Who first discovered the magnetic field. Basic properties of the magnetic field. The phenomenon of the interaction of two magnets

Introduction

What is a magnetic field? Everyone heard about him, everyone saw how the magnetized compass needle always turns with one and the same end towards the north magnetic pole, and with its other end always towards the south magnetic pole. What distinguishes a person from the most intelligent animal is that he is curious and wants to know why this is happening, how it works, that this is happening. It was to explain what was happening around him that the ancient man invented the gods. Spirits, gods in the minds of people were factors that explained everything that a person saw, heard, what luck in hunting and war depended on, who moved the Sun across the sky, who arranged a thunderstorm, poured rain and snowed, in general, everything , everything that happens. Imagine, a little grandson comes up to grandfather, points to a lightning bolt and asks: what is it, why does fire fly from a cloud into the ground, and who knocks so loudly in the clouds there? If the grandfather answered: I don’t know, then the grandson looked at him with regret and began to respect him less. But when the grandfather said that it was the god Yarilo who rides a chariot through the clouds and shoots fire arrows at bad people, the grandson listened and respected his grandfather even more. He began to be less afraid of thunder and lightning, because he knew that he was good, so Yarilo would not shoot at him.

In early childhood, when I started to play pranks, grandmother Anna said: "Shurka, look, don't be shawls, otherwise God will knock a pebble." And at the same time she pointed to the icon in the red corner on the shelf-deity. I quieted down for a while, cautiously looked at the stern peasant drawn on the blackboard, but somehow I doubted his ability to throw stones. He put a stool on the bench, climbed on it and looked on the shelf behind the icon. I didn’t see any pebbles there, and when the grandmother began to frighten me once again, he laughed and said: “He doesn’t have any stones, and in general he is painted and cannot throw himself. In the same way, our distant ancestor once doubted that it was Yarilo who was riding in the sky and shooting arrows. It was then that rational knowledge was born, when people began to doubt the omnipotence of the gods. But what did they replace them with? And they replaced the gods with the laws of nature, and strongly began to believe these laws. But where man cannot explain what is happening by the laws of nature, he left a place for the gods. That is why religion and science coexist in society to this day.

I remember how older friends showed us kids a trick. An iron nail placed on the table moved by itself on the table, and the magician under the table moved his hand. The nail followed the hand. We stared at this in surprise and did not understand why the nail was moving. When I told my mother about this trick, she explained that the guy had a magnet in his hand that attracts iron to himself, that the guy under the table moved not just his hand, but he had a magnet in his hand. At that time, this explanation satisfied my curiosity, but a little later I already wanted to understand why a magnet at a distance - through a table board, through a layer of air - attracts iron to itself. Neither my mother nor my father could answer this question. I had to wait until school. There, in a physics lesson, the teacher explained that a magnet acts on iron through a magnetic field that creates around itself, that a magnet has two poles - north and south, that some invisible magnetic lines of force come out of the north, which bend in an arc and enter South Pole.

Then I thought for the first time: it means that in the world, in addition to the visible, audible and tangible, there is something invisible and intangible. Then I thought: what if God is invisible and intangible - like this magnetic field. It seems to be nowhere, but it still exists. And on the icons in the form of a peasant, he is so foolishly depicted. I did not know then that the philosopher Spinoza, who began to consider Nature and God as one and inseparable, visible and invisible, had thought of this even before me. Nature is God!

I remember I tried to imagine this magnetic field, consisting of lines of force, and did not understand anything. I haven't seen or heard these lines. They did not smell of anything, and it was not very clear to me then to believe that there could be something around us that we do not feel in any way. Iron nails and sawdust felt the magnetic field and oriented and moved in it, but I, with my subtle sense organs, did not feel anything. This inferiority frankly oppressed me. But not just me. A. Einstein wrote about the strong surprise at the properties of the magnet he saw, which his father gave him for his birthday as a child, from the fact that he could not understand how and why these attractive properties of the magnet occur.

When the teacher of social science already in the 10th grade introduced us to the definition of matter given by V.I. Lenin: "matter is what exists around us and is given to us in sensations", I indignantly asked her: "but we do not feel the magnetic field, but it exists, is it not matter?" Yes, the sense organs alone are not enough to perceive all forms of matter, another mind is required, with the help of which, if we don’t feel something, we don’t feel it, then we understand that it exists. Having understood this, I decided to study the sciences and develop my mind, hoping that this would allow me to understand a lot. But as I expanded the space of what was understandable to me, the incomprehensible did not disappear, but only moved away, and the line of the horizon of the incomprehensible became longer, as the circle of the known increased and the length of its circumference, separating what was understood by my mind from the unknown and incomprehensible, also increased. This is the main paradox of knowledge: the more we learn and understand, the more we do not know yet. Nicholas of Cusa, who for some reason is considered a scholastic philosopher, wrote about this scientific ignorance, although the truth he discovered rather suggests that he was a dialectician.

The first mention of rocks capable of attracting iron dates back to ancient times. An old legend is connected with the magnet about the shepherd Magnus, who once discovered that his iron staff and sandals lined with iron nails were attracted to an unknown stone. Since then, this stone has been called the "stone of Magnus", or a magnet.

The origin and essence of the Earth's magnetic field, as well as magnetic fields in general, remains a mystery to this day. There are many hypotheses - options for explaining this phenomenon, but the truth is still "out there." This is how physicists define a magnetic field: A magnetic field- this is a force field acting on moving electric charges and on bodies with a magnetic moment, regardless of the state of their movement. "And further:" A magnetic field can be created by the current of charged particles and / or magnetic moments of electrons in atoms (and magnetic moments of other particles , although to a much lesser extent). In addition, it appears in the presence of a time-varying electric field. "I would not say that from a logical point of view this is a brilliant definition. To say that a magnetic field is a force field means to say nothing, it is a tautology. After all, the gravitational field "is also a force field, and the field of nuclear forces is force! The indication of the effect of a magnetic field on moving electric charges says something, this is a description of one of the properties of a magnetic field. But it is not clear whether the magnetic field acts directly on particles that have electric charges, or it acts on the magnetic fields formed by these particles, and those (the transformed fields of the particles) in turn act on the particles - they transmit the received momentum to them.

For the first time, magnetic phenomena began to be studied by the English physician and physicist William Gilbert, who wrote the work "On the magnet, magnetic bodies and the large magnet - the Earth." Then it was believed that electricity and magnetism have nothing in common. But in early XIX in. Danish scientist G.Kh. Oersted in 1820 experimentally proved that magnetism is one of the hidden forms of electricity, and confirmed this experimentally. This experience led to an avalanche of new discoveries that were of great importance. Around the conductors with electric current, a field arises, which was called magnetic. A beam of moving electrons has an effect on a magnetic needle, similar to a current-carrying conductor (Ioffe's experiment). Convection currents of electrically charged particles are similar to conduction currents in their action on a magnetic needle (Eichenwald's experiment).

The magnetic field is created only by moving electric charges or moving electrically charged bodies, as well as permanent magnets. This magnetic field differs from the electric field, which is created by both moving and stationary electric charges.

The lines of the magnetic induction vector (B) are always closed and cover the conductor with current, and the lines of the electric field begin on positive and end on negative charges, they are open. The lines of magnetic induction of a permanent magnet come out of one pole, called the north (N) and enter the other - south (S). At first it seems that there is a complete analogy with the lines of electric field strength (E). The poles of magnets play the role of magnetic charges. However, if you cut the magnet, the picture is preserved, smaller magnets are obtained - but each with its own north and south poles. It is impossible to divide the magnetic poles so that the north pole is at one piece, and the south at the other, because free (discrete) magnetic charges, unlike discrete electric charges, do not exist in nature.

The magnetic fields that exist in nature are diverse in scale and in the effects they cause. The Earth's magnetic field, which forms the Earth's magnetosphere, extends for a distance of 70-80 thousand kilometers in the direction of the Sun and for many millions of kilometers in the opposite direction. The origin of the Earth's magnetic field is associated with the movements of a liquid substance that conducts electrically charged particles in earth's core. Jupiter and Saturn have powerful magnetic fields. The magnetic field of the Sun plays an important role in all processes occurring on the Sun - flares, the appearance of spots and prominences, the birth of solar cosmic rays. The magnetic field is widely used in various industries: when loading iron scrap, when cleaning flour at bakeries from metal impurities, and also in medicine for treating patients.

What is a magnetic field

The main power characteristic of the magnetic field is magnetic induction vector. Often the vector of magnetic induction is called simply a magnetic field for brevity (although this is probably not the most strict use of the term). In fact, a vector is a quantity that has a direction in space, therefore, we can talk about the direction of magnetic induction and its magnitude. But to say that the magnetic field is only the direction of magnetic induction means not to explain very much. There is another characteristic of the magnetic field - vector potential. As the main characteristic of the magnetic field in vacuum, not the vector of magnetic induction is chosen, but the vector magnetic field strength. In vacuum, these two vectors coincide, but not in matter, but from a systematic point of view, it should be considered the main characteristic of the magnetic field precisely vector potential.

A magnetic field can be called a special kind of matter, through which interaction is carried out between moving charged particles or bodies that have a magnetic moment. Magnetic fields are a necessary (in the context of special relativity) consequence of the existence of electric fields. Magnetic and electric fields together form an electromagnetic field, the manifestations of which are, in particular, light and all other electromagnetic waves. From the point of view of quantum field theory, the magnetic interaction is like special case electromagnetic interaction - is carried by a fundamental massless boson - a photon (a particle that can be represented as a quantum excitation of an electromagnetic field), often (for example, in all cases of static fields) virtual. The magnetic field is created (generated) by the current of charged particles, or by a time-varying electric field, or by the intrinsic magnetic moments of the particles (the latter, for the sake of uniformity of the picture, can be formally reduced to electric currents).

In my opinion, these definitions are very vague. It is clear that the magnetic field is not a void, but a special kind of matter - a part real world. It is clear that the magnetic field is inextricably linked with the movement of electric charges - electric current. But how a magnetic field with an electric field form a single electromagnetic field is not clear. Most likely, there is a certain unified field, which, depending on the circumstances, manifests itself either as a magnetic field or as an electric one. Just like some kind of hermaphrodite, which in certain circumstances can be a boy, and in other circumstances - a girl.

The force acting on an electrically charged particle moving in a magnetic field is called the Lorentz force. This force is always directed perpendicular to the vector particle speed - v and the vector potential of the magnetic field - B. This force is proportional to the charge of the particle q, its speed v, perpendicular to the direction of the magnetic field vector B and is proportional to the magnitude of the magnetic field induction B. Let me explain to those who have completely forgotten school physics: force is the reason that causes the acceleration of the movement of bodies. Here the force acts not on the mass of the particle, but on its charge. In this, the Lorentz force differs from the force of gravity, which acts on the mass of particles (bodies), since the mass of a body is its gravitational charge.

The magnetic field also acts on a current-carrying conductor. The force acting on a current-carrying conductor is called the ampere force. This force is the sum of the forces acting on individual electric charges moving inside the conductor. This is the current, measured in amperes.

When two magnets interact, the same poles repel each other and the opposite poles attract. However, a detailed analysis shows that in fact this is not a completely correct description of the phenomenon. It is not clear why dipoles can never be separated within the framework of such a model. The experiment shows that no isolated body actually has a magnetic charge of the same sign. Every magnetized body has two poles - north and south. A force acts on a magnetic dipole placed in a non-uniform magnetic field, which tends to rotate it so that the magnetic moment of the dipole is co-directed (coincident in direction) with the magnetic field in which this magnetic dipole was placed.

In 1831, Michael Faraday discovered that a closed conductor, when placed in a changing magnetic field, produces an electric current. This phenomenon has been named electromagnetic induction.

M. Faraday discovered that the electromotive force (EMF) that occurs in a closed conducting circuit is proportional to the rate of change of the magnetic flux passing through the part electrical circuit located in this magnetic field. The value (EMF) does not depend on what causes the change in the flux - a change in the magnetic field itself or the movement of a part of the circuit in a magnetic field. The electric current caused by EMF is called induced current. This discovery made it possible to create generators electric current and create, in fact, our electrical civilization. Who would have thought in the 30s of the XIX century that the discovery of M. Faraday was an epoch-making civilizational discovery that determined the future of mankind?

In turn, the magnetic field can be created and changed (weakened or strengthened) by an alternating electric field created by electric currents in the form of streams of charged particles. The microscopic structure of a substance placed in an alternating magnetic field affects the strength of the current that arises in it. Some structures weaken the emerging electric current, while others strengthen it to varying degrees. One of the first studies magnetic properties substances were performed by Pierre Curie. In this regard, substances in relation to their magnetic properties are divided into two main groups:

1. Ferromagnets - substances in which, below a certain critical temperature (Curie points), a long-range ferromagnetic order of the magnetic moments of the particles of the substance is established.

2. Antiferromagnets - substances in which the antiferromagnetic order of the magnetic moments of the particles of matter - atoms or ions - has been established: the magnetic moments of the particles of the substance are directed oppositely and are equal in strength.

There are also substances of diamagnets and substances of paramagnets.

Diamagnets are substances that are magnetized against the direction of an external magnetic field.

Paramagnets are substances that are magnetized in an external magnetic field in the direction of the external magnetic field.

Types of ordering of magnetic moments of atoms in paramagnetic (a), ferromagnetic (b) and antiferromagnetic (c) substances. Figure from the site: http://encyclopaedia.biga.ru/enc/science_and_technology/ MAGNITI_I_MAGNITNIE_SVOSTVA_VESHCHESTVA.html

The above groups of substances mainly include common solid, liquid and gaseous substances. Superconductors and plasmas essentially differ from them in their interaction with the magnetic field.

The magnetic field of ferromagnets (an example is iron) is noticeable at considerable distances.

The magnetic properties of paramagnets are similar to those of ferromagnets, but are much less pronounced - at a shorter distance.

Diamagnets are not attracted, but repelled by a magnet, the force acting on diamagnets is directed opposite to that acting on ferromagnets and paramagnets.

According to Lenz's rule, the magnetic field of an electric current induced in a magnetic field is directed in such a way as to counteract the change in the magnetic flux that induces this current. I want to note that the interaction of an alternating magnetic field and the electric current induced by it and the electric field corresponds to the Le Chatelier principle. This is nothing but the auto-braking of the process, which is inherent in all processes occurring in the real world.

According to Le Chatelier's principle, every process occurring in the world gives rise to a process that has the opposite direction and slows down the process that causes it. In my opinion, this is one of the main laws of the universe, which for some reason neither physicists nor philosophers pay due attention to.

All substances are magnetic to a greater or lesser extent. If two conductors with electric currents are placed in any medium, then the strength of the magnetic interaction between the currents changes. The induction of a magnetic field created by electric currents in a substance differs from the induction of a magnetic field created by the same currents in a vacuum. The physical quantity showing how many times the magnetic field induction in a homogeneous medium differs in absolute value from the magnetic field induction in vacuum is called magnetic permeability. Vacuum has the maximum magnetic permeability.

The magnetic properties of substances are determined by the magnetic properties of atoms - electrons, protons and neutrons that make up atoms. The magnetic properties of protons and neutrons are almost 1000 times weaker than the magnetic properties of electrons. Therefore, the magnetic properties of a substance are mainly determined by the electrons that make up its atoms.

One of the most important properties of an electron is that it has not only an electric but also a magnetic field. The own magnetic field of an electron, which allegedly arises when it rotates around its axis, is called a spin field (spin - rotation). But the electron also creates a magnetic field due to its movement around the atomic nucleus, which can be likened to a circular microcurrent. Spin fields of electrons and magnetic fields due to their orbital motions determine a wide range of magnetic properties of substances.

Behavior of a paramagnet (1) and a diamagnet (2) in an inhomogeneous magnetic field. Figure from the site: http://physics.ru/courses/op25part2/content/chapter1/section/ paragraph19/theory.html

Substances are extremely diverse in their magnetic properties. For example, platinum, air, aluminum, ferric chloride are paramagnetic, and copper, bismuth, water are diamagnetic. Paramagnetic and diamagnetic samples placed in an inhomogeneous magnetic field between the poles of an electromagnet behave differently - paramagnets are drawn into the region of a strong field, while diamagnets, on the contrary, are pushed out of it.

Para- and diamagnetism is explained by the behavior of electron orbits in an external magnetic field. In atoms of diamagnetic substances, in the absence of an external field, their own magnetic fields of electrons and the fields created by their orbital motion are completely compensated. The emergence of diamagnetism is associated with the action of the Lorentz force on electron orbits. Under the action of this force, the nature of the orbital motion of electrons changes and the compensation of magnetic fields is disturbed. The resulting own magnetic field of the atom turns out to be directed against the direction of the induction of the external field.

In atoms of paramagnetic substances, the magnetic fields of electrons are not fully compensated, and the atom turns out to be similar to a small circular current. In the absence of an external field, these circular microcurrents are arbitrarily oriented, so that the total magnetic induction is zero. The external magnetic field has an orienting effect - microcurrents tend to orient themselves so that their own magnetic fields are directed in the direction of the external field induction. Due to the thermal motion of the atoms, the orientation of the microcurrents is never complete. With an increase in the external field, the orientation effect increases, so that the induction of the intrinsic magnetic field of the paramagnetic sample increases in direct proportion to the induction of the external magnetic field. The total induction of the magnetic field in the sample is the sum of the induction of the external magnetic field and the induction of the intrinsic magnetic field that arose during the magnetization process.

Atoms of any substance have diamagnetic properties, but in many cases their diamagnetism is masked by a strong paramagnetic effect. The phenomenon of diamagnetism was discovered by M. Faraday in 1845.

Ferromagnets can be strongly magnetized in a magnetic field, their magnetic permeability is very high. The group under consideration includes four chemical element: iron, nickel, cobalt, gadolinium. Of these, iron has the highest magnetic permeability. Various alloys of these elements can be ferromagnets, for example, ceramic ferromagnetic materials - ferrites.

For each ferromagnet, there is a certain temperature (the so-called temperature or Curie point), above which the ferromagnetic properties disappear, and the substance becomes a paramagnet. For iron, for example, the Curie temperature is 770°C, for cobalt 1130°C, for nickel 360°C.

Ferromagnetic materials are magnetically soft and magnetically hard. Magnetically soft ferromagnetic materials are almost completely demagnetized when the external magnetic field becomes zero. Soft magnetic materials include, for example, pure iron, electrical steel, and some alloys. These materials are used in AC devices in which continuous magnetization reversal occurs, that is, a change in the direction of the magnetic field (transformers, electric motors, etc.).

Magnetically hard materials retain their magnetization to a large extent even after they are removed from the magnetic field. Examples of magnetically hard materials are carbon steel and a number of special alloys. Magnetically hard materials are used mainly for the manufacture of permanent magnets.

characteristic feature The process of magnetization of ferromagnets is hysteresis, that is, the dependence of magnetization on the prehistory of the sample. The magnetization curve B(B0) of a ferromagnetic sample is a loop complex shape, which is called the hysteresis loop.

Dependence of the magnetic permeability of a ferromagnet on the induction of an external magnetic field. At first, a ferromagnet is magnetized quickly, but after reaching a maximum, it is magnetized more and more slowly. Figure from the site: http://physics.ru/courses/op25part2/content/chapter1/section/ paragraph19/theory.html

A typical hysteresis loop for a magnetically hard ferromagnetic material. At point 2, magnetic saturation is reached. Segment 1-3 determines the residual magnetic induction, and segment 1-4 - the coercive force, which characterizes the ability of the sample to resist demagnetization. Figure from the site: http://encyclopaedia.biga.ru/enc/science_and_technology/ MAGNITI_I_MAGNITNIE_SVOSTVA_VESHCHESTVA.html

The nature of ferromagnetism can be understood on the basis of quantum concepts. Ferromagnetism is explained by the presence of intrinsic (spin) magnetic fields of electrons. In crystals of ferromagnetic materials, conditions arise under which, due to the strong interaction of the spin magnetic fields of neighboring electrons, their parallel orientation becomes energetically favorable. As a result of such an interaction, spontaneously magnetized regions arise inside a ferromagnet crystal. These areas are called domains. Each domain is a small permanent magnet.

Illustration of the magnetization process of a ferromagnetic sample:

a - matter in the absence of an external magnetic field: its individual atoms, which are small magnets, are arranged randomly; b - magnetized substance: under the action of an external field, the atoms are oriented relative to each other in a certain order in accordance with the direction of the external field. Rice. from the site: http://encyclopaedia.biga.ru/enc/science_and_technology/MAGNITI_I_MAGNITNIE_SVOSTVA_VESHCHESTVA.html

Domains in the theory of magnetism are small magnetized regions of a material in which the moments of the magnetic field of atoms are oriented parallel to each other. The domains are separated from each other by transition layers called Bloch walls. The figure shows two domains with opposite magnetic orientations and a Bloch wall between them with an intermediate orientation. Figure from the site: http://encyclopaedia.biga.ru/enc/science_and_technology/ MAGNITI_I_MAGNITNIE_SVOSTVA_VESHCHESTVA.html

In the absence of an external magnetic field, the directions of the magnetic field induction vectors in different domains are randomly oriented in a large crystal. Such a crystal is found to be non-magnetized. When an external magnetic field is applied, the domain boundaries are displaced so that the volume of domains oriented along the external field increases. With an increase in the induction of the external field, the magnetic induction of the magnetized substance increases. In a very strong magnetic external field, domains in which their own magnetic field coincides in direction with the external field absorb all other domains, and magnetic saturation occurs.

However, it should be remembered that all these drawings and the domains and atoms depicted on them are just diagrams or models of the real phenomena of magnetism, but not the phenomena themselves. They are used as long as they do not contradict the observed facts.

A simple electromagnet designed to capture loads. The source of energy is accumulator battery direct current. Also shown are the lines of force of the electromagnet field, which can be detected by the usual method of iron filings. Figure from the site: http://encyclopaedia.biga.ru/enc/science_and_technology/ MAGNITI_I_MAGNITNIE_SVOSTVA_VESHCHESTVA.htmll

The occurrence of a magnetic field in the vicinity of a conductor through which a direct electric current is passed is illustrated by an electromagnet. Current flows through a wire that is wound around a ferromagnetic rod. The magnetizing force in this case is equal to the product of the magnitude of the electric current in the coil by the number of turns in it. This force is measured in amperes. Magnetic field strength H equal to the magnetizing force per unit length of the coil. Thus, the value H 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 H.

The magnetic field induction is a vector quantity, which is the force characteristic of the magnetic field. The direction of magnetic induction coincides with the direction indicated by a magnetic needle in a magnetic field, and the modulus of this vector is equal to the ratio of the modulus of the magnetic force that acts on a moving perpendicularly charged particle to the modulus of the speed and charge of this particle. Magnetic induction according to SI is measured in teslas (T). In the CGS system, magnetic induction is measured in gauss (gauss). In this case, 1 T = 104 Gs.

Large electromagnets with iron cores and very a large number coils operating in continuous mode, have a large magnetizing force. They create a magnetic induction in the gap between the poles up to 6 tesla (T). The magnitude of the induction is limited by mechanical stresses, heating of the coils and magnetic saturation of the core.

A number of giant electromagnets (without a core) with water cooling, and installations for creating pulsed magnetic fields were designed by P.L. Kapitsa at Cambridge and at the Institute of Physical Problems of the USSR Academy of Sciences, as well as F. Bitter at the Massachusetts Institute of Technology. On such magnets it was possible to achieve induction up to 50 T. A relatively small electromagnet, producing fields up to 6.2 T, consuming 15 kW of electrical power and cooled by liquid hydrogen, was developed at the Losalamos National Laboratory. Similar magnetic fields are obtained at very low temperatures.

The magnetic induction vector is considered one of physical quantities, which is fundamental in the theory of electromagnetism, it can be found in a huge variety of equations, in some cases directly, and sometimes through the magnetic field strength associated with it. The only area in the classical theory of electromagnetism, in which there is no vector of magnetic induction, is, perhaps, only pure electrostatics.

Ampère in 1825 suggested that electric microcurrents circulate in each atom of a magnet. But the electron was discovered only in 1897, and the model of the internal structure of the atom - in 1913, almost 100 years after Ampère's brilliant guess. In 1852, W. Weber suggested that each atom of a magnetic substance is a tiny magnetic dipole. The ultimate or complete magnetization of a substance is achieved when all individual atomic magnets are lined up in a certain order. Weber believed that molecular or atomic "friction" helped these elementary magnets maintain their order. His theory explained the magnetization of bodies when they come into contact with a magnet and their demagnetization when struck or heated. The "reproduction" of magnets was also explained when a magnetized piece or a magnetic rod was cut into pieces, when each piece always had two poles. However, this theory did not explain either the origin of the elementary magnets themselves or the phenomenon of hysteresis. In 1890, Weber's theory was improved by J. Ewing, who replaced the 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.

In 1905 P. Langevin explained the behavior of paramagnetic materials by ascribing to each atom an internal uncompensated electron current. According to Langevin, it is these currents that form tiny magnets, randomly oriented when there is no external magnetic field, but acquiring an ordered orientation after its application. In this case, the approximation to complete ordering corresponds to saturation of the magnetization. Langevin introduced the concept of the magnetic moment of an atomic magnet, equal to the product of the "magnetic charge" by the distance between the poles. According to this theory, the weak magnetism of paramagnetic materials is explained by the weak net 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. An individual domain may have linear dimensions on the order of 0.01 mm. The domains are separated from each other by the so-called Bloch walls, the thickness of which does not exceed 1000 atomic dimensions. Such walls are "transition layers", or microgradients in the magnetic nanostructure of a substance, in which the direction of the domain magnetization changes. There are two convincing experimental confirmations of the existence of domains. In 1919, G. Barkhausen established that when an external field is applied to a sample of a ferromagnetic material, its magnetization changes in small discrete portions. To reveal the domain structure of a magnet by the method of powder figures, a drop of a colloidal suspension of a ferromagnetic powder (iron oxide) 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. Such a structure can be studied under a microscope. A method has been developed for studying the magnetic field, based on the passage of polarized light through a transparent ferromagnetic material.

A free iron atom has two of its shells ( K and L), closest to the nucleus, are filled with electrons, with two on the first of them, and eight on the second. AT K-shell, the spin of one of the electrons is positive, and the other is negative. AT 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 spins of the electrons within the same shell cancel out completely, so that the total magnetic moment of the atom is zero. AT M-shell, the situation is different, because of the six electrons in the third subshell, five electrons have spins, direction

To understand what is a characteristic of a magnetic field, many phenomena should be defined. At the same time, you need to remember in advance how and why it appears. Learn what is a force field. It is also important that such a field can occur not only in magnets. In this regard, it does not hurt to mention the characteristics of the earth's magnetic field.

Emergence of the field

To begin with, it is necessary to describe the appearance of the field. After that, you can describe the magnetic field and its characteristics. It appears during the movement of charged particles. Can affect especially conductive conductors. The interaction between a magnetic field and moving charges, or conductors through which current flows, occurs due to forces called electromagnetic.

The intensity or power characteristic of the magnetic field at a certain spatial point is determined using magnetic induction. The latter is denoted by the symbol B.

Graphical representation of the field

The magnetic field and its characteristics can be represented graphically using induction lines. This definition is called lines, the tangents to which at any point will coincide with the direction of the vector y of the magnetic induction.

These lines are included in the characteristics of the magnetic field and are used to determine its direction and intensity. The higher the intensity of the magnetic field, the more data lines will be drawn.

What are magnetic lines

The magnetic lines of straight conductors with current have the shape of a concentric circle, the center of which is located on the axis of this conductor. The direction of the magnetic lines near the conductors with current is determined by the rule of the gimlet, which sounds like this: if the gimlet is located so that it will be screwed into the conductor in the direction of the current, then the direction of rotation of the handle corresponds to the direction of the magnetic lines.

For a coil with current, the direction of the magnetic field will also be determined by the gimlet rule. It is also required to rotate the handle in the direction of the current in the turns of the solenoid. The direction of the lines of magnetic induction will correspond to the direction of the translational movement of the gimlet.

It is the main characteristic of the magnetic field.

Created by one current, under equal conditions, the field will differ in its intensity in different media due to the different magnetic properties in these substances. The magnetic properties of the medium are characterized by absolute magnetic permeability. It is measured in henries per meter (g/m).

The characteristic of the magnetic field includes the absolute magnetic permeability of the vacuum, called the magnetic constant. The value that determines how many times the absolute magnetic permeability of the medium will differ from the constant is called the relative magnetic permeability.

Magnetic permeability of substances

This is a dimensionless quantity. Substances with a permeability value of less than one are called diamagnetic. In these substances, the field will be weaker than in vacuum. These properties are present in hydrogen, water, quartz, silver, etc.

Media with a magnetic permeability greater than unity are called paramagnetic. In these substances, the field will be stronger than in vacuum. These media and substances include air, aluminum, oxygen, platinum.

In the case of paramagnetic and diamagnetic substances, the value of magnetic permeability will not depend on the voltage of the external, magnetizing field. This means that the value is constant for a certain substance.

Ferromagnets belong to a special group. For these substances, the magnetic permeability will reach several thousand or more. These substances, which have the property of being magnetized and amplifying the magnetic field, are widely used in electrical engineering.

Field strength

To determine the characteristics of the magnetic field, together with the magnetic induction vector, a value called the magnetic field strength can be used. This term defines the intensity of the external magnetic field. The direction of the magnetic field in a medium with the same properties in all directions, the intensity vector will coincide with the magnetic induction vector at the field point.

The strong magnetic properties of ferromagnets are explained by the presence in them of arbitrarily magnetized small parts, which can be represented as small magnets.

In the absence of a magnetic field, a ferromagnetic substance may not have pronounced magnetic properties, since the domain fields acquire different orientations, and their total magnetic field is zero.

According to the main characteristic of the magnetic field, if a ferromagnet is placed in an external magnetic field, for example, in a coil with current, then under the influence of the external field, the domains will turn in the direction of the external field. Moreover, the magnetic field at the coil will increase, and the magnetic induction will increase. If the external field is sufficiently weak, then only a part of all domains whose magnetic fields approach the direction of the external field will flip over. As the strength of the external field increases, the number of rotated domains will increase, and at a certain value of the external field voltage, almost all parts will be rotated so that the magnetic fields are located in the direction of the external field. This state is called magnetic saturation.

Relationship between magnetic induction and intensity

The relationship between the magnetic induction of a ferromagnetic substance and the strength of an external field can be depicted using a graph called the magnetization curve. At the bend of the curve graph, the rate of increase in magnetic induction decreases. After a bend, where the tension reaches a certain value, saturation occurs, and the curve slightly rises, gradually acquiring the shape of a straight line. In this section, the induction is still growing, but rather slowly and only due to an increase in the strength of the external field.

The graphic dependence of these indicators is not direct, which means that their ratio is not constant, and the magnetic permeability of the material is not a constant indicator, but depends on the external field.

Changes in the magnetic properties of materials

With an increase in the current strength to full saturation in a coil with a ferromagnetic core and its subsequent decrease, the magnetization curve will not coincide with the demagnetization curve. With zero intensity, the magnetic induction will not have the same value, but will acquire some indicator called the residual magnetic induction. The situation with the lagging of magnetic induction from the magnetizing force is called hysteresis.

To completely demagnetize the ferromagnetic core in the coil, it is necessary to give a reverse current, which will create the necessary tension. For different ferromagnetic substances, a segment of different lengths is needed. The larger it is, the more energy is needed for demagnetization. The value at which the material is completely demagnetized is called the coercive force.

With a further increase in the current in the coil, the induction will again increase to the saturation index, but with a different direction of the magnetic lines. When demagnetizing in the opposite direction, residual induction will be obtained. The phenomenon of residual magnetism is used to create permanent magnets from substances with a high residual magnetism. From substances that have the ability to remagnetize, cores are created for electrical machines and appliances.

left hand rule

The force acting on a conductor with current has a direction determined by the rule of the left hand: when the palm of the virgin hand is located in such a way that the magnetic lines enter it, and four fingers are extended in the direction of the current in the conductor, the bent thumb will indicate the direction of force. Given power perpendicular to the induction vector and current.

A current-carrying conductor moving in a magnetic field is considered a prototype of an electric motor, which changes electrical energy into mechanical energy.

Right hand rule

During the movement of the conductor in a magnetic field, an electromotive force is induced inside it, which has a value proportional to the magnetic induction, the length of the conductor involved and the speed of its movement. This dependence is called electromagnetic induction. When determining the direction of the induced EMF in the conductor, the rule is used right hand: when the right hand is positioned in the same way as in the example from the left, the magnetic lines enter the palm, and the thumb indicates the direction of movement of the conductor, the outstretched fingers indicate the direction of the induced EMF. A conductor moving in a magnetic flux under the influence of an external mechanical force is the simplest example electric generator in which mechanical energy is converted into electrical energy.

It can be formulated differently: in a closed circuit, an EMF is induced, with any change in the magnetic flux covered by this circuit, the EDE in the circuit is numerically equal to the rate of change of the magnetic flux that covers this circuit.

This form provides an average EMF indicator and indicates the dependence of the EMF not on the magnetic flux, but on the rate of its change.

Lenz's Law

You also need to remember Lenz's law: the current induced by a change in the magnetic field passing through the circuit, with its magnetic field, prevents this change. If the turns of the coil are pierced by magnetic fluxes of different magnitudes, then the EMF induced on the whole coil is equal to the sum of the EMF in different turns. The sum of the magnetic fluxes of different turns of the coil is called flux linkage. The unit of measurement of this quantity, as well as the magnetic flux, is weber.

When the electric current in the circuit changes, the magnetic flux created by it also changes. However, according to the law electromagnetic induction, an EMF is induced inside the conductor. It appears in connection with a change in current in the conductor, therefore this phenomenon is called self-induction, and the EMF induced in the conductor is called self-induction EMF.

Flux linkage and magnetic flux depend not only on the strength of the current, but also on the size and shape of a given conductor, and the magnetic permeability of the surrounding substance.

conductor inductance

The coefficient of proportionality is called the inductance of the conductor. It denotes the ability of a conductor to create flux linkage when electricity passes through it. This is one of the main parameters of electrical circuits. For certain circuits, inductance is a constant. It will depend on the size of the contour, its configuration and the magnetic permeability of the medium. In this case, the current strength in the circuit and the magnetic flux will not matter.

The above definitions and phenomena provide an explanation of what a magnetic field is. The main characteristics of the magnetic field are also given, with the help of which it is possible to define this phenomenon.

Earth's magnetic field

A magnetic field is a force field that acts on moving electric charges and on bodies that have a magnetic moment, regardless of the state of their motion.

The sources of a macroscopic magnetic field are magnetized bodies, current-carrying conductors, and moving electrically charged bodies. The nature of these sources is the same: the magnetic field arises as a result of the movement of charged microparticles (electrons, protons, ions), and also due to the presence of their own (spin) magnetic moment in the microparticles.

An alternating magnetic field also occurs when the electric field changes over time. In turn, when the magnetic field changes in time, electric field. Full description electric and magnetic fields in their relationship give the Maxwell equations. To characterize the magnetic field, the concept of field lines of force (lines of magnetic induction) is often introduced.

To measure the characteristics of the magnetic field and the magnetic properties of substances, various types magnetometers. The unit of magnetic field induction in the CGS system is Gauss (Gs), in the International System of Units (SI) - Tesla (T), 1 T = 104 Gs. The intensity is measured, respectively, in oersteds (Oe) and amperes per meter (A / m, 1 A / m \u003d 0.01256 Oe; magnetic field energy - in Erg / cm 2 or J / m 2, 1 J / m 2 \u003d 10 erg/cm2.

Compass reacts
to the earth's magnetic field

Magnetic fields in nature are extremely diverse both in their scale and in the effects they cause. The Earth's magnetic field, which forms the Earth's magnetosphere, extends up to a distance of 70-80 thousand km in the direction of the Sun and many millions of km in the opposite direction. At the Earth's surface, the magnetic field is on average 50 μT, at the boundary of the magnetosphere ~ 10 -3 G. The geomagnetic field shields the Earth's surface and the biosphere from the flow of charged particles from the solar wind and partly from cosmic rays. The influence of the geomagnetic field itself on the vital activity of organisms is studied by magnetobiology. In near-Earth space, the magnetic field forms a magnetic trap for high-energy charged particles - the Earth's radiation belt. Particles contained in the radiation belt pose a significant danger during space flights. The origin of the Earth's magnetic field is associated with the convective movements of a conductive liquid substance in the Earth's core.

Direct measurements with the help of spacecraft showed that the cosmic bodies closest to the Earth - the Moon, the planets Venus and Mars do not have their own magnetic field, similar to the earth's. From other planets solar system only Jupiter and, apparently, Saturn have their own magnetic fields, sufficient to create planetary magnetic traps. Magnetic fields up to 10 gauss and a number of characteristic phenomena (magnetic storms, synchrotron radio emission, and others) have been found on Jupiter, indicating a significant role of the magnetic field in planetary processes.

The interplanetary magnetic field is mainly the field of the solar wind (continuously expanding plasma of the solar corona). Near the Earth's orbit, the interplanetary field is ~ 10 -4 -10 -5 Gs. The regularity of the interplanetary magnetic field can be disturbed due to the development of various types of plasma instability, the passage of shock waves, and the propagation of streams of fast particles generated by solar flares.

In all processes on the Sun - flares, the appearance of spots and prominences, the birth of solar cosmic rays, the magnetic field plays an important role. Measurements based on the Zeeman effect showed that the magnetic field of sunspots reaches several thousand gauss, prominences are held by fields of ~ 10-100 gauss (with an average value of the total magnetic field of the Sun ~ 1 gauss).

Magnetic storms

Magnetic storms are strong disturbances of the Earth's magnetic field, which sharply disrupt the smooth daily course of the elements of terrestrial magnetism. Magnetic storms last from several hours to several days and are observed simultaneously throughout the Earth.

As a rule, magnetic storms consist of preliminary, initial and main phases, as well as a recovery phase. In the preliminary phase, insignificant changes in the geomagnetic field are observed (mainly in high latitudes), as well as the excitation of characteristic short-period field oscillations. The initial phase is characterized by a sudden change in individual field components throughout the Earth, and the main phase is characterized by large field fluctuations and a strong decrease in the horizontal component. In the magnetic storm recovery phase, the field returns to its normal value.

Influence of the solar wind
to the earth's magnetosphere

Magnetic storms are caused by solar plasma flows from active regions of the Sun, superimposed on a quiet sunny wind. Therefore, magnetic storms are more often observed near the maxima of the 11-year cycle solar activity. Reaching the Earth, solar plasma flows increase the compression of the magnetosphere, causing the initial phase of a magnetic storm, and partially penetrate into the Earth's magnetosphere. The entry of high-energy particles into the upper atmosphere of the Earth and their impact on the magnetosphere lead to the generation and amplification of electric currents in it, reaching the highest intensity in the polar regions of the ionosphere, which is the reason for the presence of a high-latitude zone of magnetic activity. Changes in the magnetospheric-ionospheric current systems manifest themselves on the Earth's surface in the form of irregular magnetic disturbances.

In the phenomena of the microcosm, the role of the magnetic field is just as essential as on a cosmic scale. This is due to the existence of all particles - the structural elements of matter (electrons, protons, neutrons), a magnetic moment, as well as the action of a magnetic field on moving electric charges.

Application of magnetic fields in science and technology. Magnetic fields are usually subdivided into weak (up to 500 Gs), medium (500 Gs - 40 kGs), strong (40 kGs - 1 MGs) and superstrong (over 1 MGs). Practically all electrical engineering, radio engineering and electronics are based on the use of weak and medium magnetic fields. Weak and medium magnetic fields are obtained using permanent magnets, electromagnets, uncooled solenoids, superconducting magnets.

Magnetic field sources

All sources of magnetic fields can be divided into artificial and natural. The main natural sources of the magnetic field are the Earth's own magnetic field and the solar wind. To artificial sources can be attributed to all the electromagnetic fields that so abound in our modern world and our houses in particular. Read more about, and read on ours.

Electric transport is a powerful source of magnetic field in the range from 0 to 1000 Hz. Rail transport uses alternating current. City transport is permanent. The maximum values of the magnetic field induction in suburban electric transport reach 75 µT, the average values are about 20 µT. Average values for DC-driven vehicles are fixed at 29 µT. In trams, where the return wire is rails, the magnetic fields compensate each other at a much greater distance than the wires of a trolleybus, and inside the trolleybus the magnetic field fluctuations are small even during acceleration. But the biggest fluctuations in the magnetic field are in the subway. When the composition is sent, the magnitude of the magnetic field on the platform is 50-100 μT and more, exceeding the geomagnetic field. Even when the train has long since disappeared into the tunnel, the magnetic field does not return to its former value. Only after the composition passes the next connection point to the contact rail, the magnetic field will return to the old value. True, sometimes it does not have time: the next train is already approaching the platform, and when it slows down, the magnetic field changes again. In the car itself, the magnetic field is even stronger - 150-200 μT, that is, ten times more than in a conventional train.

The values of the induction of the magnetic fields that we most often encounter in Everyday life shown in the diagram below. Looking at this diagram, it becomes clear that we are exposed to magnetic fields all the time and everywhere. According to some scientists, magnetic fields with an induction over 0.2 µT are considered harmful. Naturally, certain precautions should be taken to protect ourselves from the harmful effects of the fields around us. Just by following a few simple rules, you can significantly reduce the impact of magnetic fields on your body.

The current SanPiN 2.1.2.2801-10 “Changes and additions No. 1 to SanPiN 2.1.2.2645-10 “Sanitary and epidemiological requirements for living conditions in residential buildings and premises” says the following: “Maximum allowable level the weakening of the geomagnetic field in the premises of residential buildings is set equal to 1.5". Also, the maximum permissible values of the intensity and strength of the magnetic field with a frequency of 50 Hz are set:

in living quarters - 5 μT or 4 A/m;
in non-residential premises of residential buildings, in residential areas, including on the territory of garden plots - 10 μT or 8 A/m.

Based on these standards, everyone can calculate how many electrical appliances can be in the on state and in the standby state in each a specific room or, on the basis of which recommendations will be issued for the normalization of living space.

What is a magnetic field

At what point does a magnet begin to attract towards itself? Around each magnet there is a magnetic field, falling into which, objects begin to be attracted to it. The size of such a field may vary depending on the size of the magnet and its own properties.

Wikipedia term:

Magnetic field - a force field acting on moving electric charges and on bodies with a magnetic moment, regardless of the state of their movement, the magnetic component of the electromagnetic field.

Where does the magnetic field come from

The magnetic field can be created by the current of charged particles or by the magnetic moments of electrons in atoms, as well as by the magnetic moments of other particles, although to a much lesser extent.

Manifestation of a magnetic field

The magnetic field manifests itself in the effect on the magnetic moments of particles and bodies, on moving charged particles or conductors with . The force acting on an electrically charged particle moving in a magnetic field is called the Lorentz force, which is always directed perpendicular to the vectors v and B. It is proportional to the charge of the particle q, the component of the velocity v, perpendicular to the direction of the magnetic field vector B, and the magnitude of the magnetic field induction B.

What objects have a magnetic field

We often do not think about it, but many (if not all) of the objects around us are magnets. We are used to the fact that a magnet is a pebble with a pronounced force of attraction towards itself, but in fact, almost everything has an attraction force, it is just much lower. Let's take at least our planet - we do not fly away into space, although we do not hold on to the surface with anything. The field of the Earth is much weaker than the field of a pebble magnet, therefore it keeps us only due to its huge size - if you have ever seen people walking on the Moon (which is four times smaller in diameter), you will clearly understand what we are talking about . The attraction of the Earth is based largely on the metal components. Its crust and core - they have a powerful magnetic field. You may have heard that near large deposits of iron ore, compasses stop showing the right direction to the north - this is because the principle of the compass is based on the interaction of magnetic fields, and iron ore attracts its needle.