What is called a magnetic field. Magnetic field and its characteristics - lecture

A magnet is a body that forms a magnetic field around itself.

The force created by a magnet will act on certain metals: iron, nickel and cobalt. Objects made of these metals are attracted by a magnet.
(a match and a cork are not attracted, a nail only to the right half of the magnet, a paper clip to any place)

There are two areas where the force of attraction is maximum. They are called poles. If you hang a magnet on a thin thread, it will unfold in a certain way. One end will always point north and the other end south. Therefore, one pole is called the north, and the other - the south.

You can clearly see the effect of the magnetic field formed around a magnet. Let's place the magnet on a surface on which metal filings have previously been poured. Under the influence of a magnetic field, the sawdust will be arranged in the form of ellipse-like curves. By the appearance of these curves, one can imagine how magnetic field lines are located in space. Their direction is usually designated from north to south.

If we take two identical magnets and try to bring their poles closer together, we will find out that different poles attract, and similar ones repel.

Our Earth also has a magnetic field called magnetic field Earth. The north end of the arrow always points north. Therefore, the north geographic pole of the Earth is the south magnetic pole because opposite magnetic poles attract. Likewise, the geographic south pole is the magnetic north pole.

The north end of the compass needle always points north, as it is attracted by the Earth's south magnetic pole.

If we place a compass under a wire that is stretched in the direction from north to south and through which a current flows, we will see that the magnetic needle will deviate. This proves that electricity creates a magnetic field around itself.

If we place several compasses under a wire through which an electric current flows, we will see that all the arrows will deviate by the same angle. This means that the magnetic field created by the wire is the same across different areas. Therefore, we can conclude that the magnetic field lines for each conductor have the form of concentric circles.

The direction of the magnetic field lines can be determined using the rule right hand. To do this, you need to mentally clasp the conductor with electric current with your right hand so that the extended thumb the right hand showed the direction of the electric current, then the bent fingers will show the direction of the magnetic field lines.

If we twist a metal wire into a spiral and run an electric current through it, then the magnetic fields of each individual turn are summed up into the total field of the spiral.

The action of the magnetic field of the spiral is similar to the action of the magnetic field of a permanent magnet. This principle formed the basis for the creation of an electromagnet. It, like a permanent magnet, has a south and north pole. The North Pole is where the magnetic field lines come from.

The strength of a permanent magnet does not change over time. With an electromagnet it is different. There are three ways to change the strength of an electromagnet.

First way. Let's place a metal core inside the spiral. In this case, the actions of the magnetic field of the core and the magnetic field of the spiral are summed up.

Second way. Let's increase the number of turns of the spiral. The more turns the spiral has, the greater the effect of the magnetic field force.

Third way. Let's increase the strength of the electric current that flows in the spiral. The magnetic fields of individual turns will increase, therefore, the total magnetic field of the spiral will also increase.

Speaker

The loudspeaker device includes an electromagnet and a permanent magnet. The electromagnet, which is connected to the loudspeaker membrane, is placed on a rigidly fixed permanent magnet. At the same time, the membrane remains mobile. Let us pass an alternating electric current through an electromagnet, the type of which depends on sound vibrations. As the electric current changes, the effect of the magnetic field in the electromagnet changes.

As a result, the electromagnet will be attracted or repelled from the permanent magnet with different strengths. Moreover, the loudspeaker membrane will perform exactly the same vibrations as the electromagnet. Thus, what was said into the microphone will be heard through the loudspeaker.

Call

An electric doorbell can be classified as an electrical relay. The reason for the intermittent sound signal is periodic short circuits and open circuits.

When the bell button is pressed, the electrical circuit is closed. The bell tongue is attracted by an electromagnet and strikes the bell. In this case, the tongue opens the electrical circuit. The current stops flowing, the electromagnet does not act and the tongue returns to its original position. The electrical circuit is closed again, the tongue is again attracted by the electromagnet and strikes the bell. This process will continue as long as we press the call button.

Electric motor

Let's install a freely rotating magnetic needle in front of the electromagnet and spin it. We can maintain this movement if we turn on the electromagnet at the moment when the magnetic needle turns the same pole towards the electromagnet.

The attractive force of the electromagnet is sufficient to ensure that the rotational movement of the needle does not stop.

(in the picture, the magnet receives a pulse whenever the red arrow is near and the button is pressed. If you press the button when the green arrow is near, the electromagnet stops)

This principle is the basis of the electric motor. Only it is not a magnetic needle that rotates in it, but an electromagnet, called an armature, in a statically fixed horseshoe-shaped magnet, which is called a stator. Due to repeated closing and opening of the circuit, the electromagnet, i.e. the anchor will rotate continuously.

Electric current enters the armature through two contacts, which are two insulated half rings. This causes the electromagnet to constantly change polarity. When opposite poles are opposite one another, the motor begins to slow down. But at this moment the electromagnet changes polarity, and now there are identical poles opposite each other. They push off and the motor continues to rotate.

Generator

Let's connect a voltmeter to the ends of the spiral and begin to swing a permanent magnet in front of its turns. In this case, the voltmeter will show the presence of voltage. From this we can conclude that the electrical conductor is affected by a changing magnetic field.

From this follows the law of electrical induction: a voltage will exist at the ends of the induction coil as long as the coil is in a changing magnetic field.

The more turns an induction coil has, the more voltage appears at its ends. The voltage can be increased by making the magnetic field stronger or by causing it to change faster. A metal core inserted inside the induction coil increases the induction voltage as the magnetic field is enhanced due to the magnetization of the core.
(the magnet begins to be waved more strongly in front of the coil, as a result of which the voltmeter needle deflects much more)

A generator is the opposite of an electric motor. Anchor, i.e. An electromagnet rotates in the magnetic field of a permanent magnet. Due to the rotation of the armature, the magnetic field acting on it is constantly changing. As a result, the resulting induction voltage changes. During a full rotation of the armature, the voltage will be positive half the time and negative half the time. An example of this is a wind generator that produces alternating voltage.

Transformer

According to the law of induction, voltage occurs when the magnetic field in the induction coil changes. But the magnetic field of the coil will change only if an alternating voltage appears in it.

The magnetic field changes from zero to a finite value. If you connect the coil to a voltage source, the resulting alternating magnetic field will create a short-term induction voltage that will counteract the main voltage. To observe the occurrence of induced voltage, it is not necessary to use two coils. This can be done with one coil, but then this process is called self-induction. The voltage in the coil reaches its maximum after some time, when the magnetic field stops changing and becomes constant.

The magnetic field changes in the same way if we disconnect the coil from the voltage source. In this case, the phenomenon of self-induction also occurs, which counteracts the falling voltage. Therefore, the voltage does not drop to zero instantly, but with a certain delay.

If we constantly connect and disconnect a voltage source to the coil, then the magnetic field around it will constantly change. At the same time, an alternating induction voltage also arises. Now, instead, let's connect the coil to an AC voltage source. After some time, an alternating induction voltage appears.

Let's connect the first coil to an alternating voltage source. Thanks to the metal core, the resulting alternating magnetic field will also act on the second coil. This means that alternating voltage can be transferred from one electric current circuit to another, even if these circuits are not connected to one another.

If we take two coils with identical parameters, then in the second we can get the same voltage that acts on the first coil. This phenomenon is used in transformers. Only the purpose of the transformer is to create a different voltage in the second coil, different from the first. To do this, the second coil must have a greater or lesser number of turns.

If the first coil had 1000 turns, and the second - 10, then the voltage in the second circuit will be only a hundredth of the voltage in the first. But the current strength increases almost a hundred times. Therefore, high voltage transformers are necessary to create great strength current

Sources constant magnetic fields (PMF) at workplaces there are permanent magnets, electromagnets, high-current direct current systems (DC transmission lines, electrolyte baths, etc.).

Permanent magnets and electromagnets are widely used in instrumentation, in magnetic washers of cranes, in magnetic separators, in devices for magnetic water treatment, in magnetohydrodynamic generators (MHD), nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) installations, as well as in physiotherapeutic practice.

The main physical parameters characterizing the PMP are field strength (N), magnetic flux (F) and magnetic induction (V). The SI unit of measurement for magnetic field strength is ampere per meter (A/m), magnetic flux - Weber (Wb ), magnetic flux density (magnetic induction) - tesla (T ).

Changes in the health status of persons working with sources of PMF were identified. Most often, these changes manifest themselves in the form of vegetative dystonia, asthenovegetative and peripheral vasovegetative syndromes or a combination thereof.

According to the current standard in our country (“Maximum permissible levels of exposure to constant magnetic fields when working with magnetic devices and magnetic materials” No. 1742-77), the PMF voltage in workplaces should not exceed 8 kA/m (10 mT). Permissible levels of PMF recommended by the International Committee on Non-Ionizing Radiation (1991) are differentiated by population, location of exposure and time of work. For professionals: 0.2 T - with full-time exposure (8 hours); 2 T - with short-term exposure to the body; 5 T - with short-term exposure to hands. For the population, the level of continuous exposure to PMF should not exceed 0.01 T.

RF EMR sources are widely used in a wide variety of industries National economy. They are used to transmit information over a distance (radio broadcasting, radiotelephone communications, television, radar, etc.). In industry, radio wave EMR is used for induction and dielectric heating of materials (hardening, melting, soldering, welding, metal spraying, heating of internal metal parts of electric vacuum devices during pumping, drying wood, heating plastics, gluing plastic compounds, heat treatment food products and etc.). EMR is widely used in scientific research(radio spectroscopy, radio astronomy) and medicine (physiotherapy, surgery, oncology). In some cases, EMI occurs as a side unused factor, for example, near overhead power lines (OHT), transformer substations, electrical appliances, including household ones. The main sources of EMF RF radiation in environment antenna systems serve radar stations(radar), radio and television stations, including mobile radio communication systems and overhead power lines.

The human and animal body is very sensitive to the effects of RF EMF.

Critical organs and systems include: central nervous system, eyes, gonads, and according to some authors, the hematopoietic system. The biological effect of these radiations depends on the wavelength (or frequency of radiation), the generation mode (continuous, pulsed) and the conditions of exposure to the body (continuous, intermittent; general, local; intensity; duration). It is noted that biological activity decreases with increasing wavelength (or decreasing frequency) of radiation. The most active are the centi-, deci and meter ranges of radio waves. Lesions caused by RF EMR can be acute or chronic. Acute ones arise under the influence of significant thermal radiation intensities. They occur extremely rarely - in case of accidents or gross violations of safety regulations at the radar. For professional conditions Chronic lesions are more typical, usually detected after several years of working with microwave EMR sources.

Main regulatory documents regulating permissible levels of exposure to RF EMR are: GOST 12.1.006 - 84 “SSBT. Electromagnetic fields of radio frequencies.

Acceptable levels" and SanPiN 2.2.4/2.1.8.055-96 " Electromagnetic radiation radio frequency range". They standardize energy exposure (EE) for electric (E) and magnetic (H) fields, as well as energy flux density (EF) for a working day (Table 5.11).

Table 5.11.

Maximum permissible levels (MAL) per working day for workers

With EMR RF

Parameter	Frequency ranges, MHz
Name	Unit	0,003-3	3-30	30-300	300-300000
EE E	(V/m) 2 *h				-
uh n	(A/m) 2 *h		-	-	-
ppe	(μW/cm 2)* h	-	-	-

For the entire population with continuous exposure, the following MRLs for electric field strength, V/m, have been established:

Frequency range MHz

0,03-0,30........................................................... 25

0,3-3,0.............................................................. 15

3-30.................................................................. 10

30-300............................................................... 3*

300-300000...................................................... 10

* Except for television stations, the remote controls for which are differentiated according to

depending on frequency from 2.5 to 5 V/m.

Devices operating in the radio frequency range include video displays of personal computer terminals. These days, personal computers (PCs) are wide application in production, in scientific research, in medical institutions, in everyday life, in universities, schools and even in kindergartens. When used in production, PCs, depending on technological tasks, can affect the human body for a long time (within the working day). In everyday life, the time you use a PC is completely uncontrollable.

For PC video display terminals (VDT), the following EMI PDUs are installed (SanPiN 2.2.2.542-96 “Hygienic requirements for video display terminals, personal electronic computers and work organization”) - table. 5.12.

Table 5.12. Maximum permissible levels of EMR generated by RCCBs

Magnetic field sources

A magnetic field is created (generated) by a current of charged particles, or a time-varying electric field, or the particles’ own magnetic moments (the latter, for the sake of uniformity of the picture, can be formally reduced to electric currents).

Calculation

IN simple cases the magnetic field of a conductor with current (including for the case of a current distributed arbitrarily over a volume or space) can be found from the Biot-Savart-Laplace law or the circulation theorem (also known as Ampere’s law). In principle, this method is limited to the case (approximation) of magnetostatics - that is, the case of constant (if we are talking about strict applicability) or rather slowly changing (if we are talking about approximate application) magnetic and electric fields.

In more difficult situations is sought as a solution to Maxwell's equations.

Manifestation of magnetic field

The magnetic field manifests itself in the effect on the magnetic moments of particles and bodies, on moving charged particles (or current-carrying conductors). 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, speed component v, perpendicular to the direction of the magnetic field vector B, and the magnitude of the magnetic field induction B. In the SI system of units, the Lorentz force is expressed as follows:

in the GHS unit system:

where square brackets denote the vector product.

Also (due to the action of the Lorentz force on charged particles moving along a conductor), a magnetic field acts on a conductor with current. The force acting on a current-carrying conductor is called Ampere force. This force consists of the forces acting on individual charges moving inside the conductor.

Interaction of two magnets

One of the most common in ordinary life manifestations of a magnetic field - the interaction of two magnets: like poles repel, opposite poles attract. It is tempting to describe the interaction between magnets as the interaction between two monopoles, and from a formal point of view this idea is quite feasible and often very convenient, and therefore practically useful (in calculations); however, detailed analysis shows that in fact this is not completely correct description phenomena (the most obvious question that cannot be explained within the framework of such a model is the question of why monopoles can never be separated, that is, why experiment shows that no isolated body actually has a magnetic charge; in addition, the weakness of the model is that it is inapplicable to the magnetic field created by a macroscopic current, and therefore, if not considered as a purely formal technique, it only leads to a complication of the theory in a fundamental sense).

It would be more correct to say that a magnetic dipole placed in a non-uniform field is acted upon by a force that tends to rotate it so that the magnetic moment of the dipole is aligned with the magnetic field. But no magnet experiences the (total) force exerted by a uniform magnetic field. Force acting on a magnetic dipole with a magnetic moment m expressed by the formula:

The force acting on a magnet (which is not a single point dipole) from a non-uniform magnetic field can be determined by summing all the forces (determined by this formula) acting on the elementary dipoles that make up the magnet.

However, an approach is possible that reduces the interaction of magnets to the Ampere force, and the formula itself above for the force acting on a magnetic dipole can also be obtained based on the Ampere force.

The phenomenon of electromagnetic induction

Vector field H measured in amperes per meter (A/m) in the SI system and in oersteds in the GHS. Oersteds and Gaussians are identical quantities; their division is purely terminological.

Magnetic field energy

The increment in magnetic field energy density is equal to:

H- magnetic field strength, B- magnetic induction

In the linear tensor approximation, magnetic permeability is a tensor (we denote it) and multiplication of a vector by it is tensor (matrix) multiplication:

or in components.

The energy density in this approximation is equal to:

- components of the magnetic permeability tensor, - tensor, represented by a matrix inverse to the matrix of the magnetic permeability tensor, - magnetic constant

When choosing coordinate axes that coincide with the main axes of the magnetic permeability tensor, the formulas in the components are simplified:

- diagonal components of the magnetic permeability tensor in its own axes (the remaining components in these special coordinates - and only in them! - are equal to zero).

In an isotropic linear magnet:

- relative magnetic permeability

In a vacuum and:

The energy of the magnetic field in the inductor can be found using the formula:

Ф - magnetic flux, I - current, L - inductance of a coil or turn with current.

Magnetic properties of substances

From a fundamental point of view, as stated above, a magnetic field can be created (and therefore - in the context of this paragraph - and weakened or strengthened) by a variable electric field, electric currents in the form of streams of charged particles or magnetic moments of particles.

The specific microscopic structure and properties of various substances (as well as their mixtures, alloys, states of aggregation, crystalline modifications, etc.) lead to the fact that at the macroscopic level they can behave quite differently under the influence of an external magnetic field (in particular, weakening or enhancing it to varying degrees).

In this regard, substances (and environments in general) with respect to their magnetic properties are divided into the following main groups:

Antiferromagnets are substances in which an antiferromagnetic order has been established for the magnetic moments of atoms or ions: the magnetic moments of substances are directed oppositely and are equal in strength.
Diamagnets are substances that are magnetized against the direction of an external magnetic field.
Paramagnetic substances are substances that are magnetized in an external magnetic field in the direction of the external magnetic field.
Ferromagnets are substances in which, below a certain critical temperature (Curie point), a long-range ferromagnetic order of magnetic moments is established
Ferrimagnets are materials in which the magnetic moments of the substance are directed in opposite directions and are not equal in strength.
The groups of substances listed above mainly include ordinary solid or (some) liquid substances, as well as gases. The interaction with the magnetic field of superconductors and plasma is significantly different.

Toki Fuko

Foucault currents (eddy currents) are closed electric currents in a massive conductor that arise when the magnetic flux penetrating it changes. They are induced currents formed in a conducting body either as a result of a change in time of the magnetic field in which it is located, or as a result of the movement of the body in a magnetic field, leading to a change in the magnetic flux through the body or any part of it. According to Lenz's rule, the magnetic field of Foucault currents is directed so as to counteract the change in magnetic flux that induces these currents.

History of the development of ideas about the magnetic field

Although magnets and magnetism were known much earlier, the study of the magnetic field began in 1269, when the French scientist Peter Peregrine (Knight Pierre of Mericourt) marked the magnetic field on the surface of a spherical magnet using steel needles and determined that the resulting magnetic field lines intersected at two points, which he called “poles” by analogy with the poles of the Earth. Nearly three centuries later, William Gilbert Colchester used the work of Peter Peregrinus and for the first time definitively stated that the Earth itself was a magnet. Published in 1600, Gilbert's work "De Magnete", laid the foundations of magnetism as a science.

Three discoveries in a row challenged this “basis of magnetism.” First, in 1819, Hans Christian Oersted discovered that electric current creates a magnetic field around itself. Then, in 1820, André-Marie Ampère showed that parallel wires carrying current in the same direction attract each other. Finally, Jean-Baptiste Biot and Félix Savart discovered a law in 1820, called the Biot-Savart-Laplace law, which correctly predicted the magnetic field around any live wire.

Expanding on these experiments, Ampère published his own successful model of magnetism in 1825. In it, he showed the equivalence of electric current in magnets, and instead of the dipoles of magnetic charges of the Poisson model, he proposed the idea that magnetism is associated with constantly flowing current loops. This idea explained why magnetic charge could not be isolated. In addition, Ampere derived the law named after him, which, like the Biot-Savart-Laplace law, correctly described the magnetic field created by direct current, and also introduced the magnetic field circulation theorem. Also in this work, Ampère coined the term "electrodynamics" to describe the relationship between electricity and magnetism.

Although the strength of the magnetic field of a moving electric charge implied in Ampere's law was not explicitly stated, Hendrik Lorentz derived it from Maxwell's equations in 1892. At the same time, the classical theory of electrodynamics was basically completed.

The twentieth century expanded views on electrodynamics, thanks to the emergence of the theory of relativity and quantum mechanics. Albert Einstein, in his 1905 paper establishing his theory of relativity, showed that electric and magnetic fields are part of the same phenomenon, considered in different systems countdown. (See Moving Magnet and the Conductor Problem—a thought experiment that ultimately helped Einstein develop special relativity). Finally, quantum mechanics was combined with electrodynamics to form quantum electrodynamics (QED).

Notes

TSB. 1973, "Soviet Encyclopedia".
In particular cases, a magnetic field can exist in the absence of an electric field, but generally speaking, a magnetic field is deeply interconnected with an electric one, both dynamically (the mutual generation of variables by the electric and magnetic fields of each other), and in the sense that during the transition to new system of reference, the magnetic and electric fields are expressed through each other, that is, generally speaking they cannot be unconditionally separated.
Yavorsky B. M., Detlaf A. A. Handbook of Physics: 2nd ed., revised. - M.: Nauka, Main editorial office of physical and mathematical literature, 1985, - 512 p.
In the SI, magnetic induction is measured in tesla (T), in the CGS system in gauss.
They coincide exactly in the CGS system of units, in SI they differ by a constant coefficient, which, of course, does not change the fact of their practical physical identity.
The most important and obvious difference here is that the force acting on a moving particle (or on a magnetic dipole) is calculated precisely through and not through . Any other physically correct and meaningful measurement method will also make it possible to measure precisely, although for formal calculations it sometimes turns out to be more convenient - which, in fact, is the point of introducing this auxiliary quantity (otherwise one would do without it altogether, using only
However, we must understand well that a number of fundamental properties of this “matter” are fundamentally different from the properties of that ordinary type of “matter” that could be designated by the term “substance”.
See Ampere's theorem.
For a uniform field, this expression gives zero force, since all derivatives are equal to zero B by coordinates.
Sivukhin D.V. General physics course. - Ed. 4th, stereotypical. - M.: Fizmatlit; Publishing house MIPT, 2004. - T. III. Electricity. - 656 s. - ISBN 5-9221-0227-3; ISBN 5-89155-086-5.

Let's understand together what a magnetic field is. After all, many people live in this field all their lives and don’t even think about it. It's time to fix it!

A magnetic field

A magnetic field- a special type of matter. It manifests itself in the action on moving electric charges and bodies that have their own magnetic moment (permanent magnets).

Important: the magnetic field does not affect stationary charges! A magnetic field is also created by moving electric charges, or by a time-varying electric field, or by the magnetic moments of electrons in atoms. That is, any wire through which current flows also becomes a magnet!

A body that has its own magnetic field.

A magnet has poles called north and south. The designations "north" and "south" are given for convenience only (like "plus" and "minus" in electricity).

The magnetic field is represented by magnetic power lines. The lines of force are continuous and closed, and their direction always coincides with the direction of action of the field forces. If metal shavings are scattered around a permanent magnet, the metal particles will show a clear picture power lines magnetic field leaving the north and entering the south pole. Graphic characteristic of a magnetic field - lines of force.

Characteristics of the magnetic field

The main characteristics of the magnetic field are magnetic induction, magnetic flux And magnetic permeability. But let's talk about everything in order.

Let us immediately note that all units of measurement are given in the system SI.

Magnetic induction B – vector physical quantity, which is the main force characteristic of the magnetic field. Denoted by the letter B . Unit of measurement of magnetic induction – Tesla (T).

Magnetic induction shows how strong the field is by determining the force it exerts on a charge. This force is called Lorentz force.

Here q - charge, v - its speed in a magnetic field, B - induction, F - Lorentz force with which the field acts on the charge.

F- physical quantity, equal to the product magnetic induction on the contour area and the cosine between the induction vector and the normal to the plane of the contour through which the flux passes. Magnetic flux is a scalar characteristic of a magnetic field.

We can say that magnetic flux characterizes the number of magnetic induction lines penetrating a unit area. Magnetic flux is measured in Weberach (Wb).

Magnetic permeability– coefficient that determines the magnetic properties of the medium. One of the parameters on which the magnetic induction of a field depends is magnetic permeability.

Our planet has been a huge magnet for several billion years. The induction of the Earth's magnetic field varies depending on the coordinates. At the equator it is approximately 3.1 times 10 to the minus fifth power of Tesla. In addition, there are magnetic anomalies where the value and direction of the field differ significantly from neighboring areas. Some of the largest magnetic anomalies on the planet - Kursk And Brazilian magnetic anomalies.

The origin of the Earth's magnetic field still remains a mystery to scientists. It is assumed that the source of the field is the liquid metal core of the Earth. The core is moving, which means the molten iron-nickel alloy is moving, and the movement of charged particles is the electric current that generates the magnetic field. The problem is that this theory ( geodynamo) does not explain how the field is kept stable.

The Earth is a huge magnetic dipole. The magnetic poles do not coincide with the geographic ones, although they are in close proximity. Moreover, the Earth's magnetic poles move. Their displacement has been recorded since 1885. For example, over the past hundred years, the magnetic pole in the Southern Hemisphere has shifted almost 900 kilometers and is now located in the Southern Ocean. The pole of the Arctic hemisphere is moving through the Arctic Ocean to the East Siberian magnetic anomaly; its movement speed (according to 2004 data) was about 60 kilometers per year. Now there is an acceleration of the movement of the poles - on average, the speed is growing by 3 kilometers per year.

What is the significance of the Earth's magnetic field for us? First of all, the Earth's magnetic field protects the planet from cosmic rays and solar wind. Charged particles from deep space do not fall directly to the ground, but are deflected by a giant magnet and move along its lines of force. Thus, all living things are protected from harmful radiation.

Several events have occurred over the course of Earth's history. inversions(changes) of magnetic poles. Pole inversion- this is when they change places. The last time this phenomenon occurred was about 800 thousand years ago, and in total there were more than 400 geomagnetic inversions in the history of the Earth. Some scientists believe that, given the observed acceleration of the movement of the magnetic poles, the next pole inversion should be expected in the next couple of thousand years.

Fortunately, a pole change is not yet expected in our century. This means that you can think about pleasant things and enjoy life in the good old constant field of the Earth, having considered the basic properties and characteristics of the magnetic field. And so that you can do this, there are our authors, to whom you can confidently entrust some of the educational troubles with confidence! and other types of work you can order using the link.

If an electric current is passed through iron, the iron will acquire magnetic properties while the current passes. Some substances, for example, hardened steel and a number of alloys do not lose their magnetic properties even after the current is turned off, unlike electromagnets.

These bodies that retain magnetization for a long time are called permanent magnets. People first learned to produce permanent magnets from natural magnets - magnetic iron ore, and then they learned to make them themselves from other substances, artificially magnetizing them.

Magnetic field of a permanent magnet

Permanent magnets have two poles called north and south magnetic fields. Between these poles, the magnetic field is located in the form of closed lines directed from the north pole to the south. The magnetic field of a permanent magnet acts on metal objects and other magnets.

If you bring two magnets close to each other with like poles, they will repel each other. And if they have different names, then they attract each other. The magnetic lines of opposite charges seem to be closed on each other.

If a metal object enters the field of a magnet, the magnet magnetizes it, and the metal object itself becomes a magnet. It is attracted by its opposite pole to the magnet, so metal bodies seem to “stick” to the magnets.

Earth's magnetic field and magnetic storms

Not only magnets have a magnetic field, but also our home planet. The Earth's magnetic field determines the action of compasses, which have been used by people since ancient times to navigate the terrain. The earth, like any other magnet, has two poles - north and south. The Earth's magnetic poles are close to the geographic poles.

The Earth's magnetic field lines "exit" from the Earth's north pole and "enter" at the location of the south pole. Physics confirms the existence of the Earth's magnetic field experimentally, but cannot yet fully explain it. It is believed that the reason for the existence of terrestrial magnetism is the currents flowing within the Earth and in the atmosphere.

From time to time, so-called “magnetic storms” occur. Due to solar activity and the emission of streams of charged particles by the Sun, the Earth's magnetic field changes briefly. In this regard, the compass may behave strangely and the transmission of various electromagnetic signals in the atmosphere is disrupted.

Such storms can cause discomfort in some sensitive people, since disturbance of normal earth magnetism causes slight changes in quite thin instrument– our body. It is believed that with the help of earth's magnetism, migratory birds and migrating animals find their way home.

In some places on Earth there are areas where the compass does not consistently point north. Such places are called anomalies. Such anomalies are most often explained by huge deposits of iron ore at shallow depths, which distort the Earth’s natural magnetic field.