After the discoveries of Oersted and Ampere, it became clear that electricity has magnetic force. Now it was necessary to confirm the influence magnetic phenomena to electric ones. Faraday brilliantly solved this problem.

Michael Faraday (1791-1867) was born in London, in one of its poorest parts. His father was a blacksmith, and his mother was the daughter of a tenant farmer. When Faraday reached school age, he was sent to elementary school. The course Faraday took here was very narrow and was limited only to learning to read, write and begin to count.

A few steps from the house in which the Faraday family lived, there was a bookshop, which was also a bookbinding establishment. This is where Faraday ended up after completing his course primary school, when the question arose about choosing a profession for him. Michael was only 13 years old at this time.

Already in his youth, when Faraday was just beginning his self-education, he sought to rely exclusively on facts and verify the messages of others with his own experiences. These aspirations dominated him all his life as the main features of his scientific activity

Physical and chemical experiments Faraday began to do this as a boy at his first acquaintance with physics and chemistry. One day Michael attended one of the lectures of Humphry Davy, the great English physicist. Faraday made a detailed note of the lecture, bound it and sent it to Davy. He was so impressed that he invited Faraday to work with him as a secretary. Soon Davy went on a trip to Europe and took Faraday with him. Over the course of two years, they visited the largest European universities.

Returning to London in 1815, Faraday began working as an assistant in one of the laboratories Royal Institution in London. At that time it was one of the best physics laboratories in the world. From 1816 to 1818, Faraday published a number of small notes and short memoirs on chemistry. Faraday's first work on physics dates back to 1818.

Based on the experiences of his predecessors and combining several of his own experiences, by September 1821 Michael published “The History of the Advances of Electromagnetism.” Already at this time he had compiled quite correct concept about the essence of the phenomenon of deflection of a magnetic needle under the influence of current. Having achieved this success, Faraday left his studies in the field of electricity for ten years, devoting himself to the study of a number of subjects of a different kind.

In 1823, Faraday made one of the most important discoveries in the field of physics - he was the first to liquefy gas, and at the same time established a simple but effective method for converting gases into liquid.

In 1824, Faraday made several discoveries in the field of physics. Among other things, he established the fact that light affects the color of glass, changing it.

The following year, Faraday again turned from physics to chemistry, and the result of his work in this area was the discovery of gasoline and sulfur-naphthalene acid.

In 1831, Faraday published a treatise on “A Special Kind of Optical Illusion,” which served as the basis for an excellent and curious optical projectile called the “chromotrope.” In the same year, another treatise by the scientist, “On Vibrating Plates,” was published.

Many of these works could themselves immortalize the name of their author. But the most important of scientific works Faraday's research is in the fields of electromagnetism and electrical induction. Strictly speaking, an important branch of physics that treats the phenomena of electromagnetism and inductive electricity, and which is currently of such enormous importance for technology, was created by Faraday out of nothing.

By the time Faraday finally devoted himself to research in the field of electricity, it was established that when under ordinary conditions The presence of an electrified body is enough for its influence to excite electricity in any other body.

At the same time, it was known that a wire through which current passes and which also represents an electrified body does not have any effect on other wires placed nearby. What caused this exception? This is the question that interested Faraday and the solution of which led him to the most important discoveries in the field of induction electricity.

As was his custom, Faraday began a series of experiments designed to clarify the essence of the matter. Faraday wound two insulated wires parallel to each other on the same wooden rolling pin. He connected the ends of one wire to a battery of ten cells, and the ends of the other to a sensitive galvanometer. When a current was passed through the first wire, Faraday turned all his attention to the galvanometer, expecting to notice by its vibrations the appearance of a current in the second wire. However, nothing of the kind happened: the galvanometer remained calm. Faraday decided to increase the current strength and introduced 120 galvanic cells. The result was the same. Faraday repeated this experiment dozens of times and still with the same success. Anyone else in his place would have left the experiments convinced that the current passing through a wire has no effect on the neighboring wire. But Faraday always tried to extract from his experiments and observations everything that they could give, and therefore, without receiving direct action on a wire connected to a galvanometer, I began to look for side effects.

He immediately noticed that the galvanometer, remaining completely calm during the entire passage of current, began to oscillate when the circuit itself was closed and when it was opened. It turned out that at the moment when a current is passed into the first wire, and also when this transmission stops, a current is also excited in the second wire, which in the first case has the opposite direction to the first current and the same with it in the second case and lasts only one instant. Secondary instantaneous currents caused by the influence of primary ones were called inductive by Faraday, and this name has remained with them to this day.

Being instantaneous, instantly disappearing after their appearance, inductive currents would have no practical significance if Faraday had not found a way, with the help of an ingenious device (a commutator), to constantly interrupt and again conduct the primary current coming from the battery along the first wire, thanks to which the second wire is continuously excited by more and more inductive currents, thus becoming constant. So it was found new source electrical energy, in addition to previously known (friction and chemical processes), - induction, and the new kind This energy is inductive electricity.

Continuing his experiments, Faraday further discovered that simply bringing a wire twisted into a closed curve close to another along which it runs galvanic current, in order to excite in the neutral wire an inductive current in the direction opposite to the galvanic current, that the removal of the neutral wire again excites in it an inductive current of the same direction as the galvanic current running along the stationary wire, and that, finally, these inductive currents are excited only during approach and departure wires to the conductor of galvanic current, and without this movement the currents are not excited, no matter how close the wires are to each other. Thus, a new phenomenon was discovered, similar to the above-described phenomenon of induction when the galvanic current closes and stops.

These discoveries in turn gave rise to new ones. If it is possible to cause an inductive current by short-circuiting and stopping the galvanic current, then wouldn’t the same result be obtained by magnetizing and demagnetizing iron? The work of Oersted and Ampere had already established the relationship between magnetism and electricity. It was known that iron becomes a magnet when an insulated wire is wound around it and a galvanic current passes through the latter, and that magnetic properties of this iron stop as soon as the current stops. Based on this, Faraday came up with this kind of experiment: two insulated wires were wound around an iron ring; with one wire wrapped around one half of the ring, and the other around the other.

A current was passed through one wire from galvanic battery, and the ends of the other were connected to a galvanometer. And so, when the current closed or stopped and when, consequently, the iron ring was magnetized or demagnetized, the galvanometer needle quickly oscillated and then quickly stopped, that is, the same instantaneous inductive currents were excited in the neutral wire - this time: already under the influence of magnetism. Thus, here for the first time magnetism was converted into electricity.

Having received these results, Faraday decided to diversify his experiments. Instead of an iron ring, he began to use an iron strip. Instead of exciting magnetism in iron by galvanic current, he magnetized the iron by touching it to a permanent steel magnet. The result was the same: always in the wire wrapped around the iron! a current was excited at the moment of magnetization and demagnetization of iron. Then Faraday introduced a steel magnet into the wire spiral - the approach and removal of the latter caused induced currents in the wire. In a word, magnetism, in the sense of exciting induction currents, acted in exactly the same way as galvanic current.

At that time, physicists were intensely interested in one thing mysterious phenomenon, discovered in 1824 by Arago and found no explanation, despite; the fact that this explanation was intensely sought by such outstanding scientists of the time as Arago himself, Ampere, Poisson, Babage and Herschel. Case I was as follows. A magnetic needle, hanging freely, quickly comes to rest if a circle of non-magnetic metal is placed under it; if then the circle is brought into rotational movement, the magnetic needle begins to move behind it. In a calm state, it was impossible to discover the slightest attraction or repulsion between the 5th circle and the arrow, while the same circle, in motion, pulled behind it not only a light arrow, but also a heavy magnet. This truly miraculous phenomenon seemed to the scientists of that time a mysterious mystery, something beyond the bounds of the natural. Faraday, based on the above data, made the assumption that a circle of non-magnetic metal, under the influence of a magnet, during rotation is run around by inductive currents, which affect the magnetic needle and drag it along the magnet. And indeed, by introducing the edge of a circle between the poles of a large horseshoe magnet and connecting the center and edge of the circle with a galvanometer with a wire, Faraday obtained a constant electric current when the circle rotated.

Following this, Faraday focused on another phenomenon that was then arousing general curiosity. As you know, if you sprinkle iron filings on a magnet, they group along certain lines called magnetic curves. Faraday, drawing attention to this phenomenon, gave magnetic curves the name “lines of magnetic force” in 1831, which later came into general use. The study of these “lines” led Faraday to a new discovery; it turned out that in order to excite induced currents, the source’s approach and distance from the magnetic pole are not necessary. To excite currents, it is enough to cross the lines of magnetic force in a known manner.

Further work Faraday's efforts in the mentioned direction acquired, from a contemporary point of view, the character of something absolutely miraculous. At the beginning of 1832, he demonstrated a device in which inductive currents were excited without the help of a magnet or galvanic current.

The device consisted of an iron strip placed in a wire coil.

This device, under ordinary conditions, did not give the slightest sign of the appearance of currents in it; but as soon as it was given a direction corresponding to the direction of the magnetic needle, a current was excited in the wire. Then Faraday gave the position of the magnetic needle to one coil and then introduced an iron strip into it: the current was again excited. The reason that caused the current in these cases was earthly magnetism, which caused inductive currents like an ordinary magnet or galvanic current. To more clearly show and prove this, Faraday undertook another experiment, which fully confirmed his considerations. He reasoned that if a circle of non-magnetic metal, such as copper, rotating in a position in which it intersects the lines of magnetic force of an adjacent magnet, produces an inductive current, then the same circle, rotating in the absence of a magnet, but in a position in which the circle will cross the lines of earthly magnetism, must also give an inductive current. And indeed, a copper circle rotated in a horizontal plane produced an inductive current that produced a noticeable deflection of the galvanometer needle.

Faraday ended his series of studies in the field of electrical induction with the discovery, made in 1835, of the “inductive influence of current on itself.” He found out that when a galvanic current is closed or opened, instantaneous inductive currents are excited in the wire itself, which serves as a conductor for this current.

Russian physicist Emil Khristoforovich Lenz (1804-1861) gave a rule for determining the direction induced current.

“The induction current is always directed in such a way that the magnetic field it creates complicates or inhibits the movement causing induction,” notes A.A. Korobko-Stefanov in his article about electromagnetic induction. - For example, when a coil approaches a magnet, the resulting induced current has such a direction that the magnetic field it creates will be opposite to the magnetic field of the magnet. As a result, repulsive forces arise between the coil and the magnet.

Lenz's rule follows from the law of conservation and transformation of energy. If induced currents accelerated the motion that caused them, then work would be created out of nothing. The coil itself, after a slight push, would rush towards the magnet, and at the same time the induction current would release heat in it. In reality, the induced current is created due to the work of bringing the magnet and the coil closer together.

Why does induced current occur? A deep explanation of the phenomenon of electromagnetic induction was given by the English physicist James Clerk Maxwell, the creator of the complete mathematical theory electro magnetic field.

To better understand the essence of the matter, consider a very simple experiment. Let the coil consist of one turn of wire and be penetrated by an alternating magnetic field perpendicular to the plane of the turn. An induced current naturally arises in the coil. Maxwell interpreted this experiment exceptionally boldly and unexpectedly. When a magnetic field changes in space, according to Maxwell, a process arises for which the presence of a wire coil has no significance. The main thing here is the emergence of closed ring lines electric field, covering a changing magnetic field.

Under the influence of the resulting electric field, electrons begin to move, and an electric current arises in the coil. A coil is simply a device that allows you to detect electric field. The essence of the phenomenon of electromagnetic induction is that an alternating magnetic field always generates an electric field with closed lines of force in the surrounding space. Such a field is called a vortex field.”

Research in the field of induction produced by earthly magnetism gave Faraday the opportunity to express the idea of ​​​​a telegraph back in 1832, which then formed the basis of this invention.

In general, it is not for nothing that the discovery of electromagnetic induction is considered one of the most outstanding discoveries of the 19th century - the work of millions of electric motors and generators is based on this phenomenon electric current worldwide...

After the discoveries of Oersted and Ampere, it became clear that electricity has magnetic force. Now it was necessary to confirm the influence of magnetic phenomena on electrical ones. Faraday brilliantly solved this problem.

Michael Faraday (1791-1867) was born in London, in one of its poorest parts. His father was a blacksmith, and his mother was the daughter of a tenant farmer. When Faraday reached school age, he was sent to primary school. The course Faraday took here was very narrow and was limited only to learning to read, write and begin to count.

A few steps from the house in which the Faraday family lived, there was a bookshop, which was also a bookbinding establishment. This is where Faraday ended up, having completed his primary school course, when the question arose about choosing a profession for him. Michael was only 13 years old at this time. Already in his youth, when Faraday was just beginning his self-education, he sought to rely exclusively on facts and verify the messages of others with his own experiences.

These aspirations dominated him all his life as the main features of his scientific activity. Faraday began to carry out physical and chemical experiments as a boy at his first acquaintance with physics and chemistry. One day Michael attended one of the lectures of Humphry Davy, the great English physicist.

Faraday made a detailed note of the lecture, bound it and sent it to Davy. He was so impressed that he invited Faraday to work with him as a secretary. Soon Davy went on a trip to Europe and took Faraday with him. Over the course of two years, they visited the largest European universities.

Returning to London in 1815, Faraday began working as an assistant in one of the laboratories of the Royal Institution in London. At that time it was one of the best physics laboratories in the world. From 1816 to 1818, Faraday published a number of small notes and short memoirs on chemistry. Faraday's first work on physics dates back to 1818.

Based on the experiences of his predecessors and combining several of his own experiences, by September 1821 Michael published “The History of the Advances of Electromagnetism.” Already at this time, he formed a completely correct concept of the essence of the phenomenon of deflection of a magnetic needle under the influence of current.

Having achieved this success, Faraday left his studies in the field of electricity for ten years, devoting himself to the study of a number of subjects of a different kind. In 1823, Faraday made one of the most important discoveries in the field of physics - he was the first to liquefy gas, and at the same time established a simple but effective method for converting gases into liquid. In 1824, Faraday made several discoveries in the field of physics.

Among other things, he established the fact that light affects the color of glass, changing it. The following year, Faraday again turned from physics to chemistry, and the result of his work in this area was the discovery of gasoline and sulfur-naphthalene acid.

In 1831, Faraday published a treatise “On a Special Kind of Optical Illusion,” which served as the basis for an excellent and curious optical projectile called the “chromotrope.” In the same year, another treatise by the scientist, “On Vibrating Plates,” was published. Many of these works could themselves immortalize the name of their author. But the most important of Faraday's scientific works are his studies in the field of electromagnetism and electrical induction.

Strictly speaking, an important branch of physics that treats the phenomena of electromagnetism and inductive electricity, and which is currently of such enormous importance for technology, was created by Faraday out of nothing.

By the time Faraday finally devoted himself to research in the field of electricity, it was established that under ordinary conditions the presence of an electrified body is sufficient for its influence to excite electricity in any other body. At the same time, it was known that a wire through which current passes and which also represents an electrified body does not have any effect on other wires placed nearby.

What caused this exception? This is the question that interested Faraday and the solution of which led him to the most important discoveries in the field of induction electricity. As was his custom, Faraday began a series of experiments designed to clarify the essence of the matter.

Faraday wound two insulated wires parallel to each other on the same wooden rolling pin. He connected the ends of one wire to a battery of ten cells, and the ends of the other to a sensitive galvanometer. When current was passed through the first wire,

Faraday turned all his attention to the galvanometer, expecting to notice from its vibrations the appearance of a current in the second wire. However, nothing of the kind happened: the galvanometer remained calm. Faraday decided to increase the current strength and introduced 120 galvanic elements into the circuit. The result was the same. Faraday repeated this experiment dozens of times and still with the same success.

Anyone else in his place would have left the experiments convinced that the current passing through a wire has no effect on the neighboring wire. But Faraday always tried to extract from his experiments and observations everything that they could give, and therefore, not receiving a direct effect on the wire connected to the galvanometer, he began to look for side effects.

He immediately noticed that the galvanometer, remaining completely calm during the entire passage of current, begins to oscillate when the circuit itself is closed and when it is opened. It turned out that at the moment when a current is passed into the first wire, and also when this transmission stops, during the second wire is also excited by a current, which in the first case has the opposite direction to the first current and the same with it in the second case and lasts only one instant.

These secondary instantaneous currents, caused by the influence of the primary ones, were called inductive by Faraday, and this name has remained with them to this day. Being instantaneous, instantly disappearing after their appearance, inductive currents would have no practical significance if Faraday had not found a way, with the help of an ingenious device (a commutator), to constantly interrupt and again conduct the primary current coming from the battery along the first wire, thanks to which the second wire is continuously excited by more and more new inductive currents, thus becoming constant. Thus, a new source of electrical energy was found, in addition to the previously known ones (friction and chemical processes), - induction, and a new type of this energy - inductive electricity.

Continuing his experiments, Faraday further discovered that simply bringing a wire twisted into a closed curve close to another through which a galvanic current flows is sufficient to excite an inductive current in the neutral wire in the direction opposite to the galvanic current, and that removing the neutral wire again excites an inductive current in it. the current is already in the same direction as the galvanic current flowing along a stationary wire, and that, finally, these inductive currents are excited only during the approach and removal of the wire to the conductor of the galvanic current, and without this movement the currents are not excited, no matter how close the wires are to each other .

Thus, a new phenomenon was discovered, similar to the above-described phenomenon of induction when the galvanic current closes and stops. These discoveries in turn gave rise to new ones. If it is possible to cause an inductive current by short-circuiting and stopping the galvanic current, then wouldn’t the same result be obtained by magnetizing and demagnetizing iron?

The work of Oersted and Ampere had already established the relationship between magnetism and electricity. It was known that iron becomes a magnet when an insulated wire is wound around it and a galvanic current passes through it, and that the magnetic properties of this iron cease as soon as the current stops.

Based on this, Faraday came up with this kind of experiment: two insulated wires were wound around an iron ring; with one wire wrapped around one half of the ring, and the other around the other. Current from a galvanic battery was passed through one wire, and the ends of the other were connected to a galvanometer. And so, when the current closed or stopped and when, consequently, the iron ring was magnetized or demagnetized, the galvanometer needle quickly oscillated and then quickly stopped, that is, the same instantaneous inductive currents were excited in the neutral wire - this time: already under the influence of magnetism.

Thus, here for the first time magnetism was converted into electricity. Having received these results, Faraday decided to diversify his experiments. Instead of an iron ring, he began to use an iron strip. Instead of exciting magnetism in iron by galvanic current, he magnetized the iron by touching it to a permanent steel magnet. The result was the same: always in the wire wrapped around the iron! a current was excited at the moment of magnetization and demagnetization of iron.

Then Faraday introduced a steel magnet into the wire spiral - the approach and removal of the latter caused induced currents in the wire. In a word, magnetism, in the sense of exciting induction currents, acted in exactly the same way as galvanic current.

At that time, physicists were intensely interested in one mysterious phenomenon, discovered in 1824 by Arago and which could not be explained, despite; the fact that this explanation was intensely sought by such outstanding scientists of the time as Arago himself, Ampere, Poisson, Babage and Herschel.

The point was as follows. A magnetic needle, hanging freely, quickly comes to rest if a circle of non-magnetic metal is placed under it; If the circle is then put into rotation, the magnetic needle begins to move behind it.

In a calm state, it was impossible to discover the slightest attraction or repulsion between the circle and the arrow, while the same circle, in motion, pulled behind it not only a light arrow, but also a heavy magnet. This truly miraculous phenomenon seemed to the scientists of that time a mysterious mystery, something beyond the bounds of the natural.

Faraday, based on the above data, made the assumption that a circle of non-magnetic metal, under the influence of a magnet, during rotation is run around by inductive currents, which affect the magnetic needle and drag it along the magnet.

And indeed, by introducing the edge of a circle between the poles of a large horseshoe magnet and connecting the center and edge of the circle with a galvanometer with a wire, Faraday obtained a constant electric current when the circle rotated.

Following this, Faraday focused on another phenomenon that was then arousing general curiosity. As you know, if you sprinkle iron filings on a magnet, they group along certain lines called magnetic curves. Faraday, drawing attention to this phenomenon, gave the basis in 1831 to magnetic curves the name “lines of magnetic force,” which then came into general use.

The study of these “lines” led Faraday to a new discovery; it turned out that in order to excite induced currents, the source’s approach and distance from the magnetic pole are not necessary. To excite currents, it is enough to cross the lines of magnetic force in a known manner.

Faraday's further work in the mentioned direction acquired, from a contemporary point of view, the character of something absolutely miraculous. At the beginning of 1832, he demonstrated a device in which inductive currents were excited without the help of a magnet or galvanic current.

The device consisted of an iron strip placed in a wire coil. This device, under ordinary conditions, did not give the slightest sign of the appearance of currents in it; but as soon as it was given a direction corresponding to the direction of the magnetic needle, a current was excited in the wire.

Then Faraday gave the position of the magnetic needle to one coil and then introduced an iron strip into it: the current was again excited. The reason that caused the current in these cases was earthly magnetism, which caused inductive currents like an ordinary magnet or galvanic current. To more clearly show and prove this, Faraday undertook another experiment, which fully confirmed his considerations.

He reasoned that if a circle of non-magnetic metal, such as copper, rotating in a position in which it intersects the lines of magnetic force of an adjacent magnet, produces an inductive current, then the same circle, rotating in the absence of a magnet, but in a position in which the circle will cross the lines of earthly magnetism, must also give an inductive current.

And indeed, a copper circle rotated in a horizontal plane produced an inductive current that produced a noticeable deflection of the galvanometer needle. Faraday ended his series of studies in the field of electrical induction with the discovery, made in 1835, of the “inductive influence of current on itself.”

He found out that when a galvanic current is closed or opened, instantaneous inductive currents are excited in the wire itself, which serves as a conductor for this current.

Russian physicist Emil Khristoforovich Lenz (1804-1861) gave a rule for determining the direction of induction current. “The induction current is always directed in such a way that the magnetic field it creates complicates or inhibits the movement causing induction,” notes A.A. Korobko-Stefanov in his article on electromagnetic induction. - For example, when a coil approaches a magnet, the resulting induced current has such a direction that the magnetic field it creates will be opposite to the magnetic field of the magnet. As a result, repulsive forces arise between the coil and the magnet.

Lenz's rule follows from the law of conservation and transformation of energy. If induced currents accelerated the motion that caused them, then work would be created out of nothing. The coil itself, after a slight push, would rush towards the magnet, and at the same time the induction current would release heat in it. In reality, the induced current is created due to the work of bringing the magnet and the coil closer together.

Why does induced current occur? A deep explanation of the phenomenon of electromagnetic induction was given by the English physicist James Clerk Maxwell, the creator of a complete mathematical theory of the electromagnetic field.

To better understand the essence of the matter, consider a very simple experiment. Let the coil consist of one turn of wire and be penetrated by an alternating magnetic field perpendicular to the plane of the turn. An induced current naturally arises in the coil. Maxwell interpreted this experiment exceptionally boldly and unexpectedly.

When a magnetic field changes in space, according to Maxwell, a process arises for which the presence of a wire coil has no significance. The main thing here is the emergence of closed annular electric field lines, covering a changing magnetic field. Under the influence of the resulting electric field, electrons begin to move, and an electric current arises in the coil. A coil is simply a device that detects an electric field.

The essence of the phenomenon of electromagnetic induction is that an alternating magnetic field always generates an electric field with closed lines of force in the surrounding space. Such a field is called a vortex field.”

Research in the field of induction produced by earthly magnetism gave Faraday the opportunity to express the idea of ​​​​a telegraph back in 1832, which then formed the basis of this invention. In general, it is not for nothing that the discovery of electromagnetic induction is considered one of the most outstanding discoveries of the 19th century - the work of millions of electric motors and electric current generators all over the world is based on this phenomenon...

Source of information: Samin D.K. “One hundred great scientific discoveries"., M.: "Veche", 2002.

Lesson topic:

Discovery of electromagnetic induction. Magnetic flux.

Target: To familiarize students with the phenomenon of electromagnetic induction.

During the classes

I. Organizational moment

II. Updating knowledge.

1. Frontal survey.

• What is Ampere's hypothesis?
• What is magnetic permeability?
• What substances are called para- and diamagnetic?
• What are ferrites?
• Where are ferrites used?
• How do we know that there is a magnetic field around the Earth?
• Where are the Earth's North and South magnetic poles?
• What processes occur in the Earth's magnetosphere?
• What is the reason for the existence of a magnetic field near the Earth?

2. Analysis of experiments.

Experiment 1

The magnetic needle on the stand was brought to the lower and then to the upper end of the tripod. Why does the arrow turn to the lower end of the tripod from either side with the south pole, and to the upper end with the north end?(All iron objects are in the Earth’s magnetic field. Under the influence of this field they are magnetized, and Bottom part the object is discovered by the northern magnetic pole, and the top one is southern.)

Experiment 2

In a large cork plug, make a small groove for a piece of wire. Place the cork in water, and place the wire on top, placing it parallel. In this case, the wire together with the plug is rotated and installed along the meridian. Why?(The wire has been magnetized and is installed in the Earth's field like a magnetic needle.)

III. Learning new material

Between moving electric charges magnetic forces act. Magnetic interactions are described based on the idea of ​​a magnetic field that exists around moving electric charges. Electric and magnetic fields are generated by the same sources - electric charges. It can be assumed that there is a connection between them.

In 1831, M. Faraday confirmed this experimentally. He discovered the phenomenon of electromagnetic induction (slides 1,2).

Experiment 1

We connect the galvanometer to the coil, and we will move it out of it permanent magnet. We observe the deflection of the galvanometer needle, a current (induction) has appeared (slide 3).

Current in a conductor occurs when the conductor is in the area of ​​action of an alternating magnetic field (slide 4-7).

Faraday represented the alternating magnetic field as a change in the number power lines, penetrating the surface limited by this contour. This number depends on induction IN magnetic field, from the area of ​​the circuit S and its orientation in a given field.

Ф=BS cos a - magnetic flux.

F [Wb] Weber (slide 8)

The induced current can have different directions, which depend on whether the magnetic flux passing through the circuit decreases or increases. The rule for determining the direction of the induction current was formulated in 1833. E. X. Lentz.

Experiment 2

We slide a permanent magnet into a lightweight aluminum ring. The ring is repelled from it, and when extended, it is attracted to the magnet.

The result does not depend on the polarity of the magnet. Repulsion and attraction are explained by the appearance of an induction current in it.

When a magnet is pushed in, the magnetic flux through the ring increases: the repulsion of the ring shows that the induced current in it has a direction in which the induction vector of its magnetic field is opposite in direction to the induction vector of the external magnetic field.

Lenz's rule:

The induced current always has a direction such that its magnetic field prevents any changes in the magnetic flux that cause the appearance of the induced current(slide 9).

IV. Conducting laboratory work

Laboratory work on the topic “Experimental verification of Lenz’s rule”

Devices and materials:milliammeter, coil-coil, arc-shaped magnet.

Progress

1. Prepare a table.

Answer:

Next important step In the development of electrodynamics after Ampere's experiments, there was the discovery of the phenomenon of electromagnetic induction. The phenomenon of electromagnetic induction was discovered by the English physicist Michael Faraday (1791 - 1867).

Faraday, while still a young scientist, like Oersted, thought that all the forces of nature are interconnected and, moreover, that they are capable of transforming into each other. It is interesting that Faraday expressed this idea even before the establishment of the law of conservation and transformation of energy. Faraday knew about Ampere's discovery, that he, figuratively speaking, converted electricity into magnetism. Reflecting on this discovery, Faraday came to the idea that if “electricity creates magnetism,” then vice versa, “magnetism must create electricity.” And back in 1823, he wrote in his diary: “Convert magnetism into electricity.” For eight years, Faraday worked to solve the problem. For a long time he was haunted by failures, and finally, in 1831, he solved it - he discovered the phenomenon of electromagnetic induction.

firstly, Faraday discovered the phenomenon of electromagnetic induction for the case when the coils are wound on the same drum. If an electric current appears or disappears in one coil as a result of connecting or disconnecting a galvanic battery from it, then a short-term current arises in the other coil at that moment. This current is detected by a galvanometer which is connected to the second coil.

Then Faraday also established the presence of an induced current in the coil when a coil in which an electric current flowed was brought closer to it or moved away from it.

finally, the third case of electromagnetic induction, which Faraday discovered, was that a current appeared in the coil when a magnet was introduced or removed from it.

Faraday's discovery attracted the attention of many physicists, who also began to study the features of the phenomenon of electromagnetic induction. The next task was to establish the general law of electromagnetic induction. It was necessary to find out how and on what the strength of the induction current in a conductor depends or on what the value of the electromotive force of induction in a conductor in which an electric current is induced depends.

This task proved difficult. It was completely solved by Faraday and Maxwell later within the framework of the doctrine of the electromagnetic field they developed. But physicists also tried to solve it, adhering to the theory of long-range action in the study of electrical and magnetic phenomena, which was common at that time.

These scientists managed to do something. At the same time, they were helped by the rule discovered by the St. Petersburg academician Emilius Christianovich Lenz (1804 - 1865) for finding the direction of the induction current in different cases electromagnetic induction. Lenz formulated it as follows: “If a metal conductor moves in the vicinity of a galvanic current or magnet, then a galvanic current is excited in it in such a direction that if the conductor were stationary, the current could cause it to move in the opposite direction; it is assumed that a conductor at rest can only move in the direction of movement or in the opposite direction.”

This rule is very convenient for determining the direction of the induced current. We still use it now, only now it is formulated somewhat differently, with the burial of the concept of electromagnetic induction, which Lenz did not use.

But historically, the main significance of Lenz’s rule was that it gave rise to the idea of ​​how to approach finding the law of electromagnetic induction. The fact is that the atom rule establishes a connection between electromagnetic induction and the phenomenon of interaction of currents. The question of the interaction of currents was already resolved by Ampere. Therefore, the establishment of this connection at first made it possible to determine the expression of the electromotive force of induction in a conductor for a number of special cases.

IN general view the law of electromagnetic induction, as we said, was established by Faraday and Maxwell.

Electromagnetic induction is the phenomenon of the occurrence of electric current in a closed circuit when the magnetic flux passing through it changes.

Electromagnetic induction was discovered by Michael Faraday on August 29, 1831. He discovered that the electromotive force arising in a closed conducting circuit is proportional to the rate of change of the magnetic flux through the surface bounded by this circuit. The magnitude of the electromotive force (EMF) does not depend on what is causing the flux change - a change in the magnetic field itself or the movement of the circuit (or part of it) in the magnetic field. The electric current caused by this emf is called induced current.

Self-induction is the occurrence of induced emf in a closed conducting circuit when the current flowing through the circuit changes.

When the current in a circuit changes, the magnetic flux through the surface bounded by this circuit also changes proportionally. A change in this magnetic flux, due to the law of electromagnetic induction, leads to the excitation of an inductive emf in this circuit.

This phenomenon is called self-induction. (The concept is related to the concept of mutual induction, being, as it were, a special case of it).

Direction Self-induced emf It always turns out that when the current in the circuit increases, the EMF of self-induction prevents this increase (directed against the current), and when the current decreases, it decreases (co-directed with the current). This property of self-induction emf is similar to the force of inertia.

The creation of the first relay was preceded by the invention in 1824 by the Englishman Sturgeon of an electromagnet - a device that converts the input electric current of a wire coil wound on an iron core into a magnetic field formed inside and outside this core. The magnetic field was recorded (detected) by its effect on the ferromagnetic material located near the core. This material was attracted to the core of the electromagnet.

Subsequently, the effect of converting the energy of electric current into mechanical energy the meaningful movement of external ferromagnetic material (anchor) formed the basis of various electromechanical devices for telecommunications (telegraphy and telephony), electrical engineering, and power engineering. One of the first such devices was an electromagnetic relay, invented by the American J. Henry in 1831.

Today we will talk about the phenomenon of electromagnetic induction. Let us reveal why this phenomenon was discovered and what benefits it brought.

Silk

People have always strived to live better. Some might think that this is a reason to accuse humanity of greed. But often we're talking about about acquiring basic household conveniences.

IN medieval Europe knew how to make wool, cotton and linen fabrics. And even at that time, people suffered from an excess of fleas and lice. At the same time, Chinese civilization has already learned how to masterfully weave silk. Clothes made from it kept bloodsuckers away from human skin. The insects' legs slid over the smooth fabric, and the lice fell off. Therefore, the Europeans wanted to dress in silk at all costs. And the merchants thought that this was another opportunity to get rich. Therefore, the Great Silk Road was built.

This was the only way to deliver the desired fabric to suffering Europe. And so many people were involved in the process that cities arose as a result, empires fought over the right to levy taxes, and some parts of the path are still the most convenient way get to the right place.

Compass and star

Mountains and deserts stood in the way of caravans with silk. It happened that the character of the area remained the same for weeks and months. Steppe dunes gave way to similar hills, one pass followed another. And people had to somehow navigate in order to deliver their valuable cargo.

The stars were the first to come to the rescue. Knowing what day it was today and what constellations to expect, an experienced traveler could always determine where south was, where east was, and where to go. But there were always not enough people with sufficient knowledge. And they didn’t know how to count time accurately back then. Sunset, sunrise - that's all the landmarks. And a snow or sandstorm, cloudy weather excluded even the possibility of seeing the polar star.

Then people (probably the ancient Chinese, but scientists are still arguing about this) realized that one mineral is always located in a certain way in relation to the cardinal points. This property was used to create the first compass. The discovery of the phenomenon of electromagnetic induction was a long way off, but a start had been made.

From compass to magnet

The name “magnet” itself goes back to the toponym. The first compasses were probably made from ore mined in the hills of Magnesia. This region is located in Asia Minor. And the magnets looked like black stones.

The first compasses were very primitive. Water was poured into a bowl or other container, and a thin disk of floating material was placed on top. And a magnetized arrow was placed in the center of the disk. One end always pointed to the north, the other to the south.

It's hard to imagine that the caravan saved water for the compass while people were dying of thirst. But do not lose direction and allow people, animals and goods to reach safe place was more important than several separate lives.

The compasses made many journeys and encountered various natural phenomena. It is not surprising that the phenomenon of electromagnetic induction was discovered in Europe, although magnetic ore was originally mined in Asia. In such an intricate way, the desire of European residents to sleep more comfortably led to the most important discovery physics.

Magnetic or electric?

In the early nineteenth century, scientists figured out how to produce direct current. The first primitive battery was created. It was enough to send a stream of electrons through metal conductors. Thanks to the first source of electricity, a number of discoveries were made.

In 1820, the Danish scientist Hans Christian Oersted found out that the magnetic needle deviates near a conductor connected to the network. The positive pole of the compass is always located in a certain way in relation to the direction of the current. The scientist carried out experiments in all possible geometries: the conductor was above or below the arrow, they were located parallel or perpendicular. The result was always the same: the switched on current set the magnet in motion. This was how the discovery of the phenomenon of electromagnetic induction was anticipated.

But the idea of ​​scientists must be confirmed by experiment. Immediately after Oersted's experiment, the English physicist Michael Faraday asked the question: “Do the magnetic and electric fields simply influence each other, or are they more closely related?” The scientist was the first to test the assumption that if an electric field causes a magnetized object to deviate, then the magnet should generate a current.

The experimental design is simple. Now any schoolchild can repeat it. A thin metal wire was coiled into the shape of a spring. Its ends were connected to a device that recorded the current. When a magnet moved near the coil, the device's arrow showed the voltage of the electric field. Thus, Faraday's law of electromagnetic induction was derived.

Continuation of experiments

But that's not all the scientist did. Since the magnetic and electric fields are closely related, it was necessary to find out how much.

To do this, Faraday supplied current to one winding and pushed it inside another similar winding with a radius larger than the first. Once again electricity was induced. Thus, the scientist proved: a moving charge generates both electric and magnetic fields at the same time.

It is worth emphasizing that we are talking about the movement of a magnet or magnetic field inside a closed loop of a spring. That is, the flow must change all the time. If this does not happen, no current is generated.

Formula

Faraday's law for electromagnetic induction is expressed by the formula

Let's decipher the symbols.

ε stands for emf or electromotive force. This quantity is scalar (that is, not vector), and it shows the work that certain forces or laws of nature apply to create a current. It should be noted that the work must necessarily be performed by non-electrical phenomena.

Φ is the magnetic flux through a closed loop. This value is the product of two others: the magnitude of the magnetic induction vector B and the area of ​​the closed loop. If the magnetic field does not act strictly perpendicular to the contour, then the cosine of the angle between vector B and the normal to the surface is added to the product.

Consequences of the discovery

This law was followed by others. Subsequent scientists established the dependence of electric current intensity on power and resistance on conductor material. New properties were studied and incredible alloys were created. Finally, humanity deciphered the structure of the atom, delved into the mystery of the birth and death of stars, and revealed the genome of living beings.

And all these achievements required a huge amount of resources, and, above all, electricity. Any production or large Scientific research were carried out where three components were available: qualified personnel, the material itself with which to work, and cheap electricity.

And this was possible where the forces of nature could impart a large torque to the rotor: rivers with a large elevation difference, valleys with strong winds, faults with excess geomagnetic energy.

I wonder what modern way obtaining electricity is not fundamentally different from Faraday's experiments. The magnetic rotor rotates very quickly inside big reel wire. The magnetic field in the winding changes all the time and an electric current is generated.

Of course, selected and best material for magnet and conductors, and the technology of the whole process is completely different. But the point is one thing: the principle discovered in the simplest system is used.