The maximum value of the magnetic field. §16
Good day, today you will find out what is a magnetic field and where does it come from.
Every person on the planet at least once, but kept magnet in hand. Starting from souvenir fridge magnets, or working magnets for collecting iron pollen and much more. As a child, it was a funny toy that stuck to black metal, but not to other metals. So what is the secret of the magnet and its magnetic field .
What is a magnetic field
At what point does a magnet begin to attract towards itself? Around each magnet there is a magnetic field, getting into which, objects begin to be attracted to it. The size of such a field may vary depending on the size of the magnet and its own properties.
Wikipedia term:
Magnetic field - a force field acting on moving electric charges and on bodies with a magnetic moment, regardless of the state of their movement, the magnetic component of the electromagnetic field.
Where does the magnetic field come from
The magnetic field can be created by the current of charged particles or by the magnetic moments of electrons in atoms, as well as by the magnetic moments of other particles, although to a much lesser extent.
Manifestation of a magnetic field
The magnetic field manifests itself in the effect on the magnetic moments of particles and bodies, on moving charged particles or conductors with. The force acting on an electrically charged particle moving in a magnetic field is called the Lorentz force, which is always directed perpendicular to the vectors v and B. It is proportional to the charge of the particle q, the component of the velocity v, perpendicular to the direction of the magnetic field vector B, and the magnitude of the magnetic field induction B.
What objects have a magnetic field
We often do not think about it, but many (if not all) of the objects around us are magnets. We are used to the fact that a magnet is a pebble with a pronounced force of attraction towards itself, but in fact, almost everything has an attraction force, it is just much lower. Let's take at least our planet - we do not fly away into space, although we do not hold on to the surface with anything. The field of the Earth is much weaker than the field of a pebble magnet, so it keeps us only due to its huge size- if you have ever seen how people walk on the moon (whose diameter is four times smaller), you will clearly understand what it is about. The attraction of the Earth is based largely on the metal components. Its crust and core - they have a powerful magnetic field. You may have heard that near large deposits of iron ore, compasses stop showing the right direction to the north - this is because the principle of the compass is based on the interaction of magnetic fields, and iron ore attracts his arrow.
For a long time, the magnetic field has raised many questions in humans, but even now it remains a little-known phenomenon. Many scientists tried to study its characteristics and properties, because the benefits and potential of using the field were indisputable facts.
Let's take everything in order. So, how does any magnetic field act and form? That's right, electric current. And the current, according to physics textbooks, is a stream of charged particles with a direction, isn't it? So, when a current passes through any conductor, a certain kind of matter begins to act around it - a magnetic field. The magnetic field can be created by the current of charged particles or by the magnetic moments of electrons in atoms. Now this field and matter have energy, we see it in electromagnetic forces that can affect the current and its charges. The magnetic field begins to act on the flow of charged particles, and they change the initial direction of motion perpendicular to the field itself.
Another magnetic field can be called electrodynamic, because it is formed near moving particles and affects only moving particles. Well, it is dynamic due to the fact that it has a special structure in rotating bions in a region of space. An ordinary electric moving charge can make them rotate and move. Bions transmit any possible interactions in this region of space. Therefore, the moving charge attracts one pole of all bions and causes them to rotate. Only he can bring them out of a state of rest, nothing else, because other forces will not be able to influence them.
In an electric field are charged particles that move very fast and can travel 300,000 km in just a second. Light has the same speed. There is no magnetic field without an electric charge. This means that the particles are incredibly closely related to each other and exist in a common electromagnetic field. That is, if there are any changes in the magnetic field, then there will be changes in the electric field. This law is also reversed.
We talk a lot about the magnetic field here, but how can you imagine it? We cannot see it with our human naked eye. Moreover, due to the incredibly fast propagation of the field, we do not have time to fix it with the help of various devices. But in order to study something, one must have at least some idea of it. It is also often necessary to depict the magnetic field in diagrams. In order to make it easier to understand it, conditional field lines are drawn. Where did they get them from? They were invented for a reason.
Let's try to see the magnetic field with the help of small metal filings and an ordinary magnet. We will pour these sawdust on a flat surface and introduce them into the action of a magnetic field. Then we will see that they will move, rotate and line up in a pattern or pattern. The resulting image will show the approximate effect of forces in a magnetic field. All forces and, accordingly, lines of force are continuous and closed in this place.
The magnetic needle has similar characteristics and properties to a compass and is used to determine direction. lines of force. If it falls into the zone of action of a magnetic field, we can see the direction of action of forces by its north pole. Then we will single out several conclusions from here: the top of an ordinary permanent magnet, from which the lines of force emanate, is designated by the north pole of the magnet. Whereas the south pole denotes the point where the forces are closed. Well, the lines of force inside the magnet are not highlighted in the diagram.
The magnetic field, its properties and characteristics are of great use, because in many problems it has to be taken into account and studied. This is the most important phenomenon in the science of physics. More complex things are inextricably linked with it, such as magnetic permeability and induction. To explain all the reasons for the appearance of a magnetic field, one must rely on real scientific facts and confirmations. Otherwise, in more complex problems, the wrong approach can violate the integrity of the theory.
Now let's give examples. We all know our planet. You say that it has no magnetic field? You may be right, but scientists say that the processes and interactions inside the Earth's core create a huge magnetic field that stretches for thousands of kilometers. But any magnetic field must have its poles. And they exist, just located a little away from the geographic pole. How do we feel it? For example, birds have developed navigation abilities, and they orient themselves, in particular, by the magnetic field. So, with his help, the geese arrive safely in Lapland. Special navigation devices also use this phenomenon.
Probably, there is no person who at least once did not think of the question of what a magnetic field is. Throughout history, they tried to explain it with ethereal whirlwinds, quirks, magnetic monopolies, and many others.
We all know that magnets with like poles facing each other repel each other, and opposite magnets attract. This power will
Vary depending on how far the two parts are from each other. It turns out that the described object creates a magnetic halo around itself. At the same time, when two alternating fields with the same frequency are superimposed, when one is shifted in space relative to the other, an effect is obtained that is commonly called a “rotating magnetic field”.
The size of the object under study is determined by the force with which the magnet is attracted to another or to iron. Accordingly, the greater the attraction, the greater the field. The force can be measured using the usual one, a small piece of iron is placed on one side, and weights are placed on the other, designed to balance the metal to the magnet.
For a more accurate understanding of the subject of the topic, you should study the fields:
Answering the question of what a magnetic field is, it is worth saying that a person also has it. At the end of 1960, thanks to the intensive development of physics, the SQUID measuring device was created. Its action is explained by the laws of quantum phenomena. It is a sensitive element of magnetometers used to study the magnetic field and such
values, such as
"SQUID" quickly began to be used to measure the fields that are generated by living organisms and, of course, by humans. This gave impetus to the development of new areas of research based on the interpretation of the information provided by such an instrument. This direction is called "biomagnetism".
Why, earlier, when determining what a magnetic field is, no research was carried out in this area? It turned out that it is very weak in organisms, and its measurement is a difficult physical task. This is related to the presence huge amount magnetic noise in the environment. Therefore, it is simply not possible to answer the question of what a human magnetic field is and to study it without the use of specialized protection measures.
Around a living organism, such a "halo" occurs for three main reasons. Firstly, due to ionic dots that appear as a result of the electrical activity of cell membranes. Secondly, due to the presence of ferrimagnetic smallest particles accidentally ingested or introduced into the body. Thirdly, when external magnetic fields are superimposed, there is a non-uniform susceptibility of various organs, which distorts the superimposed spheres.
Subject: Magnetic field
Prepared by: Baigarashev D.M.
Checked by: Gabdullina A.T.
A magnetic field
If two parallel conductors are connected to a current source so that an electric current passes through them, then, depending on the direction of the current in them, the conductors either repel or attract.
The explanation of this phenomenon is possible from the standpoint of the appearance around the conductors of a special type of matter - a magnetic field.
The forces with which current-carrying conductors interact are called magnetic.
A magnetic field- this is a special kind of matter, a specific feature of which is the action on a moving electric charge, conductors with current, bodies with a magnetic moment, with a force depending on the charge velocity vector, the direction of the current strength in the conductor and on the direction of the magnetic moment of the body.
The history of magnetism goes back to ancient times, to the ancient civilizations of Asia Minor. It was on the territory of Asia Minor, in Magnesia, that a rock was found, samples of which were attracted to each other. According to the name of the area, such samples began to be called "magnets". Any magnet in the form of a rod or a horseshoe has two ends, which are called poles; it is in this place that it is most pronounced and manifests itself magnetic properties. If you hang a magnet on a string, one pole will always point north. The compass is based on this principle. The north-facing pole of a free-hanging magnet is called the magnet's north pole (N). The opposite pole is called the south pole (S).
Magnetic poles interact with each other: like poles repel, and unlike poles attract. Similarly, the concept of an electric field surrounding an electric charge introduces the concept of a magnetic field around a magnet.
In 1820, Oersted (1777-1851) discovered that a magnetic needle located next to an electrical conductor deviates when current flows through the conductor, that is, a magnetic field is created around the current-carrying conductor. If we take a frame with current, then the external magnetic field interacts with the magnetic field of the frame and has an orienting effect on it, i.e., there is a position of the frame at which the external magnetic field has a maximum rotating effect on it, and there is a position when the torque force is zero.
The magnetic field at any point can be characterized by the vector B, which is called magnetic induction vector or magnetic induction at the point.
Magnetic induction B is a vector physical quantity, which is the force characteristic of the magnetic field at the point. It is equal to the ratio of the maximum mechanical moment of forces acting on a loop with current placed in a uniform field to the product of the current strength in the loop and its area:
The direction of the magnetic induction vector B is taken to be the direction of the positive normal to the frame, which is related to the current in the frame by the rule of the right screw, with a mechanical moment equal to zero.
In the same way as the lines of electric field strength are depicted, the lines of magnetic field induction are depicted. The line of induction of the magnetic field is an imaginary line, the tangent to which coincides with the direction B at the point.
The directions of the magnetic field at a given point can also be defined as the direction that indicates
the north pole of the compass needle placed at that point. It is believed that the lines of induction of the magnetic field are directed from the north pole to the south.
The direction of the lines of magnetic induction of the magnetic field created by an electric current that flows through a straight conductor is determined by the rule of a gimlet or a right screw. The direction of rotation of the screw head is taken as the direction of the lines of magnetic induction, which would ensure its translational movement in the direction of the electric current (Fig. 59).
where n 01 = 4 Pi 10 -7 V s / (A m). - magnetic constant, R - distance, I - current strength in the conductor.
In contrast to the lines of electrostatic field strength, which begin at positive charge and end in negative, the magnetic field lines are always closed. No magnetic charge similar to electric charge was found.
One tesla (1 T) is taken as a unit of induction - the induction of such a uniform magnetic field in which a maximum torque of 1 N m acts on a frame with an area of 1 m 2, through which a current of 1 A flows.
The induction of a magnetic field can also be determined by the force acting on a current-carrying conductor in a magnetic field.
A conductor with current placed in a magnetic field is subjected to the Ampère force, the value of which is determined by the following expression:
where I is the current strength in the conductor, l- the length of the conductor, B is the modulus of the magnetic induction vector, and is the angle between the vector and the direction of the current.
The direction of the Ampere force can be determined by the rule of the left hand: we place the palm of the left hand so that the lines of magnetic induction enter the palm, we place four fingers in the direction of the current in the conductor, then bent thumb shows the direction of the ampere force.
Considering that I = q 0 nSv and substituting this expression into (3.21), we obtain F = q 0 nSh/B sin a. The number of particles (N) in a given volume of the conductor is N = nSl, then F = q 0 NvB sin a.
Let us determine the force acting from the side of the magnetic field on a separate charged particle moving in a magnetic field:
This force is called the Lorentz force (1853-1928). The direction of the Lorentz force can be determined by the rule of the left hand: the palm of the left hand is positioned so that the lines of magnetic induction enter the palm, four fingers show the direction of movement of the positive charge, the thumb bent shows the direction of the Lorentz force.
The strength of the interaction between the two parallel conductors, through which currents I 1 and I 2 flow is equal to:
where l- the part of a conductor that is in a magnetic field. If the currents are in the same direction, then the conductors are attracted (Fig. 60), if the opposite direction, they are repelled. The forces acting on each conductor are equal in magnitude, opposite in direction. Formula (3.22) is the main one for determining the unit of current strength 1 ampere (1 A).
The magnetic properties of a substance are characterized by a scalar physical quantity - magnetic permeability, which shows how many times the induction B of a magnetic field in a substance that completely fills the field differs in absolute value from the induction B 0 of a magnetic field in vacuum:
According to their magnetic properties, all substances are divided into diamagnetic, paramagnetic and ferromagnetic.
Consider the nature of the magnetic properties of substances.
Electrons in the shell of atoms of matter move in different orbits. For simplicity, we consider these orbits to be circular, and each electron circulating around the atomic nucleus can be considered as a circular electric current. Each electron is circular current, creates a magnetic field, which we call orbital. In addition, an electron in an atom has its own magnetic field, called the spin field.
If, when introduced into an external magnetic field with induction B 0, induction B is created inside the substance< В 0 , то такие вещества называются диамагнитными (n< 1).
AT diamagnetic In materials in the absence of an external magnetic field, the magnetic fields of electrons are compensated, and when they are introduced into a magnetic field, the induction of the magnetic field of an atom becomes directed against the external field. The diamagnet is pushed out of the external magnetic field.
At paramagnetic materials, the magnetic induction of electrons in atoms is not completely compensated, and the atom as a whole turns out to be like a small permanent magnet. Usually in matter all these small magnets are oriented arbitrarily, and the total magnetic induction of all their fields is equal to zero. If you place a paramagnet in an external magnetic field, then all small magnets - atoms will turn in the external magnetic field like compass needles and the magnetic field in the substance increases ( n >= 1).
ferromagnetic are materials that are n"1. So-called domains, macroscopic regions of spontaneous magnetization, are created in ferromagnetic materials.
In different domains, the induction of magnetic fields has different directions (Fig. 61) and in a large crystal
mutually compensate each other. When a ferromagnetic sample is introduced into an external magnetic field, the boundaries of individual domains are shifted so that the volume of domains oriented along the external field increases.
With an increase in the induction of the external field B 0, the magnetic induction of the magnetized substance increases. For some values of B 0, the induction stops its sharp growth. This phenomenon is called magnetic saturation.
A characteristic feature of ferromagnetic materials is the phenomenon of hysteresis, which consists in the ambiguous dependence of the induction in the material on the induction of the external magnetic field as it changes.
The magnetic hysteresis loop is a closed curve (cdc`d`c), expressing the dependence of the induction in the material on the amplitude of the induction of the external field with a periodic rather slow change in the latter (Fig. 62).
The hysteresis loop is characterized by the following values B s , B r , B c . B s - the maximum value of the induction of the material at B 0s ; B r - residual induction equal to the value of the induction in the material when the induction of the external magnetic field decreases from B 0s to zero; -B c and B c - coercive force - a value equal to the induction of the external magnetic field necessary to change the induction in the material from residual to zero.
For each ferromagnet, there is such a temperature (Curie point (J. Curie, 1859-1906), above which the ferromagnet loses its ferromagnetic properties.
There are two ways to bring a magnetized ferromagnet into a demagnetized state: a) heat above the Curie point and cool; b) magnetize the material with an alternating magnetic field with a slowly decreasing amplitude.
Ferromagnets with low residual induction and coercive force are called soft magnetic. They find application in devices where a ferromagnet has to be frequently remagnetized (cores of transformers, generators, etc.).
Magnetically hard ferromagnets, which have a large coercive force, are used for the manufacture of permanent magnets.
Therefore, the concept itself arose in electrodynamics simultaneously with the concept of " electric field". It was introduced first by M. Faraday, and a little later - by J. Maxwell, to explain why electric charges have such a relatively short range of interaction.
On air
The fathers of electrodynamics believed that the field is created by deformation of the ether - an invisible speculative medium that fills everything that exists (Einstein, while working on the theory of relativity, abolished the concept of ether). Although modern people it may seem strange, but until the 20th century, physicists really did not doubt some kind of substance that permeates everything that exists. How magnetic fields are created and what their nature is, physicists could not explain.
When the special theory of relativity (SRT) came into use, and the ether was "officially removed", the space became "empty", but the fields continued to interact even in a vacuum, and this is impossible between non-material objects (at least according to SRT), so physicists considered necessary to assign some attributes to electric and magnetic fields. Concepts such as mass, momentum and field energy are being created.
Magnetic field properties
Its first property explains the nature of its origin: a magnetic field can only arise under the influence of moving charges (electrons) of an electric current. Power characteristic magnetic field is called magnetic induction, it is present at any point in the field.
The effect of the field extends only to moving charges, magnets and conductors. It can be of two types: variable and permanent. The magnetic field can only be measured with special devices, it is not fixed by human senses (although biologists believe that some animals can perceive changes in it). The essence of another property of the magnetic field is that it has an electrodynamic nature, not only because it can only affect moving charges, but also because it is itself generated by the movement of charges.
How to see
Although the human senses cannot detect the presence of a magnetic field, its direction can be determined using a magnetized needle. However, you can "see" the magnetic field with a sheet of paper and simple iron filings. It is necessary to put a sheet of paper on a permanent magnet, and sprinkle sawdust on top, after which the iron shavings line up along closed and continuous lines of force.
The direction of field lines is determined using the rule right hand, which is also called the "rule of the gimlet". If you take the conductor in your hand so that the thumb is in the direction of the current (the current moves from minus to plus), then the remaining fingers will indicate the direction of the lines of force.
Geomagnetism
Magnetic fields are created by moving charges, but then what is the nature of geomagnetism? Our planet has a magnetic field that protects it from harmful solar radiation, and the diameter of the field is several times greater than the diameter of the Earth. It is inhomogeneous in shape, on the "sunny side" it shrinks under the influence of the solar wind, and on the night side it stretches in the form of a long wide tail.
It is believed that on our planet magnetic fields are created by the movement of currents in the core, which consists of liquid metal. This is called the "hydromagnetic dynamo". When a substance reaches a temperature of several thousand degrees Kelvin, its conductivity becomes high enough that movements, even in a medium with a weak magnetization, begin to create electric currents, which, in turn, create magnetic fields.
In local areas, magnetic fields are created by magnetized rocks from the upper layers of the planet that form the earth's crust.
Pole movement
Since 1885, the registration of the movement of magnetic poles began. Per last century South Pole(the pole in the Southern Hemisphere) has moved 900 kilometers, and the north (Arctic) magnetic pole has moved 120 kilometers in 11 years since 1973, and another 150 kilometers over the next ten years. According to the latest data, the Arctic pole shift rate has increased from 10 up to 60 kilometers per year.
Although scientists know how the Earth's magnetic field is created, they cannot influence the movement of the poles and assume that another inversion will occur quite soon. This is a natural process, this is not the first time on the planet, but how such a process will turn out for people is unknown.
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