Who first received with the help of a magnetic field. Magnetic field theory and interesting facts about the earth's magnetic field. Magnetic field measurement

Simple things always have a complex history. Let's find out in more detail what the magnet hides in itself?

Magnet in the ancient world

The first deposits of magnetite were discovered on the territory of modern Greece, in the area Magnesia. This is how the name “magnet” came about: short for “stone from Magnesia”. By the way, the region itself is named after the Magnet tribe, and they, in turn, take their name from the mythical hero Magnet, the son of the god Zeus and Fii.

Of course, such a prosaic explanation of the origin of the name did not satisfy people's minds. And a legend was invented about a shepherd named Magnus. It was said that he was wandering with his sheep and suddenly found that the iron tip of his staff and the nails in his shoes stuck to a strange black stone. This is how the magnet was discovered.

An interesting fact from the history of magnets. The ashes of the prophet Mohammed are stored in an iron chest and located in a cave with a magnetic ceiling, which is why the chest is constantly hanging in the air without additional supports. True, only a devout Muslim who makes a pilgrimage to the Kaaba temple can be convinced of this. But the ancient pagan priests often used this technique for the manifestation of a miracle.

Magnet in nature: Kurzhunkul iron ore deposit, Kazakhstan

Mohammed's coffin experiment

History of magnets in ancient America

Do not forget that ancient history developed on several continents. The magnet in Central America was known, perhaps, even earlier than in Eurasia. On the territory of modern Guatemala“fat boys” were found - a symbol of satiety and fertility - made of magnetic rocks.

The Indians made images of turtles with a magnetic head. Since the turtle can navigate to the cardinal points, it was symbolic.

"Fat Boys" from Magnetic Rocks

Magnet in the Middle Ages

The use of a magnet as an indicator of the cardinal points was guessed in China, but no one has conducted theoretical research on this topic.

But the scientific works of European medieval scientists did not bypass the magnet. In 1260, Marco Polo brought a magnet from China to Europe - and away we go. Peter Peregrinus in 1296 published The Book of the Magnet, which described such a property of a magnet as polarity. Peter established that the poles of a magnet can attract and repel.

In 1300 John Gira created first compass making life easier for travelers and sailors. However, several scientists are fighting for the honor of being considered the inventors of the compass. For example, the Italians are firmly convinced that their compatriot Flavio Joya was the first to invent the compass.

In 1600, the work “On the magnet, magnetic bodies and on the large magnet - the Earth. A New Physiology Proven by Many Arguments and Experiments” by the English physician William Gilbert expanded the boundaries of knowledge on this subject. It became known that heating can weaken the magnet, and iron fittings can strengthen the poles. It also turned out that the Earth itself is a huge magnet.

By the way, I'm curious where the name came from. "magnetic storm". It turns out that there are days when the compass needle stops pointing north, and starts spinning randomly. This may take several hours or even several days. Since the sailors were the first to discover this phenomenon, they dubbed the phenomenon beautifully - a magnetic storm.

Magnet in modern times and today

The real breakthrough came in 1820. Like all great discoveries, it happened by accident. Just a lecturer at the university, Hans Christian Oersted, decided to demonstrate to students at a lecture that there is no connection between electricity and a magnet, they do not affect each other. To do this, the physicist turned on the electric current next to the magnetic needle. Great was his shock when the arrow deviated! This made it possible to open connection between electricity and magnetic fields. So science has made a huge leap forward.

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

A magnetic field

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

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

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

Magnetic field characteristics

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

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

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

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

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

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

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

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

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

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

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

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

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

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

One of the first drawings of the magnetic field (Rene Descartes, 1644). Although magnets and magnetism were known much earlier, the study of the magnetic field began in 1269, when the French scientist Peter Peregrine (the knight Pierre of Méricourt) noted the magnetic field on the surface of a spherical magnet using steel needles and determined that the resulting magnetic field lines intersected at two points, which he called "poles" by analogy with the poles of the Earth. Nearly three centuries later, William Gilbert Colchester used the work of Peter Peregrinus and for the first time definitively stated that the earth itself was a magnet. Published in 1600, Gilbert's work De Magnete, laid the foundations of magnetism as a science.

In 1750, John Michell stated that magnetic poles attract and repel according to the inverse square law. Charles-Augustin de Coulomb tested this assertion experimentally in 1785 and explicitly stated that the North and South Poles could not be separated. Based on this force existing between the poles, Siméon Denis Poisson, (1781-1840) created the first successful model of the magnetic field, which he presented in 1824. In this model, the magnetic H-field is produced by magnetic poles and magnetism is due to several pairs (north/south) of magnetic poles (dipoles).

Three discoveries in a row have challenged this "basis of magnetism." First, in 1819, Hans Christian Oersted discovered that an electric current creates a magnetic field around itself. Then, in 1820, André-Marie Ampère showed that parallel wires carrying current in the same direction attract each other. Finally, Jean-Baptiste Biot and Félix Savard in 1820 discovered a law called the Biot-Savart-Laplace law, which correctly predicted the magnetic field around any live wire.

Expanding on these experiments, Ampère published his own successful model of magnetism in 1825. In it, he showed the equivalence of electric current in magnets, and instead of the dipoles of magnetic charges in the Poisson model, he proposed the idea that magnetism is associated with constantly flowing current loops. This idea explained why the magnetic charge could not be isolated. In addition, Ampère deduced a law named after him, which, like the Biot-Savart-Laplace law, correctly described the magnetic field created by a direct current, and the magnetic field circulation theorem was also introduced. Also in this work, Ampère coined the term "electrodynamics" to describe the relationship between electricity and magnetism. In 1831, Michael Faraday discovered electromagnetic induction when he discovered that an alternating magnetic field generates electricity. He created a definition for this phenomenon, which is known as Faraday's law of electromagnetic induction. Later, Franz Ernst Neumann proved that for a moving conductor in a magnetic field, induction is a consequence of Ampère's law. In doing so, he introduced the vector potential of the electromagnetic field, which, as was later shown, was equivalent to the basic mechanism proposed by Faraday. In 1850, Lord Kelvin, then known as William Thomson, defined the difference between two magnetic fields as the fields H And B. The first was applicable to the Poisson model and the second to the Ampère model of induction. In addition, he deduced H And B connected to each other. Between 1861 and 1865 James Clerk Maxwell developed and published Maxwell's equations which explained and unified electricity and magnetism in classical physics. The first compilation of these equations was published in an article in 1861 entitled "On Physical Lines of Force". These equations were found to be valid, although incomplete. Maxwell completed his equations in his later work of 1865 "Dynamical theory of electromagnetic field" and determined that light is an electromagnetic wave. Heinrich Hertz experimentally confirmed this fact in 1887. Although the magnetic field strength of a moving electric charge implied in Ampère's law was not explicitly stated, in 1892 Hendrik Lorentz derived it from Maxwell's equations. At the same time, the classical theory of electrodynamics was basically completed.

The twentieth century expanded views on electrodynamics, thanks to the emergence of the theory of relativity and quantum mechanics. Albert Einstein, in his 1905 paper where his theory of relativity was grounded, showed that electric and magnetic fields are part of the same phenomenon, considered in different frames of reference - a thought experiment that eventually helped Einstein develop special relativity . Finally, quantum mechanics was combined with electrodynamics to form quantum electrodynamics (QED).

Turn magnetism into electricity

Electromagnetic induction

Grade 9

Basic course

REPEAT

1. What is a magnetic field?

2. What are its main properties?

3. How is the magnetic field depicted?

4. What is the relationship between electric current and magnetic field?

5. What are the magnetic field lines of a direct conductor with current?

6. What can be determined using the gimlet rule?

7. How are the magnetic field lines of a permanent magnet directed?

TEST

1. There is no magnetic field...

a) around a magnet b) around moving charged particles d) around a conductor with current e) around fixed charges

2) Who was the first scientist to prove that there is a magnetic field around a current-carrying conductor?

a) Archimedes b) Newton c) Oersted d) Ohm

TEST

3) Magnetic field lines in space outside a permanent magnet...

a) start at the north pole of the magnet, end at the south pole. b) start at the south pole of the magnet, end at the north pole. c) start at the north pole of the magnet, go to infinity.

d) start at the south pole of the magnet, go to infinity.

TEST

5) To increase the magnetic flux (see figure), you need:

a) replace the aluminum frame with an iron one b) raise the frame up c) take a weaker magnet d) strengthen the magnetic field

6) The conductor with current is located perpendicular to the plane of the sheet, the current is directed away from us. Choose a picture depicting the magnetic field of such a conductor with current.

Faraday's experiments (demonstration of experience)

Determine the pattern in the experiments.

Lenz's rule

The induction current arising in a closed circuit counteracts the change in the magnetic flux with which it is caused by its magnetic field.

0), or decreases (ΔФ 3. Set the direction of the lines of magnetic induction " of the magnetic field of the induction current. According to the Lenz rule, these lines should be directed opposite to the lines of magnetic induction B at ΔФ 0 and have the same direction with them at ΔФ 4. Knowing the direction of the lines magnetic induction ", find the direction of the induction current, using the gimlet rule. " width="640"

1. Determine the direction of the lines of magnetic induction of the external magnetic field.

2. Find out whether the flux of the magnetic induction vector of this field through the surface bounded by the contour (ΔФ 0) increases or decreases (ΔФ

3. Set the direction of the lines of magnetic induction "of the magnetic field of the induction current. According to the Lenz rule, these lines should be directed opposite to the lines of magnetic induction B at ΔФ 0 and have the same direction with them at ΔФ

4. Knowing the direction of the lines of magnetic induction ", find the direction of the induction current, using the gimlet rule.

Application of electromagnetic induction

Synchrophasotrons

Broadcasting

Magnetotherapy

Flowmeters

transformers

Generators

FIXING

1. Who was the first person to use a magnetic field to generate electricity?
1) Sh. Pendant 2) A. Ampère 3) M. Faraday 4) N. Tesla

2. What is the name of the phenomenon of the occurrence of an electric current in a closed circuit when the magnetic flux through the circuit changes?

1) Magnetization
2) Electrolysis
3) Electromagnetic induction
4) Resonance

3. Two identical coils are closed to galvanometers. A bar magnet is inserted into coil A, and the same bar magnet is removed from coil B. In which coil(s) will the galvanometer detect the induction current?

4. A magnet is inserted into the metal ring during the first two seconds, during the next two seconds the magnet is left motionless inside the ring, during the next two seconds it is removed from the ring. How long does the current flow in the coil?
1) 0-6s 2) 0-2s and 4-6s 3) 2-4 s 4) Only 0-2s

1) Only in coil A
2) Only in coil B
3) In both coils
4) None of the coils

5. Once a bar magnet falls through a fixed metal ring with the south pole down, and the second time with the north pole down. Ring current

6. Two identical fixed metal rings lie on a horizontal table at a great distance from each other. Two bar magnets fall with their north poles down so that one falls into the center of the first ring, and the second falls near the second ring. Before the impact of the magnets current

1) occurs in both cases
2) does not occur in any of the cases
3) occurs only in the first case
4) occurs only in the second case

1) occurs in both rings
3) occurs only in the first ring

7. Two identical fixed metal rings lie on a horizontal table at a great distance from each other. Above the first swings a magnet suspended on a thread. Above the second ring, a magnet suspended on a spring swings up and down. The point of suspension of the thread and the spring is above the centers of the rings. Current 1) occurs only in the first ring
2) occurs only in the second ring
3) occurs in both rings
4) does not occur in any of the rings

8. Once the ring falls on a vertical bar magnet so that it is put on it, the second time so that it flies past it. The plane of the ring in both cases is horizontal.

The current in the ring occurs

1) in both cases
2) in none of the cases
3) only in the first case
4) only in the second case

9. A solid conductive ring from the initial position is first displaced upward relative to the bar magnet (see Fig.), then from the same initial position it is displaced downward.

10. The conductive ring with a cut is raised to the bar magnet (see Fig.), And the solid conductive ring is shifted to the right

Induction current in the ring

At the same time, the inductive current

1) flows only in the first case
2) flows only in the second case
3) flows in both cases
4) in both cases does not flow

1) flows in both cases
2) in both cases does not flow
3) flows only in the first case
4) flows only in the second case

Test Answers

10-4

Magnetic fields occur naturally and can be created artificially. A person noticed their useful characteristics, which he learned to apply in everyday life. What is the source of the magnetic field?

How the doctrine of the magnetic field developed

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

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

What is a magnetic field

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

conductors through which electric current passes;
permanent magnets;
changing electric field.

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

Important! Mutually generate each other electric and magnetic fields that change over time. This relationship is determined by Maxwell's equations.

Magnetic field characteristics

The characteristics of the magnetic field are:

Magnetic flux, a scalar quantity that determines how many magnetic field lines pass through a given section. Designated with the letter F. Calculated according to the formula:

F = B x S x cos α,

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

The magnetic induction vector (B) shows the force acting on the charge carriers. It is directed towards the north pole, where the usual magnetic needle points. Quantitatively, magnetic induction is measured in teslas (Tl);
MP tension (N). It is determined by the magnetic permeability of various media. In a vacuum, permeability is taken as unity. The direction of the intensity vector coincides with the direction of the magnetic induction. Unit of measurement - A / m.

How to represent a magnetic field

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

MP is mathematically described as a vector field. It can be constructed by means of many vectors of magnetic induction B, each of which is directed towards the north pole of the compass needle and has a length depending on the magnetic force;
An alternative way of representing is to use lines of force. These lines never intersect, never start or stop anywhere, forming closed loops. The MF lines combine in more frequent regions where the magnetic field is strongest.

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

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

Magnetic field measurement

Since this is a vector quantity, there are two parameters for measuring MF: force and direction. Direction is easy to measure with a compass connected to the field. An example is a compass placed in the Earth's magnetic field.

Measurement of other characteristics is much more difficult. Practical magnetometers only appeared in the 19th century. Most of them work using the force that the electron feels when moving through the magnetic field.

Very accurate measurement of small magnetic fields has become practical since the discovery in 1988 of giant magnetoresistance in layered materials. This discovery in fundamental physics was quickly applied to magnetic hard disk technology for data storage in computers, resulting in a thousandfold increase in storage capacity in just a few years.

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

Interesting. A small fridge magnet creates an MF equal to 0.001 T, and the Earth's magnetic field, on average, is 0.00005 T.

The nature of the magnetic field

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

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

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

Some materials with higher magnetic permeability are capable of concentrating magnetic fields.

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

To use the rule, one must imagine that the wire is grasped by the right hand, and the thumb indicates the direction of the current. Then the other four fingers will show the direction of the magnetic induction vector around the conductor.

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

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

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

Have to take:

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

The Tesla coil will act as an electron emitter. The whole structure is connected together, and in order to ensure a sufficient potential difference, the transformer must be raised to a considerable height. Thus, an electrical circuit will be created, through which a small current will flow. It is impossible to get a large amount of electricity using this device.

Electricity and magnetism dominate many of the worlds surrounding man: from the most fundamental processes in nature to cutting-edge electronic devices.