Why does a person need to know why the earth is a magnet? The earth is a big magnet

The Earth's magnetic field is a formation generated by sources inside the planet. It is the object of study in the corresponding section of geophysics. Next, let's take a closer look at what the Earth's magnetic field is and how it is formed.

general information

Not far from the Earth's surface, approximately at a distance of three of its radii, the lines of force from the magnetic field are located along a system of “two polar charges”. There is an area called the "plasma sphere" here. With distance from the surface of the planet, the influence of the flow of ionized particles from the solar corona increases. This leads to compression of the magnetosphere from the side of the Sun, and, on the contrary, the Earth’s magnetic field is stretched from the opposite, shadow side.

Plasma Sphere

The directional movement of charged particles in the upper layers of the atmosphere (ionosphere) has a noticeable effect on the Earth's surface magnetic field. The location of the latter is one hundred kilometers and above from the surface of the planet. The Earth's magnetic field holds the plasmasphere. However, its structure strongly depends on the activity of the solar wind and its interaction with the confining layer. And the frequency of magnetic storms on our planet is determined by flares on the Sun.

Terminology

There is a concept "magnetic axis of the Earth". This is a straight line that passes through the corresponding poles of the planet. The "magnetic equator" is the large circle of the plane perpendicular to this axis. The vector on it has a direction close to horizontal. The average strength of the Earth's magnetic field is significantly dependent on geographic location. It is approximately equal to 0.5 Oe, that is, 40 A/m. At the magnetic equator, this same indicator is approximately 0.34 Oe, and near the poles it is close to 0.66 Oe. In some anomalies of the planet, for example, within the Kursk anomaly, the indicator is increased and amounts to 2 Oe. Field lines of the Earth’s magnetosphere with a complex structure , projected onto its surface and converging at its own poles, are called “magnetic meridians”.

Nature of occurrence. Assumptions and conjectures

Not long ago, the assumption about the connection between the emergence of the Earth’s magnetosphere and the flow of current in the liquid metal core, located at a distance of a quarter to a third of the radius of our planet, gained the right to exist. Scientists also have an assumption about the so-called “telluric currents” flowing near the earth’s crust. It should be said that over time there is a transformation of formation. The Earth's magnetic field has changed several times over the past one hundred and eighty years. This is recorded in the oceanic crust, and this is evidenced by studies of remanent magnetization. By comparing areas on both sides of the ocean ridges, the time of divergence of these areas is determined.

Earth's magnetic pole shift

The location of these parts of the planet is not constant. The fact of their displacements has been recorded since the end of the nineteenth century. In the Southern Hemisphere, the magnetic pole shifted by 900 km during this time and ended up in the Indian Ocean. Similar processes are taking place in the Northern part. Here the pole moves towards a magnetic anomaly in Eastern Siberia. From 1973 to 1994, the distance by which the site moved here was 270 km. These pre-calculated data were later confirmed by measurements. According to the latest data, the speed of movement of the magnetic pole of the Northern Hemisphere has increased significantly. It grew from 10 km/year in the seventies of the last century to 60 km/year at the beginning of this century. At the same time, the strength of the earth's magnetic field decreases unevenly. So, over the past 22 years, in some places it has decreased by 1.7%, and somewhere by 10%, although there are also areas where it, on the contrary, has increased. The acceleration in the displacement of the magnetic poles (by approximately 3 km per year) gives reason to assume that their movement observed today is not an excursion, but another inversion.

This is indirectly confirmed by the increase in the so-called “polar gaps” in the south and north of the magnetosphere. The ionized material of the solar corona and space rapidly penetrates into the resulting expansions. As a result, an increasing amount of energy is collected in the circumpolar regions of the Earth, which in itself is fraught with additional heating of the polar ice caps.

Coordinates

In the science of cosmic rays, geomagnetic field coordinates are used, named after the scientist McIlwain. He was the first to propose the use of them, since they are based on modified versions of the activity of charged elements in a magnetic field. For a point, two coordinates are used (L, B). They characterize the magnetic shell (McIlwain parameter) and field induction L. The latter is a parameter equal to the ratio of the average distance of the sphere from the center of the planet to its radius.

"Magnetic inclination"

Several thousand years ago, the Chinese made an amazing discovery. They found that magnetized objects can be positioned in a certain direction. And in the middle of the sixteenth century, Georg Cartmann, a German scientist, made another discovery in this area. This is how the concept of “magnetic inclination” appeared. This name refers to the angle of deviation of the arrow up or down from the horizontal plane under the influence of the planet’s magnetosphere.

From the history of research

In the region of the northern magnetic equator, which is different from the geographic equator, the northern end moves downwards, and in the southern, on the contrary, upwards. In 1600, the English physician William Gilbert first made assumptions about the presence of the Earth's magnetic field, which causes a certain behavior of objects that were previously magnetized. In his book, he described an experiment with a ball equipped with an iron arrow. As a result of his research, he came to the conclusion that the Earth is a large magnet. The English astronomer Henry Gellibrant also conducted experiments. As a result of his observations, he came to the conclusion that the Earth's magnetic field is subject to slow changes.

José de Acosta described the possibility of using a compass. He also established the difference between the Magnetic and North Poles, and in his famous History (1590) the theory of lines without magnetic deflection was substantiated. Christopher Columbus also made a significant contribution to the study of the issue under consideration. He was responsible for the discovery of the variability of magnetic declination. Transformations are made dependent on changes in geographic coordinates. Magnetic declination is the angle of deviation of the needle from the North-South direction. In connection with the discovery of Columbus, research intensified. Information about what the Earth's magnetic field is was extremely necessary for navigators. M.V. Lomonosov also worked on this problem. To study terrestrial magnetism, he recommended conducting systematic observations using permanent points (similar to observatories). It was also very important, according to Lomonosov, to do this at sea. This idea of ​​the great scientist was realized in Russia sixty years later. The discovery of the Magnetic Pole on the Canadian archipelago belongs to the polar explorer Englishman John Ross (1831). And in 1841 he discovered another pole of the planet, but in Antarctica. The hypothesis about the origin of the Earth's magnetic field was put forward by Carl Gauss. He soon proved that most of it is fed from a source inside the planet, but the reason for its minor deviations is in the external environment.

In 1905, Einstein named the cause of terrestrial magnetism one of the five main mysteries of contemporary physics.

Also in 1905, the French geophysicist Bernard Brunhes carried out measurements of the magnetism of Pleistocene lava deposits in the southern department of Cantal. The magnetization vector of these rocks was almost 180 degrees with the vector of the planetary magnetic field (his compatriot P. David obtained similar results even a year earlier). Brunhes came to the conclusion that three quarters of a million years ago, during the outpouring of lava, the direction of the geomagnetic field lines was opposite to the modern one. This is how the effect of inversion (reversal of polarity) of the Earth's magnetic field was discovered. In the second half of the 1920s, Brunhes's conclusions were confirmed by P. L. Mercanton and Monotori Matuyama, but these ideas received recognition only by the middle of the century.

We now know that the geomagnetic field has existed for at least 3.5 billion years, and during this time the magnetic poles have swapped places thousands of times (Brunhes and Matuyama studied the most recent reversal, which now bears their names). Sometimes the geomagnetic field maintains its orientation for tens of millions of years, and sometimes for no more than five hundred centuries. The inversion process itself usually takes several thousand years, and upon completion, the field strength, as a rule, does not return to its previous value, but changes by several percent.

The mechanism of geomagnetic inversion is not entirely clear to this day, and even a hundred years ago it did not allow for a reasonable explanation at all. Therefore, the discoveries of Brunhes and David only reinforced Einstein’s assessment - indeed, terrestrial magnetism was extremely mysterious and incomprehensible. But by that time it had been studied for over three hundred years, and in the 19th century it was studied by such stars of European science as the great traveler Alexander von Humboldt, the brilliant mathematician Carl Friedrich Gauss and the brilliant experimental physicist Wilhelm Weber. So Einstein truly looked to the root.

How many magnetic poles do you think our planet has? Almost everyone will say that two are in the Arctic and Antarctic. In fact, the answer depends on the definition of the concept of pole. Geographic poles are considered to be the points of intersection of the earth's axis with the surface of the planet. Since the Earth rotates as a rigid body, there are only two such points and nothing else can be thought of. But with magnetic poles the situation is much more complicated. For example, a pole can be considered a small area (ideally, again a point) where the magnetic lines of force are perpendicular to the earth's surface. However, any magnetometer records not only the planetary magnetic field, but also the fields of local rocks, ionospheric electric currents, solar wind particles and other additional sources of magnetism (and their average share is not so small, on the order of several percent). The more accurate the device, the better it does this - and therefore makes it increasingly difficult to isolate the true geomagnetic field (it is called the main one), the source of which is located in the depths of the earth. Therefore, pole coordinates determined by direct measurement are not stable even over a short period of time.

You can act differently and establish the position of the pole on the basis of certain models of terrestrial magnetism. To a first approximation, our planet can be considered a geocentric magnetic dipole, the axis of which passes through its center. Currently, the angle between it and the earth's axis is 10 degrees (several decades ago it was more than 11 degrees). With more accurate modeling, it turns out that the dipole axis is shifted relative to the center of the Earth towards the northwestern part of the Pacific Ocean by about 540 km (this is an eccentric dipole). There are other definitions.

But that is not all. The Earth's magnetic field actually does not have dipole symmetry and therefore has multiple poles, and in huge numbers. If we consider the Earth to be a magnetic quadrupole, a quadrupole, we will have to introduce two more poles - in Malaysia and in the southern part of the Atlantic Ocean. The octupole model specifies the eight poles, etc. The modern most advanced models of terrestrial magnetism operate with as many as 168 poles. It is worth noting that during the inversion, only the dipole component of the geomagnetic field temporarily disappears, while the others change much less.

Poles in reverse

Many people know that the generally accepted names of the poles are exactly the opposite. In the Arctic there is a pole to which the northern end of the magnetic needle points - therefore, it should be considered southern (like poles repel, opposite poles attract!). Likewise, the magnetic north pole is based at high latitudes in the Southern Hemisphere. However, traditionally we name the poles according to geography. Physicists have long agreed that lines of force come out of the north pole of any magnet and enter the south. It follows that the lines of earth's magnetism leave the south geomagnetic pole and are drawn towards the north. This is the convention, and you shouldn’t violate it (it’s time to remember Panikovsky’s sad experience!).

The magnetic pole, no matter how you define it, does not stand still. The North Pole of the geocentric dipole had coordinates of 79.5 N and 71.6 W in 2000, and 80.0 N and 72.0 W in 2010. The true North Pole (the one revealed by physical measurements) has shifted since 2000 from 81.0 N and 109.7 W to 85.2 N and 127.1 W. For almost the entire twentieth century it did no more than 10 km per year, but after 1980 it suddenly began to move much faster. In the early 1990s, its speed exceeded 15 km per year and continues to grow.

As Lawrence Newitt, the former head of the geomagnetic laboratory of the Canadian Geological Research Service, told Popular Mechanics, the true pole is now migrating to the northwest, moving 50 km annually. If the vector of its movement does not change for several decades, then by the middle of the 21st century it will end up in Siberia. According to a reconstruction carried out several years ago by the same Newitt, in the 17th and 18th centuries the north magnetic pole mainly shifted to the southeast and only turned to the northwest around 1860. The true south magnetic pole has been moving in the same direction for the last 300 years, and its average annual displacement does not exceed 10–15 km.

Where does the Earth's magnetic field even come from? One possible explanation is simply glaring. The Earth has an inner solid iron-nickel core, the radius of which is 1220 km. Since these metals are ferromagnetic, why not assume that the inner core has static magnetization, which ensures the existence of the geomagnetic field? The multipolarity of terrestrial magnetism can be attributed to the asymmetry of the distribution of magnetic domains inside the core. Polar migration and geomagnetic field reversals are more difficult to explain, but we can probably try.

However, nothing comes of this. All ferromagnets remain ferromagnetic (that is, they retain spontaneous magnetization) only below a certain temperature - the Curie point. For iron it is 768°C (for nickel it is much lower), and the temperature of the Earth's inner core significantly exceeds 5000 degrees. Therefore, we have to part with the hypothesis of static geomagnetism. However, it is possible that there are cooled planets with ferromagnetic cores in space.

Let's consider another possibility. Our planet also has a liquid outer core approximately 2,300 km thick. It consists of a melt of iron and nickel with an admixture of lighter elements (sulfur, carbon, oxygen and, possibly, radioactive potassium - no one knows for sure). The temperature of the lower part of the outer core almost coincides with the temperature of the inner core, and in the upper zone at the boundary with the mantle it drops to 4400°C. Therefore, it is quite natural to assume that due to the rotation of the Earth, circular currents are formed there, which may be the cause of the emergence of terrestrial magnetism.

Convective dynamo

“To explain the appearance of the poloidal field, it is necessary to take into account the vertical flows of nuclear matter. They are formed due to convection: heated iron-nickel melt floats up from the lower part of the core towards the mantle. These jets are twisted by the Coriolis force like the air currents of cyclones. In the Northern Hemisphere, updrafts rotate clockwise, while in the Southern Hemisphere they rotate counterclockwise, explains University of California professor Gary Glatzmeier. - When approaching the mantle, the core material cools down and begins to move back inward. The magnetic fields of the ascending and descending flows cancel each other, and therefore the field is not established vertically. But in the upper part of the convection jet, where it forms a loop and moves horizontally for a short time, the situation is different. In the Northern Hemisphere, the field lines, which faced west before convective ascent, rotate clockwise by 90 degrees and are oriented north. In the Southern Hemisphere, they turn counterclockwise from the east and also head north. As a result, a magnetic field is generated in both hemispheres, pointing from south to north. Although this is by no means the only possible explanation for the emergence of the poloidal field, it is considered the most likely.”

This is precisely the scheme that geophysicists discussed 80 years ago. They believed that the flows of the conducting fluid of the outer core, due to their kinetic energy, generate electric currents covering the earth's axis. These currents generate a magnetic field of predominantly dipole type, the field lines of which on the Earth's surface are elongated along the meridians (such a field is called poloidal). This mechanism evokes an association with the operation of a dynamo, hence its name.

The described scheme is beautiful and visual, but, unfortunately, wrong. It is based on the assumption that the movement of matter in the outer core is symmetrical relative to the earth's axis. However, in 1933, the English mathematician Thomas Cowling proved the theorem according to which no axisymmetric flows are capable of ensuring the existence of a long-term geomagnetic field. Even if it appears, its age will be short-lived, tens of thousands of times less than the age of our planet. We need a more complex model.

“We don’t know exactly when Earth’s magnetism arose, but it could have happened soon after the formation of the mantle and outer core,” says David Stevenson, one of the leading experts on planetary magnetism, a professor at the California Institute of Technology. - To turn on the geodynamo, an external seed field is required, and not necessarily a powerful one. This role, for example, could be taken on by the magnetic field of the Sun or the fields of currents generated in the core due to the thermoelectric effect. Ultimately, this is not too important; there were enough sources of magnetism. In the presence of such a field and the circular motion of flows of conducting fluid, the launch of an intraplanetary dynamo became simply inevitable.”

Magnetic protection

Earth's magnetism is monitored using an extensive network of geomagnetic observatories, the creation of which began in the 1830s.

For the same purposes, shipborne, aviation and space instruments are used (for example, scalar and vector magnetometers of the Danish Ørsted satellite, operating since 1999).

Geomagnetic field strengths range from approximately 20,000 nanoteslas off the coast of Brazil to 65,000 nanoteslas near the south magnetic pole. Since 1800, its dipole component has decreased by almost 13% (and since the mid-16th century by 20%), while its quadrupole component has increased slightly. Paleomagnetic studies show that for several thousand years before the beginning of our era, the intensity of the geomagnetic field stubbornly climbed up, and then began to decline. Nevertheless, the current planetary dipole moment is significantly higher than its average value over the past hundred and fifty million years (in 2010, the results of paleomagnetic measurements were published indicating that 3.5 billion years ago the Earth’s magnetic field was half as strong as it is today). This means that the entire history of human societies from the emergence of the first states to our time fell on a local maximum of the earth’s magnetic field. It is interesting to think about whether this has affected the progress of civilization. This assumption ceases to seem fantastic if we consider that the magnetic field protects the biosphere from cosmic radiation.

And here is one more circumstance that is worth noting. In our planet’s youth and even adolescence, all the matter in its core was in the liquid phase. The solid inner core formed relatively recently, perhaps only a billion years ago. When this happened, the convection currents became more orderly, which led to more stable operation of the geodynamo. Because of this, the geomagnetic field has gained in magnitude and stability. It can be assumed that this circumstance had a beneficial effect on the evolution of living organisms. In particular, the strengthening of geomagnetism improved the protection of the biosphere from cosmic radiation and thereby facilitated the exit of life from the ocean to land.

Here is the generally accepted explanation for such a launch. For simplicity, let the seed field be almost parallel to the Earth's rotation axis (in fact, it is sufficient if it has a non-zero component in this direction, which is almost inevitable). The speed of rotation of the material of the outer core decreases as the depth decreases, and due to its high electrical conductivity, the magnetic field lines move with it - as physicists say, the field is “frozen” into the medium. Therefore, the force lines of the seed field will bend, going forward at greater depths and falling behind at shallower ones. Eventually they will stretch and deform so much that they will give rise to a toroidal field, circular magnetic loops that span the Earth's axis and point in opposite directions in the northern and southern hemispheres. This mechanism is called the w-effect.

According to Professor Stevenson, it is very important to understand that the toroidal field of the outer core arose due to the poloidal seed field and, in turn, gave rise to a new poloidal field observed at the earth's surface: “Both types of planetary geodynamo fields are interconnected and cannot exist without each other.” .

15 years ago, Gary Glatzmeier, together with Paul Roberts, published a very beautiful computer model of the geomagnetic field: “In principle, to explain geomagnetism, there has long been an adequate mathematical apparatus - the equations of magnetic hydrodynamics plus equations describing the force of gravity and heat flows inside the earth's core. Models based on these equations are very complex in their original form, but they can be simplified and adapted for computer calculations. That's exactly what Roberts and I did. A run on a supercomputer made it possible to construct a self-consistent description of the long-term evolution of the speed, temperature and pressure of matter flows in the outer core and the associated evolution of magnetic fields. We also found out that if we play the simulation over time intervals of the order of tens and hundreds of thousands of years, then geomagnetic field inversions inevitably occur. So in this respect, our model does a good job of conveying the planet's magnetic history. However, there is a difficulty that has not yet been resolved. The parameters of the material of the outer core, which are included in such models, are still too far from real conditions. For example, we had to accept that its viscosity is very high, otherwise the resources of the most powerful supercomputers would not be enough. In fact, this is not the case; there is every reason to believe that it almost coincides with the viscosity of water. Our current models are powerless to take into account turbulence, which undoubtedly occurs. But computers are gaining strength every year, and in ten years there will be much more realistic simulations.”

“The operation of a geodynamo is inevitably associated with chaotic changes in the flow of iron-nickel melt, which result in fluctuations in magnetic fields,” adds Professor Stevenson. - Inversions of terrestrial magnetism are simply the strongest possible fluctuations. Since they are stochastic in nature, they can hardly be predicted in advance - at least we don’t know how to do so.”

Municipal educational institution

"Secondary school No. 4 of Zhirnovsk"

Zhirnovsky district, Volgograd region.

Why is the Earth a magnet?

Completed by: students of grade 8 "A"

Zyubina E., Rudenko A.,

Garanin S., Poluosmak N.

Head: Nemukhina E.S.

Physics teacher

Municipal educational institution "Secondary school No. 4 in Zhirnovsk"

2012

Introduction.

The question “Why is the Earth a magnet?” - very complicated. Many scientists are trying to answer it. We are also interested in this issue. Of course, you can’t reveal the secrets of nature on the fly, like a dashing swoop.

Goal of the work:

Find out why the Earth is a magnet.

Research objectives:

Systematize scientific literature on this topic.

Study the magnetic field and magnetic lines.

Get to know the properties of a magnet.

Answer the question: “Why is the Earth a magnet?”

1. What is a magnetic field and magnetic lines? A magnetic field exists around any current-carrying conductor, i.e. around moving electric charges. Electric current and magnetic field are inseparable from each other. Thus, around stationary electric charges there is only an electric field, around moving charges, i.e. electric current, there is both an electric and a magnetic field. A magnetic field appears around a conductor when a current arises in the latter, so the current should be considered as a source of the magnetic field. In this sense, we must understand the expressions “magnetic field of current” or “magnetic field created by current.” The magnetic field is the space around a magnet. It is the magnetic field that causes the magnetic needle to move.

Magnetic lines are lines along which the axes of small magnetic needles are located in a magnetic field.

2. It has been known since ancient times that a magnetic needle, freely rotating around a vertical axis, is always installed in a given place on the Earth in a certain direction. This fact is explained by the fact that there is a magnetic field around the Earth and the magnetic needle is installed along its magnetic lines. This is the basis for the use of a compass.

To test this, we conducted an experiment: first, we attached a needle to a magnet, then fixed the needle-magnet on an ordinary cork and lowered it into a cup of water. The needle has turned so that one end points to the north and the other to the south. We tried to turn the magnet needle the other way around, but it immediately returned to its previous position. It is known that the magnetic compass that sailors used in ancient times is very similar to the one we made ourselves, but it was just a magnet on a float.

We decided to check whether it is possible to separate the north magnetic pole from the south. To do this, we broke the magnet needle in half. Then we put a float on each half and lowered it into a cup of water one by one. First, we lowered the half of the needle that we wanted to deprive of the south pole, leaving it with only the north one and looking north. And the other end of the half - the one that previously lived in the middle of the needle - to the south. Thus, we were convinced that the other half, to whom we wanted to leave only the south pole, “grew” a new north pole for itself. From this experience it follows that a magnet restores any pole in place of the lost one and, moreover, instantly.

To get to the bottom of the truth and answer the question “Why is the Earth a magnet,” we looked at the structure of a magnet. So, let’s assume that every magnet consists of many microscopic magnets, the north poles of which point in one direction, and the south in the other, and scientists have been able to prove that this is exactly the case. It turns out that tiny magnets - they are called DOMAINS - are even in non-magnetized iron! But until the iron is magnetized, its domains are located “some in the forest, some for firewood.” But when iron is magnetized, all its domains turn, like miniature arrows, and begin to point their north poles in one direction and their south poles in the other.

I wonder if it is possible to demagnetize a magnet? We decided to try to do this. After heating the magnet needle in the flame of a kitchen burner and then letting it cool, we dipped the needle into iron filings and noticed that the filings were no longer attracted to the needle. Why? Everything is very simple, it is known that all substances in the world are composed of atoms. Of course, iron also consists of atoms. Moreover, the iron atoms in a domain are subject to the same “iron discipline” as the domains themselves in a magnet. But even in the most solid body, atoms continuously vibrate and “dance” in place. The more the body is heated, the faster and more disorderly this dancing is. Having heated the magnetized needle, we brought the dancing of the iron atoms to a frantic dance. It is clear that the iron discipline of the atoms in the domains was broken - the domains disappeared, and with them the magnetization. But when the needle cooled down, the domains appeared in it again, but now they look anywhere. To make them turn in one direction again, you need to re-magnetize the needle.

3.What does the earth’s magnetic field look like? Of course, you can’t put a cardboard with iron filings on the globe, but the Earth’s magnetic field can be judged by the behavior of two arrows. One arrow is a regular compass, it can only turn left and right. It is complemented by a magnetic needle that can turn up and down - it is called the TICKING ARROW. Imagining that we, having covered the entire globe with these two arrows, as well as flying around it from all sides and at different altitudes in a spaceship, we drew the magnetic lines of force of the Earth and saw what its magnetic field looks like.

During this journey, we would discover two remarkable points on Earth: the inclination arrow here becomes vertical and points downward, while the arrow of an ordinary compass does not show anything at all - it spins as it pleases. These two points are the Earth's magnetic poles.

They say that the Earth's magnetic field is tumbling. Why? We are very lucky - these days geophysicists, that is, physicists who study the Earth, are able to tap it, illuminate it and weigh it no worse than a patient’s doctor. And many of them suggest that in the depths of the globe, especially in the core of the Earth - its core, there really are a lot of iron-rich substances and even pure iron! True, in the depths of our planet it is terribly hot - at very great depths the temperature is so high that iron there is in a molten state, as if in a blast furnace.

“But can molten iron be magnetized? – we were surprised, “We just heated the needle, and then it lost its magnetic properties!”

What if, under such unusual conditions, the magnetic properties of iron are also unusual? It is quite possible (scientists admit this) that it is still capable of magnetization, despite the hellish heat. But even if the solid iron core is magnetized, we can still confidently say that it is not the iron magnet that is the main culprit that the Earth has a magnetic field.

Scientists still consider this question one of the biggest scientific mysteries. To create a magnetic field, you need either a magnetized body or an electric current. Many hypotheses have been proposed and rejected. The most correct answer at present is that the Earth's magnetic field is created by electric currents in the core; these currents are probably generated and maintained by a mechanism similar to a self-exciting dynamo. The dynamo theory was first proposed in 1919. English scientist Jerome Larmore. And in 1945 Soviet physicist Yakov Ilyich Frenkel put forward the hypothesis of the earth's dynamo in relation to the geomagnetic field, considering the presence of a liquid outer core to be the main reason. The temperature inside the core should be slightly higher than at its periphery, due to the radioactive decay of unstable elements. In this case, cold masses rush towards the center of the core, while hot masses move towards them from the center of the core. The Earth rotates, the speed of mass movement at the periphery of the core is greater than in its depths. Therefore, fluid elements moving from the center slow down the rotation of the peripheral layers of the core, and counter flows, on the contrary, accelerate the internal layers. Then the inner part of the core rotates faster than the outer one and plays the role of a rotor (rotating part) of the generator, while the outer part plays the role of a stator (stationary part). In accordance with calculations, self-excitation and the appearance of electric currents are possible in such a system. It is these currents that create the Earth's magnetic field. Proponents of this hypothesis believe that it would be more correct to call the Earth a large dynamo rather than a large magnet.

Conclusion.

We tried to fulfill our action plan. But in order to prove that the Earth’s magnetic field appeared exactly as we assumed, it is necessary to find out exactly what the flows of liquid iron in the depths of the Earth are, how they arise and how they flow. In addition, you need to compare the magnetic properties of the Earth with the magnetic properties of its sisters - the other planets of the solar system, and find out what is inside them - is there a liquid core, what flows arise in it due to the rotation of the planets? In other words, there is still a lot to do. But maybe someday we will be able to unravel the age-old mystery of nature: why is the Earth a magnet?

Literature.

1. Physics textbook 8th grade, Peryshkin A.V.. 2008

2. Why is the Earth a magnet? , M. Konstantinovsky, 1979

3. Pochemy website. net Why is the Earth a magnet?.

4. The earth is a big magnet. All about planet Earth. www.vseozemle.ru.

A magnetized bar has two magnetic poles - north and south. The magnetic field of such a bar is dipole, that is, a field with two poles (“di” means two). Its shape can be seen using iron filings. The field lines of this field run in the same way as the sawdust is oriented. Each sawdust is a compass needle. It is oriented along the magnetic field, along the tangent line of the magnetic field.

The earth is also magnetized. It has its own magnetic field with two poles; such a magnetic field can be created around the globe if a magnetized bar is placed inside the pole. But how? First, it must be placed along the Earth's rotation axis. Half the bar is in the northern hemisphere, and the other half is in the southern hemisphere.

The south magnetic pole must be directed towards the north geographic pole. Then the north magnetic pole of the bar will coincide with the south geographic pole.

After this, the block must be deflected from the Earth’s rotation axis by 11°. It is necessary to deflect it so that its south magnetic pole rests on the city of Thule (Greenland). Then the magnetic field of the bar, “tied” to the Earth in this way, will be similar to the magnetic field of the Earth.

The magnetic field of the earth's dipole is the same on all sides: day, night, morning and evening. It does not depend on the position of the Sun. Above the magnetic equator it passes horizontally. Above the magnetic poles, the Earth's magnetic field lines are directed vertically. It is generally accepted that the magnetic field is directed from the north magnetic pole to the south. This means that the Earth’s magnetic field lines are directed from bottom to top in the southern hemisphere, and from top to bottom in the northern hemisphere. Field lines leaving the north magnetic pole (in the southern hemisphere) enter the south magnetic pole in the northern hemisphere.

To avoid confusion due to the fact that the north magnetic pole is in the southern hemisphere, and the south is in the northern, we agreed to call the magnetic pole in the northern hemisphere the north geomagnetic pole. The compass needle turns north with its north magnetic pole. This is because the south magnetic pole is in the north. WE will adhere to the terminology accepted by scientists. We will assume that the north geomagnetic pole is located in the northern hemisphere (near Thule). But let's remember that there is actually a south magnetic pole there. The direction of the magnetic field lines depends on this.

Is the Earth's magnetic field really a dipole field? In principle yes, but in detail no. These details are nevertheless very important. They were established only relatively recently, when spacecraft made it possible to measure the magnetic field far beyond the Earth. These measurements made it possible to establish what the shape of the Earth's magnetic field actually is in detail.

It turned out that the Earth's magnetic field from the side of the Sun is not the same as from the opposite (night) side.

In the region adjacent to the Earth, the magnetic field is dipole and does not depend on the position and even the presence of the Sun. In a region more distant from the Earth, at distances greater than three radii of the Earth, the difference in magnetic fields is very significant. It is as follows.

The magnetic field of a dipole is characterized by "funnels" above the magnetic fields. In the real magnetic field of the Earth, these funnels are not located above the magnetic poles, but are shifted towards the equator by about 1000 km from the poles. In addition, the shape of the magnetic field lines on the day side is very different from that on the night side. Since this depends on the position of the Sun, it is the Sun that is “to blame” for this difference. How to understand the essence of this influence - the influence of the Sun on the shape of the Earth's magnetic field?

Solar wind and the Earth's magnetosphere

How can the Sun affect the Earth's magnetic field? It is quite obvious that it cannot act on the magnetic field by its attraction. Cannot act on magnetic fields and sunlight, as well as x-rays, infrared and gamma radiation. The same applies to the radio waves that the Sun emits. They, too, must be excluded from the factors on which the shape of the Earth’s magnetic field depends. What remains? Charged particles that are ejected from the atmosphere of the Sun and go into interplanetary space. We have already talked about these particles. They have different energies, and therefore different speeds. Charged particles at low speeds that continuously emanate from the Sun to all countries are called solar wind. Streams of high-energy charged particles are ejected from the solar atmosphere from time to time. They have high speeds and reach the Earth faster than solar wind particles.

We can assume that the agent that determines the shape of the Earth's magnetic field, or rather the deformation of the Earth's magnetic dipole, has been found. These are solar charged particles. It remains to be seen how charged particles do this. To understand this, we need to remember how charged particles interact with a magnetic field.

If a charged particle moves into a magnetic field, then its movement depends on this field. The only exception is when a charged particle moves strictly along the magnetic field line. In this case, the charged particle does not feel the presence of a magnetic field; it moves as if there was no magnetic field at all. If a charged particle moves across a magnetic field, then the trajectory changes: instead of a straight line before entering the field, it becomes a circle. The stronger the magnetic field, the smaller this circle (for the same particle). But on the other hand, the greater the energy of a flying particle, the more difficult it is for the magnetic field to bend its trajectory into a small circle.

There is some balance condition. In order to change the trajectory of charged particles with a certain energy, the magnetic field must have a certain magnitude and be directed perpendicular to the movement of the particles. If this condition is met, then the charged particles begin to rotate around the lines of force. The speed of their rotation and the radii of the circles in which they rotate depend on the strength of the magnetic field and the energy of the particles. Positively charged particles rotate in one direction, and negatively charged particles rotate in the opposite direction. Solar charged particles approach the Earth's magnetic field at different angles: longitudinally, perpendicularly, and obliquely. Those particles that approach along the lines of force (above the magnetic poles) must freely penetrate into the Earth's magnetic shell (magnetosphere). Those particles that approach the field lines perpendicularly will not travel far into the magnetosphere. Their trajectories twist around the magnetic field line. What will happen to particles that fall obliquely onto a magnetic field? This is all the more important to know that such particles are in the majority.

When a charged particle moves at a certain angle (but not right) to the magnetic field line, then its motion can be decomposed into two: along the field and across it. Actually, in this case we decompose the particle velocity vector into components - along the magnetic field and across it. The movement of such a particle in a magnetic field will become a spiral movement. The particle will rotate around the field line and at the same time shift along the field line. The particle trajectory will have the shape of a spiral.

The radius of this spiral and its pitch will remain unchanged if the energy of the particle and the shape and strength of the magnetic field remain unchanged. This means that the magnetic field lines must be straight, the distance between which is constant in the direction of motion of the particle. This is the condition for the uniformity of the magnetic field. But this case of a uniform magnetic field is of little interest to us. After all, the Earth's magnetic field is not uniform. How will the particles move in this case?

If the magnetic field lines converge, that is, the particle, moving in a spiral, moves into an increasingly stronger magnetic field, then its movement into this field gradually slows down. The magnetic field opposes the movement of the particle. It freely allows a particle inside only if it moves strictly along the magnetic field line. Moving in a spiral towards a stronger magnetic field, the charged particle stops going deeper at some distance. After this moment, it gradually (also in a spiral) moves in the opposite direction. The magnetic field pushes the charged particle towards a weaker field.

The Earth's magnetic field is not uniform. This can be seen in the shape of the field lines. As you move from the equator to the poles along the lines of force, you can see that they become more and more dense. This means that the magnetic field increases. In such a magnetic field, which increases in both directions from the equator, the charged particle becomes trapped. Rotating in spirals, charged particles move in such a field sequentially, being reflected from a stronger field alternately in the southern and northern hemispheres. In this case, charged particles are located above the earth's atmosphere. Such charged particles have indeed been measured in the Earth's magnetosphere. They were called radiation belts.

How is the Earth's magnetic field deformed by solar particles? Since charged particles interact with a magnetic field, they can deform this field. The stream of charged particles flying from the Sun interacts with the outermost field lines of the Earth's magnetosphere. The ends of the power lines remain in the same place, in the Earth. And the lines themselves “turn inside out” and are extended by a stream of charged particles to the night side. They cover the magnetic poles, and the funnels above the poles disappear. But new funnels are formed on the midday meridian. The new craters are approximately 1000 km away from the poles.

It is very important that these funnels can move. The stronger the energy of the solar flow of charged particles, the more lines of force it turns from the day side to the night side. The further the funnel moves away from the pole.

Under the influence of solar charged particles from the dayside, the Earth's magnetosphere is limited to a certain distance from the Earth's surface. When the Sun is calm, this distance is approximately ten Earth radii. During solar storms, the flow of solar particles intensifies and pushes the magnetosphere on the solar side closer to the Earth. At this time, the funnels move even further from the pole. During very strong solar storms, the magnetosphere on the dayside can be compressed to three Earth radii. Then the funnels move away from the pole.

Under the influence of solar charged particles, not only the position of the funnels, which are located above the poles of the dipole, changes.

Funnels not only shift towards the equator. At the same time, they change their shape. Each funnel turns into a flattened funnel-slit, in the shape of a horseshoe. It covers a certain area on the day side of the magnetosphere.

The night part of the magnetosphere bears little resemblance to the day part. If on the day side the Earth’s magnetic field extends to a maximum distance of ten Earth radii, then on the night side it exists over a huge distance equal to one hundred Earth radii or more. The Earth's magnetic field lines extend in the direction of movement of solar particles, that is, away from the Earth. This is how a trail of field lines of the Earth’s magnetosphere is formed. Experts call it the tail of the magnetosphere.

Charged particles move freely along magnetic field lines. This means that solar charged particles, through funnels on the day side, can penetrate through the magnetosphere to the Earth and its atmosphere. But inside the magnetosphere there are charged particles that are trapped there. There are also charged particles in the magnetotail. From here they move along the magnetic field lines. Where will they end up? It can be traced that they will end up in the Arctic and Antarctic.

If you follow the path of charged particles on the day and night sides of the magnetosphere, it turns out that they come exactly to the ring (oval) that glows with the aurora. Is this an accident or a pattern?

OPEN COMPETITION OF PROJECTS AND EDUCATIONAL RESEARCH WORKS “SURVEYOR”

Topic: “Properties of a magnet. The Earth is a huge magnet"

Place of work: MAOU "Secondary School No. 4" Miass

Scientific supervisor: Melnikova Olga Mikhailovna

2017

CONTENT

Introduction

ChapterI

1.2 Properties of a magnet and its structure

1.3 Magnetic field

2.1 Practical experiences to study

magnetic properties

2.1.7 Magnet instability. Magnetic field around

current carrying conductor

Conclusion

Bibliography

INTRODUCTION

According to Wikipedia, a magnet is a body that has its own magnetic field.Perhaps the word comes from ancient Greek. Magnētis líthos (Μαγνῆτις λίθος), “stone from Magnesia” - from the name of the region of Magnesia and the ancient city of Magnesia in Asia Minor, where magnetite deposits were discovered in ancient times.

Magnets surround us everywhere - in our apartments there are dozens of magnets: in electric shavers, speakers, in watches, in jars of nails, in a computer, and finally, we ourselves are also magnets: the biocurrents flowing in us give birth to a bizarre pattern of magnetic lines of force around us. The earth we live on is a giant blue magnet. The sun is a yellow plasma ball - an even more grandiose magnet. Galaxies and nebulae, barely visible through telescopes, are magnets of incomprehensible size.

In recent years, interesting information has increasingly appeared that the largest magnet, the Earth, is experiencing processes in the form of accelerating the movement of the magnetic poles.

The lack of knowledge on this issue and the desire to understand what a magnet is, what properties it has, how the mechanism of magnetic interaction is carried out and what the movement of the Earth’s magnetic poles means, determined the choice of the research topic “Properties of a magnet. The earth is a huge magnet."

The purpose of this work is to study the properties of a magnet, understand the magnetic processes of the Earth

To achieve this goal, it was necessary to formulate and solve the following tasks:

Learn about the history of the magnet

Study the properties of a magnet, its structure, types of magnets

Give the concept of the magnetic field of a magnet and the magnetic field of the Earth

Find out what processes occur in the Earth's magnetic field.

Conduct accessible experiments to understand the properties of magnets

Object of study - magnet, magnetic processes of the Earth.

Subject of study - complexactivities related to the study of magnet properties and magnetic processes of the Earth.

Hypothesis – a magnet is a body capable of creating its own magnetic field, the Earth is a magnet that has the ability to change its poles.

Relevance - The magnets around us everywhere have properties, the understanding of which is necessary for every person, both in everyday life and in industry; an understanding of the magnetic processes of the Earth is necessary in order to control irreversible processes that can cause an inversion, which is a global catastrophe.

Research methods - collecting the theoretical part, proven by practical experiments, using a magnet, a needle, a nail, iron filings, a piece of wire and a flashlight battery.

The practical significance of the work lies in the selection of simple experiments that make it possible to visually examine the properties of a magnet in order to understand the most complex processes at the level of the largest magnet - the Earth.

ChapterI. Theoretical aspects of magnetic properties

1.1 History of the magnet

The magnet has been known to man since time immemorial. An ancient legend tells about a shepherd named Magnus (in Leo Tolstoy’s story for children “Magnet” this shepherd’s name is Magnis). He once discovered that the iron tip of his stick and the nails of his boots were attracted to the black stone. This stone began to be called the “Magnus stone” or simply “magnet”, after the name of the area where iron ore was mined (the hills of Magnesia in Asia Minor). Thus, many centuries BC it was known that some rocks have the property of attracting pieces of iron. This was mentioned in the 6th century BC by the Greek physicist and philosopher Thales.

For many centuries, there has been a legend among seafarers about a magnetic rock, which is supposedly capable of attracting iron nails from a ship that sails too close to it and destroying it. Fortunately, such a strong magnetic field can only exist in the vicinity of neutron stars.

The first scientific study of the properties of a magnet was undertaken in the 13th century by the scientist Peter Peregrin. In 1269, his work “The Book of the Magnet” was published, where he wrote about many facts of magnetism: a magnet has two poles, which the scientist called north and south; It is impossible to separate the poles of a magnet from each other by breaking it. Peregrine also wrote about two types of pole-attraction and repulsion interactions. By the 12th-13th centuries AD, magnetic compasses were already used in navigation in Europe, China and other countries of the world.

In 1600, the English physician William Gilbert’s essay “On the Magnet” was published. To the already known facts, Gilbert added important observations: the strengthening of the action of magnetic poles by iron reinforcement, the loss of magnetism when heated, and others. In 1820, Danish physicist Hans Christian Oersted tried to demonstrate to his students the connections between electricity and magnetism in a lecture by turning on an electric current near a magnetic needle. According to one of his listeners, he was literally “stunned” when he saw that the magnetic needle began to oscillate after the current was turned on. Oersted's great merit is that he assessed the significance of his observation and repeated the experiment. The discovery of the interaction between magnets and electricity was of great importance. It marked the beginning of a new era in the study of electricity and magnetism.

Subsequently, many more properties of magnets were discovered and studied. It was noticed that magnets located at a distance from one another seem to act on each other: their like ends repel each other, their opposite ends attract each other. A piece of iron or steel is attracted by a magnet because it itself turns into a magnet. The magnetic state of this piece increases as the distance between it and the magnet decreases; it reaches its greatest development when the piece sticks to one or the other end of the magnet. After tearing or removing steel or iron from a magnet, they retain a magnetic state, but not to the same extent in different grades of these metals. The residual magnetism in steel is stronger than in iron.

Natural magnets were not called magnets everywhere; in different countries they were called differently: the Chinese called it chu-shi; Greeks - adamas and kalamita, Hercules stone; French - ayman; Hindus - thumbaka; the Egyptians - Ora bone, the Spaniards - piedramante; Germans - Magness and Ziegelstein; English - Loadstone. Half of these names are translated as loving. Thus, the poetic language of the ancients described the property of magnetite to attract, to “love” iron. Rich deposits of magnetic iron ore are found in the Urals, Ukraine, Karelia, and Kursk region. Natural magnets, machined from pieces of magnetic iron ore, sometimes reached large sizes. Currently, the largest known natural magnet is located at the University of Tartu. Its mass is 13 kg and its lifting force is 40 kg. Neutron stars are the most powerful magnets in the Universe. Their magnetic field is many billions of times greater than the Earth's magnetic field.

Currently, steel strips and rods, straight and horseshoe-shaped, are used to prepare artificial magnets. To impart magnetization to them, they rub these strips and rods with one end of a strong magnet, or they wrap these strips and rods with wire and pass an electric current through the wire.

The study of magnets contributed to the development of science. For example: the study of the magnetic properties of rocks made it possible to judge the conditions for the formation and transformation of minerals and rocks, and the nature of the Earth’s magnetic anomalies. This knowledge contributed to the development of the science of tectonics (the science of the structure and development of the earth's crust). Magnetic properties are also used in magnetic exploration and archaeology. Magnets are used in electric machine generators and electric motors, magnetoelectric devices, and induction electricity meters. Magnets are used to produce magnetic locks, dynamometers, galvanometers, and microwave ovens. Magnetic fields are widely used for medicinal purposes. In short, there is no area of ​​applied human activity where magnets are not used.

For thousands of years, scientists have been trying to solve the mystery of the most important and largest magnet “Earth”. Back in the 14th century, the English physicist William Gilbert made a spherical magnet, examined it with a small magnetic needle and came to the conclusion that the globe was a huge cosmic magnet.

1.2 Properties of a magnet and its structure, types of magnets

A magnet is a body that has its own magnetic field. The simplest and smallest magnet is the electron. The magnetic properties of all other magnets are due to the magnetic moments of the electrons inside them. Electron (from ancient Greek ἤλεκτρον - amber) is a stable negatively charged elementary particle. A permanent magnet is a product that retains magnetization for a long time.

The French scientist Ampere explained the magnetization of iron and steel by the existence of electric currents that circulate inside each molecule. There are magnetic fields around currents, which lead to the appearance of the magnetic properties of matter. At the time of Ampere, it was not known either about the structure of the atom or about the movement of charged particles - electrons around the nucleus. The modern theory of magnetism has confirmed the correctness of Ampere's assumption that every atom contains negatively charged particles - electrons. When electrons move, a magnetic field arises, which causes magnetization of iron and steel. Disruption of the ordered movement of electrons, demagnetization, is mainly produced by bringing materials to a certain heating level - the Curie point, by exposure to another magnetic field, usually an electromagnet.

There are permanent and non-permanent magnets. Permanent magnets can be natural or artificial.

Natural magnets are magnets created by nature. Iron ore, magnetite, is a weak magnet (Figure 1.1). Already at a distance of 1 m, the compass needle ceases to notice its existence.

Rice. 1.1 Type of magnetite

There are only three substances that can maintain magnetization for a long time - cobalt, iron and nickel. These substances retain magnetization when the nearby magnet is removed. Artificial magnets are magnets created by man by magnetizing iron or steel in a magnetic field. Artificial magnets began to be made in England in the 18th century. They are made by placing a piece of steel near a magnet, touching it to a magnet, or rubbing a strip of steel with a magnet in one direction. Types of artificial magnets are presented in Figure 1.2.

Rice. 1.2 Types of artificial magnets

Typically, artificial magnets are given the appearance of a strip - straight or horseshoe-shaped - and used as sources of a constant magnetic field. Magnets are made in a horseshoe shape to bring the poles closer together to create a strong magnetic field that can be used to lift large pieces of iron. The world's largest artificial permanent magnet weighs 2 tons and is used in the equipment of the nuclear reactor at the University of Chicago.

All substances placed in a magnetic field are magnetized differently. For example, diamagnetic materials (gold, silver, copper) and paramagnetic materials (aluminum, magnesium, manganese) are weakly magnetic substances. Ferromagnets (iron, cobalt, nickel) are highly magnetic substances and enhance the magnetic field within them thousands of times. Ferromagnets are divided into soft magnetic and hard magnetic. Soft magnetic substances, for example, pure iron, are easily magnetized, but also quickly demagnetized. Magnetically hard substances, such as steel, are slowly magnetized and also slowly demagnetized.

The addition of tungsten and cobalt to iron improves the properties of artificial magnets. A good magnetic alloy is alnico, an alloy based on aluminum, nickel and cobalt. Alnico magnets can be used to lift iron objects up to 500 times the weight of the magnet itself. Even stronger magnets are made from Magnico alloy, which contains iron, cobalt, nickel and some other additives. In Japan, they created a magnet, one square centimeter of which attracts 900 kg of cargo. The invention is a cylinder 2 cm high and 1.5 cm in diameter. The unique alloy of a neodymium magnet includes metals such as neodymium, boron and iron. Neodymium magnet is known for its attractive power and high resistance to demagnetization. It has a metallic appearance, is very popular and is used in various fields of industry, medicine, everyday life and electronics. A neodymium magnet can lift loads up to 400 kg. Heavy safes and scrap metal are often caught from the river using a neodymium-based search magnet. Neodymium magnets are used in the production of hard drives for computers. Typically these magnets are shaped like an arc. Companies that build magnetic excitation generators primarily use them because the power of the generator is directly dependent on the strength of the magnet used. Used in computer DVD drives in the shape of a small cube. They are often used in the manufacture of speakers for headphones, radios, mobile phones, smartphones, tablets, speakers, etc. for higher speaker volume. Oil filter manufacturers use neodymium magnets to trap metal shavings from petroleum products. Metal detector devices also contain these magnets. Neodymium magnets lose no more than 1-2% of their magnetization in 10 years. But they can be easily demagnetized by heating to a temperature of +70 °C or more. In medicine, neodymium magnets are used in magnetic resonance imaging machines.

A non-permanent magnet refers to the concept of an electromagnet - a device whose magnetic field is created only when an electric current flows. An electromagnet is a wire coil carrying an electric current. A distinctive property of an electromagnet is that its magnetic field is very easy to control and can be turned on and off.

Fig 1.3 Straight wire with current. Current (I) flowing through a wire creates a magnetic field (B) around the wire

If a coil with current is suspended on thin and flexible conductors, it will be installed in the same way as the magnetic needle of a compass. One end of the coil will face north, the other will face south. This means that a coil with current, like a magnetic needle, has two poles - north and south.

Fig 1.4 Poles of a current coil

There is a magnetic field around the current-carrying coil. It, like the direct current field, can be detected using sawdust (Figure 1.5). When there is current in the coil, iron filings are attracted to its ends; when the current is turned off, they fall away. The magnetic lines of the magnetic field of a current-carrying coil are also closed curves. It is generally accepted that outside the coil they are directed from the north pole of the coil to the south.

Fig 1.5 Magnetic lines of a coil with current

The greater the number of turns in it, the stronger the magnetic effect of a current-carrying coil. The magnetic effect of a current-carrying coil can be significantly enhanced without changing the number of its turns or the current strength in it. To do this, you need to insert an iron rod (core) inside the coil. Iron introduced inside the coil enhances the magnetic effect of the coil. Thus, an electromagnet is a coil with an iron core inside. An electromagnet is one of the main parts of many technical devices. Electromagnets are widely used in technology due to their remarkable properties. They quickly demagnetize when the current is turned off; depending on their purpose, they can be made in a variety of sizes; while the electromagnet is operating, its magnetic action can be adjusted by changing the current strength in the coil.

Electromagnets, which have a large lifting force, are used in factories to carry products made of steel or cast iron, as well as steel and cast iron shavings and ingots (Figure 1.6).

Fig 1.6 Application of electromagnets

Figure 1.7 shows a cross-section of a magnetic grain separator. Very fine iron filings are mixed into the grain. These sawdust do not stick to the smooth grains of healthy grains, but they do stick to the grains of weeds. Grains 1 are poured out of the hopper onto a rotating drum 2. Inside the drum there is a strong electromagnet 5. By attracting iron particles 4, it removes weed grains from the grain flow 3 and in this way cleans the grain from weeds and accidentally caught iron objects.

Fig 1.7 Magnetic separator

Electromagnets are used in telegraph, telephone and many other devices.

Every magnet has poles - the places in the magnet where the greatest interaction occurs. Every magnet, like the magnetic needle we know, must have two poles: north (N) and south (S).

Fig 1.8 Magnet poles

The poles of a magnet have an important property - they are inseparable even when the magnet is broken into pieces. Every magnet consists of many small magnets - domains. Domains are present even in non-magnetized iron in a chaotic arrangement. At the moment of magnetization, the domains turn their north poles to the north, and their south poles to the south, and remain in this state until a factor influences them, returning them to their previous state.

Fig 1.9 Location of domains in non-magnetized iron

Fig 1.10 Arrangement of domains in magnetized iron

If a magnetic needle is brought closer to another similar needle, they will turn and align themselves with opposite poles. The arrow interacts with any magnet in the same way.By bringing a magnet close to the poles of a magnetic needle, you will notice that the north pole of the needle is repelled by the north pole of the magnet and attracted to the south pole. The south pole of the arrow is repelled by the south pole of the magnet and attracted by the north pole, therefore, opposite magnetic poles attract and like magnetic poles repel. This rule also applies to electromagnets.

The interaction of magnets is explained by the fact that there is a magnetic field around any magnet. The magnetic field of one magnet acts on another magnet, and, conversely, the magnetic field of the second magnet acts on the first.

Like the magnet we are used to, the Earth is the largest magnet in our understanding.

Currently, there are no unambiguous views on the mechanism of origin of the Earth’s magnetic field. The generally accepted idea is the so-called dynamo effect. This theory originated in the 18th century, when the English scientist Henry Cavendish measured the mass of the Earth. It became clear that the density of the Earth was too high for it to consist only of rock. And Cavendish suggested that the center of our planet consists of an iron-nickel core - like most meteorites. In 1906, scientists, having studied earthquake waves, confirmed Cavendish's theory - the Earth really has an iron-nickel core, that is, a sphere approximately 6900 kilometers in diameter, which in its weight is one third of the mass of the entire planet. This core rotates at high speed in a layer of hot magma, creating whirlpools of molten nickel iron, which, in turn, create the effect of an electric current flowing in a circle. That is, it was precisely thanks to the presence of the moving core of the planet that a bar of magnet appeared to be inserted into the Earth, placed vertically north pole - south pole.

An interesting fact is that the true south magnetic pole (negative, where the magnetic field lines “enter” the planet) is located near the North Geographic Pole (in the Canadian sector of the Arctic), the true north magnetic pole (positive, where the magnetic field lines “exit” the Earth ) is now located near the South Geographic Pole (in the Indian Ocean near Antarctica). However, conventionally, the magnetic poles of the Earth are usually called in accordance with their geographical location - for convenience, the south magnetic pole is considered to be the north, and vice versa.

The Earth's south magnetic pole is approximately 2100 km away from the geographic North Pole.

Fig 1.11 Magnetic lines of the Earth's magnetic field

Thus, the Earth has four poles - two magnetic and two geographical. This discovery has been known since 1492. This phenomenon was first discovered by Columbus. When he set out across the ocean in his caravels, within a day the sailors discovered that the compass was not pointing exactly to the North, but was slightly deviating. They checked this by observing the Sun using a sextant, which allows them to determine the exact direction. But this can be done 1-2 times a day, and the ship moves constantly, guided by a compass. The next day the needle deviated even more, and a riot began on the ship. Columbus realized that the cause of the deviation was the properties of the magnetic field, and placed the ax in the place where the compass was, thereby correcting the direction of the arrow. In his logbook, Columbus noted that the magnetic field does not always point north accurately and that it needs to be measured. And from then on he began to measure the magnetic field, and Columbus became the founder of the science of terrestrial magnetism.

We can conclude that the Earth's magnetic poles do not coincide with its geographic poles. In this regard, the direction of the magnetic needle does not coincide with the direction of the geographical meridian. The angle between these two directions is called magnetic declination. Every place on Earth has its own declination angle, and the navigator of a ship or plane must have an accurate map of the magnetic declinations. Such a map is compiled according to compass readings. It is known, for example, that 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 7° to the right from the geographic meridian passing through Moscow, and in Yakutsk - 17° to the left from the corresponding meridian.

Thus, a magnet is a body that has its own magnetic field, which retains magnetization for a long time, explained by the existence of an electric current. The concepts of electric current and magnet are closely related to each other; the theory of magnetism is devoted to their relationships. Magnets have poles that are inseparable from each other. Artificial magnets are magnets created by man in order to obtain the necessary properties in strength exceeding the properties of natural magnets, and are widely used in all areas of industry and in everyday life. Magnets interact with each other - like poles attract, unlike poles repel, which is due to the presence of a magnetic field. The smallest magnet is the electron - the largest and most interesting to us is our planet Earth, which has four poles that do not coincide with each other - two magnetic poles and two geographical.

1.3 Magnetic field

The space around a magnet where magnetic forces act is called a magnetic field.

The magnetic lines of the magnetic field of a magnet (magnetic induction lines) are closed lines. Magnetic lines leave the North pole and enter the South pole, closing inside the magnet. The lines are closed, have neither beginning nor end (Figure 1.11).

Fig 1.11 Magnetic field lines

The magnetic field can be made “visible” using iron filings (Figure 1.12).

Figure 1.12 “Visible” magnetic field from iron filings.

The magnetic field lines around a current-carrying conductor depend on the direction of the current in the conductor.

There is a magnetic field of the Earth. The outer molten layers of the Earth's core are in constant motion, as a result of which magnetic fields arise in them, ultimately forming the Earth's magnetic field. The Earth's magnetic field causes magnetic anomalies, that is, some kind of deviation. Short-term anomalies - magnetic storms, permanent anomalies - iron ore deposits at shallow depths.

Magnetic storms are short-term changes in the Earth's magnetic field that greatly affect the compass needle. Observations show that the appearance of magnetic storms is associated with solar activity. During the period of increased solar activity, streams of charged particles, electrons and protons are emitted from the surface of the Sun into space. The magnetic field generated by moving charged particles changes the Earth's magnetic field and causes a magnetic storm. Magnetic storms are a short-term phenomenon.

Fig 1.13 A) magnetic storm on the Sun, b) magnetic storm on Earth.

Magnetic storms often cause poor health due to the formation of blood aggregates, that is, an increase in blood density, leading to a deterioration in oxygen metabolism.

There are areas on the globe in which the direction of the magnetic needle is constantly deviated from the direction of the Earth's magnetic line. Such areas are called areas of magnetic anomaly. One of the largest permanent magnetic anomalies is the Kursk Magnetic Anomaly. The reason for such anomalies is the huge deposits of iron ore at a relatively shallow depth.

Figure 1.14 Kursk magnetic anomaly

The Earth's magnetic field can change - increase or decrease, the main reasons for the change are: solar wind, inversion. The Earth is constantly under a stream of charged particles emitted by the Sun. This stream is called the solar wind. The solar wind creates magnetic storms and auroras. The Northern Lights are the result of the interaction of the solar wind with the Earth's magnetic field. Near the magnetic poles, particle flows come much closer to the Earth's surface. During powerful solar flares, the magnetosphere is deformed, and these particles can move into the upper layers of the atmosphere, where they collide with gas molecules, forming auroras.

Fig 1.15 Aurora

Under the influence of the solar wind, the magnetosphere is deformed, so our Earth has a long magnetic tail directed from the Sun.

Fig 1.16 Earth's magnetosphere

By studying the properties of many rocks using remanent magnetization, geophysicists have come to the conclusion that the Earth's magnetic poles have changed places many times. This has happened seven times in the last million years. 570 years ago the magnetic poles were located near the equator.

Recently, one can increasingly hear that an active process is taking place to move the Earth's poles, the so-called inversion.

In December 2011, the Earth’s geomagnetic pole shifted immediately by 200 kilometers, which was recorded by instruments of the Central Military-Technical Institute of the Ground Forces. In general, scientists are observing an acceleration of the movement of the magnetic north pole (and, as a consequence, the south pole).

An inversion today is one of the most dangerous catastrophes on a planetary scale.

At the moment of inversion, the magnetic field strength weakens, leaving people defenseless against solar radiation.

Fig 1.17 Inversion

The weakening of the Earth's magnetic field will lead to adverse consequences. Scientists from the United States back in the 60s built two chambers for experiments, in one of them earthly conditions were maintained, and the other was surrounded by a powerful metal screen, gradually reducing the strength of the Earth’s magnetic field hundreds of times. Mice, clover and wheat seeds were placed in both chambers. After a few months, the experiment showed that in the shielded chamber the mice lost their hair earlier and died earlier. Their skin was thicker compared to the control group. The skin swelled, displacing the hair follicles, which was the cause of baldness. And the plants had longer and thicker roots.

Monitoring the state of the magnetic field is very important because it acts as a barrier to powerful radioactive cosmic radiation.

Spacecraft that have flown to other planets have recorded their magnetic fields. The strongest magnetic fields are found on Jupiter, Saturn, Uranus and Neptune. Flights of interplanetary space stations and spacecraft to the Moon made it possible to establish the absence of a magnetic field. The strong magnetization of lunar soil rocks delivered to Earth allows scientists to conclude that billions of years ago the Moon could have had a magnetic field.

Thus, we can conclude that the space around the magnetic field is the space around the magnet, which represents closed magnetic lines leaving the north pole and entering the south pole. The Earth's magnetic field causes magnetic anomalies - short-term - in the form of magnetic storms, and permanent - in the form of formed areas of magnetic anomalies, the largest of which is the Kursk magnetic anomaly. The Earth's magnetic field is subject to change, the main factors being solar wind and inversion. Inversion is a process as a result of which the magnetic poles change places, and the process is accompanied by a weakening of the magnetic field - the main defender of the Earth.

Chapter 2. Practical aspects of magnetic properties

2.1 Practical experiments to study magnetic properties

2.1.1 How to create a simple artificial magnet

The simplest artificial magnet is easy to create and this can be verified with the help of a simple experiment. For the experiment you need to have a magnet, a needle, foam and a plate of water. In order for the needle to become magnetized, you need to touch it with any magnet. You can check the magnetization by lowering it into sawdust. By the number of attracted sawdust, one can judge that at the edges of the needle the attraction is much stronger than in the middle. The place where the magnet attracts the most is called the pole.

Rice. 2.1 Magnetizing the needle Fig. 2.2 Attraction of iron filings

2.1.2 How to check the presence of poles?

You can check the presence of poles by placing a magnetized needle on a float in a plate of water. After diving, the needle will line up so that one end faces north and the other south, which can be easily checked with a compass. Accordingly, the end that faces north is called the north pole, and the end that faces south is called the south pole.

Rice. 2.3 Checking with a needle-magnet compass

Rice. 2.4 Interaction of magnets - “attraction-repulsion”

2.1.3 Proof that the poles of a magnet are inseparable

It is impossible to separate the poles from each other, which is proven by experiment with dividing a magnetized needle into parts. As a result of the experiment, we can conclude that even the obtained parts of the needle have two poles.

Rice. 2.5 Dividing a magnetized needle into parts

2.1.4 Methods for demagnetizing a magnet

In the theoretical part, we concluded that every magnet consists of many tiny magnets, and each magnet has both poles: north and south. “Tiny magnets” are usually called domains. In non-magnetized iron, the domains are located in different directions. After magnetization, the domains turn in one direction with the north poles and in the other direction with the south poles. Demagnetization is possible by heating the magnet above the Curie temperature, using a strong hammer blow on the magnet, or placing the magnet in an alternating magnetic field. The latter method is used in industry to demagnetize tools, hard drives, erase information on magnetic cards, and so on. As a result of impacts, partial demagnetization of materials occurs, since a sharp mechanical impact leads to disorder of domains.

We carried out an accessible experiment with heating a previously magnetized needle. After heating the needles over a fire, the sawdust no longer attracts, which means that the magnetization has disappeared.

Rice. 2.6 Heating a magnetized needle Fig. 2.7 No magnetic field after heating

2.1.5 Visual representation of the magnetic field

The magnetic field is invisible, but we can see it by conducting an experiment with sawdust, placing a sheet of thick paper on the magnet, after having previously covered it with an even layer of iron filings. After lightly tapping the sheet, each grain of iron, having become magnetized, acquired a north and south pole, becoming a kind of magnetic arrow. The sawdust is arranged in such a way that the location of magnetic forces immediately becomes clear. At the poles, where the magnetic field is strongest, the lines along which magnetic forces act are denser, they are called magnetic lines of force.

Rice. 2.8 Visual representation of the magnetic field

At the moment of lowering the magnetized needle into the sawdust, you can notice that even before the moment of contact, the sawdust had already begun to stick to the tip, therefore, magnetic forces act at a distance.

2.1.6 Magnet interaction

One of the most common manifestations of a magnetic field in everyday life is the interaction of two magnets: like poles repel, opposite poles attract (Figure 2.4). This process can be studied using an experiment using a needle on a float. It is enough to bring a magnet to it with the north pole - the needle will turn to it with the south pole, and when you bring the magnet to the south pole, it will turn to the north. Therefore, different poles attract each other.

2.1.7 Magnet instability. Magnetic field around a conductor carrying current.

To confirm the existence of a non-permanent magnet - an electromagnet, which clearly demonstrates the relationship between electric current and a magnet, we conducted an experiment using a battery, wire, and compass. By connecting the ends of the wire to the terminals of the battery and bringing it to the compass, we were convinced that the arrow immediately changes direction to the opposite direction, which is due to the presence of a magnetic field. Having swapped the ends, we saw that the magnetic field immediately “turned over” - this is what the magnetic compass needle shows us.

From this experience we can conclude that an electromagnet is a non-permanent magnet whose magnetic field can be controlled. The direction of the magnetic lines of the magnetic field of the current is related to the direction of the current in the conductor (Figure 2.9).

Rice. 2.9. The location of the arrow after placing the conductor with current to the compass

Conclusion

The study of the theoretical aspects of magnetic properties and interactions, with their confirmation by practical experiments, made it possible to achieve the goal of this work - obtaining an understanding of the magnetic properties of the magnet and the Earth.

During the work on the project, it was found that a magnet is a body that has its own magnetic field that retains magnetization for a long time. The magnetization of bodies is explained by the existence of electric currents, that is, the concepts of electric current and magnet are interconnected, and an entire section of physics is devoted to their relationships. Magnets created by nature are weaker than artificial magnets created by man and widely used in all areas of industry and in everyday life.

Magnets, having two inseparable poles, can demagnetize when heated to a certain temperature. Magnets interact with each other, which is explained by the presence of a magnetic field. The smallest magnet is the electron and the largest magnet of interest to us is the Earth - which has four poles - two magnetic and two geographical that do not coincide with each other.

The magnetic field consists of closed lines leaving the north pole and entering the south pole. The Earth's magnetic field causes magnetic anomalies - short-term in the form of magnetic storms and areas of magnetic anomalies. The Earth's magnetic field is subject to change, the main influencing factors being the solar wind and inversion. Reversal is a process during which the magnetic poles change places, reducing the strength of the magnetic field - the main defender of the Earth.

Thus, we can conclude that the tasks set at the beginning of the project have been solved, initial knowledge has been obtained about the magnetic processes of magnets and the Earth, in relation to which I now know that the so-called “polarity reversal” is an inevitable process that is dangerous for all humanity and its individual representative. And if now they ask me the question: “Do I know where the magnetic poles are?” I will definitely ask “At what time are you interested in finding the poles?”

Bibliography

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I explore the world: Children's encyclopedia: Physics / Comp. A.A. Leonovich; Under general ed. O.G. Hinn. – M.: LLC Publishing House AST-LTD, 1998. – 480 p.

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A.I. Dyachenko Magnetic poles of the Earth. Series: Library. Mathematical education. M.: MTsNMO, 2003. – 48 p.