A message on the topic of the earth's magnetic field. What is the Earth's magnetic field

Physics work

10th grade student A

School No. 1202

Kruglova Egor

A magnetic field

In the 19th century, the connection between electricity and magnetism was discovered and the idea of ​​a magnetic field arose. According to modern concepts, conductors carrying current have force action at each other not directly, but through the magnetic fields surrounding them.

Sources 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 field strength characteristic similar to the electric field strength vector. Such a characteristic is the 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 the direction of the vector but also its magnitude.

The modulus of the magnetic induction vector is equal to the ratio of the maximum value of the Ampere force acting on a straight conductor with current to the current strength I in the conductor and its length Δ l :

This relationship is usually called Ampere's law.

In the SI system of units, the unit of magnetic induction is the induction of a magnetic field in which a maximum Ampere force of 1 N acts for each meter of conductor length at a current of 1 A. This unit is called tesla (T).

Tesla is a very large unit. The Earth's magnetic field is approximately 0.5·10–4 T. A large laboratory electromagnet can create a field of no more than 5 Tesla.

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, the left-hand rule is usually used: if you place left hand so that the induction lines enter the palm, and the extended fingers are directed along the current, then the abducted thumb will indicate the direction of the force acting on the conductor.

Left hand rule and gimlet rule.

Lines of magnetic induction fields of a permanent magnet and a coil with current

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

A magnetic field

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

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

A body that has its own magnetic field.

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

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

Characteristics of the magnetic field

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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, the coordinates of the magnetic poles are as follows: north - 77° north latitude. 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 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 recent years, the speed of movement of the magnetic poles has 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 electric currents flowing in the atmosphere at high altitudes. 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. Often magnetic storms occur 1-2 days after solar flare due to the passage of the Earth 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 from the dayside 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 spacecraft, to carry out gravimetric exploration of ore deposits, and, finally, it is impossible further development astronomy, physics and other sciences.

Most planets solar system have magnetic fields to varying degrees.
A special branch of geophysics that studies the origin and nature of the Earth's magnetic field is called geomagnetism. Geomagnetism considers the problems of the emergence and evolution of the main, constant component of the geomagnetic field, the nature of the variable component (about 1% of the main field), as well as the structure of the magnetosphere - the uppermost magnetized plasma layers of the earth's atmosphere, interacting with the solar wind and protecting the Earth from penetrating cosmic radiation . An important task is to study the patterns of variations in the geomagnetic field, since they are caused by external influences associated primarily with solar activity.

This may be surprising, but today there is no single point of view on the mechanism of the emergence of the magnetic field of planets, although the magnetic hydrodynamo hypothesis, based on the recognition of the existence of a conductive liquid outer core, is almost universally accepted. Thermal convection, that is, the mixing of matter in the outer core, contributes to the formation of ring electric currents. The speed of movement of matter in the upper part of the liquid core will be somewhat lower, and in the lower layers - greater relative to the mantle in the first case and the solid core in the second. Such slow flows cause the formation of ring-shaped (toroidal) electric fields, closed in shape, that do not extend beyond the core. Due to the interaction of toroidal electric fields with convective currents, a total magnetic field of a dipole nature arises in the outer core, the axis of which approximately coincides with the axis of rotation of the Earth. To “start” such a process, an initial, at least very weak, magnetic field is required, which can be generated by the gyromagnetic effect when a rotating body is magnetized in the direction of its rotation axis.

The solar wind also plays an important role - a flow of charged particles, mainly protons and electrons, coming from the Sun. For the Earth, the solar wind is a stream of charged particles in a constant direction, and this is nothing more than an electric current.

According to the definition of the direction of the current, it is directed in the direction opposite to the movement of negatively charged particles (electrons), i.e. from Earth to Sun. Particles that form the solar wind, having mass and charge, are carried away by the upper layers of the atmosphere in the direction of the Earth's rotation. In 1958, the Earth's radiation belt was discovered. This is a huge zone in space, covering the Earth at the equator. In the radiation belt, the main charge carriers are electrons. Their density is 2–3 orders of magnitude higher than the density of other charge carriers. And thus there is an electric current caused by the directed circular motion of solar wind particles, carried away by the circular motion of the Earth, generating an electromagnetic “vortex” field.

It should be noted that the magnetic flux caused by the current of the solar wind also penetrates the flow of hot lava rotating with the Earth inside it. As a result of this interaction, an electromotive force is induced in it, under the influence of which a current flows, which also creates a magnetic field. As a result, the Earth's magnetic field is the resulting field from the interaction of the ionospheric current and the lava current.

The actual picture of the Earth's magnetic field depends not only on the configuration of the current sheet, but also on the magnetic properties of the earth's crust, as well as on the relative location of magnetic anomalies. Here we can draw an analogy with a circuit with current in the presence of a ferromagnetic core and without it. It is known that the ferromagnetic core not only changes the configuration of the magnetic field, but also significantly enhances it.

It has been reliably established that the Earth’s magnetic field responds to solar activity, however, if we associate the emergence of the planets’ magnetic field only with current layers in the liquid core interacting with the solar wind, then we can conclude that the planets of the solar system, which have the same direction of rotation, must have the same direction magnetic fields. However, for example, Jupiter refutes this statement.

It is interesting that when the solar wind interacts with the excited magnetic field of the Earth, a torque directed towards the rotation of the Earth acts on the Earth. Thus, the Earth, relative to the solar wind, behaves similarly to a self-excited DC motor. Energy source (generator) in in this case is the Sun. Since both the magnetic field and the torque acting on the earth depend on the current of the Sun, and the latter on the degree of solar activity, then with increasing solar activity the torque acting on the Earth should increase and the speed of its rotation should increase.

Components of the geomagnetic field

The Earth's own magnetic field (geomagnetic field) can be divided into the following three main parts - main (internal) magnetic field of the Earth, including global anomalies, magnetic fields of local areas of outer shells, alternating (external) magnetic field of the Earth.

1. MAIN MAGNETIC FIELD OF THE EARTH (internal) , experiencing slow changes over time (secular variations) with periods from 10 to 10,000 years, concentrated in the intervals of 10–20, 60–100, 600–1200 and 8000 years. The latter is associated with a change in the dipole magnetic moment by a factor of 1.5–2.

Magnetic field lines created by a computer model of the geodynamo show how the structure of the Earth's magnetic field is simpler outside of it than inside the core (tangled tubes in the center). On the surface of the Earth most of The magnetic field lines come out from the inside (long yellow tubes) at the South Pole and enter inside (long blue tubes) near the North Pole.

Most people don't usually think about why the compass needle points north or south. But the planet's magnetic poles were not always positioned as they are today.

Mineral studies show that the Earth's magnetic field has changed its orientation from north to south and back hundreds of times over the 4-5 billion years of the planet's existence. However, nothing like this has happened over the past 780 thousand years, despite the fact that the average period of reversal of magnetic poles is 250 thousand years. In addition, the geomagnetic field has weakened by almost 10% since it was first measured in the 1930s. XIX century (i.e. almost 20 times faster than if, having lost its source of energy, it had reduced its strength naturally). Is the next pole shift coming?

The source of magnetic field oscillations is hidden in the center of the Earth. Our planet, like other bodies in the solar system, creates its magnetic field with the help of an internal generator, the operating principle of which is the same as that of a conventional electric, transforming kinetic energy their moving particles into the electromagnetic field. In an electric generator, movement occurs in the turns of a coil, and inside a planet or star - in a conducting liquid substance. A huge mass of molten iron with a volume 5 times larger than the Moon circulates in the core of the Earth, forming the so-called geodynamo.

Over the past ten years, scientists have developed new approaches to studying the operation of the geodynamo and its magnetic properties. Satellites transmit clear snapshots of the geomagnetic field on the Earth's surface, and modern computer modeling techniques and laboratory-created physical models help interpret orbital observational data. The experiments led scientists to a new explanation of how repolarization occurred in the past and how it may begin in the future.

In internal structure The Earth has a molten outer core, where complex turbulent convection generates a geomagnetic field.

Geodynamo energy

What powers the geodynamo? By the 40s. of the last century, physicists recognized three necessary conditions for the formation of the planet’s magnetic field, and subsequent scientific constructions were based on these provisions. The first condition is a large volume of electrically conductive liquid mass, saturated with iron, forming the outer core of the Earth. Beneath it lies the Earth's inner core, consisting of almost pure iron, and above it is 2,900 km of solid rock, dense mantle and thin crust, forming continents and ocean floors. The pressure on the core created by the earth's crust and mantle is 2 million times higher than on the surface of the Earth. The temperature of the core is also extremely high - about 5000o Celsius, as is the temperature of the surface of the Sun.

The above-described parameters of the extreme environment predetermine the second requirement for the operation of a geodynamo: the need for an energy source to set the liquid mass in motion. Internal energy, partly of thermal and partly of chemical origin, creates expulsion conditions inside the nucleus. The core heats up more at the bottom than at the top. (High temperatures have been “walled up” inside it since the formation of the Earth.) This means that the hotter, less dense metal component of the core tends to rise. When the liquid mass reaches the upper layers, it loses some of its heat, giving it to the overlying mantle. Then the liquid iron cools, becoming denser than the surrounding mass, and sinks. The process of moving heat by raising and lowering a liquid mass is called thermal convection.

Third necessary condition maintaining a magnetic field - the rotation of the Earth. The resulting Coriolis force deflects the movement of the rising liquid mass inside the Earth in the same way as it turns ocean currents and tropical cyclones, the movement vortices of which are visible in satellite images. At the center of the Earth, the Coriolis force twists the rising liquid mass into a corkscrew or spiral, like a loose spring.

The Earth has an iron-rich liquid mass concentrated at its center, sufficient energy to support convection, and a Coriolis force to swirl convection currents. This factor is extremely important for maintaining the operation of the geodynamo for millions of years. But new knowledge is needed to answer the question of how the magnetic field is formed and why the poles change places from time to time.

Repolarization

Scientists have long wondered why the Earth's magnetic poles switch places from time to time. Recent studies of vortex movements of molten masses inside the Earth make it possible to understand how repolarization occurs.

A magnetic field, much more intense and more complex than the field of the core, within which magnetic oscillations are formed, was discovered at the boundary of the mantle and core. Electric currents arising in the core prevent direct measurements of its magnetic field.

It is important that most of the geomagnetic field is generated only in four broad regions at the core-mantle boundary. Although the geodynamo produces a very strong magnetic field, only 1% of its energy travels outside the core. The general configuration of a magnetic field measured at a surface is called a dipole, which is oriented along the direction most of the time. earth's axis rotation. As in the field of a linear magnet, the main geomagnetic flow is directed from the center of the Earth in the Southern Hemisphere and towards the center in the Northern Hemisphere. (The compass needle points to the north geographic pole, since the south magnetic pole of the dipole is nearby.) Space observations have shown that the magnetic flux has an uneven global distribution, the greatest tension can be seen on the Antarctic coast, under North America and Siberia.

Ulrich R. Christensen of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany, believes that these vast areas of land have existed for thousands of years and are maintained by ever-evolving convection within the core. Could similar phenomena be the cause of pole reversals? Historical geology shows that pole changes occurred in relatively short periods of time - from 4 thousand to 10 thousand years. If the geodynamo had stopped working, the dipole would have existed for another 100 thousand years. A rapid change in polarity gives reason to believe that some unstable position violates the original polarity and causes a new change of poles.

In some cases, the mysterious instability can be explained by some chaotic change in the structure of the magnetic flux, which only accidentally leads to repolarization. However, the frequency of polarity changes, which has become more and more stable over the past 120 million years, indicates the possibility of external regulation. One of the reasons for this may be a temperature difference in the lower layer of the mantle, and as a result, a change in the nature of core outpourings.

Some symptoms of repolarization were identified when analyzing maps that were made from the Magsat and Oersted satellites. Gauthier Hulot and his colleagues from the Paris Geophysical Institute noted that long-term changes in the geomagnetic field occur at the core-mantle boundary in places where the direction of the geomagnetic flow is opposite to the normal one for a given hemisphere. The largest of the so-called reverse magnetic field stretches from the southern tip of Africa west to South America. In this area, the magnetic flux is directed inward, towards the core, while most of it in the Southern Hemisphere is directed from the center.

Regions where the magnetic field is directed in the opposite direction for a given hemisphere arise when twisted and winding magnetic field lines accidentally break through beyond the Earth's core. Areas of reverse magnetic field can significantly weaken the magnetic field on the Earth's surface, called a dipole, and indicate the beginning of a reversal of the Earth's poles. They appear when rising liquid mass pushes horizontal magnetic lines upward in the molten outer core. This convective outpouring sometimes twists and extrudes the magnetic line(s). At the same time, the rotational forces of the Earth cause a helical circulation of the melt, which can tighten the loop on the extruded magnetic line (b). When the buoyancy force is strong enough to eject the loop from the core, a pair of magnetic flux patches form at the core-mantle boundary.

The most significant discovery made by comparing the latest Oersted measurements with those taken in 1980 was that new regions of magnetic reversals continue to form, for example at the core-mantle boundary beneath the east coast of North America and the Arctic. Moreover, previously identified areas have grown and moved slightly towards the poles. At the end of the 80s. XX century David Gubbins of the University of Leeds in England, studying old maps of the geomagnetic field, noted that the spread, growth and poleward shift of sections of the inverse magnetic field explains the decline in dipole strength over historical time.

According to theoretical principles about magnetic field lines, small and large vortices arising in the liquid medium of the nucleus under the influence of the Coriolis force twist the field lines into a knot. Each rotation collects more and more lines of force in the core, thus increasing the energy of the magnetic field. If the process continues unhindered, the magnetic field intensifies indefinitely. However, electrical resistance dissipates and aligns the turns of field lines enough to stop the spontaneous growth of the magnetic field and continue the reproduction of internal energy.

Areas of intense magnetic normal and reverse fields form at the core-mantle boundary, where small and large eddies interact with east-west magnetic fields, described as toroidal, that penetrate into the core. Turbulent fluid movements can twist toroidal field lines into loops called poloidal fields, which have a north-south orientation. Sometimes twisting occurs when a fluid mass is raised. If such an outpouring is powerful enough, the top of the poloidal loop is pushed out of the nucleus (see inset on the left). As a result of this ejection, two sections are formed in which the loop crosses the core-mantle boundary. On one of them, the direction of magnetic flux appears, coinciding with general direction dipole fields in a given hemisphere; in another section the flow is directed in the opposite direction.

When rotation brings a section of the reversed magnetic field closer to the geographic pole than the section with normal flux, there is a weakening of the dipole, which is most vulnerable near its poles. This can explain the reversed magnetic field in southern Africa. With the global onset of a pole reversal, areas of reversed magnetic fields can grow throughout the region near the geographic poles.

Contour maps of the Earth's magnetic field at the core-mantle boundary, compiled from satellite measurements, show that most of the magnetic flux is directed from the center of the Earth in the Southern Hemisphere and towards the center in the Northern Hemisphere. But in some areas the opposite picture emerges. The reversed magnetic field regions grew in number and size between 1980 and 2000. If they filled the entire space at both poles, repolarization could occur.

Pole reversal models

Magnetic field maps show how, with normal polarity, most of the magnetic flux is directed away from the center of the Earth ( yellow) in the Southern Hemisphere and to its center (blue) in the Northern Hemisphere (a). The onset of repolarization is marked by the appearance of several areas of reverse magnetic field (blue in the Southern Hemisphere and yellow in the Northern Hemisphere), reminiscent of the formation of its sections at the core-mantle boundary. Over approximately 3 thousand years, they reduced the strength of the dipole field, which was replaced by a weaker, but more complex transition field at the core-mantle boundary (b). Pole reversals became a frequent occurrence after 6 thousand years, when sections of the reverse magnetic field (c) began to predominate at the core-mantle boundary. By this time, a complete reversal of the poles had also manifested itself on the surface of the Earth. But only after another 3 thousand years there was a complete replacement of the dipole, including the Earth’s core (d).

What is happening to the internal magnetic field today?

Most of us know that the geographic poles constantly make complex looping movements in the direction of the Earth's daily rotation (axis precession with a period of 25,776 years). Typically, these movements occur near the imaginary axis of rotation of the Earth and do not lead to noticeable climate change. Read more about pole shift. But few people noticed that at the end of 1998 the overall component of these movements shifted. Within a month, the pole shifted towards Canada by 50 kilometers. Currently, the North Pole is “creeping” along the 120th parallel of western longitude. It can be assumed that if the current trend in pole movement continues until 2010, the north pole could shift by 3-4 thousand kilometers. End point drift - Great Bear Lakes in Canada. The South Pole will accordingly shift from the center of Antarctica to the Indian Ocean.

The shift of magnetic poles has been recorded since 1885. Over the past 100 years, the magnetic pole in the southern hemisphere has moved almost 900 km and entered the Indian Ocean. The latest data on the state of the Arctic magnetic pole (moving towards the East Siberian world magnetic anomaly through the Arctic Ocean): showed that from 1973 to 1984 its mileage was 120 km, from 1984 to 1994. – more than 150 km. It is characteristic that these data are calculated, but they were confirmed by specific measurements of the north magnetic pole. According to data at the beginning of 2002, the drift speed of the north magnetic pole increased from 10 km/year in the 70s, to 40 km/year in 2001 year.

In addition, the strength of the earth's magnetic field drops, and very unevenly. Thus, over the past 22 years it has decreased by an average of 1.7 percent, and in some regions - for example, in the South Atlantic Ocean - by 10 percent. However, in some places on our planet the magnetic field strength, contrary to the general trend, has even increased slightly.

We emphasize that the acceleration of the movement of the poles (on average by 3 km/year per decade) and their movement along the corridors of magnetic pole inversion (more than 400 paleoinversions made it possible to identify these corridors) makes us suspect that this movement of the poles should not be seen as an excursion, and the reversal of the Earth's magnetic field.

Acceleration can bring the movement of the poles up to 200 km per year, so that the reversal will take place much faster than expected by researchers who are far from professional assessments of real polarity reversal processes.

In the history of the Earth, changes in the position of the geographic poles have occurred repeatedly, and this phenomenon is primarily associated with the glaciation of vast areas of land and dramatic changes in the climate of the entire planet. But echoes in human history received only the last catastrophe, most likely associated with the pole shift, which occurred about 12 thousand years ago. We all know that Mammoths are extinct. But everything was much more serious.

The extinction of hundreds of animal species is beyond doubt. There are discussions about the Flood and the Death of Atlantis. But one thing is certain - the echoes of the greatest catastrophe in human memory have a real basis. And it is most likely caused by a pole shift of only 2000 km.

The model below shows the magnetic field inside the core (a bunch of field lines in the center) and the appearance of a dipole (long curved lines) 500 years (a) before the middle of the repolarization of the magnetic dipole (b) and 500 years later at the stage of its completion (c).

Magnetic field of the Earth's geological past

Over the past 150 million years, repolarization has occurred hundreds of times, as evidenced by minerals magnetized by the Earth's field during the heating of rocks. Then the rocks cooled, and the minerals retained their previous magnetic orientation.

Magnetic field reversal scales: I – for the last 5 million years; II – over the last 55 million years. Black color – normal magnetization, White color– reverse magnetization (according to W.W. Harland et al., 1985)

Magnetic field reversals are a change in the sign of the axes of a symmetrical dipole. In 1906, B. Brun, measuring the magnetic properties of Neogene, relatively young lavas in central France, discovered that their magnetization was opposite in direction to the modern geomagnetic field, that is, the North and South magnetic poles seemed to have swapped places. The presence of reversely magnetized rocks is not a consequence of some unusual conditions at the time of its formation, but the result of an inversion of the Earth's magnetic field at the moment. Reversing the polarity of the geomagnetic field – major discovery in paleomagnetology, which made it possible to create the new science of magnetostratigraphy, which studies the division of rock deposits based on their direct or reverse magnetization. And the main thing here is to prove the synchronicity of these sign reversals throughout the entire globe. In this case, geologists have very effective method sediment-event correlations.

In the real magnetic field of the Earth, the time during which the polarity sign changes can be either short, up to a thousand years, or millions of years.
The time intervals of predominance of any one polarity are called geomagnetic epochs, and some of them are given the names of the outstanding geomagnetologists Bruness, Matuyama, Gauss and Hilbert. Within epochs, shorter intervals of one polarity or another are distinguished, called geomagnetic episodes. The most effective identification of intervals of direct and reverse polarity of the geomagnetic field was carried out for geologically young lava flows in Iceland, Ethiopia and other places. A limitation of these studies is that the lava eruption was an intermittent process, so it is possible that some magnetic episode may have been missed.

When it became possible to determine the position of the paleomagnetic poles of the time interval of interest to us using selected rocks of the same age, but taken on different continents, it turned out that the calculated averaged pole, say, for Upper Jurassic rocks (170 - 144 million years) of North America and the same the pole for the same rocks in Europe will be in different places. It looked like there were two North Poles, which cannot happen with a dipole system. In order for there to be one North Pole, the position of the continents on the surface of the Earth had to change. In our case, this meant the convergence of Europe and North America until their shelf edges coincide, that is, to the ocean depths of about 200 m. In other words, it is not the poles that are moving, but the continents.

The use of the paleomagnetic method made it possible to carry out detailed reconstructions of the opening of the relatively young Atlantic, Indian, and Arctic oceans and to understand the history of the development of the more ancient Pacific Ocean. The current arrangement of the continents is the result of the breakup of the supercontinent Pangea, which began about 200 million years ago. The linear magnetic field of the oceans makes it possible to determine the speed of plate movement, and its pattern provides the best information for geodynamic analysis.

Thanks to paleomagnetic studies, it was established that the split of Africa and Antarctica occurred 160 million years ago. The most ancient anomalies with an age of 170 million years (Middle Jurassic) were found along the edges of the Atlantic off the coast of North America and Africa. This is the time when the supercontinent began to disintegrate. The South Atlantic arose 120 - 110 million years ago, and the North Atlantic much later (80 - 65 million years ago), etc. Similar examples one can use any of the oceans and, as if “reading” the paleomagnetic record, reconstruct the history of their development and the movement of lithospheric plates.

World anomalies– deviations from the equivalent dipole of up to 20% of the intensity of individual areas with characteristic dimensions of up to 10,000 km. These anomalous fields experience secular variations, resulting in changes over time over many years and centuries. Examples of anomalies: Brazilian, Canadian, Siberian, Kursk. In the course of secular variations, global anomalies shift, disintegrate and re-emerge. At low latitudes there is a westerly drift in longitude at a rate of 0.2° per year.

2. MAGNETIC FIELDS OF LOCAL AREAS outer shells with a length from several to hundreds of km. They are caused by the magnetization of rocks in the upper layer of the Earth, which make up the earth's crust and are located close to the surface. One of the most powerful is the Kursk magnetic anomaly.

3. ALTERNATING MAGNETIC FIELD OF THE EARTH (also called external) is determined by sources in the form of current systems located outside the earth's surface and in its atmosphere. The main sources of such fields and their changes are corpuscular flows of magnetized plasma coming from the Sun along with the solar wind, and forming the structure and shape of the Earth's magnetosphere.

First of all, it is clear that this structure has a “layered” shape. However, sometimes one can observe a “rupture” of the upper layers, apparently occurring under the influence of increasing solar wind. For example like here:

At the same time, the degree of “heating” depends on the speed and density of the Solar wind at such a moment, which is reflected in color scheme from yellow to purple, which actually reflects the amount of pressure on the magnetic field in this zone (top right figure).

Structure of the magnetic field of the Earth's atmosphere (Earth's external magnetic field)

The Earth's magnetic field is influenced by the flow of magnetized solar plasma. As a result of interaction with the Earth's field, the outer boundary of the near-Earth magnetic field is formed, called magnetopause. It limits the earth's magnetosphere. Due to the influence of solar corpuscular flows, the size and shape of the magnetosphere are constantly changing, and an alternating magnetic field arises, determined by external sources. Its variability owes its origin to current systems developing at various altitudes from the lower layers of the ionosphere to the magnetopause. Changes in the Earth's magnetic field over time, caused by various reasons, are called geomagnetic variations, which differ both in their duration and in their localization on the Earth and in its atmosphere.

Magnetosphere is a region of near-Earth space controlled by the Earth's magnetic field. The magnetosphere is formed as a result of the interaction of the solar wind with the plasma of the upper atmosphere and the Earth's magnetic field. The shape of the magnetosphere is a cavity and a long tail, which repeat the shape of magnetic field lines. The subsolar point is on average at a distance of 10 Earth radii, and the tail of the magnetosphere extends beyond the orbit of the Moon. The topology of the magnetosphere is determined by the areas of solar plasma invasion into the magnetosphere and the nature of current systems.

The tail of the magnetosphere is formed by the lines of force of the Earth's magnetic field, emerging from the polar regions and extended under the influence of the solar wind to hundreds of Earth radii from the Sun to the night side of the Earth. As a result, the plasma of the solar wind and solar corpuscular flows seem to flow around the earth’s magnetosphere, giving it a peculiar tailed shape.
In the tail of the magnetosphere, at large distances from the Earth, the strength of the Earth's magnetic field, and therefore their protective properties, are weakened, and some particles of solar plasma are able to penetrate and enter the interior of the earth’s magnetosphere and magnetic traps of radiation belts. Penetrating into the head of the magnetosphere into the region of auroral ovals under the influence of changing pressure of the solar wind and the interplanetary field, the tail serves as a place for the formation of streams of precipitating particles, causing auroras and auroral currents. The magnetosphere is separated from interplanetary space by the magnetopause. Along the magnetopause, particles of corpuscular flows flow around the magnetosphere. The influence of the solar wind on the Earth's magnetic field is sometimes very strong. Magnetopause is the outer boundary of the Earth’s (or planet’s) magnetosphere, at which the dynamic pressure of the solar wind is balanced by the pressure of its own magnetic field. With typical solar wind parameters, the subsolar point is 9–11 Earth radii away from the center of the Earth. During periods of magnetic disturbances on Earth, the magnetopause can go beyond the geostationary orbit (6.6 Earth radii). With a weak solar wind, the subsolar point is located at a distance of 15–20 Earth radii.

Geomagnetic variations

Changes in the Earth's magnetic field over time under the influence of various factors are called geomagnetic variations. The difference between the observed magnetic field strength and its average value over any long period of time, for example, a month or a year, is called geomagnetic variation. According to observations, geomagnetic variations change continuously over time, and such changes are often periodic.

Daily variations geomagnetic fields arise regularly, mainly due to currents in the Earth's ionosphere caused by changes in the illumination of the Earth's ionosphere by the Sun during the day.

Daily geomagnetic variation for the period 03/19/2010 12:00 to 03/21/2010 00:00

The Earth's magnetic field is described by seven parameters. To measure the earth's magnetic field at any point, we must measure the direction and strength of the field. Parameters describing the direction of the magnetic field: declination (D), inclination (I). D and I are measured in degrees. The general field strength (F) is described by the horizontal component (H), the vertical component (Z) and the northern (X) and eastern (Y) components of the horizontal intensity. These components can be measured in Oersteds (1 Oersted = 1 gauss), but usually in nanoTesla (1nT x 100,000 = 1 oersted).

Irregular Variations magnetic fields arise due to the influence of the flow of solar plasma (solar wind) on the Earth’s magnetosphere, as well as changes within the magnetosphere and the interaction of the magnetosphere with the ionosphere.

The figure below shows (from left to right) images of the current magnetic field, pressure, convection currents in the ionosphere, as well as graphs of changes in the speed and density of the solar wind (V, Dens) and the values ​​of the vertical and eastern components of the Earth’s external magnetic field.

27 day variations exist as a tendency to repeat the increase in geomagnetic activity every 27 days, corresponding to the period of rotation of the Sun relative to an earthly observer. This pattern is associated with the existence of long-lived active regions on the Sun, observed during several solar revolutions. This pattern manifests itself in the form of a 27-day repeatability of magnetic activity and magnetic storms.

Seasonal variations magnetic activity are confidently identified on the basis of average monthly data on magnetic activity obtained by processing observations over several years. Their amplitude increases with increasing overall magnetic activity. It was found that seasonal variations in magnetic activity have two maxima, corresponding to the periods of the equinoxes, and two minima, corresponding to the periods of the solstices. The reason for these variations is the formation of active regions on the Sun, which are grouped in zones from 10 to 30° northern and southern heliographic latitudes. Therefore, during the periods of equinoxes, when the planes of the earth's and solar equators coincide, the Earth is most susceptible to the action of active regions on the Sun.

11 year variations. The connection between solar activity and magnetic activity is most clearly manifested when comparing long series of observations, multiples of 11 summer periods solar activity. The best known measure of solar activity is the number of sunspots. It was found that in the years of the maximum number of sunspots, magnetic activity also reaches its greatest value, but the increase in magnetic activity is somewhat delayed in relation to the increase in solar activity, so that on average this delay is one year.

Centuries-long variations – slow variations in the elements of terrestrial magnetism with periods of several years or more. Unlike diurnal, seasonal, and other variations of external origin, secular variations are associated with sources lying within the earth's core. The amplitude of secular variations reaches tens of nT/year; changes in the average annual values ​​of such elements are called the secular variation. Isolines of secular variations are concentrated around several points - centers or foci of the secular variation; in these centers the magnitude of the secular variation reaches its maximum values.

Magnetic storm - impact on the human body

The local characteristics of the magnetic field change and fluctuate, sometimes for many hours, and then restore to their previous level. This phenomenon is called a magnetic storm. Magnetic storms often begin suddenly and simultaneously across the globe.

A day after the solar flare, the shock wave of the solar wind reaches the Earth's orbit and a magnetic storm begins. Seriously ill patients clearly react from the first hours after the flare on the Sun, the rest - from the moment the storm began on Earth. What everyone has in common is a change in biorhythms during these hours. The number of cases of myocardial infarction increases the day after the outbreak (about 2 times more compared to magnetically quiet days). On the same day, a magnetospheric storm caused by the flare begins. In absolutely healthy people, the immune system is activated, there may be an increase in performance, and an improvement in mood.

Note: geomagnetic calm, lasting several days or more in a row, has a depressing effect on the body of a city dweller in many ways, like a storm - causing depression and weakened immunity. A slight “bounce” of the magnetic field within the range Kp = 0 – 3 helps to more easily withstand changes in atmospheric pressure and other weather factors.

The following gradation of Kp-index values ​​is accepted:

Kp = 0-1 – geomagnetic situation is calm (calm);

Kp = 1-2 – geomagnetic conditions from calm to slightly disturbed;

Kp = 3-4 – from slightly disturbed to disturbed;

Kp = 5 and above – weak magnetic storm (level G1);

Kp = 6 and above – average magnetic storm (G2 level);

Kp = 7 and above – strong magnetic storm (level G3); accidents are possible, deterioration of health in weather-dependent people

Kp = 8 and above – a very strong magnetic storm (level G4);

Kp = 9 – extremely strong magnetic storm (level G5) – the maximum possible value.

Online observation of the state of the magnetosphere and magnetic storms here:

As a result of numerous studies conducted at the Institute of Space Research (IKI), the Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), the Medical Academy. THEM. Sechenov and the Institute of Medical and Biological Problems of the Russian Academy of Sciences, it turned out that during geomagnetic storms in patients with pathologies of the cardiovascular system, especially those who had suffered a myocardial infarction, blood pressure jumped, blood viscosity noticeably increased, the speed of its flow in the capillaries slowed down, and vascular tone changed and stress hormones were activated.

Changes also occurred in the body of some healthy people, but they mainly caused fatigue, decreased attention, headaches, dizziness and did not pose a serious danger. The astronauts’ bodies reacted somewhat more strongly to the changes: they developed arrhythmias and changed vascular tone. Experiments in orbit also showed that it is electromagnetic fields that negatively affect the human condition, and not other factors that act on Earth, but are excluded in space. In addition, another “risk group” was identified - healthy people with an overstrained adaptation system associated with exposure to additional stress (in this case, weightlessness, which also affects the cardiovascular system).

The researchers came to the conclusion that geomagnetic storms cause the same adaptive stress as a sharp change in time zones, which disrupts a person’s biological circadian rhythms. Sudden solar flares and other manifestations of solar activity dramatically change the relatively regular rhythms of the Earth's geomagnetic field, which causes animals and people to disrupt their own rhythms and generate adaptive stress.

Healthy people cope with it relatively easily, but for people with pathologies of the cardiovascular system, with an overstrained adaptation system and for newborns, it is potentially dangerous.

It is impossible to predict the response. It all depends on many factors: on the person’s condition, on the nature of the storm, on the frequency spectrum of electromagnetic oscillations, etc. It is still unknown how changes in the geomagnetic field affect the biochemical and biophysical processes occurring in the body: what are the receivers of geomagnetic signals-receptors, does a person react to the influence electromagnetic radiation the entire body, individual organs or even individual cells. Currently, in order to study the influence of solar activity on people, a heliobiology laboratory is being opened at the Institute of Space Research.

9. N.V. Koronovsky. MAGNETIC FIELD OF THE EARTH'S GEOLOGICAL PAST // Moscow State University them. M.V. Lomonosov. Soros Educational Journal, N5, 1996, p. 56-63

Reference

Gauss (Russian designation Гс, international - G) is a unit of measurement of magnetic induction in the CGS system. Named after the German physicist and mathematician Carl Friedrich Gauss.

1 G = 100 µT;

1 T = 104 Gs.

Can be expressed through the basic units of measurement of the CGS system as follows: 1 Gs = 1 g 1/2 .cm −1/2 .s −1.

Experience

Source: physics textbooks on magnetism, Berkeley course.

Topic: m magnetic fields in matter.

Target: find out how different substances react to a magnetic field.

Let's imagine some experiments with a very strong field. Let's assume that we made a solenoid with an internal diameter of 10 cm and a length of 40 cm.

1. Coil design that creates a strong magnetic field. Shown is a cross-section of a winding through which cooling water flows. 2. Field magnitude curve B 2 on the coil axis.

Its outer diameter is 40 cm and most of the space is filled with copper winding. Such a coil will provide a constant field of 30,000 gs in the center, if you bring 400 to it kW electrical power and supply water about 120 l per minute to remove heat.

These specific data are given to show that although the device is nothing extraordinary, it is still a fairly respectable laboratory magnet.

The magnitude of the field at the center of the magnet is approximately 10 5 times the Earth's magnetic field and probably 5 or 10 times stronger than the field near any iron bar or horseshoe magnet!

Near the center of the solenoid, the field is quite uniform and decreases approximately by half on the axis near the ends of the coil.

conclusions

So, as experiments show, in such magnets the field strength (that is, induction or intensity) both inside and outside the magnet is almost five orders of magnitude greater than the Earth’s field.

Also, just twice - not “at times!” - it is smaller outside the magnet.

And at the same time, it is 5-10 times more powerful than a conventional permanent magnet.

The average earth field strength at the surface is about 0.5 Oe (5.10 -5 Tesla)

However, already a few hundred meters (if not tens) from such a magnet, the magnetic compass needle does not respond to either turning the current on or off.

At the same time, it reacts well to the earth’s field or its anomalies at the slightest change in position. What does this mean?

First of all, about the clearly underestimated figure of the induction of the earth's magnetic field - that is, not the induction itself, but how we measure it.

We measure the reaction of the frame with current, the angle of its rotation in the earth's magnetic field.

Any magnetometer is built on the principle of measuring not directly, but indirectly:

Only by the nature of the change in the tension value;

Only on the surface of the earth, near it in the atmosphere and in near space.

We do not know the source of the field with a specific maximum. We are only measuring the difference in field strength at different points, and the intensity gradient does not change too much with height. No mathematical calculations to determine the maximum when using the classical approach work here.

Effect of magnetic field - experiments

It is known that even strong magnetic fields have virtually no effect on chemical and biochemical processes. You can place your hand (without wristwatch!) into a solenoid with a field of 30 kgf without any noticeable consequences. It is difficult to say what class of substances your hand belongs to - paramagnetic or diamagnetic, but the force acting on it will, in any case, be no more than a few grams. Entire generations of mice were bred and raised in strong magnetic fields that did not affect them. significant influence. Other biological experiments also have not found noteworthy magnetic effects on biological processes.

Important to remember!

It would be wrong to assume that weak effects always pass without consequences. Such reasoning might lead to the conclusion that gravity has no energetic significance on a molecular scale, but that trees on a hillside nevertheless grow vertically. The explanation, apparently, lies in the total force acting on a biological object whose dimensions are much larger than the dimensions of the molecule. Indeed, a similar phenomenon (“tropism”) has been experimentally demonstrated in the case of seedlings growing in the presence of a very non-uniform magnetic field.

By the way, if you place your head in a strong magnetic field and shake it, you will “taste” the electrolytic current in your mouth, which is evidence of the presence of an induced electromotive force.

When interacting with matter, the roles of magnetic and electric fields are different. Because atoms and molecules are composed of slowly moving electrical charges, electrical forces dominate over magnetic forces in molecular processes.

conclusions

The impact of the magnetic field of such a magnet on biological objects is nothing more than a mosquito bite. Any Living being or the plant is constantly under the influence of much stronger earth magnetism.

Therefore, the effect of an incorrectly measured field is not noticeable.

Calculations

1 gauss=1 10 -4 tesla.

The unit of geomagnetic field strength (T) in the Cu system is ampere per meter (A/m). Another unit, Oersted (E) or gamma (G), equal to 10 -5 Oe, was also used in magnetic prospecting. However, the practically measured magnetic field parameter is magnetic induction (or magnetic flux density). The unit of magnetic induction in the C system is the tesla (T). In magnetic prospecting, a smaller unit of nanotesla (nT) is used, equal to 10 -9 Tesla. Since for most environments in which the magnetic field is studied (air, water, the vast majority of non-magnetic sedimentary rocks), the Earth’s magnetic field can be measured quantitatively either in units of magnetic induction (in nT) or in the corresponding field strength - gamma.

The figure shows the total strength of the Earth's magnetic field for the epoch of 1980. T isolines are drawn through 4 μT (from the book "Geophysical methods in regional geology" by P. Sharma).

Thus

At the poles, the vertical components of magnetic induction are approximately equal to 60 μT, and the horizontal components are zero. At the equator, the horizontal component is approximately 30 µT, and the vertical component is zero.

Just like that modern science about geomagnetism has long abandoned the basic principle of magnetism, two magnets placed flat to each other tend to connect with opposite poles.

That is, judging by the last phrase at the equator there is no force (vertical component) attracting the magnet to the earth! As repulsive as it is!

Do these two magnets not attract each other? That is, there is no force of attraction, but there is a force of tension? Nonsense!

But at the poles with this arrangement of the magnet it is there, but the horizontal force disappears.

Moreover, the difference is only 2 times between these components!

We simply take two magnets and make sure that in this position the magnet first unfolds and then attracts. SOUTH POLE to NORTH POLE!