Magnetic field and its graphic representation. Inhomogeneous and homogeneous magnetic field (Eryutkin E.S.). Presentation - test in physics "Electromagnetic field The figure shows the magnetic lines of the field created
From the 8th grade physics course, you know that a magnetic field is generated by an electric current. It exists, for example, around a metal conductor with current. In this case, the current is created by electrons moving in a direction along the conductor. A magnetic field also arises when the current passes through an electrolyte solution, where charge carriers are positively and negatively charged ions moving towards each other.
Since electric current is the directed movement of charged particles, we can say that the magnetic field is created by moving charged particles, both positive and negative.
Recall that, according to Ampere's hypothesis, ring currents arise in atoms and molecules of matter as a result of the movement of electrons.
Figure 85 shows that in permanent magnets these elementary ring currents are oriented in the same way. Therefore, the magnetic fields formed around each such current have the same directions. These fields reinforce each other, creating a field in and around the magnet.
Rice. 85. Illustration of Ampère's hypothesis
For a visual presentation magnetic field magnetic lines are used (they are also called magnetic field lines) 1. Recall that magnetic lines are imaginary lines along which small magnetic needles placed in a magnetic field would be located.
A magnetic line can be drawn through any point in space where a magnetic field exists.
Figure 86 shows that a magnetic line (both rectilinear and curvilinear) is drawn so that at any point of this line the tangent to it coincides with the axis of the magnetic needle placed at this point.
Rice. 86. At any point of the magnetic line, the tangent to it coincides with the axis of the magnetic needle placed at this point
Magnetic lines are closed. For example, the picture of the magnetic lines of a straight conductor with current is a concentric circle lying in a plane perpendicular to the conductor.
Figure 86 shows that the direction of the magnetic line at any of its points is conditionally taken as the direction that indicates North Pole a magnetic needle placed at that point.
In those regions of space where the magnetic field is stronger, the magnetic lines are drawn closer to each other, i.e., thicker than in those places where the field is weaker. For example, the field shown in Figure 87 is stronger on the left than on the right.
Rice. 87. Magnetic lines are closer to each other in those places where the magnetic field is stronger
Thus, according to the pattern of magnetic lines, one can judge not only the direction, but also the magnitude of the magnetic field (i.e., at what points in space the field acts on the magnetic needle with greater force, and at which - with less).
Consider the picture of the magnetic field lines of a permanent bar magnet (Fig. 88). From the 8th grade physics course, you know that magnetic lines come out of the north pole of the magnet and enter the south. Inside the magnet, they are directed from the south pole to the north. Magnetic lines have neither beginning nor end: they are either closed or, as middle line in the figure, go from infinity to infinity.
Rice. 88. Picture of the magnetic field of a permanent bar magnet
Rice. 89. Magnetic lines of a magnetic field created by a rectilinear conductor with current
Outside the magnet, magnetic lines are densest at its poles. This means that the field is strongest near the poles, and as you move away from the poles, it weakens. The closer to the pole of the magnet the magnetic needle is located, the greater the modulus of force the field of the magnet acts on it. Since the magnetic lines are curved, the direction of the force with which the field acts on the needle also changes from point to point.
Thus, the force with which the field of a strip magnet acts on a magnetic needle placed in this field can be different both in absolute value and in direction at different points of the field.
Such a field is called inhomogeneous. The lines of an inhomogeneous magnetic field are curved, their density varies from point to point.
Another example of a non-uniform magnetic field is the field around a rectilinear current-carrying conductor. Figure 89 shows a section of such a conductor, located perpendicular to the plane of the drawing. The circle indicates the cross section of the conductor. The dot means that the current is directed from behind the drawing to us, as if we see the tip of an arrow indicating the direction of the current (the current directed from us beyond the drawing is indicated by a cross, as if we see the tail of an arrow directed along the current).
From this figure it can be seen that the magnetic lines of the field created by a rectilinear conductor with current are concentric circles, the distance between which increases with distance from the conductor.
In a certain limited region of space, it is possible to create a uniform magnetic field, i.e., a field, at any point of which the force of action on the magnetic needle is the same in magnitude and direction.
Figure 90 shows the magnetic field that occurs inside the solenoid - a cylindrical wire coil with current. The field inside the solenoid can be considered homogeneous if the length of the solenoid is much greater than its diameter (outside the solenoid, the field is inhomogeneous, its magnetic lines are approximately the same as those of a bar magnet). From this figure it can be seen that the magnetic lines of a uniform magnetic field are parallel to each other and are located with the same density.
Rice. 90. Magnetic field of the solenoid
The field inside the permanent bar magnet in its central part is also homogeneous (see Fig. 88).
For the image of the magnetic field, the following method is used. If the lines of a uniform magnetic field are located perpendicular to the plane of the drawing and are directed from us beyond the drawing, then they are depicted with crosses (Fig. 91, a), and if because of the drawing towards us, then with dots (Fig. 91, b). As in the case of current, each cross is, as it were, the tail plumage of an arrow flying from us, and the point is the tip of an arrow flying towards us (in both figures, the direction of the arrows coincides with the direction of the magnetic lines).
Rice. 91. Magnetic field lines directed perpendicular to the plane of the drawing: a - from the observer; b - to the observer
Questions
- What is the source of the magnetic field?
- What creates the magnetic field of a permanent magnet?
- What are magnetic lines? What is taken as their direction at any point in it?
- How are the magnetic needles in a magnetic field, the lines of which are rectilinear; curvilinear?
- 0 what can be judged by the pattern of magnetic field lines?
- What kind of magnetic field - homogeneous or inhomogeneous - is formed around a bar magnet; around a straight conductor with current; inside a solenoid whose length is much greater than its diameter?
- What can be said about the modulus and direction of the force acting on the magnetic needle at different points of the inhomogeneous magnetic field; uniform magnetic field?
- What is the difference between the location of magnetic lines in non-uniform and uniform magnetic fields?
Exercise 31
1 In § 37 a more precise name and definition of these lines will be given.
The topic of this lesson will be the magnetic field and its graphic representation. We will discuss inhomogeneous and uniform magnetic field. To begin with, we will give a definition of the magnetic field, tell you what it is connected with and what properties it has. Let's learn how to depict it on charts. We will also learn how an inhomogeneous and uniform magnetic field is determined.
Today we will first of all repeat what a magnetic field is. A magnetic field - force field that forms around a conductor through which an electric current flows. It has to do with moving charges..
Now it is necessary to note magnetic field properties. You know that there are several fields associated with a charge. In particular, the electric field. But we will discuss exactly the magnetic field created by moving charges. The magnetic field has several properties. First: magnetic field is created by moving electric charges. In other words, a magnetic field is formed around a conductor through which an electric current flows. The next property that says how the magnetic field is defined. It is determined by the action on another moving electric charge. Or, they say, to another electric current. We can determine the presence of a magnetic field by the action on the compass needle, on the so-called. magnetic needle.
Another property: magnetic field exerts force. Therefore, they say that the magnetic field is material.
These three properties are the hallmarks of a magnetic field. After we have decided what a magnetic field is, and have determined the properties of such a field, it is necessary to say how the magnetic field is investigated. First of all, the magnetic field is investigated using a loop with current. If we take a conductor, make a round or square frame out of this conductor, and pass an electric current through this frame, then in a magnetic field this frame will rotate in a certain way.
Rice. 1. The frame with current rotates in an external magnetic field
By the way this frame turns, we can judge magnetic field. There is only one here important condition: the frame must be very small or it must be very small compared to the distances at which we study the magnetic field. Such a frame is called a current loop.
We can also explore the magnetic field with the help of magnetic needles, placing them in a magnetic field and observing their behavior.
Rice. 2. Action of a magnetic field on magnetic needles
The next thing we're going to talk about is how a magnetic field can be depicted. As a result of research that has been carried out over time, it has become clear that the magnetic field can be conveniently depicted using magnetic lines. To observe magnetic lines Let's do one experiment. For our experiment, we will need a permanent magnet, metal iron filings, glass and a sheet of white paper.
Rice. 3. Iron filings line up along magnetic field lines
We cover the magnet with a glass plate, and put a sheet of paper on top, a white sheet of paper. Sprinkle iron filings on top of a sheet of paper. As a result, it will be seen how the magnetic field lines appear. What we will see are the magnetic field lines of a permanent magnet. They are also sometimes called the spectrum of magnetic lines. Note that the lines exist in all three directions, not just in the plane.
magnetic line- an imaginary line along which the axes of the magnetic arrows would line up.
Rice. 4. Schematic representation of the magnetic line
Look, the figure shows the following: the line is curved, the direction of the magnetic line is determined by the direction of the magnetic needle. The direction indicates the north pole of the magnetic needle. It is very convenient to depict lines with the help of arrows.
Rice. 5. How the direction of the lines of force is indicated
Now let's talk about the properties of magnetic lines. First, magnetic lines have neither beginning nor end. These are closed lines. Since the magnetic lines are closed, there are no magnetic charges.
Second: these are lines that do not intersect, do not break, do not twist in any way. With the help of magnetic lines, we can characterize the magnetic field, imagine not only its shape, but also talk about the force effect. If we depict a greater density of such lines, then in this place, at this point in space, we will have a greater force action.
If the lines are parallel to each other, their density is the same, then in this case they say that magnetic field is uniform. If, on the contrary, this is not the case, i.e. the density is different, the lines are curved, then such a field will be called heterogeneous. At the end of the lesson, I would like to draw your attention to the following figures.
Rice. 6. Inhomogeneous magnetic field
First, we now know that magnetic lines can be represented by arrows. And the figure represents precisely the inhomogeneous magnetic field. The density in different places is different, which means that the force effect of this field on the magnetic needle will be different.
The following figure shows an already homogeneous field. The lines are directed in the same direction, and their density is the same.
Rice. 7. Uniform magnetic field
A uniform magnetic field is the field that occurs inside a coil with a large number turns or inside a rectilinear, bar magnet. The magnetic field outside the strip magnet, or what we observed today in the lesson, this field is inhomogeneous. To fully understand all this, let's look at the table.
List of additional literature:
Belkin I.K. Electric and magnetic fields // Kvant. - 1984. - No. 3. - S. 28-31. Kikoin A.K. Where does magnetism come from? // Quantum. - 1992. - No. 3. - P. 37-39,42 Leenson I. Riddles of the magnetic needle // Kvant. - 2009. - No. 3. - S. 39-40. Elementary textbook of physics. Ed. G.S. Landsberg. T. 2. - M., 1974
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Tasks D13. A magnetic field. Electromagnetic induction
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An electric current was passed through a light conductive frame located between the poles of a horseshoe magnet, the direction of which is indicated by arrows in the figure.
Solution.
The magnetic field will be directed from the north pole of the magnet to the south (perpendicular to the AB side of the frame). The Ampere force acts on the sides of the frame with current, the direction of which is determined by the left-hand rule, and the value is . Thus, forces equal in magnitude but opposite in direction will act on the AB side of the frame and the side parallel to it: on the left side “from us”, and on the right side “on us”. The forces will not act on the other sides, since the current in them flows parallel to the field lines of force. Thus, the frame will begin to rotate clockwise when viewed from above.
As it rotates, the direction of the force will change and the moment the frame rotates 90°, the torque will change direction, so the frame will not rotate any further. For some time, the frame will oscillate in this position, and then it will be in the position indicated in Figure 4.
Answer: 4
Source: GIA in Physics. main wave. Option 1313.
An electric current flows through the coil, the direction of which is shown in the figure. At the same time, at the ends of the iron core of the coil
1) magnetic poles are formed: at the end 1 - the north pole; at the end 2 - south
2) magnetic poles are formed: at the end 1 - the south pole; at the end 2 - northern
3) electric charges accumulate: at the end 1 - a negative charge; end 2 - positive
4) electric charges accumulate: at the end 1 - a positive charge; at the end of 2 - negative
Solution.
When charged particles move, a magnetic field always arises. Let's use the right hand rule to determine the direction of the magnetic induction vector: let's direct our fingers along the current line, then the bent thumb will indicate the direction of the magnetic induction vector. Thus, the lines of magnetic induction are directed from end 1 to end 2. The lines of the magnetic field enter the south magnetic pole and exit the north.
The correct answer is numbered 2.
Note.
Inside the magnet (coil), the magnetic field lines go from the south pole to the north.
Answer: 2
Source: GIA in Physics. main wave. Option 1326., OGE-2019. main wave. Option 54416
The figure shows a pattern of magnetic field lines from two bar magnets, obtained using iron filings. Which poles of bar magnets, judging by the location of the magnetic needle, correspond to areas 1 and 2?
1) 1 - the north pole; 2 - south
2) 1 - south; 2 - north pole
3) both 1 and 2 - to the north pole
4) both 1 and 2 - to the south pole
Solution.
Since the magnetic lines are closed, the poles cannot be both south and north at the same time. The letter N (North) denotes the north pole, S (South) - the south. The north pole is attracted to the south. Therefore, area 1 is the south pole, area 2 is the north pole.
The use of tests in the classroom makes it possible to carry out real individualization and differentiation of learning; make timely corrective work in the teaching process; to reliably evaluate and manage the quality of education. The proposed tests on the topic “Magnetic field” contain 10 tasks each.
Test #1
1. A magnet creates a magnetic field around itself. Where will the action of this field be manifested most strongly?
A. Near the poles of a magnet.
B. At the center of the magnet.
C. The action of the magnetic field manifests itself evenly at each point of the magnet.
Correct answer: A.
2. Is it possible to use a compass on the moon to navigate the terrain?
A. You can't.
B. You can.
B. It is possible, but only on the plains.
Correct answer: A.
3. Under what condition does a magnetic field appear around a conductor?
A. When an electric current occurs in a conductor.
B. When the conductor is folded in half.
B. When the conductor is heated.
Correct answer: A.
A. Up.
B. Down.
B. Right.
G. Left.
Correct answer: B.
5. Specify the fundamental property of the magnetic field?
A. His lines of force always have sources: they start on positive charges and end on negative ones.
B. The magnetic field has no sources. There are no magnetic charges in nature.
Q. His lines of force always have sources: they start on negative charges and end on positive ones.
Correct answer: B.
6.Choose the picture showing the magnetic field.
Correct answer: fig.2
7. Current flows through the wire ring. Specify the direction of the magnetic induction vector.
A. Down.
B. Up.
B. Right.
Correct answer: B.
8. How the core coils shown in the figure behave.
A. Do not interact.
B. Turn around.
B. Push off.
Correct answer: A.
9. The iron core was removed from the current coil. How will the picture of magnetic induction change?
A. The density of magnetic lines will increase many times over.
B. The density of magnetic lines will decrease many times over.
B. The pattern of magnetic lines will not change.
Correct answer: B.
10. In what way can the poles of a magnetic coil with current be changed?
A. Insert the core into the coil.
B. Change the direction of the current in the coil.
B. Turn off the power source.
D. Increase the current.
Correct answer: B.
Test #2
1. In Iceland and France, the nautical compass began to be used in the 12th and 13th centuries. A magnetic bar was fixed in the center of a wooden cross, then this structure was placed in water, and the cross, turning, was installed in the north-south direction. Which pole of the magnetic bar will turn to the north magnetic pole Earth?
A. Severny.
B. Southern.
Correct answer: B.
2. What substance is not attracted by a magnet at all?
A. Iron.
B. Nickel.
B. Glass.
Correct answer: B.
3. An insulated wire is laid inside the wall covering. How to find the location of the wire without disturbing the wall covering?
A. Bring a magnetic needle to the wall. A conductor with current and an arrow will interact.
B. Light up the walls. Strengthening the light will indicate the location of the wire.
B. The location of the wire cannot be determined without breaking the wall covering.
Correct answer: A.
4. The figure shows the location of the magnetic needle. How is the vector of magnetic induction directed at point A?
A. Down.
B. Up.
B. Right.
G. Left.
Correct answer: A.
5. What is the feature of magnetic induction lines?
A. Lines of magnetic induction start on positive charges and end on negative charges.
B. Lines have neither beginning nor end. They are always closed.
Correct answer: B.
6. Conductor with current is perpendicular to the plane. Which figure shows the lines of magnetic induction correctly?
Fig.1 Fig.2 Fig.3 Fig.4
Correct answer: Fig. four.
7. Current flows through the wire ring. Specify the direction of the current if the magnetic induction vector is directed upwards.
A. Counterclockwise.
B. Clockwise.
Correct answer: A.
8. Determine the nature of the interaction of the coils shown in the figure.
A. Are attracted.
B. Push off.
B. Do not interact.
Correct answer: B.
9. The frame with current in the magnetic field rotates. What device uses this phenomenon?
A. Laser disc.
B. Ammeter.
B. Electromagnet.
Correct answer: B.
10. Why does a frame with current placed between the poles of a permanent magnet rotate?
A. Due to the interaction of the magnetic fields of the frame and the magnet.
B. Due to action electric field magnet frames.
B. Due to the action of the magnetic field of the magnet on the charge in the coil.
Correct answer: A.
Literature: Physics. Grade 8: textbook for general educational documents / A.V. Peryshkin. - Bustard, 2006.
Topics USE codifier : interaction of magnets, magnetic field of a conductor with current.
The magnetic properties of matter have been known to people for a long time. Magnets got their name from the ancient city of Magnesia: a mineral (later called magnetic iron ore or magnetite) was widespread in its vicinity, pieces of which attracted iron objects.
Interaction of magnets
On two sides of each magnet are located North Pole and South Pole. Two magnets are attracted to each other by opposite poles and repel by like poles. Magnets can act on each other even through a vacuum! All this is reminiscent of the interaction of electric charges, however the interaction of magnets is not electrical. This is evidenced by the following experimental facts.
The magnetic force weakens when the magnet is heated. The strength of the interaction of point charges does not depend on their temperature.
The magnetic force is weakened by shaking the magnet. Nothing similar happens with electrically charged bodies.
Positive electric charges can be separated from negative ones (for example, when electrifying bodies). But it is impossible to separate the poles of the magnet: if you cut the magnet into two parts, then poles also appear at the cut point, and the magnet breaks up into two magnets with opposite poles at the ends (oriented in exactly the same way as the poles of the original magnet).
So the magnets always bipolar, they exist only in the form dipoles. Isolated magnetic poles (so-called magnetic monopoles- analogues of electric charge) in nature do not exist (in any case, they have not yet been experimentally detected). This is perhaps the most impressive asymmetry between electricity and magnetism.
Like electrically charged bodies, magnets act on electrical charges. However, the magnet only acts on moving charge; If the charge is at rest relative to the magnet, then no magnetic force acts on the charge. On the contrary, an electrified body acts on any charge, regardless of whether it is at rest or in motion.
By modern ideas theory of short-range action, the interaction of magnets is carried out through magnetic field. Namely, a magnet creates a magnetic field in the surrounding space, which acts on another magnet and causes a visible attraction or repulsion of these magnets.
An example of a magnet is magnetic needle compass. With the help of a magnetic needle, one can judge the presence of a magnetic field in a given region of space, as well as the direction of the field.
Our planet Earth is a giant magnet. Not far from the geographic north pole of the Earth is the south magnetic pole. Therefore, the north end of the compass needle, turning to the south magnetic pole of the Earth, points to the geographical north. Hence, in fact, the name "north pole" of the magnet arose.
Magnetic field lines
The electric field, we recall, is investigated with the help of small test charges, by the action on which one can judge the magnitude and direction of the field. An analogue of a test charge in the case of a magnetic field is a small magnetic needle.
For example, you can get some geometric idea of the magnetic field by placing very small compass needles at different points in space. Experience shows that the arrows will line up along certain lines - the so-called magnetic field lines. Let us define this concept in the form of the following three paragraphs.
1. Lines of a magnetic field, or magnetic lines of force, are directed lines in space that have next property: a small compass needle placed at each point on such a line is oriented tangent to that line.
2. The direction of the magnetic field line is the direction of the northern ends of the compass needles located at the points of this line.
3. The thicker the lines go, the stronger the magnetic field in a given region of space..
The role of compass needles can be successfully performed by iron filings: in a magnetic field, small filings are magnetized and behave exactly like magnetic needles.
So, having poured iron filings around a permanent magnet, we will see approximately the following picture of magnetic field lines (Fig. 1).
Rice. 1. Permanent magnet field
The north pole of the magnet is indicated in blue and the letter ; the south pole - in red and the letter . Note that the field lines exit the north pole of the magnet and enter the south pole, because it is to the south pole of the magnet that the north end of the compass needle will point.
Oersted's experience
Despite the fact that electrical and magnetic phenomena have been known to people since antiquity, no relationship between them has been observed for a long time. For several centuries, research on electricity and magnetism proceeded in parallel and independently of each other.
The remarkable fact that electrical and magnetic phenomena are actually related to each other was first discovered in 1820 in the famous experiment of Oersted.
The scheme of Oersted's experiment is shown in fig. 2 (image from rt.mipt.ru). Above the magnetic needle (and - the north and south poles of the arrow) is a metal conductor connected to a current source. If you close the circuit, then the arrow turns perpendicular to the conductor!
This simple experiment pointed directly to the relationship between electricity and magnetism. The experiments that followed Oersted's experience firmly established the following pattern: magnetic field is generated electric currents and acts on currents.
Rice. 2. Oersted's experiment
The picture of the lines of the magnetic field generated by a conductor with current depends on the shape of the conductor.
Magnetic field of a straight wire with current
The magnetic field lines of a straight wire carrying current are concentric circles. The centers of these circles lie on the wire, and their planes are perpendicular to the wire (Fig. 3).
Rice. 3. Field of a direct wire with current
There are two alternative rules for determining the direction of direct current magnetic field lines.
hour hand rule. The field lines go counterclockwise when viewed so that the current flows towards us..
screw rule(or gimlet rule, or corkscrew rule- it's closer to someone ;-)). The field lines go where the screw (with conventional right-hand thread) must be turned to move along the thread in the direction of the current.
Use whichever rule suits you best. It's better to get used to the clockwise rule - you will see for yourself later that it is more universal and easier to use (and then remember it with gratitude in your first year when you study analytic geometry).
On fig. 3, something new has also appeared: this is a vector, which is called magnetic field induction, or magnetic induction. The magnetic induction vector is an analogue of the electric field strength vector: it serves power characteristic magnetic field, determining the force with which the magnetic field acts on moving charges.
We will talk about forces in a magnetic field later, but for now we will only note that the magnitude and direction of the magnetic field is determined by the magnetic induction vector. At each point in space, the vector is directed in the same direction as the north end of the compass needle placed at this point, namely, tangent to the field line in the direction of this line. The magnetic induction is measured in teslach(Tl).
As in the case of an electric field, for the induction of a magnetic field, superposition principle. It lies in the fact that induction of magnetic fields created at a given point by various currents are added vectorially and give the resulting vector of magnetic induction:.
The magnetic field of a coil with current
Consider a circular coil through which a direct current circulates. We do not show the source that creates the current in the figure.
The picture of the field lines of our revolution will have approximately next view(Fig. 4).
Rice. 4. Field of the coil with current
It will be important for us to be able to determine in which half-space (relative to the plane of the coil) the magnetic field is directed. Again we have two alternative rules.
hour hand rule. The field lines go there, looking from where the current seems to be circulating counterclockwise.
screw rule. The field lines go where the screw (with conventional right hand threads) would move if rotated in the direction of the current.
As you can see, the roles of the current and the field are reversed - in comparison with the formulations of these rules for the case of direct current.
The magnetic field of a coil with current
Coil it will turn out, if tightly, coil to coil, wind the wire into a sufficiently long spiral (Fig. 5 - image from the site en.wikipedia.org). The coil may have several tens, hundreds or even thousands of turns. The coil is also called solenoid.
Rice. 5. Coil (solenoid)
The magnetic field of one turn, as we know, does not look very simple. Fields? individual turns of the coil are superimposed on each other, and it would seem that the result should be a very confusing picture. However, this is not the case: the field of a long coil has an unexpectedly simple structure (Fig. 6).
Rice. 6. coil field with current
In this figure, the current in the coil goes counterclockwise when viewed from the left (this will happen if, in Fig. 5, the right end of the coil is connected to the “plus” of the current source, and the left end to the “minus”). We see that the magnetic field of the coil has two characteristic properties.
1. Inside the coil, away from its edges, the magnetic field is homogeneous: at each point, the magnetic induction vector is the same in magnitude and direction. The field lines are parallel straight lines; they bend only near the edges of the coil when they go out.
2. Outside the coil, the field is close to zero. The more turns in the coil, the weaker field outside of her.
Note that an infinitely long coil does not emit a field at all: there is no magnetic field outside the coil. Inside such a coil, the field is uniform everywhere.
Doesn't it remind you of anything? A coil is the "magnetic" counterpart of a capacitor. You remember that the capacitor creates a uniform electric field inside itself, the lines of which are curved only near the edges of the plates, and outside the capacitor the field is close to zero; a capacitor with infinite plates does not release the field at all, and the field is uniform everywhere inside it.
And now - the main observation. Compare, please, the picture of the magnetic field lines outside the coil (Fig. 6) with the field lines of the magnet in Fig. one . It's the same thing, isn't it? And now we come to a question that you probably had a long time ago: if a magnetic field is generated by currents and acts on currents, then what is the reason for the appearance of a magnetic field near a permanent magnet? After all, this magnet does not seem to be a conductor with current!
Ampère's hypothesis. Elementary currents
At first, it was thought that the interaction of magnets was due to special magnetic charges concentrated at the poles. But, unlike electricity, no one could isolate the magnetic charge; after all, as we have already said, it was not possible to obtain separately the north and south poles of the magnet - the poles are always present in the magnet in pairs.
Doubts about magnetic charges were aggravated by the experience of Oersted, when it turned out that the magnetic field is generated by an electric current. Moreover, it turned out that for any magnet it is possible to choose a conductor with a current of the appropriate configuration, such that the field of this conductor coincides with the field of the magnet.
Ampere put forward a bold hypothesis. There are no magnetic charges. The action of a magnet is explained by closed electric currents inside it..
What are these currents? These elementary currents circulate within atoms and molecules; they are associated with the movement of electrons in atomic orbits. The magnetic field of any body is made up of the magnetic fields of these elementary currents.
Elementary currents can be randomly located relative to each other. Then their fields cancel each other, and the body does not show magnetic properties.
But if elementary currents are coordinated, then their fields, adding up, reinforce each other. The body becomes a magnet (Fig. 7; the magnetic field will be directed towards us; the north pole of the magnet will also be directed towards us).
Rice. 7. Elementary magnet currents
Ampere's hypothesis about elementary currents clarified the properties of magnets. Heating and shaking a magnet destroys the arrangement of its elementary currents, and the magnetic properties weaken. The inseparability of the magnet poles became obvious: at the place where the magnet was cut, we get the same elementary currents at the ends. The ability of a body to be magnetized in a magnetic field is explained by the coordinated alignment of elementary currents that “turn” properly (read about the rotation of a circular current in a magnetic field in the next sheet).
Ampere's hypothesis turned out to be correct - this was shown by the further development of physics. The concept of elementary currents has become an integral part of the theory of the atom, developed already in the twentieth century - almost a hundred years after Ampère's brilliant conjecture.
