Who was the first to obtain using a magnetic field. History of the magnet

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 by the middle of the 19th century became the basis of a unified theory of electromagnetic phenomena. Most likely, the unusual properties of the natural mineral magnetite (magnetic iron ore, Fe3O4) were 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 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 that was pulling the iron tip of his staff towards itself, but this, in all likelihood, is just a beautiful legend.

Natural magnets were also of interest in Ancient China. 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 marine compasses appeared in China; 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 an external magnetic field, the magnetic moments of the domains are randomly oriented in the ferromagnet; in the 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 celestial sphere and borrowed their names for areas of maximum magnetic force - that’s why we are now talking 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 Maricura to be the undisputed pioneer of European science. 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 own experiences with a ball of magnetite, 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 “large 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 Hilbert, the science of magnetism up to early XIX century has advanced very little. 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 particles in its composition. magnetic particles- 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, using 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 strength 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 electric current- a galvanic battery, also known as a voltaic battery. After this, the discovery of the connection between electricity and magnetism was a matter of time. It could have happened already next year, when French chemist Nicolas Gauthereau noticed that two parallel wires carrying current were 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 an article and sent it to several publications on July 21 scientific journals. 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 actually started research program, thanks to which he took 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, and then moved on. By the end of 1821, he made a device where 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 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 connected to an 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, in the second winding, electrical impulses, caused by the appearance or disappearance of magnetic lines of force. In other words, he discovered that the reason electromotive force are 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. Concept 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 of 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.

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

A magnetic field

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

Characteristics of the magnetic field

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Electrical and magnetic phenomena have been known to mankind since ancient times, after all, lightning was seen, and many ancients knew about magnets that attract certain metals. The Baghdad battery, invented 4000 years ago, is one of the evidence that long before our days, humanity used electricity, and apparently knew how it works. However, it is believed that until the beginning of the 19th century, electricity and magnetism were always considered separately from each other, accepted as unrelated phenomena, and belonged to different branches of physics.

The study of the magnetic field began in 1269, when the French scientist Peter Peregrine (Knight Pierre of Mericourt) marked 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.

Oersted, in his experiments, only in 1819 discovered the deflection of a compass needle located near a current-carrying conductor, and then the scientist concluded that there was some kind of relationship between electrical and magnetic phenomena.

5 years later, in 1824, Ampere was able to mathematically describe the interaction of a current-carrying conductor with a magnet, as well as the interaction of conductors with each other, so it appeared: “the force acting on a current-carrying conductor placed in a uniform magnetic field is proportional to the length of the conductor, the current strength and sine of the angle between the magnetic induction vector and the conductor."

Regarding the effect of a magnet on current, Ampere suggested that there are microscopic closed currents inside a permanent magnet, which create the magnetic field of the magnet, which interacts with the magnetic field of the current-carrying conductor.

For example, by moving a permanent magnet near a conductor, you can obtain a pulsating current in it, and by applying a pulsating current to one of the coils, on a common iron core with which the second coil is located, a pulsating current will also appear in the second coil.

33 years later, in 1864, Maxwell was able to mathematically generalize already known electrical and magnetic phenomena - he created electromagnetic field theory, according to which the electromagnetic field includes interconnected electric and magnetic fields. Thus, thanks to Maxwell, the scientific mathematical unification of the results of previous experiments in electrodynamics became possible.

The consequence of these important conclusions of Maxwell was his prediction that, in principle, any change in the electromagnetic field should generate electromagnetic waves, which propagate in space and in dielectric media with a certain finite speed, which depends on the magnetic and dielectric constant wave propagation environment.

For vacuum, this speed turned out to be equal to the speed of light, and therefore Maxwell suggested that light is also an electromagnetic wave, and this assumption was later confirmed (although long before Oersted’s experiments, Jung pointed out the wave nature of light).

Maxwell created the mathematical basis of electromagnetism, and in 1884 the famous Maxwell equations appeared in their modern form. In 1887, Hertz confirmed Maxwell's theory regarding: the receiver will record the electromagnetic waves sent by the transmitter.

Classical electrodynamics studies electromagnetic fields. Within the framework of quantum electrodynamics, electromagnetic radiation is considered as a stream of photons, in which the electromagnetic interaction is carried by carrier particles - photons - massless vector bosons, which can be represented as elementary quantum excitations of the electromagnetic field. Thus, a photon is a quantum of the electromagnetic field from the point of view of quantum electrodynamics.

Electromagnetic interaction seems today to be one of the fundamental interactions in physics, and the electromagnetic field is one of the fundamental physical fields along with gravitational and fermion fields.

Physical properties of the electromagnetic field

The presence of an electric or magnetic field, or both, in space can be judged by the force action exerted by the electromagnetic field on a charged particle or on a current.

The electric field acts on electric charges, both moving and stationary, with a certain force depending on the electric field strength at a given point in space in this moment time, and on the value of the test charge q.

Knowing the force (magnitude and direction) with which the electric field acts on the test charge, and knowing the magnitude of the charge, we can find the electric field strength E at a given point in space.

The electric field is created by electric charges, its lines of force begin on positive charges (conditionally flow from them), and end on negative charges (conditionally flow into them). Thus, electric charges are sources of electric field. Another source of electric field is a changing magnetic field, as shown mathematically Maxwell's equations.

The force acting on an electric charge from the electric field is part of the force acting on a given charge from the electromagnetic field.

A magnetic field is created by moving electric charges (currents) or time-varying electric fields (as evidenced by Maxwell's equations), and acts only on moving electric charges.

The force of the magnetic field on a moving charge is proportional to the magnetic field induction, the magnitude of the moving charge, the speed of its movement and the sine of the angle between the magnetic field induction vector B and the direction of the speed of the charge. This force is often called the Lorentz force, but is only the “magnetic” part of it.

In fact, the Lorentz force includes electric and magnetic components. A magnetic field is created by moving electric charges (currents), its lines of force are always closed and surround the current.

Convert magnetism into electricity

Electromagnetic induction

9th grade

Basic course

REPEAT

1. What is a magnetic field?

2. What are its main properties?

3. How is a magnetic field represented?

4. What relationship exists between electric current and magnetic field?

5. What are the magnetic field lines of a straight conductor carrying current?

6. What can be determined using the gimlet rule?

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

TEST

1. The magnetic field does not exist...

a) around the magnet b) around moving charged particles d) around a conductor with current d) around stationary 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) begin at the north pole of the magnet and end at the south pole. b) begin at the south pole of the magnet and end at the north pole. c) begin at the north pole of the magnet and go to infinity.

d) begin at the south pole of the magnet and 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. Select a picture depicting the magnetic field of such a current-carrying conductor.

Faraday's experiments (demonstration of experience)

Determine the pattern in the experiments.

Lenz's rule

• The induced current arising in a closed circuit with its magnetic field counteracts the change in the magnetic flux that causes it.

0), or decreases (ΔФ 3. Set the direction of the magnetic induction lines " of the magnetic field of the induced current. These lines should be, according to Lenz’s rule, directed opposite to the lines of magnetic induction B at ΔФ 0 and have the same direction as 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 magnetic induction lines  external magnetic field.

2. Find out whether the flux of the magnetic induction vector of this field through the surface limited 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 induced current. These lines should be, according to Lenz's rule, directed opposite to the lines of magnetic induction B at ΔФ 0 and have the same direction as them at ΔФ

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

Application of electromagnetic induction

Synchrophasotrons

Broadcasting

Magnetotherapy

Flow meters

Transformers

Generators

FIXING

• 1. Who was the first to produce electric current using a magnetic field?
• 1) Sh. Pendant 2) A. Ampere 3) M. Faraday 4) N. Tesla

• 2. What is the name of the phenomenon of the occurrence of 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 connected to galvanometers. A strip magnet is inserted into coil A, and the same strip magnet is removed from coil B. In which coil(s) will the galvanometer detect the induced current?

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

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

• 5. Once a strip magnet falls through a stationary metal ring with its south pole down, and a second time with its north pole down. Ring current

• 6. Two identical motionless metal rings lie on a horizontal table at a large distance from each other. Two bar magnets fall with their north poles down so that one hits the center of the first ring, and the second falls next to the second ring. Before the magnets strike, the 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 motionless metal rings lie on a horizontal table at a large distance from each other. A magnet suspended on a thread swings above the first one. Above the second ring, a magnet suspended by a spring swings up and down. The suspension point of the thread and spring is located 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 strip magnet so that it fits 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. The solid conductive ring is first shifted upward from the initial position relative to the strip magnet (see figure), then from the same initial position it is shifted downward.

• 10. The conductive ring with a cut is raised to the strip magnet (see figure), and the solid conductive ring is shifted to the right

• Induction current in the ring

• In this case, the induction current

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

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

Answers to the test

• 10-4

One of the first drawings of a magnetic field (René 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 (Knight Pierre of Mericourt) marked 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 experimentally tested this claim in 1785 and directly stated that the North and South Pole could not be separated. Based on this force existing between the poles, Simeon 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 occurs due to several pairs (north/south) of magnetic poles (dipoles).

Three discoveries in a row challenged this “basis of magnetism.” First, in 1819, Hans Christian Oersted discovered that 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 Savart discovered a law called the Biot-Savart-Laplace law in 1820, 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 of the Poisson model, he proposed the idea that magnetism is associated with constantly flowing current loops. This idea explained why magnetic charge could not be isolated. In addition, Ampere derived the law named after him, which, like the Biot-Savart-Laplace law, correctly described the magnetic field created by direct current, and the theorem on the circulation of the magnetic field 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 produces electricity. He created a definition of 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 Ampere's law. In doing so, he introduced the electromagnetic field vector potential, which was later shown to be equivalent to the basic mechanism proposed by Faraday. In 1850, Lord Kelvin, then known as William Thomson, identified the difference between the two magnetic fields as H And B. The first was applicable to the Poisson model, and the second to the Ampere induction model. Moreover, he outputted as 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 set of these equations was published in a paper 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 "Dynamic theory of the electromagnetic field" and determined that light is electromagnetic waves. Heinrich Hertz experimentally confirmed this fact in 1887. Although the force of the magnetic field of a moving vehicle implied in Ampere's law electric charge 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 establishing his theory of relativity, showed that electric and magnetic fields are part of the same phenomenon, considered in different systems reference - a thought experiment that ultimately helped Einstein develop the special theory of relativity. Finally, quantum mechanics was combined with electrodynamics to form quantum electrodynamics (QED).