What is called a magnetic field. Magnetic field and electromagnetism

A magnetic field- this is the material medium through which interaction occurs between conductors with current or moving charges.

Properties of magnetic field:

Characteristics of the magnetic field:

To study the magnetic field, a test circuit with current is used. It is small in size, and the current in it is much less than the current in the conductor creating the magnetic field. On opposite sides of the current-carrying circuit, forces from the magnetic field act that are equal in magnitude, but directed in opposite directions, since the direction of the force depends on the direction of the current. The points of application of these forces do not lie on the same straight line. Such forces are called a couple of forces. As a result of the action of a pair of forces, the circuit cannot move translationally; it rotates around its axis. The rotating action is characterized torque.

, Where l–leverage couple of forces(distance between points of application of forces).

As the current in the test circuit or the area of the circuit increases, the torque of the pair of forces will increase proportionally. The ratio of the maximum moment of force acting on the circuit with current to the magnitude of the current in the circuit and the area of the circuit is a constant value for a given point in the field. It's called magnetic induction.

, Where
-magnetic moment circuit with current.

Unit magnetic induction – Tesla [T].

Magnetic moment of the circuit– vector quantity, the direction of which depends on the direction of the current in the circuit and is determined by right screw rule: clench your right hand into a fist, point four fingers in the direction of the current in the circuit, then thumb will indicate the direction of the magnetic moment vector. The magnetic moment vector is always perpendicular to the contour plane.

Behind direction of the magnetic induction vector take the direction of the vector of the magnetic moment of the circuit, oriented in the magnetic field.

Magnetic induction line– a line whose tangent at each point coincides with the direction of the magnetic induction vector. Magnetic induction lines are always closed and never intersect. Magnetic induction lines of a straight conductor with current have the form of circles located in a plane perpendicular to the conductor. The direction of the magnetic induction lines is determined by the right-hand screw rule. Magnetic induction lines of circular current(turns with current) also have the form of circles. Each coil element is length
can be imagined as a straight conductor that creates its own magnetic field. For magnetic fields, the principle of superposition (independent addition) applies. The total vector of magnetic induction of the circular current is determined as the result of the addition of these fields in the center of the turn according to the right-hand screw rule.

If the magnitude and direction of the magnetic induction vector are the same at every point in space, then the magnetic field is called homogeneous. If the magnitude and direction of the magnetic induction vector at each point do not change over time, then such a field is called permanent.

Magnitude magnetic induction at any point in the field is directly proportional to the current strength in the conductor creating the field, inversely proportional to the distance from the conductor to a given point in the field, depends on the properties of the medium and the shape of the conductor creating the field.

, Where
ON 2 ; Gn/m – magnetic constant of vacuum,

-relative magnetic permeability of the medium,

-absolute magnetic permeability of the medium.

Depending on the value of magnetic permeability, all substances are divided into three classes:

As the absolute permeability of the medium increases, the magnetic induction at a given point in the field also increases. The ratio of magnetic induction to the absolute magnetic permeability of the medium is a constant value for a given poly point, e is called tension.

The vectors of tension and magnetic induction coincide in direction. The magnetic field strength does not depend on the properties of the medium.

Ampere power– the force with which the magnetic field acts on a current-carrying conductor.

Where l– length of the conductor, - the angle between the magnetic induction vector and the direction of the current.

The direction of the Ampere force is determined by left hand rule: left hand positioned so that the component of the magnetic induction vector, perpendicular to the conductor, enters the palm, four extended fingers are directed along the current, then the thumb bent by 90 0 will indicate the direction of the Ampere force.

The result of the Ampere force is the movement of the conductor in a given direction.

E if = 90 0 , then F=max, if = 0 0 , then F = 0.

Lorentz force– the force of the magnetic field on a moving charge.

, where q is the charge, v is the speed of its movement, - the angle between the vectors of tension and speed.

The Lorentz force is always perpendicular to the magnetic induction and velocity vectors. The direction is determined by left hand rule(fingers follow the movement of the positive charge). If the direction of the particle's velocity is perpendicular to the magnetic induction lines of a uniform magnetic field, then the particle moves in a circle without changing its kinetic energy.

Since the direction of the Lorentz force depends on the sign of the charge, it is used to separate charges.

Magnetic flux– a value equal to the number of magnetic induction lines that pass through any area located perpendicular to the magnetic induction lines.

, Where - the angle between the magnetic induction and the normal (perpendicular) to the area S.

Unit– Weber [Wb].

Magnetic flux measurement methods:

Changing the orientation of the site in a magnetic field (changing the angle)

Changing the area of a circuit placed in a magnetic field

Change in current strength creating a magnetic field

Changing the distance of the circuit from the magnetic field source

Changes in the magnetic properties of the medium.

F Araday recorded an electric current in a circuit that did not contain a source, but was located next to another circuit containing a source. Moreover, the current in the first circuit arose in the following cases: with any change in the current in circuit A, with relative movement of the circuits, with the introduction of an iron rod into circuit A, with the movement of a permanent magnet relative to circuit B. Directed movement of free charges (current) occurs only in an electric field. This means that a changing magnetic field generates an electric field, which sets in motion the free charges of the conductor. This electric field is called induced or vortex.

Differences between a vortex electric field and an electrostatic one:

The source of the vortex field is a changing magnetic field.

The vortex field strength lines are closed.

The work done by this field to move a charge along a closed circuit is not zero.

The energy characteristic of a vortex field is not the potential, but induced emf– a value equal to the work of external forces (forces of non-electrostatic origin) to move a unit of charge along a closed circuit.

.Measured in Volts[IN].

A vortex electric field occurs with any change in the magnetic field, regardless of whether there is a conducting closed circuit or not. The circuit only allows one to detect the vortex electric field.

Electromagnetic induction- this is the occurrence of induced emf in a closed circuit with any change in the magnetic flux through its surface.

The induced emf in a closed circuit generates an induced current.

Direction of induction current determined by Lenz's rule: the induced current is in such a direction that the magnetic field created by it counteracts any change in the magnetic flux that generated this current.

Faraday's law for electromagnetic induction: The induced emf in a closed loop is directly proportional to the rate of change of magnetic flux through the surface bounded by the loop.

T oki fuko– eddy induction currents that arise in large conductors placed in a changing magnetic field. The resistance of such a conductor is low, since it has a large cross-section S, so the Foucault currents can be large in value, as a result of which the conductor heats up.

Self-induction- this is the occurrence of induced emf in a conductor when the current strength in it changes.

A conductor carrying current creates a magnetic field. Magnetic induction depends on the current strength, therefore the intrinsic magnetic flux also depends on the current strength.

, where L is the proportionality coefficient, inductance.

Unit inductance – Henry [H].

Inductance conductor depends on its size, shape and magnetic permeability of the medium.

Inductance increases with increasing length of the conductor, the inductance of a turn is greater than the inductance of a straight conductor of the same length, the inductance of a coil (a conductor with a large number of turns) is greater than the inductance of one turn, the inductance of a coil increases if an iron rod is inserted into it.

Faraday's law for self-induction:
.

Self-induced emf is directly proportional to the rate of change of current.

Self-induced emf generates a self-induction current, which always prevents any change in the current in the circuit, that is, if the current increases, the self-induction current is directed in the opposite direction; when the current in the circuit decreases, the self-induction current is directed in the same direction. The greater the inductance of the coil, the greater the self-inductive emf that occurs in it.

Magnetic field energy is equal to the work that the current does to overcome the self-induced emf during the time while the current increases from zero to the maximum value.

Electromagnetic vibrations– these are periodic changes in charge, current strength and all characteristics of electric and magnetic fields.

Electrical oscillatory system(oscillating circuit) consists of a capacitor and an inductor.

Conditions for the occurrence of oscillations:

The system must be brought out of equilibrium; to do this, charge the capacitor. Electric field energy of a charged capacitor:

The system must return to a state of equilibrium. Under the influence of an electric field, charge transfers from one plate of the capacitor to another, that is, an electric current appears in the circuit, which flows through the coil. As the current increases in the inductor, a self-induction emf arises; the self-induction current is directed in the opposite direction. When the current in the coil decreases, the self-induction current is directed in the same direction. Thus, the self-induction current tends to return the system to a state of equilibrium.

The electrical resistance of the circuit should be low.

Ideal oscillatory circuit has no resistance. The vibrations in it are called free.

For any electrical circuit, Ohm's law is satisfied, according to which the emf acting in the circuit is equal to the sum of the voltages in all sections of the circuit. There is no current source in the oscillatory circuit, but a self-inductive emf appears in the inductor, which is equal to the voltage across the capacitor.

Conclusion: the charge of the capacitor changes according to a harmonic law.

Capacitor voltage:
.

Current strength in the circuit:
.

Magnitude
- current amplitude.

The difference from the charge on
.

Period of free oscillations in the circuit:

Energy electric field capacitor:

Coil magnetic field energy:

The energies of the electric and magnetic fields vary according to a harmonic law, but the phases of their oscillations are different: when the energy of the electric field is maximum, the energy of the magnetic field is zero.

Total energy of the oscillatory system:
.

IN ideal contour the total energy does not change.

During the oscillation process, the energy of the electric field is completely converted into the energy of the magnetic field and vice versa. This means that the energy at any moment in time is equal to either the maximum energy of the electric field or the maximum energy of the magnetic field.

Real oscillating circuit contains resistance. The vibrations in it are called fading.

Ohm's law will take the form:

Provided that the damping is small (the square of the natural frequency of oscillations is much greater than the square of the damping coefficient), the logarithmic damping decrement is:

With strong damping (the square of the natural frequency of oscillation is less than the square of the oscillation coefficient):

This equation describes the process of discharging a capacitor into a resistor. In the absence of inductance, oscillations will not occur. According to this law, the voltage on the capacitor plates also changes.

Total Energy in a real circuit decreases, since heat is released into the resistance R during the passage of current.

Transition process- a process that occurs in electrical circuits when transitioning from one operating mode to another. Estimated by time ( ), during which the parameter characterizing the transition process will change by e times.

For circuit with capacitor and resistor:
.

Maxwell's theory of the electromagnetic field:

1 position:

Any alternating electric field generates a vortex magnetic field. An alternating electric field was called a displacement current by Maxwell, since it, like an ordinary current, causes a magnetic field.

To detect the displacement current, consider the passage of current through a system in which a capacitor with a dielectric is connected.

Bias current density:
. The current density is directed in the direction of the voltage change.

Maxwell's first equation:
- the vortex magnetic field is generated by both conduction currents (moving electric charges) and displacement currents (alternating electric field E).

2 position:

Any alternating magnetic field generates a vortex electric field - the basic law of electromagnetic induction.

Maxwell's second equation:
- connects the rate of change of magnetic flux through any surface and the circulation of the electric field strength vector that arises at the same time.

Any conductor carrying current creates a magnetic field in space. If the current is constant (does not change over time), then the magnetic field associated with it is also constant. A changing current creates a changing magnetic field. There is an electric field inside a conductor carrying current. Therefore, a changing electric field creates a changing magnetic field.

The magnetic field is vortex, since the lines of magnetic induction are always closed. The magnitude of the magnetic field strength H is proportional to the rate of change of the electric field strength . Direction of the magnetic field strength vector associated with changes in electric field strength right screw rule: clench your right hand into a fist, point your thumb in the direction of the change in electric field strength, then the bent 4 fingers will indicate the direction of the magnetic field strength lines.

Any changing magnetic field creates a vortex electric field, the tension lines of which are closed and located in a plane perpendicular to the magnetic field strength.

The magnitude of the intensity E of the vortex electric field depends on the rate of change of the magnetic field . The direction of vector E is related to the direction of change in the magnetic field H by the left screw rule: clench your left hand into a fist, point your thumb in the direction of the change in the magnetic field, bent four fingers will indicate the direction of the lines of intensity of the vortex electric field.

The set of interconnected vortex electric and magnetic fields represents electromagnetic field. The electromagnetic field does not remain at the point of origin, but propagates in space in the form of a transverse electromagnetic wave.

Electromagnetic wave– this is the propagation in space of vortex electric and magnetic fields connected with each other.

Condition for the occurrence of an electromagnetic wave– movement of the charge with acceleration.

Electromagnetic Wave Equation:

- cyclic frequency of electromagnetic oscillations

t – time from the beginning of oscillations

l – distance from the wave source to a given point in space

- wave propagation speed

The time it takes a wave to travel from its source to a given point.

Vectors E and H in an electromagnetic wave are perpendicular to each other and to the speed of propagation of the wave.

Source of electromagnetic waves– conductors through which rapidly alternating currents flow (macroemitters), as well as excited atoms and molecules (microemitters). The higher the oscillation frequency, the better electromagnetic waves are emitted in space.

Properties of electromagnetic waves:

All electromagnetic waves are transverse

In a homogeneous medium, electromagnetic waves propagate at a constant speed, which depends on the properties of the environment:

- relative dielectric constant of the medium

- dielectric constant of vacuum,
F/m, Cl 2 /nm 2

- relative magnetic permeability of the medium

- magnetic constant of vacuum,
ON 2 ; Gn/m

Electromagnetic waves reflected from obstacles, absorbed, scattered, refracted, polarized, diffracted, interfered.

Volumetric energy densityelectromagnetic field consists of volumetric energy densities of electric and magnetic fields:

Wave energy flux density - wave intensity:

-Umov-Poynting vector.

All electromagnetic waves are arranged in a series of frequencies or wavelengths (
). This row is electromagnetic wave scale.

Low frequency vibrations. 0 – 10 4 Hz. Obtained from generators. They radiate poorly

Radio waves. 10 4 – 10 13 Hz. They are emitted by solid conductors carrying rapidly alternating currents.

Infrared radiation– waves emitted by all bodies at temperatures above 0 K, due to intra-atomic and intra-molecular processes.

Visible light– waves that act on the eye, causing visual sensation. 380-760 nm

Ultraviolet radiation. 10 – 380 nm. Visible light and UV arise when the movement of electrons in the outer shells of an atom changes.

X-ray radiation. 80 – 10 -5 nm. Occurs when the movement of electrons changes inner shells atom.

Gamma radiation. Occurs during the decay of atomic nuclei.

A magnetic field this is the matter that arises around sources electric current, and also 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 the vector physical quantity entitled 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 our 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 the conductor placed in the magnetic field.

That's all. Be sure to ask any questions you have in the comments.

Determination of magnetic field. His sources

Definition

A magnetic field is one of the forms of an electromagnetic field that acts only on moving bodies that have an electric charge or magnetized bodies, regardless of their movement.

The sources of this field are constant electric currents, moving electric charges (bodies and particles), magnetized bodies, alternating electric fields. The sources of constant magnetic field are direct currents.

Properties of magnetic field

At a time when the study of magnetic phenomena had just begun, researchers paid special attention to the fact that there are poles in magnetized bars. In them magnetic properties appeared especially clearly. At the same time, it was clearly visible that the poles of the magnet were different. Opposite poles attracted, and like poles repelled. Gilbert proposed the idea of the existence of “magnetic charges”. These ideas were supported and developed by Coulomb. Based on Coulomb's experiments, the force characteristic of a magnetic field became the force with which the magnetic field acts on a magnetic charge equal to unity. Coulomb drew attention to the significant differences between the phenomena of electricity and magnetism. The difference is already evident in the fact that electric charges can be separated and obtain bodies with an excess of positive or negative charge, whereas it is impossible to separate the north and south poles of a magnet and obtain a body with only one pole. From the impossibility of dividing a magnet into exclusively “northern” or “southern”, Coulomb decided that these two types of charges are inseparable in each elementary particle magnetizing substance. Thus, it was recognized that every particle of matter - an atom, a molecule or a group of them - is something like a micro magnet with two poles. In this case, the magnetization of a body is the process of orientation of its elementary magnets under the influence of an external magnetic field (analogous to the polarization of dielectrics).

The interaction of currents is realized through magnetic fields. Oersted discovered that the magnetic field is excited by current and has an orienting effect on the magnetic needle. Oersted had a current-carrying conductor located above a magnetic needle, which could rotate. When current flowed in the conductor, the arrow turned perpendicular to the wire. A change in the direction of the current caused a reorientation of the needle. From Oersted's experiment it followed that the magnetic field has a direction and should be characterized by a vector quantity. This quantity was called magnetic induction and denoted: $\overrightarrow(B).$ $\overrightarrow(B)$ is similar to the strength vector for the electric field ($\overrightarrow(E)$). The analogue of the displacement vector $\overrightarrow(D)\ $for the magnetic field has become the vector $\overrightarrow(H)$ - called the magnetic field strength vector.

A magnetic field only affects a moving electric charge. A magnetic field is generated by moving electric charges.

Magnetic field of a moving charge. Magnetic field of a coil with current. Superposition principle

Magnetic field of an electric charge that moves with constant speed, has the form:

\[\overrightarrow(B)=\frac((\mu )_0)(4\pi )\frac(q\left[\overrightarrow(v)\overrightarrow(r)\right])(r^3)\left (1\right),\]

where $(\mu )_0=4\pi \cdot (10)^(-7)\frac(H)(m)(in\SI)$ is the magnetic constant, $\overrightarrow(v)$ is the speed movement of the charge, $\overrightarrow(r)$ is the radius vector that determines the location of the charge, q is the magnitude of the charge, $\left[\overrightarrow(v)\overrightarrow(r)\right]$ is the vector product.

Magnetic induction of an element with current in the SI system:

where $\ \overrightarrow(r)$ is the radius vector drawn from the current element to the point under consideration, $\overrightarrow(dl)$ is the element of the conductor with current (the direction of the current is specified), $\vartheta$ is the angle between $ \overrightarrow(dl)$ and $\overrightarrow(r)$. The direction of the vector $\overrightarrow(dB)$ is perpendicular to the plane in which $\overrightarrow(dl)$ and $\overrightarrow(r)$ lie. Determined by the right screw rule.

For a magnetic field, the superposition principle holds:

\[\overrightarrow(B)=\sum((\overrightarrow(B))_i\left(3\right),)\]

where $(\overrightarrow(B))_i$ are individual fields that are generated by moving charges, $\overrightarrow(B)$ is the total magnetic field induction.

Example 1

Task: Find the ratio of the forces of magnetic and Coulomb interaction of two electrons that move with the same speeds $v$ in parallel. The distance between particles is constant.

\[\overrightarrow(F_m)=q\left[\overrightarrow(v)\overrightarrow(B)\right]\left(1.1\right).\]

The field that creates the second moving electron is equal to:

\[\overrightarrow(B)=\frac((\mu )_0)(4\pi )\frac(q\left[\overrightarrow(v)\overrightarrow(r)\right])(r^3)\left (1.2\right).\]

Let the distance between electrons be equal to $a=r\ (constant)$. We use the algebraic property of the vector product (Lagrange’s identity ($\left[\overrightarrow(a)\left[\overrightarrow(b)\overrightarrow(c)\right]\right]=\overrightarrow(b)\left(\overrightarrow(a )\overrightarrow(c)\right)-\overrightarrow(c)\left(\overrightarrow(a)\overrightarrow(b)\right)$))

\[(\overrightarrow(F))_m=\frac((\mu )_0)(4\pi )\frac(q^2)(a^3)\left[\overrightarrow(v)\left[\overrightarrow (v)\overrightarrow(a)\right]\right]=\left(\overrightarrow(v)\left(\overrightarrow(v)\overrightarrow(a)\right)-\overrightarrow(a)\left(\overrightarrow (v)\overrightarrow(v)\right)\right)=-\frac((\mu )_0)(4\pi )\frac(q^2\overrightarrow(a)v^2)(a^3) \ ,\]

$\overrightarrow(v)\left(\overrightarrow(v)\overrightarrow(a)\right)=0$, since $\overrightarrow(v\bot )\overrightarrow(a)$.

Force modulus $F_m=\frac((\mu )_0)(4\pi )\frac(q^2v^2)(a^2),\ $where $q=q_e=1.6\cdot 10^( -19)Kl$.

The modulus of the Coulomb force, which acts on an electron, in the field is equal to:

Let's find the force ratio $\frac(F_m)(F_q)$:

\[\frac(F_m)(F_q)=\frac((\mu )_0)(4\pi )\frac(q^2v^2)(a^2):\frac(q^2)((4 \pi (\varepsilon )_0a)^2)=(\mu )_0((\varepsilon )_0v)^2.\]

Answer: $\frac(F_m)(F_q)=(\mu )_0((\varepsilon )_0v)^2.$

Example 2

Task: A direct current of force I circulates along a coil with current in the form of a circle of radius R. Find the magnetic induction in the center of the circle.

Let us select an elementary section on the current-carrying conductor (Fig. 1); as a basis for solving the problem, we use the induction formula for a current-carrying coil element:

where $\ \overrightarrow(r)$ is the radius vector drawn from the current element to the point under consideration, $\overrightarrow(dl)$ is the element of the conductor with current (the direction of the current is specified), $\vartheta$ is the angle between $ \overrightarrow(dl)$ and $\overrightarrow(r)$. Based on Fig. 1 $\vartheta=90()^\circ $, therefore (2.1) will be simplified, in addition, the distance from the center of the circle (the point where we are looking for the magnetic field) of the conductor element with current is constant and equal to the radius of the turn (R), therefore we have:

All current elements will generate magnetic fields that are directed along the x axis. This means that the resulting magnetic field induction vector can be found as the sum of the projections of individual vectors$\ \ \overrightarrow(dB).$ Then, according to the principle of superposition, the total magnetic field induction can be obtained by passing to the integral:

Substituting (2.2) into (2.3), we get:

Answer: $B$=$\frac((\mu )_0)(2)\frac(I)(R).$

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 the electric field changes over time. In turn, when the magnetic field changes over time, an electric field appears. 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.

Various types of magnetometers are used to measure the characteristics of the magnetic field and the magnetic properties of substances. 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 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 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.

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, passage 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 a 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. The entry of high-energy particles into the upper atmosphere of the Earth and their impact on the magnetosphere leads 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 manifest themselves 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. Main natural sources The magnetic field is the planet Earth's own magnetic field and the solar wind. Artificial sources include all the electromagnetic fields with which our world is so abundant. 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. Maximum values Magnetic field induction in suburban electric transport reaches 75 μT, average values are about 20 μT. Average values for DC-driven vehicles are 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;
in non-residential premises of residential buildings, in residential areas, 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 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.

What else?

We people are no exception. Thanks to the biocurrents flowing in the body, there is an invisible pattern of its power lines around us. Planet Earth is a huge magnet. And even more grandiose is the plasma ball of the sun. The dimensions of galaxies and nebulae, incomprehensible to the human mind, rarely allow the idea that all of these are also magnets.

Modern science requires the creation of new large and super-powerful magnets, the areas of application of which are related to thermonuclear fusion, generation of electrical energy, acceleration of charged particles in synchrotrons, and recovery of sunken ships. Creating a super-strong field using is one of the tasks of modern physics.

Let's clarify the concepts

A magnetic field is a force acting on charged bodies that are in motion. It “does not work” with stationary objects (or those without a charge) and serves as one of the forms of the electromagnetic field, which exists as a more general concept.

If bodies can create a magnetic field around themselves and themselves experience the force of its influence, they are called magnets. That is, these objects are magnetized (have the corresponding moment).

Different materials react differently to external fields. Those that weaken its action internally are called paramagnets, and those that strengthen it are called diamagnetics. Certain materials have the property of amplifying their external magnetic field a thousandfold. These are ferromagnets (cobalt, nickel with iron, gadolinium, as well as compounds and alloys of the mentioned metals). Those of them that, when exposed to a strong external field, themselves acquire magnetic properties are called hard magnetic. Others, capable of behaving like magnets only under the direct influence of the field and ceasing to be such when it disappears, are soft magnetic.

A little bit of history

People have been studying the properties of permanent magnets since very, very ancient times. They are mentioned in the works of scientists Ancient Greece as early as 600 BC. Natural (naturally occurring) magnets can be found in magnetic ore deposits. The most famous of the large natural magnets is kept at the University of Tartu. It weighs 13 kilograms, and the load that can be lifted with its help is 40 kg.

Humanity has learned to create artificial magnets using various ferromagnets. The value of powdered ones (made of cobalt, iron, etc.) lies in the ability to hold a load weighing 5000 times its own weight. Artificial specimens can be permanent (obtained from or electromagnets having a core, the material of which is soft magnetic iron. The voltage field in them arises due to the passage of electric current through the wires of the winding, which surrounds the core.

The first serious book containing attempts scientific research properties of a magnet - the work of the London physician Gilbert, published in 1600. This work contains the entire set of information available at that time regarding magnetism and electricity, as well as the author’s experiments.

Man tries to adapt any of the existing phenomena to practical life. Of course, the magnet was no exception.

How are magnets used?

What properties of magnets has humanity adopted? Its scope of application is so wide that we have the opportunity to only briefly touch upon the main, most famous devices and areas of application of this wonderful item.

A compass is a well-known device for determining directions on the ground. Thanks to it, routes are laid for aircraft and ships, ground transport, and pedestrian traffic purposes. These instruments can be magnetic (pointer type), used by tourists and topographers, or non-magnetic (radio and hydrocompasses).

The first compasses were made in the 11th century and were used in navigation. Their action is based on the free rotation in a horizontal plane of a long needle made of magnetic material, balanced on an axis. One end of it always faces south, the other to north. In this way, you can always accurately find out the main directions regarding the cardinal points.

Main areas

The areas where the properties of magnets have found their main application are radio and electrical engineering, instrument making, automation and telemechanics. Relays, magnetic circuits, etc. are made from it. In 1820, the property of a conductor with current was discovered to influence the needle of a magnet, forcing it to turn. At the same time, another discovery was made - a pair of parallel conductors, through which a current of the same direction passes, have the property of mutual attraction.

Thanks to this, an assumption was made about the reason for the properties of the magnet. All such phenomena arise in connection with currents, including those circulating inside magnetic materials. Modern ideas in science completely coincide with this assumption.

About engines and generators

Based on it, many varieties of electric motors and electric generators have been created, that is, rotary-type machines, the operating principle of which is based on the conversion of mechanical energy into electrical energy (we are talking about generators) or electrical energy into mechanical energy (we are talking about engines). Any generator operates on the principle electromagnetic induction, that is, EMF (electromotive force) occurs in a wire that moves in a magnetic field. An electric motor operates based on the phenomenon of force arising in a current-carrying wire placed in a transverse field.

Using the force of interaction of the field with the current that passes through the winding turns of their moving parts, devices called magnetoelectric operate. An induction electricity meter acts as a new powerful AC electric motor with two windings. A conductive disk located between the windings is subject to rotation by a torque whose force is proportional to the power consumption.

What about in everyday life?

Equipped with a miniature battery, electric wrist watch familiar to everyone. Thanks to the use of a pair of magnets, a pair of inductors and a transistor, their design is much simpler in terms of the number of parts available than that of a mechanical watch.

Electromagnetic type locks or cylinder locks equipped with magnetic elements are increasingly used. Both the key and the lock are equipped with a combination dial. When the correct key is inserted into the lock hole, they are attracted to the desired position. internal elements magnetic lock that allows it to be opened.

The action of magnets is the basis for the design of dynamometers and galvanometers (a highly sensitive device with which weak currents are measured). The properties of magnets are used in the production of abrasives. This is the name given to sharp, small and very hard particles that are needed for mechanical processing (grinding, polishing, scraping) of a wide variety of objects and materials. During their production, the ferrosilicon required as part of the mixture partially settles to the bottom of the furnaces, and is partially introduced into the composition of the abrasive. Magnets are required to remove it from there.

Science and communication

Thanks to the magnetic properties of substances, science has the opportunity to study the structure of the most different bodies. We can only mention magnetochemistry or (a method for detecting defects by studying the distortion of the magnetic field in certain areas of products).

They are also used in the production of ultra-high frequency range equipment, radio communication systems (military purposes and on commercial lines), during heat treatment, both at home and in Food Industry products (everyone is familiar microwaves). It is almost impossible, within the framework of one article, to list all those highly complex technical devices and areas of application where the magnetic properties of substances are used today.

Medical field

The field of diagnostics and medical therapy was no exception. Thanks to generating x-ray radiation Electronic linear accelerators carry out tumor therapy; proton beams are generated in cyclotrons or synchrotrons, which have advantages over X-rays in local directionality and increased efficiency in the treatment of eye and brain tumors.

As for biological science, even before the middle of the last century, the vital functions of the body were in no way connected with the existence of magnetic fields. The scientific literature was occasionally replenished with isolated reports of one or another of their medical effects. But since the sixties, publications on the biological properties of magnets have flowed in an avalanche.

Before and now

However, attempts to treat people with it were made by alchemists back in the 16th century. There have been many successful attempts to cure toothache, nervous disorders, insomnia and many problems internal organs. It seems that the magnet found its use in medicine no later than in navigation.

Over the last half century, magnetic bracelets have been widely used, popular among patients with impaired blood pressure. Scientists seriously believed in the ability of a magnet to increase the resistance of the human body. Using electromagnetic devices, they learned to measure the speed of blood flow, take samples or administer the necessary medications from capsules.

A magnet is used to remove small metal particles that get into the eye. The work of electrical sensors is based on its action (any of us is familiar with the procedure for taking an electrocardiogram). Nowadays, the collaboration of physicists with biologists to study the deep mechanisms of the influence of the magnetic field on the human body is becoming increasingly closer and necessary.

Neodymium magnet: properties and applications

Neodymium magnets are considered to have the greatest impact on human health. They consist of neodymium, iron and boron. Chemical formula theirs is NdFeB. The main advantage of such a magnet is the strong impact of its field at a relatively small size. Thus, the weight of a magnet with a force of 200 gauss is about 1 g. For comparison, an iron magnet of equal strength has a weight approximately 10 times greater.

Another undoubted advantage of the magnets mentioned is their good stability and the ability to preserve the necessary qualities for hundreds of years. Over the course of a century, a magnet loses its properties by only 1%.

How exactly are they treated with a neodymium magnet?

With its help, they improve blood circulation, stabilize blood pressure, and fight migraines.

The properties of neodymium magnets began to be used for treatment about 2000 years ago. Mentions of this type of therapy are found in manuscripts Ancient China. They were then treated by applying magnetized stones to the human body.

Therapy also existed in the form of attaching them to the body. Legend claims that Cleopatra owed her excellent health and unearthly beauty to constantly wearing a magnetic bandage on her head. In the 10th century, Persian scientists described in detail the beneficial effects of the properties of neodymium magnets on the human body in the event of eliminating inflammation and muscle spasms. Based on the surviving evidence of that time, one can judge their use to increase muscle strength, bone strength and reduce joint pain.

From all ailments...

Evidence of the effectiveness of this effect was published in 1530 by the famous Swiss doctor Paracelsus. In his writings, the doctor described the magical properties of a magnet that can stimulate the body’s powers and cause self-healing. A huge number of diseases in those days began to be overcome using a magnet.

Self-medication with this remedy has become widespread in the United States. post-war years(1861-1865), when there was a categorical shortage of medicines. It was used both as a medicine and as a pain reliever.

Since the 20th century medicinal properties got a magnet scientific basis. In 1976, the Japanese doctor Nikagawa introduced the concept of magnetic field deficiency syndrome. Research has established its exact symptoms. They consist of weakness, fatigue, decreased performance and sleep disturbances. There are also migraines, joint and spinal pain, problems with digestive and cardiovascular systems in the form of hypotension or hypertension. The syndrome concerns both the field of gynecology and skin changes. The use of magnetic therapy can quite successfully normalize these conditions.

Science does not stand still

Scientists continue to experiment with magnetic fields. Experiments are carried out both on animals and birds, and on bacteria. Weak magnetic field conditions reduce success metabolic processes in experimental birds and mice, bacteria suddenly stop reproducing. With prolonged field deficiency, living tissues undergo irreversible changes.

It is to combat all such phenomena and the numerous ones caused by them negative consequences Magnetic therapy as such is used. It seems that at present everything beneficial features magnets have not yet been adequately studied. Doctors have many interesting discoveries and new developments ahead of them.