into a 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. AT next year Faraday again turns from physics to chemistry, and the result of his work in this area is the discovery of gasoline and sulfuric naphthalene acid.

In 1831, Faraday published a treatise On a Special Kind of Optical Illusion, which served as the basis for a beautiful 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 by themselves immortalize the name of their author. But the most important of scientific works Faraday are his research in the field of e electromagnetism and electrical induction.

Strictly speaking, the important branch of physics, which treats the phenomena of electromagnetism and inductive electricity, and which is currently of such great 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 with ordinary conditions the presence of an electrified body is sufficient for its influence to excite electricity in every other body. At the same time, it was known that the wire through which the current passes and which is also 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 major discoveries in the field of induction electricity. As usual, Faraday began a series of experiments that were supposed 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 elements, and the ends of the other to a sensitive galvanometer. When the current was passed through the first wire,

Faraday turned all his attention to the galvanometer, expecting to notice from its oscillations the appearance of a current in the second wire as well. However, there was nothing of the kind: the galvanometer remained calm. Faraday decided to increase the current and introduced 120 galvanic cells into the circuit. The result is the same. Faraday repeated this experiment dozens of times, all with the same success.

Anyone else in his place would have left the experiment, convinced that the current passing through the wire has no effect on the adjacent wire. But Faraday always tried to extract from his experiments and observations everything that they could give, and therefore, not having received 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 the current, began to oscillate at the very closing of the circuit and at its opening. the second wire is also excited by a current, which in the first case has the opposite direction to the first current and is the same with it in the second case and lasts only one instant.

These secondary instantaneous currents, caused by the influence of primary ones, were called inductive by Faraday, and this name has been preserved for them until now. 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 (commutator), to constantly interrupt and again conduct the primary current coming from the battery through the first wire, due to which in the second wire is continuously excited by more and more inductive currents, thus becoming constant. So a new source was found electrical energy, in addition to previously known (friction and chemical processes), - induction, and the new kind this energy - induction electricity.

Continuing his experiments, Faraday further discovered that a simple approximation of a wire twisted into a closed curve to another, along which a galvanic current flows, is enough to excite an inductive current in the direction opposite to the galvanic current in a neutral wire, that the removal of a neutral wire again excites an inductive current in it. the current is already in the same direction as the galvanic current flowing along a fixed 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 during the closing and termination of the galvanic current. These discoveries in turn gave rise to new ones. If it is possible to produce an inductive current by closing and stopping the galvanic current, would not the same result be obtained from the magnetization and demagnetization of iron?

The work of Oersted and Ampère 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 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; moreover, one wire was wound around one half of the ring, and the other around the other. A 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 oscillated rapidly and then quickly stopped, that is, all 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 band. Instead of exciting magnetism in iron with a galvanic current, he magnetized the iron by touching it to a permanent steel magnet. The result was the same: in the wire wrapped around the iron, always! the 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 in the wire induction currents. In a word, magnetism, in the sense of excitation of inductive currents, acted in exactly the same way as the galvanic current.