Magnetic field is its basic physical properties. Basic properties of a magnetic field

According to modern ideas, it was formed approximately 4.5 billion years ago, and from that moment our planet has been surrounded by a magnetic field. Everything on Earth, including people, animals and plants, is affected by it.

The magnetic field extends to an altitude of about 100,000 km (Fig. 1). It deflects or captures solar wind particles that are harmful to all living organisms. These charged particles form the Earth's radiation belt, and the entire region of near-Earth space in which they are located is called magnetosphere(Fig. 2). On the side of the Earth illuminated by the Sun, the magnetosphere is limited by a spherical surface with a radius of approximately 10-15 Earth radii, and on the opposite side it is extended like a comet's tail over a distance of up to several thousand Earth radii, forming a geomagnetic tail. The magnetosphere is separated from the interplanetary field by a transition region.

Earth's magnetic poles

The axis of the earth's magnet is inclined relative to the earth's rotation axis by 12°. It is located approximately 400 km away from the center of the Earth. The points at which this axis intersects the surface of the planet are magnetic poles. The Earth's magnetic poles do not coincide with the true geographic poles. Currently, the coordinates of the magnetic poles are as follows: north - 77° north latitude. and 102°W; southern - (65° S and 139° E).

Rice. 1. The structure of the Earth’s magnetic field

Rice. 2. Structure of the magnetosphere

Lines of force running from one magnetic pole to another are called magnetic meridians. An angle is formed between the magnetic and geographic meridians, called magnetic declination. Every place on Earth has its own declination angle. In the Moscow region the declination angle is 7° to the east, and in Yakutsk it is about 17° to the west. This means that the northern end of the compass needle in Moscow deviates by T to the right of the geographic meridian passing through Moscow, and in Yakutsk - by 17° to the left of the corresponding meridian.

A freely suspended magnetic needle is located horizontally only on the line of the magnetic equator, which does not coincide with the geographical one. If you move north of the magnetic equator, the northern end of the needle will gradually descend. The angle formed by a magnetic needle and a horizontal plane is called magnetic inclination. At the North and South magnetic poles, the magnetic inclination is greatest. It is equal to 90°. At the North Magnetic Pole, a freely suspended magnetic needle will be installed vertically with its northern end down, and at the South Magnetic Pole its southern end will go down. Thus, the magnetic needle shows the direction of the magnetic field lines above the earth's surface.

Over time, the position of the magnetic poles relative to the earth's surface changes.

The magnetic pole was discovered by explorer James C. Ross in 1831, hundreds of kilometers from its current location. On average, it moves 15 km in one year. In recent years, the speed of movement of the magnetic poles has increased sharply. For example, the North Magnetic Pole is currently moving at a speed of about 40 km per year.

The reversal of the Earth's magnetic poles is called magnetic field inversion.

Throughout the geological history of our planet, the Earth's magnetic field has changed its polarity more than 100 times.

The magnetic field is characterized by intensity. In some places on Earth, magnetic field lines deviate from the normal field, forming anomalies. For example, in the area of ​​the Kursk Magnetic Anomaly (KMA), the field strength is four times higher than normal.

There are daily variations in the Earth's magnetic field. The reason for these changes in the Earth's magnetic field is electric currents flowing in the atmosphere at high altitudes. They are caused by solar radiation. Under the influence of the solar wind, the Earth's magnetic field is distorted and acquires a “trail” in the direction from the Sun, which extends for hundreds of thousands of kilometers. The main cause of the solar wind, as we already know, is the enormous ejections of matter from the solar corona. As they move towards the Earth, they turn into magnetic clouds and lead to strong, sometimes extreme disturbances on the Earth. Particularly strong disturbances of the Earth's magnetic field - magnetic storms. Some magnetic storms begin suddenly and almost simultaneously across the entire Earth, while others develop gradually. They can last for several hours or even days. Magnetic storms often occur 1-2 days after a solar flare due to the Earth passing through a stream of particles ejected by the Sun. Based on the delay time, the speed of such a corpuscular flow is estimated at several million km/h.

During strong magnetic storms, the normal operation of the telegraph, telephone and radio is disrupted.

Magnetic storms are often observed at latitude 66-67° (in the aurora zone) and occur simultaneously with auroras.

The structure of the Earth's magnetic field varies depending on the latitude of the area. The permeability of the magnetic field increases towards the poles. Over the polar regions, the magnetic field lines are more or less perpendicular to the earth's surface and have a funnel-shaped configuration. Through them, part of the solar wind from the dayside penetrates into the magnetosphere and then into the upper atmosphere. During magnetic storms, particles from the tail of the magnetosphere rush here, reaching the boundaries of the upper atmosphere in the high latitudes of the Northern and Southern Hemispheres. It is these charged particles that cause the auroras here.

So, magnetic storms and daily changes in the magnetic field are explained, as we have already found out, by solar radiation. But what is the main reason that creates the permanent magnetism of the Earth? Theoretically, it was possible to prove that 99% of the Earth’s magnetic field is caused by sources hidden inside the planet. The main magnetic field is caused by sources located in the depths of the Earth. They can be roughly divided into two groups. The main part of them is associated with processes in the earth's core, where, due to continuous and regular movements of electrically conductive matter, a system of electric currents is created. The other is due to the fact that the rocks of the earth’s crust, when magnetized by the main electric field (the field of the core), create their own magnetic field, which is summed with the magnetic field of the core.

In addition to the magnetic field around the Earth, there are other fields: a) gravitational; b) electric; c) thermal.

Gravitational field The earth is called the gravity field. It is directed along a plumb line perpendicular to the surface of the geoid. If the Earth had the shape of an ellipsoid of revolution and masses were evenly distributed in it, then it would have a normal gravitational field. The difference between the intensity of the real gravitational field and the theoretical one is a gravity anomaly. Different material composition and density of rocks cause these anomalies. But other reasons are also possible. They can be explained by the following process - the equilibrium of the solid and relatively light earth's crust on the heavier upper mantle, where the pressure of the overlying layers is equalized. These currents cause tectonic deformations, the movement of lithospheric plates and thereby create the macrorelief of the Earth. Gravity holds the atmosphere, hydrosphere, people, animals on Earth. Gravity must be taken into account when studying processes in the geographic envelope. The term " geotropism" are the growth movements of plant organs, which, under the influence of the force of gravity, always ensure the vertical direction of growth of the primary root perpendicular to the surface of the Earth. Gravity biology uses plants as experimental subjects.

If gravity is not taken into account, it is impossible to calculate the initial data for launching rockets and spacecraft, to carry out gravimetric exploration of ore deposits, and, finally, the further development of astronomy, physics and other sciences is impossible.

There is probably no person who has not at least once thought about what a magnetic field is. Throughout history, they have tried to explain it with ethereal vortices, quirks, magnetic monopolies, and much more.

We all know that magnets facing each other with like poles repel, and those with opposite poles attract. This power will

Vary depending on how far the two parts are from each other. It turns out that the object being described creates a magnetic halo around itself. At the same time, when two alternating fields having the same frequency are superimposed, when one is shifted in space relative to the other, an effect is obtained that is commonly called a “rotating magnetic field.”

The size of the object being studied is determined by the force with which a magnet is attracted to another or to iron. Accordingly, the greater the attraction, the greater the field. The force can be measured using the usual means of placing a small piece of iron on one side, and weights on the other, designed to balance the metal against the magnet.

For a more accurate understanding of the subject matter, you should study the fields:

Answering the question about what a magnetic field is, it is worth saying that humans also have it. At the end of 1960, thanks to the intensive development of physics, the SQUID measuring device was created. Its action is explained by the laws of quantum phenomena. It is a sensitive element of magnetometers used to study the magnetic field and such

quantities, for example, like

“SQUID” quickly began to be used to measure fields generated by living organisms and, of course, humans. This gave impetus to the development of new areas of research based on the interpretation of the information supplied by such a device. This direction is called “biomagnetism”.

Why, when determining what a magnetic field is, were no studies carried out in this area before? It turned out that it is very weak in organisms, and its measurement is a difficult physical task. This is due to the presence of a huge amount of magnetic noise in the surrounding space. Therefore, it is simply not possible to answer the question of what the human magnetic field is and study it without the use of specialized protective measures.

Such a “halo” appears around a living organism for three main reasons. Firstly, thanks to ionic points that appear as a result of the electrical activity of cell membranes. Secondly, due to the presence of ferrimagnetic tiny particles that enter the body accidentally or are introduced into the body. Third, when external magnetic fields are superimposed, the result is heterogeneous susceptibility of different organs, which distorts the superimposed spheres.

The Earth's magnetic field is a formation generated by sources inside the planet. It is the object of study in the corresponding section of geophysics. Next, let's take a closer look at what the Earth's magnetic field is and how it is formed.

general information

Not far from the Earth's surface, approximately at a distance of three of its radii, the lines of force from the magnetic field are located along a system of “two polar charges”. There is an area called the "plasma sphere" here. With distance from the surface of the planet, the influence of the flow of ionized particles from the solar corona increases. This leads to compression of the magnetosphere from the side of the Sun, and, on the contrary, the Earth’s magnetic field is stretched from the opposite, shadow side.

Plasma Sphere

The directional movement of charged particles in the upper layers of the atmosphere (ionosphere) has a noticeable effect on the Earth's surface magnetic field. The location of the latter is one hundred kilometers and above from the surface of the planet. The Earth's magnetic field holds the plasmasphere. However, its structure strongly depends on the activity of the solar wind and its interaction with the confining layer. And the frequency of magnetic storms on our planet is determined by flares on the Sun.

Terminology

There is a concept "magnetic axis of the Earth". This is a straight line that passes through the corresponding poles of the planet. The "magnetic equator" is the large circle of the plane perpendicular to this axis. The vector on it has a direction close to horizontal. The average strength of the Earth's magnetic field is significantly dependent on geographic location. It is approximately equal to 0.5 Oe, that is, 40 A/m. At the magnetic equator, this same indicator is approximately 0.34 Oe, and near the poles it is close to 0.66 Oe. In some anomalies of the planet, for example, within the Kursk anomaly, the indicator is increased and amounts to 2 Oe. Field lines of the Earth’s magnetosphere with a complex structure , projected onto its surface and converging at its own poles, are called “magnetic meridians”.

Nature of occurrence. Assumptions and conjectures

Not long ago, the assumption about the connection between the emergence of the Earth’s magnetosphere and the flow of current in the liquid metal core, located at a distance of a quarter to a third of the radius of our planet, gained the right to exist. Scientists also have an assumption about the so-called “telluric currents” flowing near the earth’s crust. It should be said that over time there is a transformation of formation. The Earth's magnetic field has changed several times over the past one hundred and eighty years. This is recorded in the oceanic crust, and this is evidenced by studies of remanent magnetization. By comparing areas on both sides of the ocean ridges, the time of divergence of these areas is determined.

Earth's magnetic pole shift

The location of these parts of the planet is not constant. The fact of their displacements has been recorded since the end of the nineteenth century. In the Southern Hemisphere, the magnetic pole shifted by 900 km during this time and ended up in the Indian Ocean. Similar processes are taking place in the Northern part. Here the pole moves towards a magnetic anomaly in Eastern Siberia. From 1973 to 1994, the distance by which the site moved here was 270 km. These pre-calculated data were later confirmed by measurements. According to the latest data, the speed of movement of the magnetic pole of the Northern Hemisphere has increased significantly. It grew from 10 km/year in the seventies of the last century to 60 km/year at the beginning of this century. At the same time, the strength of the earth's magnetic field decreases unevenly. So, over the past 22 years, in some places it has decreased by 1.7%, and somewhere by 10%, although there are also areas where it, on the contrary, has increased. The acceleration in the displacement of the magnetic poles (by approximately 3 km per year) gives reason to assume that their movement observed today is not an excursion, but another inversion.

This is indirectly confirmed by the increase in the so-called “polar gaps” in the south and north of the magnetosphere. The ionized material of the solar corona and space rapidly penetrates into the resulting expansions. As a result, an increasing amount of energy is collected in the circumpolar regions of the Earth, which in itself is fraught with additional heating of the polar ice caps.

Coordinates

In the science of cosmic rays, geomagnetic field coordinates are used, named after the scientist McIlwain. He was the first to propose the use of them, since they are based on modified versions of the activity of charged elements in a magnetic field. For a point, two coordinates are used (L, B). They characterize the magnetic shell (McIlwain parameter) and field induction L. The latter is a parameter equal to the ratio of the average distance of the sphere from the center of the planet to its radius.

"Magnetic inclination"

Several thousand years ago, the Chinese made an amazing discovery. They found that magnetized objects can be positioned in a certain direction. And in the middle of the sixteenth century, Georg Cartmann, a German scientist, made another discovery in this area. This is how the concept of “magnetic inclination” appeared. This name refers to the angle of deviation of the arrow up or down from the horizontal plane under the influence of the planet’s magnetosphere.

From the history of research

In the region of the northern magnetic equator, which is different from the geographic equator, the northern end moves downwards, and in the southern, on the contrary, upwards. In 1600, the English physician William Gilbert first made assumptions about the presence of the Earth's magnetic field, which causes a certain behavior of objects that were previously magnetized. In his book, he described an experiment with a ball equipped with an iron arrow. As a result of his research, he came to the conclusion that the Earth is a large magnet. The English astronomer Henry Gellibrant also conducted experiments. As a result of his observations, he came to the conclusion that the Earth's magnetic field is subject to slow changes.

José de Acosta described the possibility of using a compass. He also established the difference between the Magnetic and North Poles, and in his famous History (1590) the theory of lines without magnetic deflection was substantiated. Christopher Columbus also made a significant contribution to the study of the issue under consideration. He was responsible for the discovery of the variability of magnetic declination. Transformations are made dependent on changes in geographic coordinates. Magnetic declination is the angle of deviation of the needle from the North-South direction. In connection with the discovery of Columbus, research intensified. Information about what the Earth's magnetic field is was extremely necessary for navigators. M.V. Lomonosov also worked on this problem. To study terrestrial magnetism, he recommended conducting systematic observations using permanent points (similar to observatories). It was also very important, according to Lomonosov, to do this at sea. This idea of ​​the great scientist was realized in Russia sixty years later. The discovery of the Magnetic Pole on the Canadian archipelago belongs to the polar explorer Englishman John Ross (1831). And in 1841 he discovered another pole of the planet, but in Antarctica. The hypothesis about the origin of the Earth's magnetic field was put forward by Carl Gauss. He soon proved that most of it is fed from a source inside the planet, but the reason for its minor deviations is in the external environment.

Just as a stationary electric charge acts on another charge through an electric field, an electric current acts on another current through magnetic field. The effect of a magnetic field on permanent magnets is reduced to its effect on charges moving in the atoms of a substance and creating microscopic circular currents.

The doctrine of electromagnetism based on two provisions:

• the magnetic field acts on moving charges and currents;
• a magnetic field arises around currents and moving charges.

Magnet interaction

Permanent magnet(or magnetic needle) is oriented along the Earth's magnetic meridian. The end that points north is called north pole(N), and the opposite end is south pole(S). Bringing two magnets closer to each other, we note that their like poles repel, and their unlike poles attract ( rice. 1 ).

If we separate the poles by cutting a permanent magnet into two parts, we will find that each of them will also have two poles, i.e. will be a permanent magnet ( rice. 2 ). Both poles - north and south - are inseparable from each other and have equal rights.

The magnetic field created by the Earth or permanent magnets is represented, like an electric field, by magnetic lines of force. A picture of the magnetic field lines of a magnet can be obtained by placing a sheet of paper over it, on which iron filings are sprinkled in an even layer. When exposed to a magnetic field, the sawdust becomes magnetized - each of them has north and south poles. The opposite poles tend to move closer to each other, but this is prevented by the friction of the sawdust on the paper. If you tap the paper with your finger, the friction will decrease and the filings will be attracted to each other, forming chains depicting magnetic field lines.

On rice. 3 shows the location of sawdust and small magnetic arrows in the field of a direct magnet, indicating the direction of the magnetic field lines. This direction is taken to be the direction of the north pole of the magnetic needle.

Oersted's experience. Magnetic field of current

At the beginning of the 19th century. Danish scientist Ørsted made an important discovery when he discovered action of electric current on permanent magnets . He placed a long wire near a magnetic needle. When current was passed through the wire, the arrow rotated, trying to position itself perpendicular to it ( rice. 4 ). This could be explained by the emergence of a magnetic field around the conductor.

The magnetic field lines created by a straight conductor carrying current are concentric circles located in a plane perpendicular to it, with centers at the point through which the current passes ( rice. 5 ). The direction of the lines is determined by the right screw rule:

If the screw is rotated in the direction of the field lines, it will move in the direction of the current in the conductor .

The strength characteristic of the magnetic field is magnetic induction vector B . At each point it is directed tangentially to the field line. Electric field lines begin on positive charges and end on negative ones, and the force acting on the charge in this field is directed tangentially to the line at each point. Unlike the electric field, the magnetic field lines are closed, which is due to the absence of “magnetic charges” in nature.

The magnetic field of a current is fundamentally no different from the field created by a permanent magnet. In this sense, an analogue of a flat magnet is a long solenoid - a coil of wire, the length of which is significantly greater than its diameter. The diagram of the lines of the magnetic field created by him, shown in rice. 6 , is similar to that for a flat magnet ( rice. 3 ). The circles indicate the cross sections of the wire forming the solenoid winding. Currents flowing through the wire away from the observer are indicated by crosses, and currents in the opposite direction - towards the observer - are indicated by dots. The same notations are accepted for magnetic field lines when they are perpendicular to the drawing plane ( rice. 7 a, b).

The direction of the current in the solenoid winding and the direction of the magnetic field lines inside it are also related by the rule of the right screw, which in this case is formulated as follows:

If you look along the axis of the solenoid, the current flowing in a clockwise direction creates a magnetic field in it, the direction of which coincides with the direction of movement of the right screw ( rice. 8 )

Based on this rule, it is easy to understand that the solenoid shown in rice. 6 , the north pole is its right end, and the south pole is its left.

The magnetic field inside the solenoid is uniform - the magnetic induction vector has a constant value there (B = const). In this respect, the solenoid is similar to a parallel-plate capacitor, within which a uniform electric field is created.

Force acting in a magnetic field on a current-carrying conductor

It was experimentally established that a force acts on a current-carrying conductor in a magnetic field. In a uniform field, a straight conductor of length l, through which a current I flows, located perpendicular to the field vector B, experiences the force: F = I l B .

The direction of the force is determined left hand rule:

If the four outstretched fingers of the left hand are placed in the direction of the current in the conductor, and the palm is perpendicular to vector B, then the extended thumb will indicate the direction of the force acting on the conductor (rice. 9 ).

It should be noted that the force acting on a conductor with current in a magnetic field is not directed tangentially to its lines of force, like an electric force, but perpendicular to them. A conductor located along the lines of force is not affected by magnetic force.

The equation F = IlB allows you to give a quantitative characteristic of the magnetic field induction.

Attitude does not depend on the properties of the conductor and characterizes the magnetic field itself.

The magnitude of the magnetic induction vector B is numerically equal to the force acting on a conductor of unit length located perpendicular to it, through which a current of one ampere flows.

In the SI system, the unit of magnetic field induction is the tesla (T):

A magnetic field. Tables, diagrams, formulas

(Interaction of magnets, Oersted's experiment, magnetic induction vector, vector direction, superposition principle. Graphic representation of magnetic fields, magnetic induction lines. Magnetic flux, energy characteristic of the field. Magnetic forces, Ampere force, Lorentz force. Movement of charged particles in a magnetic field. Magnetic properties of matter, Ampere's hypothesis)

Topic: Magnetic field

Prepared by: Baygarashev D.M.

Checked by: Gabdullina A.T.

A magnetic field

If two parallel conductors are connected to a current source so that an electric current passes through them, then, depending on the direction of the current in them, the conductors either repel or attract.

An explanation of this phenomenon is possible from the position of the emergence of a special type of matter around the conductors - a magnetic field.

The forces with which current-carrying conductors interact are called magnetic.

A magnetic field- this is a special type of matter, the specific feature of which is the effect on a moving electric charge, current-carrying conductors, bodies with a magnetic moment, with a force depending on the charge velocity vector, the direction of the current in the conductor and the direction of the magnetic moment of the body.

The history of magnetism goes back to ancient times, to the ancient civilizations of Asia Minor. It was on the territory of Asia Minor, in Magnesia, that rocks were found, samples of which were attracted to each other. Based on the name of the area, such samples began to be called “magnets”. Any bar or horseshoe-shaped magnet has two ends called poles; It is in this place that its magnetic properties are most pronounced. If you hang a magnet on a string, one pole will always point north. The compass is based on this principle. The north-facing pole of a free-hanging magnet is called the magnet's north pole (N). The opposite pole is called the south pole (S).

Magnetic poles interact with each other: like poles repel, and unlike poles attract. Similar to the concept of an electric field surrounding an electric charge, the concept of a magnetic field around a magnet is introduced.

In 1820, Oersted (1777-1851) discovered that a magnetic needle located next to an electrical conductor is deflected when current flows through the conductor, i.e., a magnetic field is created around the current-carrying conductor. If we take a frame with current, then the external magnetic field interacts with the magnetic field of the frame and has an orienting effect on it, i.e. there is a position of the frame at which the external magnetic field has a maximum rotating effect on it, and there is a position when the torque force is zero.

The magnetic field at any point can be characterized by vector B, which is called vector of magnetic induction or magnetic induction at the point.

Magnetic induction B is a vector physical quantity, which is a force characteristic of the magnetic field at a point. It is equal to the ratio of the maximum mechanical moment of forces acting on a frame with current placed in a uniform field to the product of the current strength in the frame and its area:

The direction of the magnetic induction vector B is taken to be the direction of the positive normal to the frame, which is related to the current in the frame by the rule of the right screw, with a mechanical torque equal to zero.

In the same way as the electric field strength lines were depicted, the magnetic field induction lines are depicted. The magnetic field line is an imaginary line, the tangent to which coincides with the direction B at a point.

The directions of the magnetic field at a given point can also be defined as the direction that indicates

the north pole of the compass needle placed at this point. It is believed that the magnetic field lines are directed from the north pole to the south.

The direction of the magnetic induction lines of the magnetic field created by an electric current that flows through a straight conductor is determined by the gimlet or right-hand screw rule. The direction of the magnetic induction lines is taken to be the direction of rotation of the screw head, which would ensure its translational movement in the direction of the electric current (Fig. 59).

where n01 = 4 Pi 10 -7 V s/(A m). - magnetic constant, R - distance, I - current strength in the conductor.

Unlike electrostatic field lines, which begin at a positive charge and end at a negative charge, magnetic field lines are always closed. No magnetic charge similar to electric charge was detected.

One tesla (1 T) is taken as a unit of induction - the induction of such a uniform magnetic field in which a maximum mechanical torque of 1 N m acts on a frame with an area of ​​1 m2, through which a current of 1 A flows.

The magnetic field induction can also be determined by the force acting on a current-carrying conductor in a magnetic field.

A current-carrying conductor placed in a magnetic field is acted upon by an Ampere force, the magnitude of which is determined by the following expression:

where I is the current strength in the conductor, l - the length of the conductor, B is the magnitude of the magnetic induction vector, and is the angle between the vector and the direction of the current.

The direction of the Ampere force can be determined by the rule of the left hand: we place the palm of the left hand so that the magnetic induction lines enter the palm, we place four fingers in the direction of the current in the conductor, then the bent thumb shows the direction of the Ampere force.

Taking into account that I = q 0 nSv, and substituting this expression into (3.21), we obtain F = q 0 nSh/B sin a. The number of particles (N) in a given volume of a conductor is N = nSl, then F = q 0 NvB sin a.

Let us determine the force exerted by the magnetic field on an individual charged particle moving in a magnetic field:

This force is called the Lorentz force (1853-1928). The direction of the Lorentz force can be determined by the rule of the left hand: we place the palm of the left hand so that the lines of magnetic induction enter the palm, four fingers show the direction of movement of the positive charge, the large bent finger shows the direction of the Lorentz force.

The interaction force between two parallel conductors carrying currents I 1 and I 2 is equal to:

Where l - part of a conductor located in a magnetic field. If the currents are in the same direction, then the conductors attract (Fig. 60), if they are in the opposite direction, they repel. The forces acting on each conductor are equal in magnitude and opposite in direction. Formula (3.22) is the basis for determining the unit of current 1 ampere (1 A).

The magnetic properties of a substance are characterized by a scalar physical quantity - magnetic permeability, which shows how many times the induction B of the magnetic field in a substance that completely fills the field differs in magnitude from the induction B 0 of the magnetic field in a vacuum:

According to their magnetic properties, all substances are divided into diamagnetic, paramagnetic And ferromagnetic.

Let us consider the nature of the magnetic properties of substances.

Electrons in the shell of atoms of a substance move in different orbits. To simplify, we consider these orbits to be circular, and each electron orbiting an atomic nucleus can be considered as a circular electric current. Each electron, like a circular current, creates a magnetic field, which we call orbital. In addition, an electron in an atom has its own magnetic field, called a spin field.

If, when introduced into an external magnetic field with induction B 0, induction B is created inside the substance< В 0 , то такие вещества называются диамагнитными (n< 1).

IN diamagnetic In materials in the absence of an external magnetic field, the magnetic fields of electrons are compensated, and when they are introduced into a magnetic field, the induction of the magnetic field of the atom becomes directed against the external field. The diamagnetic material is pushed out of the external magnetic field.

U paramagnetic materials, the magnetic induction of electrons in atoms is not completely compensated, and the atom as a whole turns out to be like a small permanent magnet. Usually in a substance all these small magnets are oriented randomly, and the total magnetic induction of all their fields is zero. If you place a paramagnet in an external magnetic field, then all the small magnets - atoms will turn in the external magnetic field like compass needles and the magnetic field in the substance will increase ( n >= 1).

Ferromagnetic are those materials in which n" 1. In ferromagnetic materials, so-called domains are created, macroscopic regions of spontaneous magnetization.

In different domains, magnetic field inductions have different directions (Fig. 61) and in a large crystal

mutually compensate each other. When a ferromagnetic sample is introduced into an external magnetic field, the boundaries of individual domains shift so that the volume of domains oriented along the external field increases.

With an increase in the induction of the external field B 0, the magnetic induction of the magnetized substance increases. At some values ​​of B 0, the induction stops sharply increasing. This phenomenon is called magnetic saturation.

A characteristic feature of ferromagnetic materials is the phenomenon of hysteresis, which consists in the ambiguous dependence of the induction in the material on the induction of the external magnetic field when it changes.

The magnetic hysteresis loop is a closed curve (cdc`d`c), expressing the dependence of the induction in the material on the amplitude of the induction of the external field with a periodic rather slow change in the latter (Fig. 62).

The hysteresis loop is characterized by the following values: B s, Br, B c. B s - maximum value of material induction at B 0s; In r is the residual induction, equal to the induction value in the material when the induction of the external magnetic field decreases from B 0s to zero; -B c and B c - coercive force - a value equal to the induction of the external magnetic field necessary to change the induction in the material from residual to zero.

For each ferromagnet there is a temperature (Curie point (J. Curie, 1859-1906), above which the ferromagnet loses its ferromagnetic properties.

There are two ways to bring a magnetized ferromagnet into a demagnetized state: a) heat above the Curie point and cool; b) magnetize the material with an alternating magnetic field with a slowly decreasing amplitude.

Ferromagnets with low residual induction and coercive force are called soft magnetic. They find application in devices where ferromagnets often have to be remagnetized (cores of transformers, generators, etc.).

Magnetically hard ferromagnets, which have a high coercive force, are used to make permanent magnets.