The magnetic field is the same. Properties of electromagnetic waves

Let's understand together what a magnetic field is. After all, many people live in this field all their lives and do not even think about it. Time to fix it!

A magnetic field

A magnetic field – special kind matter. It manifests itself in action on moving electric charges and bodies that have their own magnetic moment (permanent magnets).

Important: a magnetic field does not act on stationary charges! A magnetic field is also created by moving electric charges, or changing in time electric field, or 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 "northern" and "southern" are given only for convenience (as "plus" and "minus" in electricity).

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

Magnetic field characteristics

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

Immediately, we note that all units of measurement are given in the system SI.

Magnetic induction B – vector physical quantity, which is the main power characteristic of the magnetic field. Denoted by letter B . The unit of measurement of magnetic induction - Tesla (Tl).

Magnetic induction indicates how strong a field is by determining the force with which it acts on a charge. This force is called Lorentz force.

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

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

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

Magnetic permeability is the coefficient that determines the magnetic properties of the medium. One of the parameters on which the magnetic induction of the field depends is the 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 about 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. One of the largest magnetic anomalies on the planet - Kursk and Brazilian magnetic anomaly.

The origin of the Earth's magnetic field is still 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 that 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 are moving. Their displacement has been recorded since 1885. For example, over the past hundred years, the magnetic pole in the Southern Hemisphere has shifted by almost 900 kilometers and is now in the Southern Ocean. The pole of the Arctic hemisphere is moving across the Arctic Ocean towards the East Siberian magnetic anomaly, the speed of its movement (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 the 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.

During the history of the Earth, there have been several inversions(changes) of magnetic poles. Pole inversion is when they change places. The last time this phenomenon occurred about 800 thousand years ago, and there were more than 400 geomagnetic reversals in the history of the Earth. Some scientists believe that, given the observed acceleration of the movement of the magnetic poles, the next pole reversal should be expected in the next couple of thousand years.

Fortunately, no reversal of poles is expected in our century. So, you can think about the pleasant and enjoy life in the good old constant field of the Earth, having considered the main properties and characteristics of the magnetic field. And so that you can do this, there are our authors, who can be entrusted with some of the educational troubles with confidence in success! and other types of work you can order at the link.

Earth's magnetic field

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

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

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

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

Compass reacts
to the earth's magnetic field

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

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

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

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

Magnetic storms

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

As a rule, magnetic storms consist of preliminary, initial and main phases, as well as a recovery phase. In the preliminary phase, insignificant changes in the geomagnetic field are observed (mainly 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. In the magnetic storm recovery phase, the field returns to its normal value.

Influence of the solar wind
to the earth's magnetosphere

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

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

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

Magnetic field sources

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

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

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

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

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

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

What is a magnetic field - definition

A magnetic field is a force field acting on moving charged particles. The size of the magnetic field depends on the rate of its change. According to this feature, two types of magnetic field are distinguished: dynamic and gravitational.

The gravitational magnetic field arises only near elementary particles and is formed depending on the features of their structure. The sources of a dynamic magnetic field are moving electric charges or charged bodies, current-carrying conductors, as well as magnetized substances.

Magnetic field properties

The great French scientist André Ampere managed to find out two fundamental properties of the magnetic field:

The main difference between a magnetic field and an electric field and its main property is that it is relative. If you take a charged body, leave it motionless in any frame of reference, and place a magnetic needle nearby, it will, as usual, point north. That is, it will not detect any field other than the earth's. If you start moving this charged body relative to the arrow, then it will begin to turn - this indicates that when the charged body moves, a magnetic field also arises, in addition to the electric one. Thus, a magnetic field appears if and only if there is a moving charge.
The magnetic field acts on another electric current. So, you can detect it by tracing the movement of charged particles - in a magnetic field they will deviate, conductors with current will move, the frame with current will turn, magnetized substances will shift. Here we should recall the magnetic compass needle, usually painted in blue color- it's just a piece of magnetized iron. It always points north because the Earth has a magnetic field. Our entire planet is a huge magnet: the South Magnetic Belt is located at the North Pole, and the North Magnetic Pole is located at the South Geographic Pole.

In addition, the properties of the magnetic field include the following characteristics:

The strength of the magnetic field is described by magnetic induction - this is a vector quantity that determines the strength with which the magnetic field affects moving charges.
The magnetic field can be of constant and variable type. The first is generated by an electric field that does not change in time, the induction of such a field is also unchanged. The second is most often generated using inductors powered by alternating current.
The magnetic field cannot be perceived by the human senses and is recorded only by special sensors.

When connected to two parallel conductors electric current, they will attract or repel, depending on the direction (polarity) of the connected current. This is explained by the appearance of a special kind of matter around these conductors. This matter is called the magnetic field (MF). Magnetic force is the force with which conductors act on each other.

The theory of magnetism arose in antiquity, in the ancient civilization of Asia. In Magnesia, in the mountains, they found a special rock, pieces of which could be attracted to each other. By the name of the place, this breed was called "magnets". A bar magnet contains two poles. Its magnetic properties are especially pronounced at the poles.

A magnet hanging on a thread will show the sides of the horizon with its poles. Its poles will be turned north and south. The compass works on this principle. Opposite poles of two magnets attract and like poles repel.

Scientists have found that a magnetized needle, located near the conductor, deviates when an electric current passes through it. This suggests that an MF is formed around it.

The magnetic field affects:

Moving electric charges.
Substances called ferromagnets: iron, cast iron, their alloys.

Permanent magnets are bodies that have a common magnetic moment of charged particles (electrons).

1 - South pole of the magnet
2 - North pole of the magnet
3 - MP on the example of metal filings
4 - Direction of the magnetic field

Field lines appear when a permanent magnet approaches a paper sheet on which a layer of iron filings is poured. The figure clearly shows the places of the poles with oriented lines of force.

Magnetic field sources

Electric field that changes with time.
mobile charges.
permanent magnets.

We have known permanent magnets since childhood. They were used as toys that attracted various metal parts to themselves. They were attached to the refrigerator, they were built into various toys.

Electric charges that are in motion often have more magnetic energy than permanent magnets.

Properties

chief hallmark and the property of the magnetic field is relativity. If a charged body is left motionless in a certain frame of reference, and a magnetic needle is placed nearby, then it will point to the north, and at the same time it will not “feel” an extraneous field, except for the earth's field. And if the charged body begins to move near the arrow, then magnetic field will appear around the body. As a result, it becomes clear that the MF is formed only when a certain charge moves.
The magnetic field is able to influence and influence the electric current. It can be detected by monitoring the movement of charged electrons. In a magnetic field, particles with a charge will deviate, conductors with a flowing current will move. The current-powered frame will rotate, and the magnetized materials will move a certain distance. The compass needle is most often colored blue. It is a strip of magnetized steel. The compass is always oriented to the north, since the Earth has a magnetic field. The whole planet is like a big magnet with its poles.

The magnetic field is not perceived by human organs, and can only be detected by special devices and sensors. It is variable and permanent. An alternating field is usually created by special inductors that operate on alternating current. A constant field is formed by a constant electric field.

rules

Consider the basic rules for the image of a magnetic field for various conductors.

gimlet rule

The line of force is depicted in a plane, which is located at an angle of 90 0 to the current path so that at each point the force is directed tangentially to the line.

To determine the direction of magnetic forces, you need to remember the rule of a gimlet with a right-hand thread.

The gimlet must be positioned along the same axis as the current vector, the handle must be rotated so that the gimlet moves in the direction of its direction. In this case, the orientation of the lines is determined by turning the handle of the gimlet.

Ring Gimlet Rule

The translational movement of the gimlet in the conductor, made in the form of a ring, shows how the induction is oriented, the rotation coincides with the current flow.

The lines of force have their continuation inside the magnet and cannot be open.

A magnetic field different sources summed up with each other. In doing so, they create a common field.

Magnets with the same pole repel each other, while those with different poles attract. The value of the strength of interaction depends on the distance between them. As the poles approach, the force increases.

Magnetic field parameters

Stream chaining ( Ψ ).
Magnetic induction vector ( AT).
Magnetic flux ( F).

The intensity of the magnetic field is calculated by the size of the magnetic induction vector, which depends on the force F, and is formed by the current I through a conductor having a length l: V \u003d F / (I * l).

Magnetic induction is measured in Tesla (Tl), in honor of the scientist who studied the phenomena of magnetism and dealt with their calculation methods. 1 T is equal to the induction of the magnetic flux by the force 1 N on length 1m straight conductor at an angle 90 0 to the direction of the field, with a flowing current of one ampere:

1 T = 1 x H / (A x m).

left hand rule

The rule finds the direction of the magnetic induction vector.

If the palm of the left hand is placed in the field so that the magnetic field lines enter the palm from the north pole at 90 0, and 4 fingers are placed along the current, thumb shows the direction of the magnetic force.

If the conductor is at a different angle, then the force will directly depend on the current and the projection of the conductor onto a plane at a right angle.

The force does not depend on the type of conductor material and its cross section. If there is no conductor, and the charges move in another medium, then the force will not change.

When the direction of the magnetic field vector in one direction of one magnitude, the field is called uniform. Different environments affect the size of the induction vector.

magnetic flux

Magnetic induction passing through a certain area S and limited by this area is a magnetic flux.

If the area has a slope at some angle α to the induction line, the magnetic flux is reduced by the size of the cosine of this angle. Its greatest value is formed when the area is at right angles to the magnetic induction:

**F \u003d B * S.**

Magnetic flux is measured in a unit such as "weber", which is equal to the flow of induction by the value 1 T by area in 1 m 2.

Flux linkage

This concept is used to create general meaning magnetic flux, which is created from a certain number of conductors located between the magnetic poles.

When the same current I flows through the winding with the number of turns n, the total magnetic flux formed by all the turns is the flux linkage.

Flux linkage Ψ measured in webers, and is equal to: Ψ = n * F.

Magnetic properties

Permeability determines how much the magnetic field in a particular medium is lower or higher than the field induction in a vacuum. A substance is said to be magnetized if it has its own magnetic field. When a substance is placed in a magnetic field, it becomes magnetized.

Scientists have determined the reason why bodies acquire magnetic properties. According to the hypothesis of scientists, there are electric currents of microscopic magnitude inside substances. An electron has its own magnetic moment, which has a quantum nature, moves along a certain orbit in atoms. It is these small currents that determine the magnetic properties.

If the currents move randomly, then the magnetic fields caused by them are self-compensating. The external field makes the currents ordered, so a magnetic field is formed. This is the magnetization of the substance.

Various substances can be divided according to the properties of interaction with magnetic fields.

They are divided into groups:

Paramagnets- substances that have magnetization properties in the direction of the external field, with a low possibility of magnetism. They have a positive field strength. These substances include ferric chloride, manganese, platinum, etc.
Ferrimagnets- substances with magnetic moments that are unbalanced in direction and value. They are characterized by the presence of uncompensated antiferromagnetism. Field strength and temperature affect their magnetic susceptibility (various oxides).
ferromagnets- substances with increased positive susceptibility, depending on the intensity and temperature (crystals of cobalt, nickel, etc.).
Diamagnets– have the property of magnetization in the opposite direction of the external field, that is, negative meaning magnetic susceptibility, independent of the intensity. In the absence of a field, this substance will not have magnetic properties. These substances include: silver, bismuth, nitrogen, zinc, hydrogen and other substances.
Antiferromagnets - have a balanced magnetic moment, resulting in the formation low degree magnetization of matter. When heated, they undergo a phase transition of the substance, in which paramagnetic properties arise. When the temperature drops below a certain limit, such properties will not appear (chromium, manganese).

The considered magnets are also classified into two more categories:

Soft magnetic materials . They have low coercive force. In weak magnetic fields, they can saturate. During the process of magnetization reversal, they have insignificant losses. As a result, such materials are used for the production of cores. electrical devices operating on alternating voltage ( , generator, ).
hard magnetic materials. They have an increased value of coercive force. To remagnetize them, a strong magnetic field is required. Such materials are used in the production of permanent magnets.

Magnetic properties various substances find their use in technical designs and inventions.

Magnetic circuits

Combining multiple magnetic substances called a magnetic circuit. They are similarities and are determined by analogous laws of mathematics.

Based on magnetic circuits electrical devices, inductance, . In a functioning electromagnet, the flow flows through a magnetic circuit made of a ferromagnetic material and air, which is not a ferromagnet. The combination of these components is a magnetic circuit. Many electrical devices contain magnetic circuits in their design.

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

Emergence of the field

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

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

Graphical representation of the field

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

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

What are magnetic lines

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

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

It is the main characteristic of the magnetic field.

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

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

Magnetic permeability of substances

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

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

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

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

Field strength

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

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

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

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

Relationship between magnetic induction and intensity

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

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

Changes in the magnetic properties of materials

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

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

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

left hand rule

The force acting on a conductor with current has a direction determined by the rule of the left hand: when the palm of the virgin hand is located in such a way that 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 the current.

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

Right hand rule

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

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

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

Lenz's Law

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

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

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

conductor inductance

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

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

The magnetic field is the same. Properties of electromagnetic waves

A magnetic field