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, it was created measuring device"SQUID." Its action is explained by the laws of quantum phenomena. It is a sensitive element of magnetometers used for research 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.
To understand what is a characteristic of a magnetic field, many phenomena must be defined. At the same time, you need to remember in advance how and why it appears. Find out what is the strength characteristic of a magnetic field. It is important that such a field can occur not only in magnets. In this regard, it would not hurt to mention the characteristics of the earth’s magnetic field.
Emergence of the field
First we need to describe the emergence of the field. Then you can describe the magnetic field and its characteristics. It appears during the movement of charged particles. May affect in particular live conductors. The interaction between a magnetic field and moving charges, or conductors through which current flows, occurs due to forces called electromagnetic.
The intensity or strength characteristic of a magnetic field at a certain spatial point is determined using magnetic induction. The latter is designated by the symbol B.
Graphical representation of the field
The magnetic field and its characteristics can be represented in graphical form using induction lines. This definition refers to lines whose tangents at any point will coincide with the direction of the magnetic induction vector.
These lines are included in the characteristics of the magnetic field and are used to determine its direction and intensity. The higher the intensity of the magnetic field, the more of these lines will be drawn.
What are magnetic lines
Magnetic lines in straight current-carrying conductors have the shape of a concentric circle, the center of which is located on the axis of the given conductor. The direction of magnetic lines near current-carrying conductors is determined by the gimlet rule, which sounds like this: if the gimlet is positioned so that it is screwed into the conductor in the direction of the current, then the direction of rotation of the handle corresponds to the direction of the magnetic lines.
In a coil with current, the direction of the magnetic field will also be determined by the gimlet rule. It is also required to rotate the handle in the direction of the current in the solenoid turns. The direction of the magnetic induction lines will correspond to the direction forward motion gimlet.
It is the main characteristic of a magnetic field.
Created by one current, under equal conditions, the field will differ in its intensity in different environments due to different magnetic properties in these substances. The magnetic properties of the medium are characterized by absolute magnetic permeability. It is measured in henry per meter (g/m).
The characteristics of the magnetic field include the absolute magnetic permeability of the vacuum, called the magnetic constant. The value that determines how many times the absolute magnetic permeability of the medium will differ from the constant is called relative magnetic permeability.
Magnetic permeability of substances
This is a dimensionless quantity. Substances with a permeability value of less than one are called diamagnetic. In these substances the field will be weaker than in a vacuum. These properties are present in hydrogen, water, quartz, silver, etc.
Media with a magnetic permeability exceeding unity are called paramagnetic. In these substances the field will be stronger than in a vacuum. These environments and substances include air, aluminum, oxygen, and platinum.
In the case of paramagnetic and diamagnetic substances, the value of magnetic permeability will not depend on the voltage of the external, magnetizing field. This means that the quantity is constant for a certain substance.
A special group includes ferromagnets. For these substances, the magnetic permeability will reach several thousand or more. These substances, which have the property of being magnetized and enhancing a magnetic field, are widely used in electrical engineering.
Field strength
To determine the characteristics of a magnetic field, a value called magnetic field strength can be used along with the magnetic induction vector. This term determines the intensity of the external magnetic field. The direction of the magnetic field in a medium with identical properties in all directions, the intensity vector will coincide with the magnetic induction vector at the field point.
The strength of ferromagnets is explained by the presence in them of arbitrarily magnetized small parts, which can be represented in the form of small magnets.
With no magnetic field, a ferromagnetic substance may not have pronounced magnetic properties, since the fields of the domains acquire different orientations, and their total magnetic field is zero.
According to the main characteristic of the magnetic field, if a ferromagnet is placed in an external magnetic field, for example, in a coil with current, then under the influence of the external field the domains will turn in the direction of the external field. Moreover, the magnetic field at the coil will increase, and the magnetic induction will increase. If the external field is weak enough, then only a part of all domains will turn over, the magnetic fields of which are close in direction to the direction of the external field. As the external field strength increases, the number of rotated domains will increase, and with a certain value voltage of the external field, almost all parts will be rotated so that the magnetic fields will be located in the direction of the external field. This state is called magnetic saturation.
Relationship between magnetic induction and tension
The relationship between the magnetic induction of a ferromagnetic substance and the external field strength can be depicted using a graph called a magnetization curve. At the point where the curve graph bends, the rate of increase in magnetic induction decreases. After bending, where the tension reaches a certain value, saturation occurs, and the curve rises slightly, gradually taking on the shape of a straight line. In this area, the induction is still growing, but rather slowly and only due to an increase in the external field strength.
The graphical dependence of the indicator data is not direct, which means that their ratio is not constant, and the magnetic permeability of the material is not a constant indicator, but depends on the external field.
Changes in the magnetic properties of materials
When the current strength is increased to complete saturation in a coil with a ferromagnetic core and then decreased, the magnetization curve will not coincide with the demagnetization curve. With zero intensity, the magnetic induction will not have the same value, but will acquire a certain indicator called residual magnetic induction. The situation where magnetic induction lags behind the magnetizing force is called hysteresis.
To completely demagnetize the ferromagnetic core in the coil, it is necessary to give a reverse current, which will create the necessary voltage. Different ferromagnetic substances require a piece of different lengths. The larger it is, the greater the amount of energy required for demagnetization. The value at which complete demagnetization of the material occurs is called coercive force.
With a further increase in the current in the coil, the induction will again increase to saturation, but with a different direction of the magnetic lines. When demagnetizing in the opposite direction, residual induction will be obtained. The phenomenon of residual magnetism is used when creating permanent magnets from substances with a high index of residual magnetism. Cores are created from substances that have the ability to remagnetize electric machines and instruments.
Left hand rule
The force affecting a current-carrying conductor has a direction determined by the left-hand rule: when the palm of the virgin hand is positioned in such a way that the magnetic lines enter it, and four fingers are extended in the direction of the current in the conductor, the bent thumb will indicate the direction of the force. This force is perpendicular to the induction vector and current.
A current-carrying conductor moving in a magnetic field is considered a prototype of an electric motor that changes electrical energy to mechanical.
Right hand rule
When a conductor moves in a magnetic field, an electromotive force is induced within it, which has a value proportional to the magnetic induction, the length of the conductor involved and the speed of its movement. This dependence is called electromagnetic induction. When determining the direction of the induced emf in a conductor, use the rule right hand: when the right hand is positioned in the same way as in the example with the left, the magnetic lines enter the palm, and the thumb indicates the direction of movement of the conductor, the extended fingers will indicate the direction of the induced EMF. A conductor moving in a magnetic flux under the influence of an external mechanical force is the simplest example electric generator, in which mechanical energy is converted into electrical energy.
It can be formulated differently: in closed loop EMF is induced; with any change in the magnetic flux covered by this circuit, the EMF in the circuit is numerically equal to the rate of change of the magnetic flux that covers this circuit.
This form provides an average EMF indicator and indicates the dependence of the EMF not on the magnetic flux, but on the rate of its change.
Lenz's law
You also need to remember Lenz's law: the current induced when the magnetic field passing through the circuit changes, its magnetic field prevents this change. If the turns of a coil are penetrated by magnetic fluxes of different magnitudes, then the EMF induced throughout the whole coil is equal to the sum of the EDE in different turns. The sum of the magnetic fluxes of different turns of the coil is called flux linkage. The unit of measurement for this quantity, as well as for magnetic flux, is Weber.
When it changes electric current in the circuit there is a change in the magnetic flux created by it. At the same time, according to the law electromagnetic induction, an EMF is induced inside the conductor. It appears in connection with a change in current in the conductor, therefore this phenomenon is called self-induction, and the EMF induced in the conductor is called self-induction EMF.
Flux linkage and magnetic flux depend not only on current strength, but also on the size and shape of a given conductor, and the magnetic permeability of the surrounding substance.
Conductor inductance
The proportionality factor is called the inductance of the conductor. It refers to the ability of a conductor to create flux linkage when electricity passes through it. This is one of the main parameters of electrical circuits. For certain circuits, inductance is a constant value. It will depend on the size of the circuit, its configuration and the magnetic permeability of the medium. In this case, the current strength in the circuit and the magnetic flux will not matter.
The above definitions and phenomena provide an explanation of what a magnetic field is. The main characteristics of the magnetic field are also given, with the help of which this phenomenon can be defined.
Earth's magnetic field
A magnetic field is a force field that acts on moving electric charges and on bodies that have a magnetic moment, regardless of their state of motion.
The sources of the macroscopic magnetic field are magnetized bodies, current-carrying conductors, and moving electrically charged bodies. The nature of these sources is the same: the magnetic field arises as a result of the movement of charged microparticles (electrons, protons, ions), as well as due to the presence of the microparticles’ own (spin) magnetic moment.
An alternating magnetic field also occurs when it changes over time electric field. In turn, when the magnetic field changes over time, a electric field. Full description electric and magnetic fields in their relationship give Maxwell's equations. To characterize the magnetic field, the concept of field lines (magnetic induction lines) is often introduced.
To measure the characteristics of the magnetic field and the magnetic properties of substances, they use various types magnetometers. The unit of magnetic field induction in the CGS system of units is Gauss (G), in the International System of Units (SI) - Tesla (T), 1 T = 104 G. The intensity is measured, respectively, in oersteds (Oe) and amperes per meter (A/m, 1 A/m = 0.01256 Oe; magnetic field energy - in Erg/cm2 or J/m2, 1 J/m2 = 10 erg/cm2.
Compass reacts
to the Earth's magnetic field
Magnetic fields in nature are extremely diverse both in their scale and in the effects they cause. The Earth's magnetic field, which forms the Earth's magnetosphere, extends to a distance of 70-80 thousand km in the direction of the Sun and many millions of km in the opposite direction. At the Earth's surface the magnetic field is on average 50 μT, at the boundary of the magnetosphere ~ 10 -3 G. The geomagnetic field shields the Earth's surface and biosphere from the flow of charged particles of the solar wind and partially cosmic rays. Magnetobiology studies the influence of the geomagnetic field itself on the life activity of organisms. In near-Earth space, the magnetic field forms a magnetic trap for charged particles of high energy - the Earth's radiation belt. The particles contained in the radiation belt pose a significant danger when flying into space. The origin of the Earth's magnetic field is associated with convective movements of conductive liquid matter in the earth's core.
Direct measurements using spacecraft have shown that those closest to Earth cosmic bodies- The Moon, the planets Venus and Mars do not have their own magnetic field similar to the Earth’s. From other planets solar system only Jupiter and, apparently, Saturn have their own magnetic fields sufficient to create planetary magnetic traps. Magnetic fields up to 10 G and a number of characteristic phenomena (magnetic storms, synchrotron radio emission, and others) have been discovered on Jupiter, indicating a significant role of the magnetic field in planetary processes.
© Photo: http://www.tesis.lebedev.ru
Sun Photography
in a narrow spectrum
The interplanetary magnetic field is mainly the field of the solar wind (the continuously expanding plasma of the solar corona). Near the Earth's orbit, the interplanetary field is ~ 10 -4 -10 -5 Gs. The regularity of the interplanetary magnetic field may be disrupted due to the development various types plasma instability, the passage of shock waves and the propagation of streams of fast particles generated by solar flares.
In all processes on the Sun - flares, the appearance of spots and prominences, the birth of solar cosmic rays, the magnetic field plays vital role. Measurements based on the Zeeman effect have shown that the magnetic field of sunspots reaches several thousand Gauss, the prominences are held by fields of ~ 10-100 Gauss (with an average value of the total magnetic field of the Sun ~ 1 Gauss).
Magnetic storms
Magnetic storms are strong disturbances in the Earth’s magnetic field, sharply disrupting the smooth daily cycle of the elements of the earth’s magnetism. Magnetic storms last from several hours to several days and are observed simultaneously throughout the entire Earth.
As a rule, magnetic storms consist of preliminary, initial and main phases, as well as a recovery phase. In the preliminary phase, minor changes in the geomagnetic field are observed (mainly at high latitudes), as well as the excitation of characteristic short-period field oscillations. The initial phase is characterized by a sudden change in individual field components throughout the Earth, and the main phase is characterized by large field fluctuations and a strong decrease in the horizontal component. During the recovery phase of the magnetic storm, the field returns to its normal value.
Influence of solar wind
to the Earth's magnetosphere
Magnetic storms are caused by streams of solar plasma from active regions of the Sun superimposed on the calm solar wind. Therefore, magnetic storms are more often observed near the maxima of the 11-year cycle of solar activity. Reaching the Earth, solar plasma streams increase the compression of the magnetosphere, causing the initial phase of a magnetic storm, and partially penetrate into the Earth's magnetosphere. High energy particles entering upper atmosphere The Earth and their impact on the magnetosphere lead to the generation and intensification of electric currents in it, reaching their greatest intensity in the polar regions of the ionosphere, which is associated with the presence of a high-latitude zone of magnetic activity. Changes in magnetospheric-ionospheric current systems appear on the Earth's surface in the form of irregular magnetic disturbances.
In the phenomena of the microworld, the role of the magnetic field is as significant as on a cosmic scale. This is explained by the existence of a magnetic moment in all particles - structural elements of matter (electrons, protons, neutrons), as well as the effect of a magnetic field on moving electric charges.
Application of magnetic fields in science and technology. Magnetic fields are usually divided into weak (up to 500 Gs), medium (500 Gs - 40 kGs), strong (40 kGs - 1 MGs) and ultra-strong (over 1 MGs). Almost all electrical engineering, radio engineering and electronics are based on the use of weak and medium magnetic fields. Weak and medium magnetic fields are obtained using permanent magnets, electromagnets, uncooled solenoids, and superconducting magnets.
Magnetic field sources
All sources of magnetic fields can be divided into artificial and natural. The main natural sources of the magnetic field are the planet Earth's own magnetic field and the solar wind. Artificial sources include all electromagnetic fields, which ours is so abundant in modern world, and our homes in particular. Read more about and read on ours.
Electrically driven vehicles are a powerful source of magnetic field in the range from 0 to 1000 Hz. Rail transport uses alternating current. City transport is constant. The maximum values of magnetic field induction in suburban electric transport reach 75 μT, the average values are about 20 μT. Average values for vehicles driven by direct current recorded at 29 µT. In trams, where the return wire is the rails, the magnetic fields cancel each other over a much greater distance than in the trolleybus wires, and inside the trolleybus the fluctuations in the magnetic field are small even during acceleration. But the largest fluctuations in the magnetic field are in the subway. When the train departs, the magnetic field on the platform is 50-100 µT or more, exceeding the geomagnetic field. Even when the train has long disappeared into the tunnel, the magnetic field does not return to its previous value. Only after the train has passed the next connection point to the contact rail will the magnetic field return to its old value. True, sometimes it doesn’t have time: the next train is already approaching the platform and when it slows down, the magnetic field changes again. In the carriage itself, the magnetic field is even stronger - 150-200 µT, that is, ten times more than in a regular train.
The induction values of magnetic fields that we most often encounter in Everyday life are shown in the diagram below. Looking at this diagram, it is clear that we are exposed to magnetic fields all the time and everywhere. According to some scientists, magnetic fields with induction above 0.2 µT are considered harmful. It is natural that certain precautions should be taken to protect ourselves from the harmful effects of the fields around us. Simply by following a few simple rules, you can significantly reduce the impact of magnetic fields on your body.
The current SanPiN 2.1.2.2801-10 “Changes and additions No. 1 to SanPiN 2.1.2.2645-10 “Sanitary and epidemiological requirements for living conditions in residential buildings and premises” says the following: “The maximum permissible level of attenuation of the geomagnetic field in the premises of residential buildings is established equal to 1.5". Also set to the limit valid values intensity and strength of a magnetic field with a frequency of 50 Hz:
- in residential premises - 5 µT or 4 A/m;
- V non-residential premises residential buildings, in residential areas, including on the territory garden plots —10 µT or 8 A/m.
Based on these standards, everyone can calculate how many electrical appliances can be turned on and in a standby state in each specific room, or on the basis of which recommendations will be issued for normalizing the living space.
Related videos
A short scientific film about the Earth's magnetic field
References
1. Great Soviet Encyclopedia.
The magnetic field has long raised many questions in humans, but even now remains a little-known phenomenon. Many scientists tried to study its characteristics and properties, because the benefits and potential of using the field were undeniable facts.
Let's look at everything in order. So, how does any magnetic field operate and form? That's right, from electric current. And current, according to physics textbooks, is a directional flow of charged particles, isn’t it? So, when a current passes through any conductor, a certain type of matter begins to act around it - a magnetic field. A magnetic field can be created by a current of charged particles or by the magnetic moments of electrons in atoms. Now this field and matter have energy, we see it in electromagnetic forces that can affect the current and its charges. The magnetic field begins to influence the flow of charged particles, and they change the initial direction of movement perpendicular to the field itself.
A magnetic field can also be called electrodynamic, because it is formed near moving particles and affects only moving particles. Well, it is dynamic due to the fact that it has a special structure in rotating bions in a region of space. An ordinary moving electric charge can make them rotate and move. Bions transmit any possible interactions in this region of space. Therefore, a moving charge attracts one pole of all bions and makes them rotate. Only he can bring them out of their state of rest, nothing else, because other forces will not be able to influence them.
In an electric field there are charged particles that move very quickly and can travel 300,000 km in just a second. Light has the same speed. A magnetic field cannot exist without an electric charge. This means that the particles are incredibly closely related to each other and exist in a common electromagnetic field. That is, if there are any changes in the magnetic field, then there will be changes in the electric one. This law is also reverse.
We talk a lot about the magnetic field here, but how can we imagine it? We cannot see it with our human naked eye. Moreover, due to the incredibly fast propagation of the field, we do not have time to detect it using various devices. But in order to study something, you need to have at least some idea about it. It is also often necessary to depict a magnetic field in diagrams. To make it easier to understand, we carry out conditional power lines fields. Where did they get them from? They were invented for a reason.
Let's try to see the magnetic field using small metal filings and an ordinary magnet. Let's pour these sawdust onto a flat surface and expose them to a magnetic field. Then we will see that they will move, rotate and line up in a pattern or pattern. The resulting image will show the approximate effect of forces in the magnetic field. All forces and, accordingly, lines of force are continuous and closed in this place.
A magnetic needle has similar characteristics and properties to a compass, and is used to determine the direction of lines of force. If it falls into the zone of action of a magnetic field, we can see the direction of action of the forces from its north pole. Then let us highlight several conclusions from here: the top of an ordinary permanent magnet, from which the lines of force emanate, is designated the north pole of the magnet. Whereas south pole indicate the point where the forces are closed. Well, the lines of force inside the magnet are not highlighted in the diagram.
The magnetic field, its properties and characteristics have a fairly wide application, because in many problems it has to be taken into account and studied. This is the most important phenomenon in the science of physics. More complex things such as magnetic permeability and induction are inextricably linked with it. To explain all the reasons for the appearance of a magnetic field, we must rely on real scientific facts and confirmations. Otherwise in more complex tasks the wrong approach can destroy the integrity of the theory.
Now let's give examples. We all know our planet. Will you say that it has no magnetic field? You may be right, but scientists say that processes and interactions inside the Earth's core give rise to a huge magnetic field that stretches for thousands of kilometers. But in any magnetic field there must be its poles. And they exist, they are just located a little away from the geographic pole. How do we feel it? For example, birds have developed navigation abilities, and they navigate, in particular, by the magnetic field. So, with his help, the geese arrive safely in Lapland. Special navigation devices also use this phenomenon.
A magnetic field This is the matter that arises around sources of electric current, as well as around permanent magnets. In space, the magnetic field is displayed as a combination of forces that can influence magnetized bodies. This action is explained by the presence of driving discharges at the molecular level.
A magnetic field is formed only around electric charges that are in motion. That is why the magnetic and electric fields are integral and together form electromagnetic field. The components of the magnetic field are interconnected and influence each other, changing their properties.
Properties of magnetic field:
1. A magnetic field arises under the influence of driving charges of electric current.
2. At any point, the magnetic field is characterized by a vector of a physical quantity called magnetic induction, which is the strength characteristic of the magnetic field.
3. A magnetic field can only affect magnets, current-carrying conductors and moving charges.
4. The magnetic field can be constant or alternating type
5. The magnetic field is measured only by special instruments and cannot be perceived by human senses.
6. The magnetic field is electrodynamic, since it is generated only by the movement of charged particles and affects only charges that are in motion.
7. Charged particles move along a perpendicular trajectory.
The size of the magnetic field depends on the rate of change of the magnetic field. According to this feature, there are two types of magnetic fields: dynamic magnetic field And gravitational magnetic field. Gravitational magnetic field appears only near elementary particles and is formed depending on the structural features of these particles.
Magnetic moment occurs when a magnetic field acts on a conductive frame. In other words, the magnetic moment is a vector that is located on the line that runs perpendicular to the frame.
The magnetic field can be represented graphically using magnetic lines of force. These lines are drawn in such a direction that the direction of the field forces coincides with the direction of the field line itself. Magnetic lines of force are continuous and closed at the same time.
The direction of the magnetic field is determined using a magnetic needle. The lines of force also determine the polarity of the magnet, the end with the output of the force lines is the north pole, and the end with the input of these lines is the south pole.
It is very convenient to visually evaluate the magnetic field using ordinary iron filings and a piece of paper.
If we put a sheet of paper on a permanent magnet and sprinkle sawdust on top, then the iron particles will line up according to the magnetic field lines.
The direction of the power lines for a conductor is conveniently determined by the famous gimlet rule or right hand rule. If we wrap our hand around the conductor so that the thumb points in the direction of the current (from minus to plus), then the 4 remaining fingers will show us the direction of the magnetic field lines. 
And the direction of the Lorentz force is the force with which the magnetic field acts on a charged particle or conductor with current, according to left hand rule.
If we place left hand in a magnetic field so that 4 fingers look in the direction of the current in the conductor, and the lines of force enter the palm, then the thumb will indicate the direction of the Lorentz force, the force acting on a conductor placed in a magnetic field. 
That's all. Be sure to ask any questions you have in the comments.