History of the development of ideas about the magnetic field. History of a magnet Who was the first to use a magnetic

Magnetism has been studied since ancient times, and over the past two centuries it has become the basis of modern civilization.

Alexey Levin

Humanity has been collecting knowledge about magnetic phenomena for at least three and a half thousand years (the first observations of electrical forces took place a thousand years later). Four hundred years ago, at the dawn of physics, the magnetic properties of substances were separated from the electrical ones, after which for a long time both were studied independently. Thus, an experimental and theoretical base was created, which became mid-19th century, the basis of a unified theory of electromagnetic phenomena. Most likely, unusual properties The natural mineral magnetite (magnetic iron ore, Fe3O4) was known in Mesopotamia back in the Bronze Age. And after the emergence of iron metallurgy, it was impossible not to notice that magnetite attracts iron products. The father of Greek philosophy, Thales of Miletus (approximately 640−546 BC), already thought about the reasons for such attraction, who explained it by the special animation of this mineral (Thales also knew that amber rubbed on wool attracts dry leaves and small splinters, and therefore he endowed him with spiritual strength). Later, Greek thinkers talked about invisible vapors enveloping magnetite and iron and attracting them to each other. It is not surprising that the word “magnet” itself also has Greek roots. Most likely, it goes back to the name of Magnesia-y-Sipila, a city in Asia Minor, near which magnetite lay. The Greek poet Nikander mentioned the shepherd Magnis, who found himself next to a rock, which pulled the iron tip of his staff toward itself, but this, in all likelihood, is just a beautiful legend.

Ancient China was also interested in natural magnets. The ability of magnetite to attract iron is mentioned in the treatise "Spring and Autumn Records of Master Liu", dating back to 240 BC. A century later, the Chinese noticed that magnetite had no effect on either copper or ceramics. In the VII-VIII centuries. /bm9icg===>ekah they found out that a freely suspended magnetized iron needle turns towards the North Star. As a result, in the second half of the 11th century, real nautical compasses, European sailors mastered them a hundred years later. Around the same time, the Chinese discovered that the magnetized needle points east of the north direction and thereby discovered magnetic declination, far ahead of European navigators in this matter, who came to this conclusion only in the 15th century.

Small magnets

In a ferromagnet, the intrinsic magnetic moments of the atoms are aligned in parallel (the energy of this orientation is minimal). As a result, magnetized areas are formed, domains - microscopic (10−4-10−6 m) permanent magnets separated by domain walls. In the absence of external magnetic field The magnetic moments of the domains are randomly oriented in the ferromagnet; in an external field, the boundaries begin to shift, so that domains with moments parallel to the field displace all others - the ferromagnet is magnetized.

The Birth of the Science of Magnetism

The first description of the properties of natural magnets in Europe was made by the Frenchman Pierre de Maricourt. In 1269, he served in the army of King Charles of Anjou of Sicily, which besieged the Italian city of Lucera. From there he sent a document to a friend in Picardy, which went down in the history of science as the “Letter on the Magnet” (Epistola de Magnete), where he spoke about his experiments with magnetic iron ore. Maricourt noticed that in every piece of magnetite there were two areas that were especially strong at attracting iron. He saw a parallel between these zones and the poles of the celestial sphere and borrowed their names for areas of maximum magnetic force - which is why we now talk about the north and south magnetic poles. If you break a piece of magnetite in two, writes Maricourt, each fragment will have its own poles. Maricourt not only confirmed that both attraction and repulsion occur between pieces of magnetite (this was already known), but for the first time associated this effect with the interaction between opposite (north and south) or like poles.

Many historians of science consider Maricourt to be the undisputed pioneer of European experimental science. In any case, his notes on magnetism were circulated in dozens of lists, and after the advent of printing, they were published as a separate brochure. They were quoted with respect by many naturalists until the 17th century. This work was well known to the English naturalist and physician (physician to Queen Elizabeth and her successor James I) William Gilbert, who in 1600 published (as expected, in Latin) a wonderful work “On the Magnet, Magnetic Bodies and the Great Magnet - the Earth.” " In this book, Gilbert not only provided almost all known information about the properties of natural magnets and magnetized iron, but also described his own experiments with a magnetite ball, with the help of which he reproduced the main features of terrestrial magnetism. For example, he discovered that at both magnetic poles of such a “little Earth” (terrella in Latin), the compass needle is set perpendicular to its surface, at the equator - parallel, and at middle latitudes - in an intermediate position. This is how Hilbert modeled the magnetic inclination, the existence of which had been known in Europe for more than half a century (in 1544, this phenomenon was first described by the Nuremberg mechanic Georg Hartmann).

A revolution in navigation. The compass made a real revolution in maritime navigation, making global travel not isolated cases, but a familiar, regular routine.

Gilbert also reproduced the geomagnetic declination on his model, which he attributed to the not perfectly smooth surface of the ball (and therefore, on a planetary scale, explained this effect by the attraction of the continents). He discovered that highly heated iron loses its magnetic properties, but when cooled they are restored. Finally, Gilbert was the first to make a clear distinction between the attraction of a magnet and the attraction of rubbed amber, which he called electric force (from the Latin name for amber, electrum). In general, it was an extremely innovative work, appreciated by both contemporaries and descendants. Gilbert's statement that the Earth should be considered a “big magnet” became the second fundamental scientific conclusion about physical properties of our planet (the first is the discovery of its spherical shape, made back in Antiquity).

Two centuries break

After Gilbert, the science of magnetism made very little progress until the beginning of the 19th century. What has been accomplished during this time can literally be counted on one’s fingers. In 1640, Galileo's student Benedetto Castelli explained the attraction of magnetite by the presence of many tiny magnetic particles in its composition - the first and very imperfect guess that the nature of magnetism should be sought at the atomic level. The Dutchman Sebald Brugmans noticed in 1778 that bismuth and antimony were repelled by the poles of a magnetic needle - this was the first example of a physical phenomenon that Faraday called diamagnetism 67 years later. In 1785, Charles-Augustin Coulomb, through precision measurements on a torsion balance, showed that the force of interaction between magnetic poles is inversely proportional to the square of the distance between them - just like the force of interaction between electric charges (in 1750, the Englishman John Michell came to a similar conclusion, but the Coulomb conclusion is much more reliable).

But the study of electricity in those years moved by leaps and bounds. It's not difficult to explain. Natural magnets remained the only primary sources of magnetic force—science knew no others. Their power is stable, it cannot be changed (except perhaps destroyed by heat), much less generated by at will. It is clear that this circumstance greatly limited the possibilities of the experimenters.

Electricity was in a much more advantageous position - because it could be received and stored. The first static charge generator was built in 1663 by the burgomaster of Magdeburg, Otto von Guericke (the famous Magdeburg hemispheres are also his brainchild). A century later, such generators became so widespread that they were even demonstrated at high society receptions. In 1744, the German Ewald Georg von Kleist and a little later the Dutchman Pieter van Musschenbroek invented the Leyden jar - the first electric capacitor; At the same time, the first electrometers appeared. As a result, by the end of the 18th century, science knew much more about electricity than at its beginning. But the same could not be said about magnetism.

And then everything changed. In 1800, Alessandro Volta invented the first chemical source of electric current, the voltaic battery, also known as a voltaic cell. After this, the discovery of the connection between electricity and magnetism was a matter of time. It could have taken place as early as the next year, when the French chemist Nicolas Gauthereau noticed that two parallel wires carrying current are attracted to each other. However, neither he, nor the great Laplace, nor the wonderful experimental physicist Jean-Baptiste Biot, who later observed this phenomenon, attached any significance to it. Therefore, priority rightly went to the scientist, who had long assumed the existence of such a connection and devoted many years to searching for it.

From Copenhagen to Paris

Everyone has read the fairy tales and stories of Hans Christian Andersen, but few people know that when the future author of “The Naked King” and “Thumbelina” reached Copenhagen as a fourteen-year-old teenager, he found a friend and patron in the person of his double namesake, an ordinary professor of physics and chemistry at the University of Copenhagen Hans Christian Oersted. And both glorified their country throughout the world.

The variety of magnetic fields Ampere studied the interaction between parallel conductors carrying current. His ideas were developed by Faraday, who proposed the concept of magnetic lines of force.

Since 1813, Oersted quite consciously tried to establish a connection between electricity and magnetism (he was an adherent of the great philosopher Immanuel Kant, who believed that all natural forces have an internal unity). Oersted used compasses as indicators, but for a long time to no avail. Oersted expected the magnetic force of the current to be parallel to itself, and to obtain maximum torque he placed the electrical wire perpendicular to the compass needle. Naturally, the arrow did not react when the current was turned on. And only in the spring of 1820, during a lecture, Oersted stretched the wire parallel to the arrow (either to see what would come of it, or he came up with a new hypothesis - historians of physics are still arguing about this). And it was here that the needle swung - not too much (Oersted had a low-power battery), but still noticeably.

True, the great discovery had not yet taken place. For some reason, Oersted interrupted the experiments for three months and returned to them only in July. And it was then that he realized that “the magnetic effect of an electric current is directed along the circles enclosing this current.” This was a paradoxical conclusion, since rotating forces had not previously appeared either in mechanics or in any other branch of physics. Ørsted outlined his findings in a paper and submitted it to several scientific journals on July 21. Then he no longer studied electromagnetism, and the baton passed to other scientists. The Parisians were the first to accept it. On September 4, the famous physicist and mathematician Dominic Arago spoke about Oersted's discovery at a meeting of the Academy of Sciences. His colleague Andre-Marie Ampere decided to study the magnetic effect of currents and literally the next day began experiments. First of all, he repeated and confirmed Oersted's experiments, and in early October he discovered that parallel conductors attract if currents flow through them in the same direction, and repel if in opposite directions. Ampere studied the interaction between non-parallel conductors and presented it with a formula (Ampere's law). He also showed that coiled conductors carrying current rotate in a magnetic field, like a compass needle (and incidentally invented a solenoid - a magnetic coil). Finally, he put forward a bold hypothesis: undamped microscopic parallel circular currents flow inside magnetized materials, which are the cause of their magnetic action. At the same time, Biot and Felix Savart jointly identified a mathematical relationship that allows one to determine the intensity of the magnetic field created by direct current (Biot-Savart's law).

To emphasize the novelty of the effects studied, Ampere proposed the term “electrodynamic phenomena” and constantly used it in his publications. But this was not yet electrodynamics in the modern sense. Oersted, Ampere and their colleagues worked with direct currents that created static magnetic forces. Physicists had yet to discover and explain truly dynamic, non-stationary electromagnetic processes. This problem was solved in the 1830s–1870s. About a dozen researchers from Europe (including Russia - remember Lenz’s rule) and the USA had a hand in it. However, the main merit undoubtedly belongs to two titans of British science - Faraday and Maxwell.

London tandem

For Michael Faraday, 1821 was truly a fateful year. He received the coveted position of Superintendent of the Royal Institution of London and, virtually by accident, began a research program that has earned him a unique place in the history of world science.

Magnetic and not so much. Different substances behave differently in an external magnetic field, this is due to the different behavior of the atoms’ own magnetic moments. The best known are ferromagnets; there are paramagnets, antiferromagnets and ferrimagnets, as well as diamagnets, the atoms of which do not have their own magnetic moments (in an external field they are weakly magnetized “against the field”).

It happened like this. The editor of the Annals of Philosophy, Richard Phillips, invited Faraday to write a critical review of new works on the magnetic action of current. Faraday not only followed this advice and published “Historical Sketch of Electromagnetism,” but began his own research, which lasted for many years. First, like Ampere, he repeated Oersted's experiment, after which he moved on. By the end of 1821, he had made a device in which a current-carrying conductor rotated around a strip magnet, and another magnet rotated around a second conductor. Faraday suggested that both the magnet and the live wire are surrounded by concentric lines of force, lines of force, which determine their mechanical action. This was already the embryo of the concept of a magnetic field, although Faraday himself did not use such a term.

At first, he considered field lines a convenient method for describing observations, but over time he became convinced of their physical reality (especially since he found a way to observe them using iron filings scattered between magnets). By the end of the 1830s, he clearly realized that the energy, the source of which was permanent magnets and live conductors, was distributed in a space filled with lines of force. In fact, Faraday was already thinking in field theoretical terms, in which he was significantly ahead of his contemporaries.

But his main discovery was different. In August 1831, Faraday was able to make magnetism generate electric current. His device consisted of an iron ring with two opposing windings. One of the spirals could be closed to electric battery, the other was connected to a conductor located above the magnetic compass. The arrow did not change position if a direct current flowed through the first coil, but swung when it was turned on and off. Faraday realized that at this time electrical impulses arose in the second winding, caused by the appearance or disappearance of magnetic lines of force. In other words, he discovered that electromotive force is caused by changes in the magnetic field. This effect was also discovered by the American physicist Joseph Henry, but he published his results later than Faraday and did not make such serious theoretical conclusions.

Electromagnets and solenoids underlie many technologies, without which it is impossible to imagine modern civilization: from electricity-generating electric generators, electric motors, transformers to radio communications and, in general, almost all modern electronics.

Towards the end of his life, Faraday came to the conclusion that new knowledge about electromagnetism needed mathematical formulation. He decided that this task would be up to James Clerk Maxwell, a young professor at Marischal College in the Scottish city of Aberdeen, which he wrote to him about in November 1857. And Maxwell really united all the then knowledge about electromagnetism into a single mathematical theory. This work was largely accomplished in the first half of the 1860s, when he became professor of natural philosophy at King's College London. The concept of an electromagnetic field first appeared in 1864 in a memoir presented to the Royal Society of London. Maxwell introduced this term to designate “that part of space which contains and surrounds bodies in an electric or magnetic state,” and specifically emphasized that this space can be either empty or filled with any kind of matter.

The main result of Maxwell's work was a system of equations connecting electromagnetic phenomena. In his Treatise on Electricity and Magnetism, published in 1873, he called them the general equations of the electromagnetic field, and today they are called Maxwell's equations. Later, they were generalized more than once (for example, to describe electromagnetic phenomena in various media), and also rewritten using an increasingly sophisticated mathematical formalism. Maxwell also showed that these equations admit of solutions involving undamped transverse waves, of which visible light is a special case.

Maxwell's theory introduced magnetism as a special kind of interaction between electric currents. Quantum physics The 20th century added only two new points to this picture. We now know that electromagnetic interactions are carried by photons and that electrons and many other elementary particles have their own magnetic moments. All experimental and theoretical work in the field of magnetism is built on this foundation.

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

Magnet in the Ancient World

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

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 traveling with his sheep and suddenly discovered that the iron tip of his staff and the nails in his shoes were stuck to a strange black stone. This is how the magnet was discovered.

Interesting fact from the history of magnets. The ashes of the Prophet Mohammed are kept in an iron chest and are located in a cave with a magnetic ceiling, which is why the chest constantly hangs in the air without additional support. 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 to perform a miracle.

Magnet in nature: Kurzhunkul iron ore deposit, Kazakhstan

Experiment "Mohammed's coffin"

History of magnets in Ancient America

Don't forget that ancient history developed on several continents. The magnet was known in Central America, 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 magnetic heads. Since the turtle can navigate by the cardinal directions, this was symbolic.

"Fat boys" from magnetic rocks

Magnet in the Middle Ages

It was thought of in China to use a magnet as an indicator of the cardinal directions, but no one conducted theoretical research on this topic.

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

In 1300 John of 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, Italians firmly believe that their compatriot Flavio Gioia was the first to invent a compass.

In 1600, the work “On the Magnet, Magnetic Bodies and the Great Magnet – the Earth.” New physiology, proven by many arguments and experiments,” the English physician William Gilbert expanded the boundaries of knowledge about this subject. It became known that heating can weaken a 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, but begins to spin randomly. This can last for several hours or even several days. Since sailors were the first to discover this phenomenon, they dubbed the phenomenon beautifully - a magnetic storm.

Magnet in modern times and our days

The real breakthrough occurred in 1820. Like all great discoveries, this happened by accident. It’s just that a university teacher, Hans Christian Oersted, decided to demonstrate to students during a lecture that there is no connection between electricity and a magnet, they do not influence each other. To do this, the physicist turned on an electric current next to the magnetic needle. Great was his shock when the needle deviated! This allowed us to open connection between electricity and magnetic fields. So science made a huge leap forward.

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

How did the doctrine of the magnetic field develop?

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

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

What is a magnetic field

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

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

Characteristics of the magnetic field

The characteristics of the magnetic field are:

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

F = B x S x cos α,

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

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

How to represent a magnetic field

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

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

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

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

Magnetic field measurement

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

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

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

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

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

The nature of the magnetic field

Magnetism and magnetic fields are manifestations of electromagnetic force. There are two possible ways to organize an energy charge in motion and, therefore, 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 depending on the distance. This is described by Ampere's law.

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

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

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

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

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

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 there is atmospheric air as an insulating spacer. The giant capacitor maintains a constant charge due to the influence of the earth's MF. Using this knowledge, you can create a scheme for obtaining electrical energy from the Earth's magnetic field. True, the result will be low voltage values.

You need to take:

grounding device;
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 entire structure is connected together, and 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. Get large number electricity is not possible using this device.

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

Video

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

Magnetic field

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

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

A body that has its own magnetic field.

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

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

Characteristics of the magnetic field

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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History of electricity

Electricity, a set of phenomena caused by the existence, movement and interaction of electrically charged bodies or particles. Interaction electric charges carried out using an electromagnetic field (in the case of stationary electric charges - an electrostatic field).

Moving charges (electric current), along with the electric one, also excite a magnetic field, i.e., they generate an electromagnetic field, through which electromagnetic interaction occurs (the study of magnetism is an integral part of the general study of electricity). Electromagnetic phenomena are described by classical electrodynamics, which is based on Maxwell’s equations

The laws of the classical theory of electricity cover a huge set of electromagnetic processes. Among the 4 types of interactions (electromagnetic, gravitational, strong and weak) existing in nature, electromagnetic ones take first place in terms of breadth and variety of manifestations. This is due to the fact that all bodies are built from electrically charged particles of opposite signs, the interactions between which, on the one hand, are many orders of magnitude more intense than gravitational and weak ones, and on the other hand, are long-range in contrast to strong interactions. The structure of atomic shells, the cohesion of atoms into molecules (chemical forces) and the formation of condensed matter are determined by electromagnetic interaction.

The simplest electrical and magnetic phenomena have been known since ancient times. Minerals have been found that attract pieces of iron, and it has also been discovered that amber (Greek electron, elektron, hence the term electricity), rubbed on wool, attracts light objects (electrification by friction). However, only in 1600 W. Gilbert first established the difference between electrical and magnetic phenomena. He discovered the existence of magnetic poles and their inseparability from each other, and also established that the globe is a giant magnet.

In the XVII - 1st half of the XVIII centuries. Numerous experiments were carried out with electrified bodies, the first electrostatic machines based on electrification by friction were built, the existence of electric charges of two kinds was established (C. Dufay), and the electrical conductivity of metals was discovered (English scientist S. Gray). With the invention of the first capacitor - the Leyden jar (1745) - it became possible to accumulate large electrical charges. In 1747-53, Franklin outlined the first consistent theory of electrical phenomena, finally established the electrical nature of lightning and invented the lightning rod.

In the 2nd half of the 18th century. quantitative study of electrical and magnetic phenomena began. The first ones appeared measuring instruments- electroscopes of various designs, electrometers. G. Cavendish (1773) and C. Coulomb (1785) experimentally established the law of interaction of stationary point electric charges (Cavendish’s works were published only in 1879).

This basic law of electrostatics (Coulomb's law) for the first time made it possible to create a method for measuring electric charges by the forces of interaction between them. Coulomb also established the law of interaction between the poles of long magnets and introduced the concept of magnetic charges concentrated at the ends of magnets.

The next stage in the development of the science of electricity is associated with the discovery at the end of the 18th century. L. Galvani "animal electricity" and works A.Volty, who invented the first source of electric current - a galvanic element (the so-called voltaic column, 1800), creating a continuous (direct) current for a long time. In 1802, V.V. Petrov, having built a galvanic cell of much greater power, discovered the electric arc, studied its properties and pointed out the possibility of using it for lighting, as well as for melting and welding metals. G. Davy obtained previously unknown metals - sodium and potassium - by electrolysis of aqueous solutions of alkalis (1807). J.P. Joule established (1841) that the amount of heat generated in a conductor by electric current is proportional to the square of the current; this law was substantiated (1842) by the precise experiments of E.H. Lenz (Joule-Lenz law).

G. Ohm established (1826) the quantitative dependence of electric current on voltage in the circuit. K.F. Gauss formulated (1830) the fundamental theorem of electrostatics.

The most fundamental discovery was made by H. Oersted in 1820; he discovered the effect of electric current on a magnetic needle - a phenomenon that testified to the connection between electricity and magnetism. Following this, in the same year A.M. Ampere established the law of interaction of electric currents (Ampere's law). He also showed that the properties of permanent magnets can be explained on the basis of the assumption that constant electric currents (molecular currents) circulate in the molecules of magnetized bodies. Thus, according to Ampere, all magnetic phenomena are reduced to the interactions of currents, while magnetic charges do not exist. Since the discoveries of Oersted and Ampere, the doctrine of magnetism has become an integral part of the doctrine of electricity.

From the 2nd quarter of the 19th century. The rapid penetration of electricity into technology began. In the 20s The first electromagnets appeared. One of the first uses of electricity was the telegraph apparatus, in the 30s and 40s. Electric motors and current generators were built, and in the 40s, electric lighting devices, etc. The practical use of electricity subsequently increased more and more, which in turn had a significant impact on the doctrine of electricity.

In the 30-40s. XIX century M. Faraday, the creator of the general doctrine of electromagnetic phenomena, in which all electrical and magnetic phenomena are considered from a single point of view, made a great contribution to the development of the science of electricity. With the help of experiments, he proved that the effects of electric charges and currents do not depend on the method of their production [before Faraday, they distinguished between “ordinary” (obtained by electrification by friction), atmospheric, “galvanic”, magnetic, thermoelectric, “animal” and other types of energy. ].

Arago's experiment ("rotation magnetism").

In 1831, Faraday discovered electromagnetic induction - the excitation of an electric current in a circuit located in an alternating magnetic field. This phenomenon (also observed in 1832 by J. Henry) forms the foundation of electrical engineering. In 1833-34 Faraday established the laws of electrolysis; These works of his marked the beginning of electrochemistry. Later, trying to find the relationship between electrical and magnetic phenomena and optical ones, he discovered the polarization of dielectrics (1837), the phenomena of paramagnetism and diamagnetism (1845), magnetic rotation of the plane of polarization of light (1845), etc.

Faraday first introduced the concept of electric and magnetic fields. He denied the concept of action at a distance, the proponents of which believed that bodies directly (through emptiness) act on each other at a distance.

According to Faraday's ideas, the interaction between charges and currents is carried out through intermediate agents: charges and currents create electric or (respectively) magnetic fields in the surrounding space, with the help of which the interaction is transmitted from point to point (the concept of short-range action). His ideas about electric and magnetic fields were based on the concept of lines of force, which he considered as mechanical formations in a hypothetical medium - the ether, similar to stretched elastic threads or cords.

Faraday's ideas about the reality of the electromagnetic field did not immediately gain recognition. The first mathematical formulation of the laws of electromagnetic induction was given by f. Neumann in 1845 in the language of the concept of long-range action.

He also introduced the important concepts of coefficients of self- and mutual induction of currents. The meaning of these concepts was fully revealed later, when W. Thomson (Lord Kelvin) developed (1853) the theory of electrical oscillations in a circuit consisting of a capacitor (capacitance) and a coil (inductance).
Of great importance for the development of the doctrine of electricity was the creation of new instruments and methods of electrical measurements, as well as a unified system of electrical and magnetic units of measurement created by Gauss and W. Weber.

In 1846, Weber pointed out the relationship between current strength and the density of electrical charges in a conductor and the speed of their ordered movement. He also established the law of interaction of moving point charges, which contained a new universal electrodynamic constant, which is the ratio of electrostatic and electromagnetic charge units and has the dimension of speed.

When experimentally determined (Weber and F. Kohlrausch, 1856), this constant was obtained with a value close to the speed of light; this was a definite indication of the connection between electromagnetic phenomena and optical ones.

In 1861-73, the doctrine of electricity was developed and completed in the works of J. C. Maxwell. Based on the empirical laws of electromagnetic phenomena and introducing the hypothesis about the generation of a magnetic field by an alternating electric field, Maxwell formulated the fundamental equations of classical electrodynamics, named after him. At the same time, he, like Faraday, considered electromagnetic phenomena as a certain form of mechanical processes in the ether.

The main new consequence arising from these equations is the existence electromagnetic waves, propagating at the speed of light. Maxwell's equations formed the basis of the electromagnetic theory of light. Maxwell's theory found decisive confirmation in 1886-89, when G. Hertz experimentally established the existence of electromagnetic waves. After its discovery, attempts were made to establish communication using electromagnetic waves, culminating in the creation of radio, and intensive research in the field of radio engineering began.

At the end of the 19th - beginning of the 20th centuries. A new stage in the development of the theory of electricity began. Research into electrical discharges culminated in J. J. Thomson's discovery of the discrete nature of electrical charges. In 1897 he measured the ratio of the charge of an electron to its mass, and in 1898 he determined the absolute value of the charge of an electron. H. Lorentz, relying on Thomson's discovery and the conclusions of molecular kinetic theory, laid the foundations for the electronic theory of the structure of matter. In classical electronic theory, matter is considered as a collection of electrically charged particles, the movement of which is subject to the laws of classical mechanics. Maxwell's equations are obtained from the equations of electron theory by statistical averaging.

Attempts to apply the laws of classical electrodynamics to the study of electromagnetic processes in moving media have encountered significant difficulties. Trying to resolve them, A. Einstein came (1905) to the relativity of the theory. This theory finally refuted the idea of the existence of an ether endowed with mechanical properties. After the creation of the theory of relativity, it became obvious that the laws of electrodynamics cannot be reduced to the laws of classical mechanics.

At small space-time intervals, the quantum properties of the electromagnetic field, which are not taken into account by the classical theory of electricity, become significant. The quantum theory of electromagnetic processes - quantum electrodynamics - was created in the 2nd quarter of the 20th century. The quantum theory of matter and field already goes beyond the study of electricity and studies more fundamental problems concerning the laws of motion of elementary particles and their structure.

With the discovery of new facts and the creation of new theories, the importance of the classical doctrine of electricity did not decrease; only the limits of applicability of classical electrodynamics were determined. Within these limits, Maxwell's equations and classical electron theory remain valid, being the foundation of the modern theory of electricity.

Classical electrodynamics forms the basis of most branches of electrical engineering, radio engineering, electronics and optics (with the exception of quantum electronics). Using its equations, a huge number of theoretical and applied problems have been solved. In particular, numerous problems of plasma behavior in laboratory conditions and in space are solved using Maxwell's equations.