Opposite magnetic poles attract and like ones attract. Opposite magnetic poles attract, like magnetic poles repel

There are two magnets different types. Some are so-called permanent magnets, made from “hard magnetic” materials. Their magnetic properties are not related to the use of external sources or currents. Another type includes the so-called electromagnets with a core made of “soft magnetic” iron. The magnetic fields they create are mainly due to the fact that the wire of the winding surrounding the core passes electric current.

Magnetic poles and magnetic field.

The magnetic properties of a bar magnet are most noticeable near its ends. If such a magnet is hung by the middle part so that it can rotate freely in a horizontal plane, then it will take a position approximately corresponding to the direction from north to south. The end of the rod pointing north is called the north pole, and the opposite end is called the south pole. Opposite poles of two magnets attract each other, and like poles repel each other.

If a bar of non-magnetized iron is brought close to one of the poles of a magnet, the latter will become temporarily magnetized. In this case, the pole of the magnetized bar closest to the pole of the magnet will be opposite in name, and the far one will have the same name. The attraction between the pole of the magnet and the opposite pole induced by it in the bar explains the action of the magnet. Some materials (such as steel) themselves become weak permanent magnets after being near a permanent magnet or electromagnet. A steel rod can be magnetized by simply passing the end of a permanent bar magnet along its end.

So, a magnet attracts other magnets and objects from magnetic materials without being in contact with them. This action at a distance is explained by the existence in the space around the magnet magnetic field. Some idea of ​​the intensity and direction of this magnetic field can be obtained by pouring iron filings onto a sheet of cardboard or glass placed on a magnet. The sawdust will line up in chains in the direction of the field, and the density of the sawdust lines will correspond to the intensity of this field. (They are thickest at the ends of the magnet, where the intensity of the magnetic field is greatest.)

M. Faraday (1791–1867) introduced the concept of closed induction lines for magnets. The induction lines extend into the surrounding space from the magnet at its north pole, enter the magnet at its south pole, and pass inside the magnet material from the south pole back to the north, forming a closed loop. Full number The induction lines coming out of a magnet is called magnetic flux. Density magnetic flux, or magnetic induction ( IN), is equal to the number of induction lines passing along the normal through an elementary area of ​​unit size.

Magnetic induction determines the force with which a magnetic field acts on a current-carrying conductor located in it. If the conductor through which the current passes I, is located perpendicular to the induction lines, then according to Ampere’s law the force F, acting on the conductor, is perpendicular to both the field and the conductor and is proportional to the magnetic induction, current strength and length of the conductor. Thus, for magnetic induction B you can write an expression

Where F– force in newtons, I– current in amperes, l– length in meters. The unit of measurement for magnetic induction is tesla (T).

Galvanometer.

A galvanometer is a sensitive instrument for measuring weak currents. A galvanometer uses the torque produced by the interaction of a horseshoe-shaped permanent magnet with a small current-carrying coil (a weak electromagnet) suspended in the gap between the poles of the magnet. The torque, and therefore the deflection of the coil, is proportional to the current and the total magnetic induction in the air gap, so that the scale of the device is almost linear for small deflections of the coil.

Magnetizing force and magnetic field strength.

Next, we should introduce another quantity characterizing the magnetic effect of electric current. Suppose that current passes through the wire of a long coil, inside of which there is a magnetizable material. The magnetizing force is the product of the electric current in the coil and the number of its turns (this force is measured in amperes, since the number of turns is a dimensionless quantity). Magnetic field strength N equal to the magnetizing force per unit length of the coil. Thus, the value N measured in amperes per meter; it determines the magnetization acquired by the material inside the coil.

In a vacuum magnetic induction B proportional to the magnetic field strength N:

Where m 0 – so-called magnetic constant having a universal value of 4 p H 10 –7 H/m. In many materials the value B approximately proportional N. However, in ferromagnetic materials the ratio between B And N somewhat more complicated (as will be discussed below).

In Fig. 1 shows a simple electromagnet designed to grip loads. The energy source is a DC battery. The figure also shows the field lines of the electromagnet, which can be detected by the usual method of iron filings.

Large electromagnets with iron cores and very a large number ampere-turns operating in continuous mode have a large magnetizing force. They create a magnetic induction of up to 6 Tesla in the gap between the poles; this induction is limited only by mechanical stress, heating of the coils and magnetic saturation of the core. A number of giant water-cooled electromagnets (without a core), as well as installations for creating pulsed magnetic fields, were designed by P.L. Kapitsa (1894–1984) in Cambridge and at the Institute of Physical Problems of the USSR Academy of Sciences and F. Bitter (1902–1967) in Massachusetts Institute of Technology. With such magnets it was possible to achieve induction of up to 50 Tesla. A relatively small electromagnet that produces fields of up to 6.2 Tesla, consumes 15 kW of electrical power and is cooled by liquid hydrogen, was developed at the Losalamos National Laboratory. Similar fields are obtained at cryogenic temperatures.

Magnetic permeability and its role in magnetism.

Magnetic permeability m is a quantity characterizing the magnetic properties of a material. Ferromagnetic metals Fe, Ni, Co and their alloys have very high maximum permeabilities - from 5000 (for Fe) to 800,000 (for supermalloy). In such materials at relatively low field strengths H large inductions occur B, but the relationship between these quantities is, generally speaking, nonlinear due to the phenomena of saturation and hysteresis, which are discussed below. Ferromagnetic materials are strongly attracted by magnets. They lose their magnetic properties at temperatures above the Curie point (770° C for Fe, 358° C for Ni, 1120° C for Co) and behave like paramagnets, for which induction B up to very high tension values H is proportional to it - exactly the same as it is in a vacuum. Many elements and compounds are paramagnetic at all temperatures. Paramagnetic substances are characterized by the fact that they become magnetized in an external magnetic field; if this field is turned off, the paramagnetic substances return to a non-magnetized state. Magnetization in ferromagnets is maintained even after the external field is turned off.

In Fig. Figure 2 shows a typical hysteresis loop for a magnetically solid (with big losses) ferromagnetic material. It characterizes the ambiguous dependence of the magnetization of a magnetically ordered material on the strength of the magnetizing field. With increasing magnetic field strength from the initial (zero) point ( 1 ) magnetization occurs along the dashed line 1 –2 , and the value m changes significantly as the magnetization of the sample increases. At the point 2 saturation is achieved, i.e. with a further increase in voltage, the magnetization no longer increases. If we now gradually decrease the value H to zero, then the curve B(H) no longer follows the same path, but passes through the point 3 , revealing, as it were, a “memory” of material about “ past history", hence the name "hysteresis". It is obvious that in this case some residual magnetization is retained (segment 1 –3 ). After changing the direction of the magnetizing field to the opposite direction, the curve IN (N) passes the point 4 , and the segment ( 1 )–(4 ) corresponds to the coercive force that prevents demagnetization. Further increase in values ​​(- H) brings the hysteresis curve to the third quadrant - the section 4 –5 . The subsequent decrease in value (- H) to zero and then increasing positive values H will lead to the closure of the hysteresis loop through the points 6 , 7 And 2 .

Hard magnetic materials are characterized by a wide hysteresis loop, covering a significant area on the diagram and therefore corresponding to large values ​​of remanent magnetization (magnetic induction) and coercive force. A narrow hysteresis loop (Fig. 3) is characteristic of soft magnetic materials, such as mild steel and special alloys with high magnetic permeability. Such alloys were created with the aim of reducing energy losses caused by hysteresis. Most of these special alloys, like ferrites, have high electrical resistance, which reduces not only magnetic losses, but also electrical losses caused by eddy currents.

Magnetic materials with high permeability are produced by annealing, carried out by holding at a temperature of about 1000 ° C, followed by tempering (gradual cooling) to room temperature. In this case, preliminary mechanical and thermal treatment, as well as the absence of impurities in the sample, are very important. For transformer cores at the beginning of the 20th century. silicon steels were developed, the value m which increased with increasing silicon content. Between 1915 and 1920, permalloys (alloys of Ni and Fe) appeared with a characteristic narrow and almost rectangular hysteresis loop. Especially high values magnetic permeability m at small values H the alloys differ in hypernic (50% Ni, 50% Fe) and mu-metal (75% Ni, 18% Fe, 5% Cu, 2% Cr), while in perminvar (45% Ni, 30% Fe, 25% Co ) value m practically constant over a wide range of changes in field strength. Among modern magnetic materials, mention should be made of supermalloy, an alloy with the highest magnetic permeability (it contains 79% Ni, 15% Fe and 5% Mo).

Theories of magnetism.

For the first time, the guess that magnetic phenomena are ultimately reduced to electrical phenomena arose from Ampere in 1825, when he expressed the idea of ​​​​closed internal microcurrents circulating in each atom of a magnet. However, without any experimental confirmation of the presence of such currents in matter (the electron was discovered by J. Thomson only in 1897, and the description of the structure of the atom was given by Rutherford and Bohr in 1913), this theory “faded.” In 1852, W. Weber suggested that every atom magnetic substance is a tiny magnet, or magnetic dipole, so that complete magnetization of a substance is achieved when all the individual atomic magnets are aligned in in a certain order(Fig. 4, b). Weber believed that molecular or atomic “friction” helps these elementary magnets maintain their order despite the disturbing influence of thermal vibrations. His theory was able to explain the magnetization of bodies upon contact with a magnet, as well as their demagnetization upon impact or heating; finally, the “reproduction” of magnets when cutting a magnetized needle or magnetic rod into pieces was also explained. And yet this theory did not explain either the origin of the elementary magnets themselves, or the phenomena of saturation and hysteresis. Weber's theory was improved in 1890 by J. Ewing, who replaced his hypothesis of atomic friction with the idea of ​​interatomic confining forces that help maintain the ordering of the elementary dipoles that make up a permanent magnet.

The approach to the problem, once proposed by Ampere, received a second life in 1905, when P. Langevin explained the behavior of paramagnetic materials by attributing to each atom an internal uncompensated electron current. According to Langevin, it is these currents that form tiny magnets that are randomly oriented when there is no external field, but acquire an orderly orientation when it is applied. In this case, the approach to complete order corresponds to saturation of magnetization. In addition, Langevin introduced the concept of a magnetic moment, which for an individual atomic magnet is equal to the product of the “magnetic charge” of a pole and the distance between the poles. Thus, the weak magnetism of paramagnetic materials is due to the total magnetic moment created by uncompensated electron currents.

In 1907, P. Weiss introduced the concept of “domain”, which became an important contribution to modern theory magnetism. Weiss imagined domains as small “colonies” of atoms, within which the magnetic moments of all atoms, for some reason, are forced to maintain the same orientation, so that each domain is magnetized to saturation. An individual domain can have linear dimensions of the order of 0.01 mm and, accordingly, a volume of the order of 10–6 mm 3. The domains are separated by so-called Bloch walls, the thickness of which does not exceed 1000 atomic sizes. The “wall” and two oppositely oriented domains are shown schematically in Fig. 5. Such walls represent “transition layers” in which the direction of domain magnetization changes.

In the general case, three sections can be distinguished on the initial magnetization curve (Fig. 6). In the initial section, the wall, under the influence of an external field, moves through the thickness of the substance until it encounters a defect crystal lattice, which stops her. By increasing the field strength, you can force the wall to move further, through the middle section between the dashed lines. If after this the field strength is again reduced to zero, then the walls will no longer return to their original position, so the sample will remain partially magnetized. This explains the hysteresis of the magnet. At the final section of the curve, the process ends with the saturation of the magnetization of the sample due to the ordering of the magnetization inside the last disordered domains. This process is almost completely reversible. Magnetic hardness is exhibited by those materials that have atomic lattice contains many defects that impede the movement of interdomain walls. This can be achieved mechanically and heat treatment, for example by compressing and then sintering the powdered material. In alnico alloys and their analogues, the same result is achieved by fusing metals into a complex structure.

In addition to paramagnetic and ferromagnetic materials, there are materials with so-called antiferromagnetic and ferrimagnetic properties. The difference between these types of magnetism is explained in Fig. 7. Based on the concept of domains, paramagnetism can be considered as a phenomenon caused by the presence in the material of small groups of magnetic dipoles, in which individual dipoles interact very weakly with each other (or do not interact at all) and therefore, in the absence of an external field, take only random orientations ( Fig. 7, A). In ferromagnetic materials, within each domain there is a strong interaction between individual dipoles, leading to their ordered parallel alignment (Fig. 7, b). In antiferromagnetic materials, on the contrary, the interaction between individual dipoles leads to their antiparallel ordered alignment, so that the total magnetic moment of each domain is zero (Fig. 7, V). Finally, in ferrimagnetic materials (for example, ferrites) there is both parallel and antiparallel ordering (Fig. 7, G), resulting in weak magnetism.

There are two convincing experimental confirmations of the existence of domains. The first of them is the so-called Barkhausen effect, the second is the method of powder figures. In 1919, G. Barkhausen established that when an external field is applied to a sample of ferromagnetic material, its magnetization changes in small discrete portions. From the point of view of domain theory, this is nothing more than an abrupt advance of the interdomain wall, encountering on its way individual defects that delay it. This effect is usually detected using a coil in which a ferromagnetic rod or wire is placed. If you alternately bring a strong magnet towards and away from the sample, the sample will be magnetized and remagnetized. Abrupt changes in the magnetization of the sample change the magnetic flux through the coil, and an induction current is excited in it. The voltage generated in the coil is amplified and fed to the input of a pair of acoustic headphones. Clicks heard through headphones indicate an abrupt change in magnetization.

To identify the domain structure of a magnet using the powder figure method, a drop of a colloidal suspension of ferromagnetic powder (usually Fe 3 O 4) is applied to a well-polished surface of a magnetized material. Powder particles settle mainly in places of maximum inhomogeneity of the magnetic field - at the boundaries of domains. This structure can be studied under a microscope. A method based on the passage of polarized light through a transparent ferromagnetic material has also been proposed.

Weiss's original theory of magnetism in its main features has retained its significance to this day, having, however, received an updated interpretation based on the idea of ​​uncompensated electron spins as a factor determining atomic magnetism. The hypothesis about the existence of an electron’s own momentum was put forward in 1926 by S. Goudsmit and J. Uhlenbeck, and at present it is electrons as spin carriers that are considered “elementary magnets”.

To explain this concept, consider (Fig. 8) a free atom of iron, a typical ferromagnetic material. Its two shells ( K And L), those closest to the nucleus are filled with electrons, with the first of them containing two and the second containing eight electrons. IN K-shell, the spin of one of the electrons is positive, and the other is negative. IN L-shell (more precisely, in its two subshells), four of the eight electrons have positive spins, and the other four have negative spins. In both cases, the electron spins within one shell are completely compensated, so that the total magnetic moment is zero. IN M-shell, the situation is different, since out of the six electrons located in the third subshell, five electrons have spins directed in one direction, and only the sixth in the other. As a result, four uncompensated spins remain, which determines the magnetic properties of the iron atom. (In the external N-shell has only two valence electrons, which do not contribute to the magnetism of the iron atom.) The magnetism of other ferromagnets, such as nickel and cobalt, is explained in a similar way. Since neighboring atoms in an iron sample strongly interact with each other, and their electrons are partially collectivized, this explanation should be considered only as a visual, but very simplified diagram of the real situation.

The theory of atomic magnetism, based on taking into account the electron spin, is supported by two interesting gyromagnetic experiments, one of which was carried out by A. Einstein and W. de Haas, and the other by S. Barnett. In the first of these experiments, a cylinder of ferromagnetic material was suspended as shown in Fig. 9. If current is passed through the winding wire, the cylinder rotates around its axis. When the direction of the current (and therefore the magnetic field) changes, it turns in the opposite direction. In both cases, the rotation of the cylinder is due to the ordering of the electron spins. In Barnett's experiment, on the contrary, a suspended cylinder, sharply brought into a state of rotation, becomes magnetized in the absence of a magnetic field. This effect is explained by the fact that when the magnet rotates, a gyroscopic moment is created, which tends to rotate the spin moments in the direction of its own axis of rotation.

For a more complete explanation of the nature and origin of short-range forces that order neighboring atomic magnets and counteract the disordering influence of thermal motion, one should turn to quantum mechanics. A quantum mechanical explanation of the nature of these forces was proposed in 1928 by W. Heisenberg, who postulated the existence of exchange interactions between neighboring atoms. Later, G. Bethe and J. Slater showed that exchange forces increase significantly with decreasing distance between atoms, but upon reaching a certain minimum interatomic distance they drop to zero.

MAGNETIC PROPERTIES OF SUBSTANCE

One of the first extensive and systematic studies of the magnetic properties of matter was undertaken by P. Curie. He established that, according to their magnetic properties, all substances can be divided into three classes. The first category includes substances with pronounced magnetic properties, similar to the properties of iron. Such substances are called ferromagnetic; their magnetic field is noticeable at considerable distances ( cm. higher). The second class includes substances called paramagnetic; Their magnetic properties are generally similar to those of ferromagnetic materials, but much weaker. For example, the force of attraction to the poles of a powerful electromagnet can tear an iron hammer out of your hands, and to detect the attraction of a paramagnetic substance to the same magnet, you usually need very sensitive analytical balances. The last, third class includes the so-called diamagnetic substances. They are repelled by an electromagnet, i.e. The force acting on diamagnetic materials is directed opposite to that acting on ferro- and paramagnetic materials.

Measurement of magnetic properties.

When studying magnetic properties, two types of measurements are most important. The first of them is measuring the force acting on a sample near a magnet; This is how the magnetization of the sample is determined. The second includes measurements of “resonant” frequencies associated with the magnetization of matter. Atoms are tiny "gyros" and in a magnetic field precess (like a regular top under the influence of the torque created by gravity) at a frequency that can be measured. In addition, a force acts on free charged particles moving at right angles to the magnetic induction lines, just like the electron current in a conductor. It causes the particle to move in a circular orbit, the radius of which is given by

R = mv/eB,

Where m– particle mass, v– its speed, e is its charge, and B– magnetic field induction. The frequency of such a circular motion is

Where f measured in hertz, e– in pendants, m– in kilograms, B- in Tesla. This frequency characterizes the movement of charged particles in a substance located in a magnetic field. Both types of motion (precession and motion along circular orbits) can be excited by alternating fields with resonant frequencies equal to the “natural” frequencies characteristic of a given material. In the first case, the resonance is called magnetic, and in the second - cyclotron (due to its similarity with the cyclic motion of a subatomic particle in a cyclotron).

Speaking about the magnetic properties of atoms, it is necessary to pay special attention to their angular momentum. The magnetic field acts on the rotating atomic dipole, tending to rotate it and place it parallel to the field. Instead, the atom begins to precess around the direction of the field (Fig. 10) with a frequency depending on the dipole moment and the strength of the applied field.

Atomic precession is not directly observable because all atoms in a sample precess at a different phase. If we apply a small alternating field directed perpendicular to the constant ordering field, then a certain phase relationship is established between the precessing atoms and their total magnetic moment begins to precess with a frequency equal to the precession frequency of individual magnetic moments. The angular velocity of precession is important. As a rule, this value is of the order of 10 10 Hz/T for magnetization associated with electrons, and of the order of 10 7 Hz/T for magnetization associated with positive charges in the nuclei of atoms.

A schematic diagram of a setup for observing nuclear magnetic resonance (NMR) is shown in Fig. 11. The substance being studied is introduced into a uniform constant field between the poles. If a radiofrequency field is then excited using a small coil surrounding the test tube, a resonance can be achieved at a specific frequency equal to the precession frequency of all nuclear “gyros” in the sample. The measurements are similar to tuning a radio receiver to the frequency of a specific station.

Magnetic resonance methods make it possible to study not only the magnetic properties of specific atoms and nuclei, but also the properties of their environment. The fact is that magnetic fields in solids and molecules are inhomogeneous, since they are distorted by atomic charges, and the details of the experimental resonance curve are determined by the local field in the region where the precessing nucleus is located. This makes it possible to study the structural features of a particular sample using resonance methods.

Calculation of magnetic properties.

The magnetic induction of the Earth's field is 0.5 x 10 –4 Tesla, while the field between the poles of a strong electromagnet is about 2 Tesla or more.

The magnetic field created by any configuration of currents can be calculated using the Biot-Savart-Laplace formula for magnetic field induction, created by the element current Calculation of the field created by contours different shapes and cylindrical coils, in many cases very complex. Below are formulas for a number of simple cases. Magnetic induction (in tesla) of the field created by a long straight wire carrying current I

The field of a magnetized iron rod is similar to the external field of a long solenoid, with the number of ampere-turns per unit length corresponding to the current in the atoms on the surface of the magnetized rod, since the currents inside the rod cancel each other (Fig. 12). By the name of Ampere, such a surface current is called Ampere. Magnetic field strength H a, created by the Ampere current, is equal to the magnetic moment per unit volume of the rod M.

If an iron rod is inserted into the solenoid, then in addition to the fact that the solenoid current creates a magnetic field H, the ordering of atomic dipoles in the magnetized rod material creates magnetization M. In this case, the total magnetic flux is determined by the sum of the real and Ampere currents, so that B = m 0(H + H a), or B = m 0(H+M). Attitude M/H called magnetic susceptibility and is designated Greek letter c; c– dimensionless quantity characterizing the ability of a material to be magnetized in a magnetic field.

Magnitude B/H, which characterizes the magnetic properties of a material, is called magnetic permeability and is denoted by m a, and m a = m 0m, Where m a- absolute, and m– relative permeability,

In ferromagnetic substances the quantity c may have very large values– up to 10 4 е 10 6 . Magnitude c Paramagnetic materials have a little more than zero, and diamagnetic materials have a little less. Only in a vacuum and very weak fields quantities c And m are constant and independent of the external field. Induction dependence B from H is usually nonlinear, and its graphs, the so-called. magnetization curves, for different materials and even with different temperatures can vary significantly (examples of such curves are shown in Fig. 2 and 3).

The magnetic properties of matter are very complex, and their deep understanding requires a careful analysis of the structure of atoms, their interactions in molecules, their collisions in gases and their mutual influence in solids and liquids; The magnetic properties of liquids are still the least studied.

At home, at work, in our own car or on public transport, we are surrounded by various types of magnets. They power motors, sensors, microphones and many other common things. Moreover, in each area, devices with different characteristics and features are used. In general, the following types of magnets are distinguished:

What types of magnets are there?

Electromagnets. The design of such products consists of an iron core on which turns of wire are wound. By applying electric current with different parameters of magnitude and direction, it is possible to obtain magnetic fields the required strength and polarity.

The name of this group of magnets is an abbreviation of the names of its components: aluminum, nickel and cobalt. The main advantage of alnico alloy is the material’s unsurpassed temperature stability. Other types of magnets cannot boast of being able to be used at temperatures up to +550 ⁰ C. At the same time, this lightweight material is characterized by a weak coercive force. This means that it can be completely demagnetized when exposed to a strong external magnetic field. At the same time, thanks to its affordable price Alnico is an indispensable solution in many scientific and industrial sectors.

Modern magnetic products

So, we've sorted out the alloys. Now let's move on to what types of magnets there are and what uses they can find in everyday life. In fact, there is a huge variety of options for such products:

1) Toys. Darts without sharp darts, board games, educational designs - the forces of magnetism make familiar entertainment much more interesting and exciting.

2) Mounts and holders. Hooks and panels will help you conveniently organize your space without dusty installation and drilling into walls. The permanent magnetic force of the fasteners proves to be indispensable in the home workshop, boutiques and stores. In addition, they will find worthy use in any room.

3) Office magnets. Magnetic boards are used for presentations and planning meetings, which allow you to clearly and in detail present any information. They also prove extremely useful in school classrooms and university classrooms.

Properties of permanent magnets. 1. Different names magnetic poles attract, like names repel. 2. Magnetic lines are closed lines. Outside the magnet, magnetic lines leave "N" and enter "S", closing inside the magnet. In 1600 English physician G.H. Gilbert deduced the basic properties of permanent magnets.

Slide 9 from the presentation "Permanent magnets, the Earth's magnetic field". The size of the archive with the presentation is 2149 KB.

Physics 8th grade

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Magnet poles (attraction and repulsion between magnet poles)
Magnetic poles (attraction and detraction between magnetic poles)

Like poles of a magnet repel, opposite poles attract. You can easily verify this if you take two magnets and try to bring them closer together. different sides. At first glance, due to the property of magnetic poles of the same name to repel, it is possible to make an experiment on magnetic levitation: when one magnet hangs in the air above another magnet (due to the fact that the repulsion between the magnets compensates for the attraction of the upper magnet by the Earth).

Magnetic levitation is a well-known experiment. Many have seen (at least in a photo) how a piece of a superconductor hovers over a magnet. Or a drop of water and even a frog, which hovered between the poles of a powerful magnet.

A superconductor is a diamagnetic material (just like water or a frog). With two permanent magnets (i.e., ferromagnets), such a trick, alas, will not work. The magnets will either repel and leave the sphere of interaction, or turn with opposite poles and attract each other. A stable equilibrium is impossible here. Let me quote from the book Nurbey Vladimirovich Gulia - Amazing physics: What the textbooks were silent about; chapter Does Mohammed's coffin fly? :

"...in 1842, Professor S. Earnshaw published an article in the Proceedings of the Cambridge University, where he proved that a ferromagnetic body located in the field of permanent magnets cannot be in a state of stable equilibrium. That is, Earnshaw did with the help of mathematics what Hilbert expressed in words - he imposed a ban on the free floating of magnets and the metals attracted by them, and by no combination of magnets and iron pieces it is possible to suspend either one or the other so that they do not touch any other bodies."

In other words, to observe magnetic levitation involving only ferromagnets, one of them needs contact with other bodies. For example, one of the ferromagnets can be tied to a thread. Of course, this will not be real levitation, although it may look impressive.

I came across two magnets that were shaped like washers with holes in the center. The diameter of the holes was such that the magnets fit freely onto the glass rod. Placed the stick vertically. I wrapped tape around the bottom of the stick so that the bottom magnet would not fall through or fly down. I put the magnets on the stick. If the magnets touched with the same poles, the top magnet was pushed upward and “hung” on the stick. Of course, this was not full-fledged levitation, because... If it weren’t for the stick, the magnets would have turned opposite poles towards each other and stuck together. To demonstrate this, you need to remove the top magnet, turn it over and put it back on the wand. The magnets will be attracted.

Improved: 10.03.16

About magnets

Magnet - a body that has magnetization.

Field – this is the space within which one object (Source) influences, not necessarily by direct contact, another object (Receiver). If the Source of influence is a magnet, then the field is considered magnetic.

Magnetic field - this is the space around everyone from the poles of a magnet and for this reason it has no restrictions in all directions ! The center of each magnetic field is the corresponding pole of the magnet.

More than one Source can be present in a certain limited space at the same time. The intensity of these Sources will not necessarily be the same. Accordingly, there can also be more than one center.

The resulting field in this case will not be uniform. At each Receiver point of such a field, the intensity will correspond to the sum of the intensities of the magnetic fields generated by all centers.

In this case, the northern magnetic fields and the southern magnetic fields should be considered to be of different signs. For example, if at some point of the total field the intensity of the southern magnetic field located there coincides with the intensity of the northern magnetic field located here, then the total intensity at the discussed Receiver point from the interaction of both fields will be equal to zero.

Permanent magnet - a product capable of maintaining its magnetization after the external magnetic field is turned off.

Electromagnet - a device in which a magnetic field is created in a coil only when an electric current flows through it.

The general property of any magnet, regardless of the type of magnetic field (north or south) isattraction to materials containing iron (Fe ) . With bismuth, an ordinary magnet works on repulsion. Physics cannot explain either effect, although an unlimited number of hypotheses can be proposed ! Some grades of stainless steel, which also contain iron, are excluded from this rule (“attraction”) - physics also cannot explain this feature, although an unlimited number of hypotheses can also be proposed !

Magnetic pole - one of the sides of the magnet. If a magnet is hung by the middle part so that the poles have a vertical orientation and it (the magnet) can rotate freely in the horizontal plane, then one of the sides of the magnet will turn towards the north pole of the Earth. Accordingly, the opposite side will turn towards the south pole. The side of the magnet directed towards the north pole of the Earth is calledsouth pole magnet, and the opposite side -north pole magnet.

A magnet attracts other magnets and objects made of magnetic materials without even being in contact with them. This action at a distance is explained by the existencemagnetic field in the space around both magnetic poles of a magnet.

Opposite poles of two magnets usually are attracted to each other , and the same names are usually mutualrepulse .

Why "usually"? Yes, because sometimes they meet anomalous phenomena, when, for example, opposite poles neither attract nor repel each other ! This phenomenon has a name "magnetic pit " Physics can't explain it !

In my experiments, I also encountered situations where like poles attract (instead of the expected mutual repulsion), and unlike poles repel (instead of the expected mutual attraction) ! This phenomenon doesn’t even have a name, and physics also can’t explain it yet. !

If a piece of non-magnetized iron is brought close to one of the poles of a magnet, the latter will become temporarily magnetized.

This material is considered magnetic.

In this case, the edge of the piece closest to the magnet will become a magnetic pole, the name of which is opposite to the name of the near pole of the magnet, and the far end of the piece will become a pole of the same name as the near pole of the magnet.

In this case, there are two opposite poles two magnets: a Source magnet and a conditional magnet (made of iron).

It was mentioned above that in the space between these magnets there is an algebraic addition of the intensities of the interacting fields. And, since the fields turn out to be of different signs, a zone of total magnetic field with zero (or almost zero) intensity is formed between the magnets. In what follows I will call such a zone “Zerozona ».

Since “Nature abhors a vacuum,” we can assume that she (Nature) strives to fill the void with the nearest material “at hand.” In our case, such material is magnetic fields, between which a zero zone (Zerozone) has formed. To do this, it is necessary to bring both Sources of different signs closer together (bring the centers of magnetic fields closer together) until the zero zone between the fields completely disappears ! If, of course, nothing interferes with the movement of centers (bringing magnets closer together) !

Here is an explanation of the mutual attraction of opposite magnetic poles and the mutual attraction of a magnet with a piece of iron !

By analogy with attraction, we can consider the phenomenon of repulsion.

In this option, magnetic fields of the same sign appear in the zone of mutual influence. Of course, they also add together algebraically. Because of this, at the Receiver points between the magnets, a zone appears with an intensity higher than the intensities in neighboring areas. In what follows I will call such a zone “Maxisona ».

It is logical to assume that Nature strives to balance this nuisance and move the centers of interacting fields away from each other in order to smooth out the intensity of the field in Maxison.

With this explanation, it turns out that none of the poles of the magnet can move the piece of iron away from itself ! Because a piece of iron, being in a magnetic field, will always turn into a conditional temporary magnet and, therefore, magnetic poles will always form on it (on the piece of iron). Moreover, the near pole of the newly formed temporary magnet is opposite to the pole of the Source magnet. Consequently, a piece of iron located in the magnetic field of the Source pole will be attracted to the Source magnet (BUT not attract it ! )!

A conditional magnet, formed from a piece of iron placed in a magnetic field, behaves like a magnet only in relation to the Source magnet. But, if another piece of iron is placed next to this conditional magnet (piece of iron), then these two pieces of piece of iron will behave in relation to each other like ordinary two pieces of piece of iron ! In other words, the first magnet-piece of iron, as it were, forgets that it is a magnet ! It is only important that the thickness of the first piece of iron is sufficiently noticeable (for my home magnets - at least 2 mm) and the transverse dimension is larger than the size of the second piece of iron !

But the pole of the same name of a forcibly inserted magnet (this is no longer a simple piece of iron) will definitely move the same pole away from itself if there are no obstacles !

In physics textbooks, and sometimes in reputable works on physics, it is written that some idea of ​​​​the intensity of the magnetic field and the change in this intensity in space can be obtained by pouring iron filings onto a sheet of substrate (cardboard, plastic, plywood, glass or any non-magnetic material) placed on a magnet. The sawdust will line up in chains in the directions of varying field intensity, and the density of the sawdust lines will correspond to the very intensity of this field.

So this is cleandeception !!! It looks like it never occurred to anyone to conduct a real experiment and pour in this sawdust !

The sawdust will gather in two dense piles. One pile will form around the north pole of the magnet, and the other around its south pole !

An interesting fact is that just in the middle between the two heaps (in Zerozon) in general NOT will no sawdust ! This experiment casts doubt on the existence of the notorious magneticpower lines , which must leave the north pole of the magnet and enter its south pole !

M. Faraday, to put it mildly, was wrong !

If there is a lot of sawdust, then as it moves away from the pole of the magnet, the pile will decrease and thin out, which is an indicator of the weakening of the intensity of the magnetic field as the Receiver point moves away in space from the Source point on the pole of the magnet. The observed decrease in magnetic field intensity, of course, does not depend on the presence or absence of sawdust on the experimental substrate ! Reduction – objective !

But the decrease in the density of the sawdust coating on the substrate can be explained by the presence of friction of the sawdust on the substrate (on cardboard, on glass, etc.). Friction prevents the weakened attraction from moving the sawdust towards the pole of the magnet. And the farther from the pole, the less strength attraction and, thus, the less sawdust will be able to approach the pole. But, if you shake the substrate, then ALL the sawdust will gather as close as possible to the nearest pole ! The visible non-uniform density of the sawdust coating will thus be leveled out !

In the middle zone of the cross sections of the magnet, two magnetic fields are added algebraically: northern and southern. The total field density between the poles is the result of the algebraic addition of intensities from opposite fields. In the very middle section, the sum of these intensities will be exactly zero (a Zerozone is formed). For this reason, in this section there should be no sawdust at all and they actually No!

As you move away from the middle of the magnet (from the Zerozone) towards the magnetic pole (any), the intensity of the magnetic field will increase, reaching a maximum at the pole itself. The gradient of change in the middle intensity is many times higher than the gradient of change in the outer intensity.

But, in any case, the sawdust will NEVER line up in at least the semblance of some lines connecting North Pole magnet with its south pole !

Physics operates with the term “Magnetic flux ».

So, there is NOT anymagnetic flux !

After all " flow " means "unidirectional movement of material particles or parts" ! If these particles are magnetic, then the flow is considered magnetic.

There are, of course, also figurative phrases such as “stream of words”, “stream of thoughts”, “stream of troubles” and similar phrases. But to physical phenomena they have no relationship.

But in a real magnetic field, nothing moves anywhere ! There is only a magnetic field, the intensity of which decreases with distance from the nearest pole of the Source magnet.

If a flow existed, then a mass of particles would constantly flow out of the mass of the magnet ! And over time, the mass of the original magnet would noticeably decrease ! However, practice does not confirm this !

Since the existence of the notorious magnetic lines of force is not confirmed by practice, the term itself becomes far-fetched and invented.magnetic flux ».

Physics, by the way, gives such an interpretation of the magnetic flux, which only confirms the impossibility of “magnetic flux» in Nature:

« Magnetic flux"- physical quantity equal to the flux density of lines of force passing through an infinitesimal area dS ... (Continued interpretation can be viewed on the Internet).

Already from the beginning of the definition it follows nonsense ! « Flow", it turns out that this is the ordered movement of “lines of force” that do not exist in Nature ! Which in itself is already nonsense ! It is impossible from lines at all ( ! ) to form a “Flow”, since the line is NOT a material object (substance) ! And it is even more NOT possible to form a flow from non-existent lines !

What follows is no less interesting message! It turns out that the totality of non-existent lines of force forms a certain “density”. According to the principle: the more lines that do not exist in Nature are collected in a limited section, the denser the non-existent bundle of non-existent lines becomes !

Finally, " Flow" - this, according to physicists, is a physical size!

What is called - " WE HAVE ARRIVED» !!!

I invite the Reader to figure it out for himself and understand why, say, “dream” cannot be a physical quantity?

Even if " Magnetic flux"existed, then in any case "Movement" (and "Flow" is "Movement") cannot exist size! "“Value” can be some movement parameter, for example: “Speed” of movement, “Acceleration” of movement, but not the “Movement” itself. !

Because simply the term "Magnetic flux“Physics couldn’t digest it, physicists had to supplement this term somewhat. Now physicists have it - “Magnetic induction flux "(although, due to illiteracy, it is often found simply "Magnetic flux») !

Radish horseradish, of course, is not sweeter !

« Induction » is not a material substance ! Therefore, it cannot form a thread ! « Induction" is just a foreign translation from the Russian term "Guidance», « Transition from private to general» !

You can use the term "Magnetic induction ", as the influence of a magnetic field, but the term "Magnetic induction flux» !

In physics there is a term "Magnetic flux density » !

But, thank God, it is difficult for physicists to define this concept ! And that’s why they (physicists) don’t give it !

And, if in physics a concept meaning nothing has taken root, such as “magnetic flux density", which for some reason is confused with the concept "magnetic induction", That:

Magnetic flux density (really NOT existing), it is more logical to count not the number of lines of force that do not exist in Nature per unit section perpendicular to any non-existent line of force, but attitude the number of sawdust found in a unit section of the magnetic field relative to the number of the same sawdust, taken as a unit, in the same unit section, but at the pole itself, if the sections under consideration are perpendicular tomagnetic field vector .

I suggest instead of the meaningless term "Magnetic flux density"to use a more logical term that defines the force with which the Source of the magnetic field can influence the Receiver - "Magnetic field intensity » !

This is something similar to “Electromagnetic field strength».

Of course, no one will ever measure these amounts of sawdust. ! Yes, no one will ever need this !

In physics the term “Magnetic induction » !

It is a vector quantity (i.e. “Magnetic induction" is a vector) and shows with what force and in what direction the magnetic field acts on a moving charge !

I immediately give a significant amendment to the interpretation accepted in physics !

Magnetic field NOT valid on charge! Regardless of whether this charge is moving or not !

The magnetic field of the Source interactswith magnetic field , generated moving charge !

It turns out that "magnetic induction" is nothing more than "strength", pushing a current-carrying conductor ! A "strength", pushing a conductor with current, is nothing more than "Magnetic induction» !

And in physics the following message is proposed: “The direction from the south pole is taken as the positive direction of the magnetic induction vector S to the north pole N magnetic needle freely positioned in a magnetic field.”

What if there is no compass needle nearby? ! While?

Then I suggest the following !

If the conductor with current is located in the zone of the northern magnetic field, then the vector comes from closest to the conductor The source point is at the north pole of the magnet and intersects the conductor.

If the conductor with current is in the zone of the southern magnetic field, then the vector comes from the Receiver point closest to the magnetic pole on the conductor to the nearest Source point on south pole magnet.

In other words, in any case, the shortest distance from the conductor to the nearest pole is taken. Further, depending on this distance, the magnitude of the force of the direct influence of the magnetic field on the conductor is taken (best of all - from an experimental graph of the dependence of magnetic force on distance).

I propose to perceive the shortest distance described as “Magnetic field vector ».

Thus, it turns out that an unlimited set of magnetic fields around one magnet (and, accordingly, the number of magnetic field vectors) can be isolated ! As many as you can build normals to the surfaces of the magnetic poles.