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

Properties 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 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:

Electric field energy of a 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 during the transition 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 density The electromagnetic field consists of the volumetric energy densities of the 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.– 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 in the inner shells of an atom changes.

Gamma radiation. Occurs during the decay of atomic nuclei.

Magnetic fields occur in nature and can be created artificially. The man noticed them useful characteristics which I learned to apply in everyday life. What is the source of the magnetic field?

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Earth's magnetic field

How the doctrine of the magnetic field developed

The magnetic properties of some substances were noticed in ancient times, but their study really began in medieval Europe. Using small steel needles, a scientist from France, Peregrine, discovered the intersection of magnetic force lines at certain points - the poles. Only three centuries later, guided by this discovery, Gilbert continued to study it and subsequently defended his hypothesis that the Earth has its own magnetic field.

The rapid development of the theory of magnetism began at the beginning of the 19th century, when Ampere discovered and described the influence of the electric field on the emergence of a magnetic field, and Faraday’s discovery of electromagnetic induction established an inverse relationship.

What is a magnetic field

A magnetic field manifests itself in a force effect on electric charges that are in motion, or on bodies that have a magnetic moment.

Magnetic field sources:

1. Conductors through which electric current passes;
2. Permanent magnets;
3. Changing electric field.

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Magnetic field sources

The root cause of the appearance of a magnetic field is identical for all sources: electrical microcharges - electrons, ions or protons - have their own magnetic moment or are in directional motion.

Important! Electric and magnetic fields mutually generate each other, changing over time. This relationship is determined by Maxwell's equations.

Characteristics of the magnetic field

The characteristics of the magnetic field are:

1. Magnetic flux, a scalar quantity that determines how many magnetic field lines pass through a given cross section. Denoted by the letter F. Calculated using the formula:

F = B x S x cos α,

where B is the magnetic induction vector, S is the section, α is the angle of inclination of the vector to the perpendicular drawn to the section plane. Unit of measurement – ​​weber (Wb);

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Magnetic flux

1. The magnetic induction vector (B) shows the force acting on the charge carriers. It is directed towards the north pole, where a regular magnetic needle points. Magnetic induction is measured quantitatively in Tesla (T);
2. MF tension (N). Determined by the magnetic permeability of various media. In a vacuum, permeability is taken as unity. The direction of the tension vector coincides with the direction of magnetic induction. Unit of measurement – ​​A/m.

How to represent a magnetic field

It is easy to see the manifestations of a magnetic field using the example of a permanent magnet. It has two poles and depending on the orientation the two magnets attract or repel. The magnetic field characterizes the processes occurring during this:

1. The MP is mathematically described as a vector field. It can be constructed by means of many vectors of magnetic induction B, each of which is directed towards the north pole of the compass needle and has a length depending on the magnetic force;
2. An alternative way of representing this is to use field lines. These lines never intersect, do not start or stop anywhere, forming closed loops. The MF lines are combined into areas with a more frequent location, where the magnetic field is the strongest.

Important! The density of the field lines indicates the strength of the magnetic field.

Although the MF cannot actually be seen, field lines are easy to visualize in real world, placing iron filings in the MP. Each particle behaves like a tiny magnet with a north and south pole. The result is a pattern similar to lines of force. A person is not able to feel the impact of MP.

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Magnetic field lines

Magnetic field measurement

Since this is a vector quantity, there are two parameters for measuring MF: force and direction. The direction can be easily measured using a compass connected to the field. An example is a compass placed in the Earth's magnetic field.

Measuring other characteristics is much more difficult. Practical magnetometers did not appear until the 19th century. Most of them work by using the force that the electron feels as it moves along the MP.

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Magnetometer

Very precise measurement of small magnetic fields has become practically feasible since the discovery in 1988 of giant magnetoresistance in layered materials. This discovery in fundamental physics was quickly applied to magnetic technology hard drive for storing data on computers, leading to a thousandfold increase in storage capacity in just a few years.

In generally accepted measurement systems, MP is measured in tests (T) or gauss (G). 1 T = 10000 Gs. Gauss is often used because Tesla is too large a field.

Interesting. A small magnet on a refrigerator creates a magnetic field equal to 0.001 Tesla, and the Earth's magnetic field on average is 0.00005 Tesla.

The nature of the magnetic field

Magnetism and magnetic fields are manifestations of electromagnetic force. There are two possible ways, how to organize the energy charge in motion and, consequently, the magnetic field.

The first is to connect the wire to a current source, an MF is formed around it.

Important! As the current (the number of charges in motion) increases, the MP increases proportionally. As you move away from the wire, the field decreases depending on the distance. This is described by Ampere's law.

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Ampere's law

Some materials that have higher magnetic permeability are capable of concentrating magnetic fields.

Since the magnetic field is a vector, it is necessary to determine its direction. For ordinary current flowing through a straight wire, the direction can be found using the rule right hand.

To use the rule, you need to imagine that the wire is grasped with your right hand, and your thumb indicates the direction of the current. Then the four remaining fingers will show the direction of the magnetic induction vector around the conductor.

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Right hand rule

The second way to create a magnetic field is to use the fact that in some substances electrons appear that have their own magnetic moment. This is how permanent magnets work:

1. Although atoms often have many electrons, they mostly bond so that the total magnetic field of the pair cancels out. Two electrons paired in this way are said to have opposite spin. Therefore, in order to magnetize something, you need atoms that have one or more electrons with the same spin. For example, iron has four such electrons and is suitable for making magnets;
2. The billions of electrons found in atoms can be randomly oriented, and there will be no overall MF, no matter how many unpaired electrons the material has. It must be stable at low temperatures to provide an overall preferred orientation of electrons. High magnetic permeability causes the magnetization of such substances under certain conditions outside the influence of magnetic fields. These are ferromagnetic;
3. Other materials may exhibit magnetic properties in the presence of an external magnetic field. The external field serves to align all electron spins, which disappears after the MF is removed. These substances are paramagnetic. The metal of a refrigerator door is an example of a paramagnetic material.

Earth's magnetic field

The earth can be represented in the form of capacitor plates, the charge of which has the opposite sign: “minus” - y earth's surface and “plus” – in the ionosphere. Between them there is atmospheric air as an insulating spacer. The giant capacitor maintains a constant charge due to the influence of the earth's MF. Using this knowledge, you can create a scheme for obtaining electrical energy from the Earth's magnetic field. True, the result will be low voltage values.

Have to take:

• grounding device;
• the wire;
• Tesla transformer capable of generating high-frequency oscillations and creating a corona discharge, ionizing the air.

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Tesla Coil

The Tesla coil will act as an electron emitter. The entire structure is connected together, and to ensure a sufficient potential difference, the transformer must be raised to a considerable height. Thus, it will be created electrical circuit, through which a small current will flow. Get a large number of electricity is not possible using this device.

Electricity and magnetism dominate many of the worlds around us, from the most fundamental processes in nature to cutting-edge electronic devices.

Video

The sources of the magnetic field are moving electric charges (currents) . A magnetic field arises in the space surrounding current-carrying conductors, just as an electric field arises in the space surrounding stationary electric charges. The magnetic field of permanent magnets is also created by electric microcurrents circulating inside the molecules of a substance (Ampere's hypothesis).

To describe the magnetic field, it is necessary to introduce a force characteristic of the field, similar to the vector tensions electric field. This characteristic is magnetic induction vector The magnetic induction vector determines the forces acting on currents or moving charges in a magnetic field.
The positive direction of the vector is taken to be the direction from the south pole S to the north pole N of the magnetic needle, which is freely positioned in the magnetic field. Thus, by examining the magnetic field created by a current or a permanent magnet using a small magnetic needle, it is possible at every point in space

In order to quantitatively describe the magnetic field, it is necessary to indicate a method for determining not only
direction of the vector but and its moduleThe module of the magnetic induction vector is equal to the ratio of the maximum value
Ampere force acting on a straight conductor with current, to the current strength I in the conductor and its length Δ l :

The Ampere force is directed perpendicular to the magnetic induction vector and the direction of the current flowing through the conductor. To determine the direction of the Ampere force is usually used left hand rule: if you position your left hand so that the induction lines enter the palm, and the outstretched fingers are directed along the current, then the abducted thumb will indicate the direction of the force acting on the conductor.

Interplanetary magnetic field

If interplanetary space were a vacuum, then the only magnetic fields in it could only be the fields of the Sun and planets, as well as a field of galactic origin that extends along the spiral branches of our Galaxy. In this case, the fields of the Sun and planets in interplanetary space would be extremely weak.
In fact, interplanetary space is not a vacuum, but is filled with ionized gas emitted by the Sun (solar wind). The concentration of this gas is 1-10 cm -3, typical velocities are between 300 and 800 km/s, the temperature is close to 10 5 K (recall that the temperature of the corona is 2×10 6 K).
sunny wind– outflow of plasma from the solar corona into interplanetary space. At the level of the Earth's orbit, the average speed of solar wind particles (protons and electrons) is about 400 km/s, the number of particles is several tens per 1 cm 3.

The English scientist William Gilbert, court physician to Queen Elizabeth, was the first to show in 1600 that the Earth is a magnet, the axis of which does not coincide with the axis of rotation of the Earth. Consequently, around the Earth, like around any magnet, there is a magnetic field. In 1635, Gellibrand discovered that the earth's magnetic field was slowly changing, and Edmund Halley conducted the world's first magnetic survey of the oceans and created the world's first magnetic maps (1702). In 1835, Gauss carried out a spherical harmonic analysis of the Earth's magnetic field. He created the world's first magnetic observatory in Göttingen.

A few words about magnetic cards. Typically, every 5 years, the distribution of the magnetic field on the Earth's surface is represented by magnetic maps of three or more magnetic elements. On each of these maps, isolines are drawn along which a given element has a constant value. Lines of equal declination D are called isogons, inclinations I are called isoclines, and magnitudes of total strength B are called isodynamic lines or isodines. The isomagnetic lines of the elements H, Z, X and Y are called isolines of the horizontal, vertical, northern or eastern components, respectively.

Let's return to the drawing. It shows a circle with an angular radius of 90° - d, which describes the position of the Sun on the earth's surface. The great circle arc drawn through point P and the geomagnetic pole B intersects this circle at points H' n and H' m, which indicate the position of the Sun, respectively, at the moments of geomagnetic noon and geomagnetic midnight of point P. These moments depend on the latitude of point P. Positions The sun at local true noon and midnight are indicated by points H n and H m, respectively. When d is positive (summer in the northern hemisphere), then morning half geomagnetic day is not equal to the evening one. At high latitudes, geomagnetic time can be very different from true or mean time for most of the day.
Speaking about time and coordinate systems, let's also talk about taking into account the eccentricity of the magnetic dipole. The eccentric dipole has been slowly drifting outward (north and west) since 1836. Has it crossed the equatorial plane? around 1862. Its radial trajectory is located in the area of ​​Gilbert Island in Pacific Ocean

EFFECT OF MAGNETIC FIELD ON CURRENT

Within each sector, the solar wind speed and particle density vary systematically. Rocket observations show that both parameters increase sharply at the sector boundary. At the end of the second day after passing the sector boundary, the density very quickly, and then, after two or three days, it slowly begins to increase. The solar wind speed decreases slowly on the second or third day after reaching its peak. The sector structure and the noted variations in velocity and density are closely related to magnetospheric disturbances. The sector structure is quite stable, so the entire stream structure rotates with the Sun for at least several solar revolutions, passing over the Earth approximately every 27 days.

Every person in modern world surrounded by many invisible waves and elements: magnetic fields, ultraviolet and x-rays, station signals mobile communications. However, these “entities” are invisible, although they influence the human body, and they can only be recognized with the help of special devices.

However, Japanese scientists have taken a step forward to make waves invisible to the human eye visible. The researchers conducted an experiment using experimental rats and taught these animals to recognize magnetic fields by using a digital compass that was connected to the brain. The rats read information using electrodes, and the compass sent impulses when the animal's head was turned in one direction or another. During the experiment, the animals could not use their organs of vision, which were tightly covered with fabric.

Scientists were very surprised when they noticed that rodents learned to recognize a completely new source of information. The “training” period turned out to be quite short - only two or three days. Rats began to navigate quite successfully in space and navigate labyrinths in search of food, and they did this no less effectively than ordinary animals that could navigate using their own eyes.

Researchers believe that by using such technology, teaching a person to “see” magnetic fields, ultraviolet light or X-rays would be a very useful acquisition for it.

M magnetic field- a component of the electromagnetic field, with the help of which interaction between moving electrically charged particles is carried out.

A magnetic field causes a force to be exerted on moving electric charges. Fixed electric charges do not interact with a magnetic field, but elementary particles with non-zero spin, which have their own magnetic moment, are a source of a magnetic field and the magnetic field causes a force on them, even if they are at rest.
A magnetic field is formed, for example, in the space around a conductor through which current flows or around a permanent magnet.

Generation of magnetic field

Unlike electric charges, there are no magnetic charges that would create a magnetic field in a similar way. Theoretically, such charges, which are called magnetic monopoles, could exist. In this case, the electric and magnetic fields would be completely symmetrical.

Thus, the smallest unit that can produce a magnetic field is a magnetic dipole. A magnetic dipole is different in that it always has two poles where the field lines begin and end. Microscopic magnetic dipoles are associated with the spins of elementary particles. Both charged elementary particles, such as electrons, and neutral ones, such as neutrons, have a magnetic dipole. Elementary particles with non-zero spin can be thought of as small magnets. Usually, particles with opposite spin values ​​pair, which leads to compensation of the magnetic fields they create, but in some cases it is possible for the spins of many particles to align in the same direction, which leads to the formation of permanent magnets.

A magnetic field - is also created by moving electrical charges, that is, electric current.

Creation electric charge the field depends on the reference system. Relative to an observer moving at the same speed as the charge, the charge is motionless, and such an observer will record the electric field created by Tilke. Another observer, moving at a different speed, will record both the electric and magnetic fields. Thus, electric and magnetic fields are interconnected and are components general electromagnetic field.

When electric current flows through a conductor, it remains electrically neutral, but the charge carriers in it move, so only a magnetic field appears around the conductor. The magnitude of this field is determined by Biot-Savart's law, and the direction can be determined using Ampere's rule or the right-hand rule. Such a field is vortex, i.e. its lines of force are closed.

A magnetic field is also created by an alternating electric field. According to the law of electromagnetic induction, an alternating magnetic field generates an alternating electric field, which is also a vortex. The mutual creation of electric and magnetic fields by alternating magnetic and electric fields leads to the possibility of propagation of electromagnetic waves in space.

Effect of magnetic field

The effect of a magnetic field on moving charges is determined by the Lorentz force.
The force acting on a current-carrying conductor in a magnetic field is called the Ampere force. The forces of interaction between conductors and current are determined by Ampere's law.
Neutral substances without electricity can be pulled into a magnetic field (paramagnetic) or pushed out of it (diamagnetic). Expulsion of diamagnetic materials from a magnetic field can be used for levitation.
Ferromagnets are magnetized in a magnetic field and retain a magnetic moment when the applied field is removed.

Units

Magnetic induction B is measured in carpenter in the SI system, and in Gauss in the CGS system. Magnetic field strength H is measured in A/m in the CI system and in Oersted in the CGS system.

Measurement

The magnetic field is measured by magnetometers. Mechanical magnetometers determine the field strength by the deflection of the current-carrying coil. Weak magnetic fields are measured by magnetometers based on the Josephson effect - SQUID. The magnetic field can be measured based on the nuclear magnetic resonance effect, the Hall effect and other methods.

Creation

Magnetic fields are widely used in technology and for scientific purposes. To create it, permanent magnets and electromagnets are used. A uniform magnetic field can be obtained using Helmholtz coils. Superconductor electromagnets are used to create the powerful magnetic fields needed to operate accelerators or to contain plasma in nuclear fusion facilities.

According to modern ideas, it was formed approximately 4.5 billion years ago, and from that moment our planet has been surrounded by a magnetic field. Everything on Earth, including people, animals and plants, is affected by it.

The magnetic field extends to an altitude of about 100,000 km (Fig. 1). It deflects or captures solar wind particles that are harmful to all living organisms. These charged particles form the Earth's radiation belt, and the entire region of near-Earth space in which they are located is called magnetosphere(Fig. 2). On the side of the Earth illuminated by the Sun, the magnetosphere is limited by a spherical surface with a radius of approximately 10-15 Earth radii, and on the opposite side it is extended like a comet's tail over a distance of up to several thousand Earth radii, forming a geomagnetic tail. The magnetosphere is separated from the interplanetary field by a transition region.

Earth's magnetic poles

The axis of the earth's magnet is inclined relative to the earth's rotation axis by 12°. It is located approximately 400 km away from the center of the Earth. The points at which this axis intersects the surface of the planet are magnetic poles. The Earth's magnetic poles do not coincide with the true geographic poles. Currently coordinates magnetic poles the following: northern - 77° N. and 102°W; southern - (65° S and 139° E).

Rice. 1. The structure of the Earth’s magnetic field

Rice. 2. Structure of the magnetosphere

Lines of force running from one magnetic pole to another are called magnetic meridians. An angle is formed between the magnetic and geographic meridians, called magnetic declination. Every place on Earth has its own declination angle. In the Moscow region the declination angle is 7° to the east, and in Yakutsk it is about 17° to the west. This means that the northern end of the compass needle in Moscow deviates by T to the right of the geographic meridian passing through Moscow, and in Yakutsk - by 17° to the left of the corresponding meridian.

A freely suspended magnetic needle is located horizontally only on the line of the magnetic equator, which does not coincide with the geographical one. If you move north of the magnetic equator, the northern end of the needle will gradually descend. The angle formed by a magnetic needle and a horizontal plane is called magnetic inclination. At the North and South magnetic poles, the magnetic inclination is greatest. It is equal to 90°. At the North Magnetic Pole, a freely suspended magnetic needle will be installed vertically with its northern end down, and at the South Magnetic Pole its southern end will go down. Thus, the magnetic needle shows the direction of the magnetic field lines above the earth's surface.

Over time, the position of the magnetic poles relative to the earth's surface changes.

The magnetic pole was discovered by explorer James C. Ross in 1831, hundreds of kilometers from its current location. On average, it moves 15 km in one year. IN last years the speed of movement of the magnetic poles increased sharply. For example, the North Magnetic Pole is currently moving at a speed of about 40 km per year.

The reversal of the Earth's magnetic poles is called magnetic field inversion.

Throughout the geological history of our planet, the Earth's magnetic field has changed its polarity more than 100 times.

The magnetic field is characterized by intensity. In some places on Earth, magnetic field lines deviate from the normal field, forming anomalies. For example, in the area of ​​the Kursk Magnetic Anomaly (KMA), the field strength is four times higher than normal.

There are daily variations in the Earth's magnetic field. The reason for these changes in the Earth's magnetic field is the electric currents flowing in the atmosphere at high altitude. They are caused by solar radiation. Under the influence of the solar wind, the Earth's magnetic field is distorted and acquires a “trail” in the direction from the Sun, which extends for hundreds of thousands of kilometers. The main cause of the solar wind, as we already know, is the enormous ejections of matter from the solar corona. As they move towards the Earth, they turn into magnetic clouds and lead to strong, sometimes extreme disturbances on the Earth. Particularly strong disturbances of the Earth's magnetic field - magnetic storms. Some magnetic storms begin suddenly and almost simultaneously across the entire Earth, while others develop gradually. They can last for several hours or even days. Magnetic storms often occur 1-2 days after a solar flare due to the Earth passing through a stream of particles ejected by the Sun. Based on the delay time, the speed of such a corpuscular flow is estimated at several million km/h.

During strong magnetic storms, the normal operation of the telegraph, telephone and radio is disrupted.

Magnetic storms are often observed at latitude 66-67° (in the aurora zone) and occur simultaneously with auroras.

The structure of the Earth's magnetic field varies depending on the latitude of the area. The permeability of the magnetic field increases towards the poles. Over the polar regions, the magnetic field lines are more or less perpendicular to the earth's surface and have a funnel-shaped configuration. Through them part of the solar wind with day side penetrates into the magnetosphere and then into the upper atmosphere. During magnetic storms, particles from the tail of the magnetosphere rush here, reaching the boundaries of the upper atmosphere in the high latitudes of the Northern and Southern Hemispheres. It is these charged particles that cause the auroras here.

So, magnetic storms and daily changes in the magnetic field are explained, as we have already found out, by solar radiation. But what is the main reason that creates the permanent magnetism of the Earth? Theoretically, it was possible to prove that 99% of the Earth’s magnetic field is caused by sources hidden inside the planet. The main magnetic field is caused by sources located in the depths of the Earth. They can be roughly divided into two groups. The main part of them is associated with processes in the earth's core, where, due to continuous and regular movements of electrically conductive matter, a system of electric currents is created. The other is due to the fact that the rocks of the earth’s crust, when magnetized by the main electric field (the field of the core), create their own magnetic field, which is summed with the magnetic field of the core.

In addition to the magnetic field around the Earth, there are other fields: a) gravitational; b) electric; c) thermal.

Gravitational field The earth is called the gravity field. It is directed along a plumb line perpendicular to the surface of the geoid. If the Earth had the shape of an ellipsoid of revolution and masses were evenly distributed in it, then it would have a normal gravitational field. The difference between the intensity of the real gravitational field and the theoretical one is a gravity anomaly. Different material composition and density of rocks cause these anomalies. But other reasons are also possible. They can be explained by the following process - the equilibrium of the solid and relatively light earth's crust on the heavier upper mantle, where the pressure of the overlying layers is equalized. These currents cause tectonic deformations, the movement of lithospheric plates and thereby create the macrorelief of the Earth. Gravity holds the atmosphere, hydrosphere, people, animals on Earth. Gravity must be taken into account when studying processes in the geographic envelope. The term " geotropism" are the growth movements of plant organs, which, under the influence of the force of gravity, always ensure the vertical direction of growth of the primary root perpendicular to the surface of the Earth. Gravity biology uses plants as experimental subjects.

If gravity is not taken into account, it is impossible to calculate the initial data for launching rockets and spaceships, make gravimetric exploration of ore minerals and, finally, the further development of astronomy, physics and other sciences is impossible.