What is a magnetic field line. Magnetic field lines

Themes USE codifier : interaction of magnets, magnetic field of a conductor with current.

The magnetic properties of matter have been known to people for a long time. Magnets got their name from the ancient city of Magnesia: a mineral (later called magnetic iron ore or magnetite) was widespread in its vicinity, pieces of which attracted iron objects.

Interaction of magnets

On two sides of each magnet are located North Pole and South Pole. Two magnets are attracted to each other by opposite poles and repel by like poles. Magnets can act on each other even through a vacuum! All this is reminiscent of the interaction of electric charges, however the interaction of magnets is not electrical. This is evidenced by the following experimental facts.

The magnetic force weakens when the magnet is heated. The strength of the interaction of point charges does not depend on their temperature.

The magnetic force is weakened by shaking the magnet. Nothing similar happens with electrically charged bodies.

Positive electric charges can be separated from negative ones (for example, when bodies are electrified). But it is impossible to separate the poles of the magnet: if you cut the magnet into two parts, then poles also appear at the place of the cut, and the magnet breaks up into two magnets with opposite poles at the ends (oriented in exactly the same way as the poles of the original magnet).

So the magnets always bipolar, they exist only in the form dipoles. Isolated magnetic poles (so-called magnetic monopoles- analogues of electric charge) in nature do not exist (in any case, they have not yet been experimentally detected). This is perhaps the most impressive asymmetry between electricity and magnetism.

Like electrically charged bodies, magnets act on electrical charges. However, the magnet only acts on moving charge; If the charge is at rest relative to the magnet, then no magnetic force acts on the charge. On the contrary, an electrified body acts on any charge, regardless of whether it is at rest or in motion.

According to modern concepts of the theory of short-range action, the interaction of magnets is carried out through magnetic field . Namely, a magnet creates a magnetic field in the surrounding space, which acts on another magnet and causes a visible attraction or repulsion of these magnets.

An example of a magnet is magnetic needle compass. With the help of a magnetic needle, one can judge the presence of a magnetic field in a given region of space, as well as the direction of the field.

Our planet Earth is a giant magnet. Not far from the geographic north pole of the Earth is the south magnetic pole. Therefore, the north end of the compass needle, turning to the south magnetic pole of the Earth, points to the geographical north. Hence, in fact, the name "north pole" of the magnet arose.

Magnetic field lines

The electric field, we recall, is investigated with the help of small test charges, by the action on which one can judge the magnitude and direction of the field. An analogue of a test charge in the case of a magnetic field is a small magnetic needle.

For example, you can get some geometric idea of ​​the magnetic field if you place in different points spaces are very small compass needles. Experience shows that the arrows will line up along certain lines - the so-called magnetic field lines. Let us define this concept in the form next three points.

1. Magnetic field lines, or magnetic lines of force- these are directed lines in space that have the following property: a small compass needle placed at each point of such a line is oriented tangentially to this line.

2. The direction of the magnetic field line is the direction of the northern ends of the compass needles located at the points of this line.

3. The thicker the lines go, the stronger the magnetic field in a given region of space..

The role of compass needles can be successfully performed by iron filings: in a magnetic field, small filings are magnetized and behave exactly like magnetic needles.

So, pouring iron filings around permanent magnet, we will see approximately the following pattern of magnetic field lines (Fig. 1).

Rice. 1. Permanent magnet field

The north pole of the magnet is indicated in blue and the letter ; the south pole - in red and the letter . Note that the field lines exit the north pole of the magnet and enter the south pole, because it is to the south pole of the magnet that the north end of the compass needle will point.

Oersted's experience

Although electrical and magnetic phenomena were known to people since antiquity, no relationship between them long time was not observed. For several centuries, research on electricity and magnetism proceeded in parallel and independently of each other.

The remarkable fact that electrical and magnetic phenomena are actually related to each other was first discovered in 1820 in the famous experiment of Oersted.

The scheme of Oersted's experiment is shown in fig. 2 (image from rt.mipt.ru). Above the magnetic needle (and - the north and south poles of the arrow) is a metal conductor connected to a current source. If you close the circuit, then the arrow turns perpendicular to the conductor!
This simple experiment pointed directly to the relationship between electricity and magnetism. The experiments that followed Oersted's experience firmly established the following pattern: the magnetic field is generated by electric currents and acts on currents.

Rice. 2. Oersted's experiment

The picture of the lines of the magnetic field generated by a conductor with current depends on the shape of the conductor.

Magnetic field of a straight wire with current

The magnetic field lines of a straight wire carrying current are concentric circles. The centers of these circles lie on the wire, and their planes are perpendicular to the wire (Fig. 3).

Rice. 3. Field of a direct wire with current

There are two alternative rules for determining the direction of direct current magnetic field lines.

hour hand rule. The field lines go counterclockwise when viewed so that the current flows towards us..

screw rule(or gimlet rule, or corkscrew rule- it's closer to someone ;-)). The field lines go where the screw (with conventional right-hand thread) must be turned to move along the thread in the direction of the current.

Use whichever rule suits you best. It's better to get used to the clockwise rule - you yourself will later see that it is more universal and easier to use (and then remember it with gratitude in your first year when you study analytic geometry).

On fig. 3, something new has also appeared: this is a vector, which is called magnetic field induction, or magnetic induction. The magnetic induction vector is an analog of the intensity vector electric field: he serves power characteristic magnetic field, determining the force with which the magnetic field acts on moving charges.

We will talk about forces in a magnetic field later, but for now we will only note that the magnitude and direction of the magnetic field is determined by the magnetic induction vector. At each point in space, the vector is directed in the same direction as the north end of the compass needle placed at this point, namely, tangent to the field line in the direction of this line. The magnetic induction is measured in teslach(Tl).

As in the case of an electric field, for the induction of a magnetic field, superposition principle. It lies in the fact that induction of magnetic fields created at a given point by various currents are added vectorially and give the resulting vector of magnetic induction:.

The magnetic field of a coil with current

Consider a circular coil through which a direct current circulates. We do not show the source that creates the current in the figure.

The picture of the lines of the field of our turn will have approximately the following form (Fig. 4).

Rice. 4. Field of the coil with current

It will be important for us to be able to determine in which half-space (relative to the plane of the coil) the magnetic field is directed. Again we have two alternative rules.

hour hand rule. The field lines go there, looking from where the current seems to be circulating counterclockwise.

screw rule. The field lines go where the screw (with conventional right hand threads) would move if rotated in the direction of the current.

As you can see, the roles of the current and the field are reversed - in comparison with the formulations of these rules for the case of direct current.

The magnetic field of a coil with current

Coil it will turn out, if tightly, coil to coil, wind the wire into a sufficiently long spiral (Fig. 5 - image from the site en.wikipedia.org). The coil may have several tens, hundreds or even thousands of turns. The coil is also called solenoid.

Rice. 5. Coil (solenoid)

The magnetic field of one turn, as we know, does not look very simple. Fields? individual turns of the coil are superimposed on each other, and it would seem that the result should be a very confusing picture. However, this is not the case: the field of a long coil has an unexpectedly simple structure (Fig. 6).

Rice. 6. coil field with current

In this figure, the current in the coil goes counterclockwise when viewed from the left (this will happen if, in Fig. 5, the right end of the coil is connected to the “plus” of the current source, and the left end to the “minus”). We see that the magnetic field of the coil has two characteristic properties.

1. Inside the coil, away from its edges, the magnetic field is homogeneous: at each point, the magnetic induction vector is the same in magnitude and direction. The field lines are parallel straight lines; they bend only near the edges of the coil when they go out.

2. Outside the coil, the field is close to zero. The more turns in the coil, the weaker the field outside it.

Note that an infinitely long coil does not emit a field at all: there is no magnetic field outside the coil. Inside such a coil, the field is uniform everywhere.

Doesn't it remind you of anything? A coil is the "magnetic" counterpart of a capacitor. You remember that a capacitor creates a homogeneous electric field, whose lines are bent only near the edges of the plates, and outside the capacitor, the field is close to zero; a capacitor with infinite plates does not release the field at all, and the field is uniform everywhere inside it.

And now - the main observation. Compare, please, the picture of the magnetic field lines outside the coil (Fig. 6) with the field lines of the magnet in Fig. one . It's the same thing, isn't it? And now we come to a question that you probably had a long time ago: if a magnetic field is generated by currents and acts on currents, then what is the reason for the appearance of a magnetic field near a permanent magnet? After all, this magnet does not seem to be a conductor with current!

Ampère's hypothesis. Elementary currents

At first, it was thought that the interaction of magnets was due to special magnetic charges concentrated at the poles. But, unlike electricity, no one could isolate the magnetic charge; after all, as we have already said, it was not possible to obtain separately the north and south poles of the magnet - the poles are always present in the magnet in pairs.

Doubts about magnetic charges were aggravated by the experience of Oersted, when it turned out that the magnetic field is generated by an electric current. Moreover, it turned out that for any magnet it is possible to choose a conductor with a current of the appropriate configuration, such that the field of this conductor coincides with the field of the magnet.

Ampere put forward a bold hypothesis. There are no magnetic charges. The action of a magnet is explained by closed electric currents inside it..

What are these currents? These elementary currents circulate within atoms and molecules; they are associated with the movement of electrons in atomic orbits. The magnetic field of any body is made up of the magnetic fields of these elementary currents.

Elementary currents can be randomly located relative to each other. Then their fields cancel each other, and the body does not show magnetic properties.

But if elementary currents are coordinated, then their fields, adding up, reinforce each other. The body becomes a magnet (Fig. 7; the magnetic field will be directed towards us; the north pole of the magnet will also be directed towards us).

Rice. 7. Elementary magnet currents

Ampere's hypothesis about elementary currents clarified the properties of magnets. Heating and shaking a magnet destroys the arrangement of its elementary currents, and magnetic properties weaken. The inseparability of the magnet poles became obvious: at the place where the magnet was cut, we get the same elementary currents at the ends. The ability of a body to be magnetized in a magnetic field is explained by the coordinated alignment of elementary currents that “turn” properly (read about the rotation of a circular current in a magnetic field in the next sheet).

Ampère's hypothesis turned out to be correct - it showed further development physics. The concept of elementary currents has become an integral part of the theory of the atom, developed already in the twentieth century - almost a hundred years after Ampère's brilliant guess.

Already in the VI century. BC. in China, it was known that some ores had the ability to attract each other and attract iron objects. Pieces of such ores were found near the city of Magnesia in Asia Minor, so they got the name magnets.

What is the interaction between a magnet and iron objects? Recall why electrified bodies are attracted? Because a peculiar form of matter is formed near an electric charge - an electric field. Around the magnet there is a similar form of matter, but it has a different nature of origin (after all, the ore is electrically neutral), it is called magnetic field.

To study the magnetic field, straight or horseshoe-shaped magnets are used. Certain places of the magnet have the greatest attractive effect, they are called poles(North and South). Opposite magnetic poles attract, and like poles repel.

For the power characteristic of the magnetic field, use magnetic field induction vector B. The magnetic field is graphically depicted using lines of force ( lines of magnetic induction). Lines are closed, have neither beginning nor end. The place from which the magnetic lines come out is the North Pole (North), the magnetic lines enter the South Pole (South).

The magnetic field can be made "visible" with iron filings.

The magnetic field of a current-carrying conductor

And now what we found Hans Christian Oersted and André Marie Ampère in 1820. It turns out that a magnetic field exists not only around a magnet, but also around any conductor with current. Any wire, for example, the cord from a lamp, through which an electric current flows, is a magnet! A wire with current interacts with a magnet (try to bring a compass to it), two wires with current interact with each other.

The lines of force of the direct current magnetic field are circles around the conductor.

Direction of the magnetic induction vector

The direction of the magnetic field at a given point can be defined as the direction that indicates the north pole of a compass needle placed at that point.

The direction of the lines of magnetic induction depends on the direction of the current in the conductor.

The direction of the induction vector is determined by the rule gimlet or rule right hand.

Magnetic induction vector

This is a vector quantity that characterizes the force action of the field.

Induction of the magnetic field of an infinite rectilinear conductor with current at a distance r from it:

Magnetic field induction at the center of a thin circular coil of radius r:

Magnetic field induction solenoid(a coil whose turns are energized in series in one direction):

Superposition principle

If the magnetic field at a given point in space is created by several sources of the field, then the magnetic induction is the vector sum of the inductions of each of the fields separately

The Earth is not only a large negative charge and a source of an electric field, but at the same time, the magnetic field of our planet is similar to the field of a giant direct magnet.

Geographic south is close to magnetic north, and geographic north is close to magnetic south. If the compass is placed in the Earth's magnetic field, then its north arrow is oriented along the lines of magnetic induction in the direction of the south magnetic pole, that is, it will tell us where the geographic north is located.

The characteristic elements of terrestrial magnetism change very slowly over time - secular changes. However, magnetic storms occur from time to time, when the Earth's magnetic field is strongly distorted for several hours, and then gradually returns to its previous values. Such a drastic change affects people's well-being.

The Earth's magnetic field is a "shield" covering our planet from particles penetrating from outer space ("solar wind"). Near the magnetic poles, particle flows come much closer to the Earth's surface. During powerful solar flares, the magnetosphere is deformed, and these particles can pass into the upper layers of the atmosphere, where they collide with gas molecules, forming auroras.

Particles of iron dioxide on a magnetic film are well magnetized during the recording process.

The maglev trains glide over the surface with absolutely no friction. The train is capable of speeds up to 650 km/h.

The work of the brain, the pulsation of the heart is accompanied by electrical impulses. In this case, a weak magnetic field arises in the organs.

Magnetic field, what is it? - special kind matter;
Where does it exist? - around moving electric charges (including around a current-carrying conductor)
How to discover? - using a magnetic needle (or iron filings) or by its action on a current-carrying conductor.

Oersted's experience:

The magnetic needle turns if electricity begins to flow through the conductor. current, because A magnetic field is formed around a current-carrying conductor.

Interaction of two conductors with current:

Each current-carrying conductor has its own magnetic field around it, which acts with some force on the adjacent conductor.

Depending on the direction of currents, conductors can attract or repel each other.

remember the past academic year:

MAGNETIC LINES (or otherwise lines of magnetic induction)

How to depict a magnetic field? - with the help of magnetic lines;
Magnetic lines, what is it?

These are imaginary lines along which magnetic needles are placed in a magnetic field. Magnetic lines can be drawn through any point of the magnetic field, they have a direction and are always closed.

Think back to last school year:

INHOMOGENEOUS MAGNETIC FIELD

Characteristics of an inhomogeneous magnetic field: the magnetic lines are curved; the density of the magnetic lines is different; the force with which the magnetic field acts on the magnetic needle is different at different points of this field in magnitude and direction.

Where does an inhomogeneous magnetic field exist?

Around a straight current-carrying conductor;

Around the bar magnet;

Around the solenoid (coils with current).

HOMOGENEOUS MAGNETIC FIELD

Characteristics of a homogeneous magnetic field: magnetic lines are parallel straight lines; the density of magnetic lines is the same everywhere; the force with which the magnetic field acts on the magnetic needle is the same at all points of this field in magnitude direction.

Where does a uniform magnetic field exist?
- inside the bar magnet and inside the solenoid, if its length is much greater than the diameter.

INTERESTING

The ability of iron and its alloys to be highly magnetized disappears when heated to a high temperature. Pure iron loses this ability when heated to 767 ° C.

Powerful magnets, used in many modern products, can affect the performance of pacemakers and implanted heart devices in cardiac patients. Ordinary iron or ferrite magnets, which are easily distinguished by their dull gray coloration, have little strength and are of little concern.
However, recently there have been very strong magnets- brilliant silver in color and representing an alloy of neodymium, iron and boron. The magnetic field they create is very strong, which is why they are widely used in computer disks, headphones and speakers, as well as in toys, jewelry and even clothing.

Once on the roads of the main city of Mallorca, the French military ship "La Rolain" appeared. His condition was so miserable that the ship barely reached the berth on its own. When French scientists, including twenty-two-year-old Arago, boarded the ship, it turned out that the ship was destroyed by lightning. While the commission was inspecting the ship, shaking their heads at the sight of the burnt masts and superstructures, Arago hurried to the compasses and saw what he expected: the compass needles pointed in different directions ...

A year later, digging through the remains of a Genoese ship that had crashed near Algiers, Arago discovered that the compass needles had been demagnetized. . The ship was heading south towards the rocks, deceived by a lightning-struck magnetic compass.

V. Kartsev. Magnet for three millennia.

The magnetic compass was invented in China.
Already 4,000 years ago, caravaners took with them clay pot and "took care of him on the road more than all your expensive cargoes." In it, on the surface of the liquid on a wooden float, lay a stone that loves iron. He could turn and, all the time, pointed to the travelers in the direction of the south, which, in the absence of the Sun, helped them to go to the wells.
At the beginning of our era, the Chinese learned how to make artificial magnets by magnetizing an iron needle.
And only a thousand years later, Europeans began to use a magnetized compass needle.

EARTH'S MAGNETIC FIELD

The earth is a large permanent magnet.
The South Magnetic Pole, although located, by earthly standards, near the North Geographic Pole, they are nevertheless separated by about 2000 km.
There are territories on the surface of the Earth where its own magnetic field is strongly distorted by the magnetic field of iron ores occurring at a shallow depth. One of these territories is the Kursk magnetic anomaly located in the Kursk region.

The magnetic induction of the Earth's magnetic field is only about 0.0004 Tesla.
___

The Earth's magnetic field is affected by increased solar activity. Approximately once every 11.5 years, it increases so much that radio communication is disrupted, the well-being of people and animals worsens, and the compass needles begin to “dance” unpredictably from side to side. In this case, they say that a magnetic storm is coming. It usually lasts from several hours to several days.

The Earth's magnetic field changes its orientation from time to time, making both secular fluctuations (lasting 5–10 thousand years) and completely reorienting, i.e. reversing magnetic poles (2–3 times per million years). This is indicated by the magnetic field of distant epochs "frozen" in sedimentary and volcanic rocks. The behavior of the geomagnetic field cannot be called chaotic, it obeys a kind of "schedule".

The direction and magnitude of the geomagnetic field are determined by the processes taking place in the Earth's core. The characteristic time of the polarity reversal, determined by the inner solid core, is from 3 to 5 thousand years, and determined by the outer liquid core, it is about 500 years. These times can explain the observed dynamics of the geomagnetic field. Computer modelling taking into account various intraterrestrial processes, it showed the possibility of a reversal of the magnetic field in about 5 thousand years.

FOCUSES WITH MAGNETS

The "temple of charms, or the mechanical, optical and physical cabinet of Mr. Gamuletsky de Coll" by the famous Russian illusionist Gamuletsky, which existed until 1842, became famous, among other things, for the fact that visitors climbing the stairs decorated with candelabra and carpeted with carpets could still notice from afar top platform stairs, a gilded figure of an angel, made in natural human growth, which hovered in a horizontal position above the office door without being suspended or supported. Everyone could make sure that the figure did not have any supports. When visitors entered the platform, the angel raised his hand, brought the horn to his mouth and played it, moving his fingers in the most natural way. For ten years, Gamuletsky said, I have been laboring to find the point and weight of the magnet and iron in order to keep the angel in the air. In addition to labor, I used a lot of money for this miracle.

In the Middle Ages, the so-called "obedient fish", made of wood, were a very common illusion number. They swam in the pool and obeyed the slightest wave of the magician's hand, which made them move in all possible directions. The secret of the trick was extremely simple: a magnet was hidden in the sleeve of the magician, and pieces of iron were inserted into the heads of the fish.
Closer to us in time were the manipulations of the Englishman Jonas. His signature number: Jonas invited some viewers to put the clock on the table, after which he, without touching the clock, arbitrarily changed the position of the hands.
The modern embodiment of such an idea is electromagnetic clutches, well known to electricians, with the help of which it is possible to rotate devices separated from the engine by some kind of obstacle, for example, a wall.

In the mid-80s of the 19th century, a rumor swept about the scientist elephant, who could not only add and subtract, but even multiply, divide and extract roots. This was done in the following way. The trainer, for example, asked the elephant: "What is seven eight?" There was a board with numbers in front of the elephant. After the question, the elephant took the pointer and confidently showed the number 56. In the same way, division and extraction were carried out. square root. The trick was simple enough: there was a small electromagnet hidden under each number on the board. When the elephant was asked a question, a current was applied to the winding of a magnet located meaning the correct answer. The iron pointer in the elephant's trunk was itself attracted to the correct number. The answer came automatically. Despite the simplicity of this training, the secret of the trick could not be unraveled for a long time, and the "learned elephant" enjoyed tremendous success.

Without a doubt, the magnetic field lines are now known to everyone. At least, even at school, their manifestation is demonstrated in physics lessons. Remember how the teacher placed a permanent magnet (or even two, combining the orientation of their poles) under a sheet of paper, and on top of it he poured metal filings taken in the labor training room? It is quite clear that the metal had to be held on the sheet, but something strange was observed - lines were clearly traced along which sawdust lined up. Notice - not evenly, but in stripes. These are the magnetic field lines. Or rather, their manifestation. What happened then and how can it be explained?

Let's start from afar. Together with us in the visible physical world coexists a special kind of matter - a magnetic field. It provides interaction between moving elementary particles or larger bodies with electric charge or natural Electrical and are not only interconnected with each other, but often generate themselves. For example, a wire carrying electricity creates a magnetic field around itself. The reverse is also true: the action of alternating magnetic fields on a closed conducting circuit creates a movement of charge carriers in it. The latter property is used in generators that supply electrical energy to all consumers. A striking example of electromagnetic fields is light.

The lines of force of the magnetic field around the conductor rotate or, which is also true, are characterized by a directed vector of magnetic induction. The direction of rotation is determined by the gimlet rule. The indicated lines are a convention, since the field spreads evenly in all directions. The thing is that it can be represented as an infinite number of lines, some of which have a more pronounced tension. That is why some “lines” are clearly traced in and sawdust. Interestingly, the lines of force of the magnetic field are never interrupted, so it is impossible to say unequivocally where the beginning is and where the end is.

In the case of a permanent magnet (or similar electromagnet), there are always two poles that have received conventional names North and South. The lines mentioned in this case are rings and ovals connecting both poles. Sometimes this is described in terms of interacting monopoles, but then a contradiction arises, according to which the monopoles cannot be separated. That is, any attempt to divide the magnet will result in several bipolar parts.

Of great interest are the properties of lines of force. We have already talked about continuity, but the ability to create an electric current in a conductor is of practical interest. The meaning of this is as follows: if the conducting circuit is crossed by lines (or the conductor itself is moving in a magnetic field), then additional energy is imparted to the electrons in the outer orbits of the atoms of the material, allowing them to begin independent directed movement. It can be said that the magnetic field seems to “knock out” charged particles from crystal lattice. This phenomenon has been named electromagnetic induction and is currently the main way to obtain primary electrical energy. It was discovered experimentally in 1831 by the English physicist Michael Faraday.

The study of magnetic fields began as early as 1269, when P. Peregrine discovered the interaction of a spherical magnet with steel needles. Almost 300 years later, W. G. Colchester suggested that he himself was a huge magnet with two poles. Further, magnetic phenomena were studied by such famous scientists as Lorentz, Maxwell, Ampère, Einstein, etc.

A magnetic field - power field , acting on moving electric charges and on bodies with magnetic moment, regardless of the state of their movement;magnetic component of the electromagnetic fields .

The magnetic field lines are imaginary lines, the tangents to which at each point of the field coincide in direction with the magnetic induction vector.

For a magnetic field, the principle of superposition is valid: at each point in space, the vector of magnetic induction B∑ → B∑→created at this point by all sources of magnetic fields is equal to the vector sum of the magnetic induction vectors bk→ Bk→created at this point by all sources of magnetic fields:

28. Law of Biot-Savart-Laplace. Full current law.

The formulation of Biot Savart Laplace's law is as follows: When passing direct current along a closed loop in vacuum, for a point at a distance r0 from the loop, the magnetic induction will have the form.

where I current in the circuit

gamma contour along which the integration is carried out

r0 arbitrary point

Full current law this is the law relating the circulation of the magnetic field strength vector and the current.

The circulation of the magnetic field strength vector along the circuit is equal to the algebraic sum of the currents covered by this circuit.

29. Magnetic field of a conductor with current. Magnetic moment of circular current.

30. The action of a magnetic field on a conductor with current. Ampere's law. Interaction of currents .

F = B I l sinα ,

where α - the angle between the vectors of magnetic induction and current,B - magnetic field induction,I - current in the conductor,l - conductor length.

Interaction of currents. If two wires are included in the DC circuit, then: Closely spaced parallel conductors connected in series repel each other. Conductors connected in parallel attract each other.

31. Action of electric and magnetic fields on a moving charge. Lorentz force.

Lorentz force - force, with which electromagnetic field according to the classical (non-quantum) electrodynamics acts on point charged particle. Sometimes the Lorentz force is called the force acting on a moving with a speed charge only from the side magnetic field, often the full force - from the electromagnetic field in general , in other words, from the side electric and magnetic fields.

32. The action of a magnetic field on matter. Dia-, para- and ferromagnets. Magnetic hysteresis.

B= B 0 + B 1

where B⃗ B → - magnetic field induction in matter; B⃗ 0 B→0 - magnetic field induction in vacuum, B⃗ 1 B→1 - magnetic induction of the field that arose due to the magnetization of the substance.

Substances for which the magnetic permeability is slightly less than unity (μ< 1), называются diamagnets, slightly greater than one (μ > 1) - paramagnets.

ferromagnet - the substance or material in which the phenomenon is observed ferromagnetism, i.e., the appearance of spontaneous magnetization at a temperature below the Curie temperature.

Magnetic hysteresis - phenomenon dependencies vector magnetization and vector magnetic fields in substance not only from attached external fields, but and from background this sample