Magnetic field, characteristics of the magnetic field. A magnetic field. Properties of magnetic field
Magnetic fields occur in nature and can be created artificially. The man noticed them useful characteristics, which I learned to use in Everyday life. What is the source magnetic field?
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Earth's magnetic field
How the doctrine of the magnetic field developed
The magnetic properties of some substances were noticed in ancient times, but their study really began in medieval Europe. Using small steel needles, a scientist from France, Peregrine, discovered the intersection of magnetic force lines at certain points - the poles. Only three centuries later, guided by this discovery, Gilbert continued to study it and subsequently defended his hypothesis that the Earth has its own magnetic field.
The rapid development of the theory of magnetism began at the beginning of the 19th century, when Ampere discovered and described the influence of the electric field on the occurrence of a magnetic field, and Faraday's discovery electromagnetic induction established an inverse relationship.
What is a magnetic field
A magnetic field manifests itself in a force effect on electric charges that are in motion, or on bodies that have a magnetic moment.
Magnetic field sources:
- Conductors through which electric current passes;
- Permanent magnets;
- Changing electric field.
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Magnetic field sources
The root cause of the appearance of a magnetic field is identical for all sources: electrical microcharges - electrons, ions or protons - have their own magnetic moment or are in directional motion.
Important! Electric and magnetic fields mutually generate each other, changing over time. This relationship is determined by Maxwell's equations.
Characteristics of the magnetic field
The characteristics of the magnetic field are:
- Magnetic flux, a scalar quantity that determines how many magnetic field lines pass through a given cross section. Denoted by the letter F. Calculated using the formula:
F = B x S x cos α,
where B is the magnetic induction vector, S is the section, α is the angle of inclination of the vector to the perpendicular drawn to the section plane. Unit of measurement – weber (Wb);
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Magnetic flux
- The magnetic induction vector (B) shows the force acting on the charge carriers. It is directed towards the north pole, where the usual magnetic needle points. Magnetic induction is measured quantitatively in Tesla (T);
- MF tension (N). Determined by the magnetic permeability of various media. In a vacuum, permeability is taken as unity. The direction of the tension vector coincides with the direction of magnetic induction. Unit of measurement – A/m.
How to represent a magnetic field
It is easy to see the manifestations of a magnetic field using the example of a permanent magnet. It has two poles and depending on the orientation the two magnets attract or repel. The magnetic field characterizes the processes occurring during this:
- The MP is mathematically described as a vector field. It can be constructed by means of many vectors of magnetic induction B, each of which is directed towards the north pole of the compass needle and has a length depending on the magnetic force;
- An alternative way of representing this is to use field lines. These lines never intersect, do not start or stop anywhere, forming closed loops. The MF lines are combined into areas with a more frequent location, where the magnetic field is the strongest.
Important! The density of the field lines indicates the strength of the magnetic field.
Although the MP cannot be seen in reality, the field lines can be easily visualized in the real world by placing iron filings in the MP. Each particle behaves like a tiny magnet with a north and south pole. The result is a pattern similar to lines of force. A person is not able to feel the impact of MP.
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Magnetic field lines
Magnetic field measurement
Since this is a vector quantity, there are two parameters for measuring MF: force and direction. The direction can be easily measured using a compass connected to the field. An example is a compass placed in the Earth's magnetic field.
Measuring other characteristics is much more difficult. Practical magnetometers did not appear until the 19th century. Most of them work by using the force that the electron feels as it moves along the MP.
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Magnetometer
Very precise measurement of small magnetic fields has become practically feasible since the discovery in 1988 of giant magnetoresistance in layered materials. This discovery in fundamental physics was quickly applied to magnetic technology hard drive for storing data on computers, leading to a thousandfold increase in storage capacity in just a few years.
In generally accepted measurement systems, MP is measured in tests (T) or gauss (G). 1 T = 10000 Gs. Gauss is often used because Tesla is too large a field.
Interesting. A small magnet on a refrigerator creates a magnetic field equal to 0.001 Tesla, and the Earth's magnetic field on average is 0.00005 Tesla.
The nature of the magnetic field
Magnetism and magnetic fields are manifestations of electromagnetic force. There are two possible ways to organize an energy charge in motion and, therefore, a magnetic field.
The first is to connect the wire to a current source, an MF is formed around it.
Important! As the current (the number of charges in motion) increases, the MP increases proportionally. As you move away from the wire, the field decreases depending on the distance. This is described by Ampere's law.
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Ampere's law
Some materials that have higher magnetic permeability are capable of concentrating magnetic fields.
Since the magnetic field is a vector, it is necessary to determine its direction. For ordinary current flowing through a straight wire, the direction can be found using the right hand rule.
To use the rule, you need to imagine that the wire is wrapped around right hand, A thumb indicates the direction of the current. Then the four remaining fingers will show the direction of the magnetic induction vector around the conductor.
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Right hand rule
The second way to create a magnetic field is to use the fact that in some substances electrons appear that have their own magnetic moment. This is how permanent magnets work:
- Although atoms often have many electrons, they mostly bond so that the total magnetic field of the pair cancels out. Two electrons paired in this way are said to have opposite spin. Therefore, in order to magnetize something, you need atoms that have one or more electrons with the same spin. For example, iron has four such electrons and is suitable for making magnets;
- The billions of electrons found in atoms can be randomly oriented, and there will be no overall MF, no matter how many unpaired electrons the material has. It must be stable at low temperatures to provide an overall preferred orientation of electrons. High magnetic permeability causes the magnetization of such substances under certain conditions outside the influence of magnetic fields. These are ferromagnetic;
- Other materials may exhibit magnetic properties in the presence of an external magnetic field. The external field serves to align all electron spins, which disappears after the MF is removed. These substances are paramagnetic. The metal of a refrigerator door is an example of a paramagnetic material.
Earth's magnetic field
The earth can be represented in the form of capacitor plates, the charge of which has the opposite sign: “minus” at the earth’s surface and “plus” in the ionosphere. Between them is atmospheric air as an insulating gasket. The giant capacitor maintains a constant charge due to the influence of the earth's MF. Using this knowledge, you can create a scheme for obtaining electrical energy from the Earth's magnetic field. True, the result will be low voltage values.
Have to take:
- grounding device;
- the wire;
- Tesla transformer capable of generating high-frequency oscillations and creating a corona discharge, ionizing the air.
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Tesla Coil
The Tesla coil will act as an electron emitter. The entire structure is connected together, and to ensure a sufficient potential difference, the transformer must be raised to a considerable height. Thus, an electrical circuit will be created through which a small current will flow. Get a large number of electricity is not possible using this device.
Electricity and magnetism dominate many of the worlds around us, from the most fundamental processes in nature to cutting-edge electronic devices.
Video
The magnetic field has long raised many questions in humans, but even now remains a little-known phenomenon. Many scientists tried to study its characteristics and properties, because the benefits and potential of using the field were undeniable facts.
Let's look at everything in order. So, how does any magnetic field operate and form? That's right, from electric current. And current, according to physics textbooks, is a directional flow of charged particles, isn’t it? So, when a current passes through any conductor, a certain type of matter begins to act around it - a magnetic field. A magnetic field can be created by a 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 influence the flow of charged particles, and they change the initial direction of movement perpendicular to the field itself.
A magnetic field can also 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 moving electric charge can make them rotate and move. Bions transmit any possible interactions in this region of space. Therefore, a moving charge attracts one pole of all bions and makes them rotate. Only he can bring them out of their state of rest, nothing else, because other forces will not be able to influence them.
In an electric field there are charged particles that move very quickly and can travel 300,000 km in just a second. Light has the same speed. A magnetic field cannot exist 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 one. This law is also reverse.
We talk a lot about the magnetic field here, but how can we 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 detect it using various devices. But in order to study something, you need to have at least some idea about it. It is also often necessary to depict a magnetic field in diagrams. To make it easier to understand, 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 using small metal filings and an ordinary magnet. Let's pour these sawdust onto a flat surface and expose them to 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 the magnetic field. All forces and, accordingly, lines of force are continuous and closed in this place.
A magnetic needle has similar characteristics and properties to a compass, and is used to determine the direction of lines of force. If it falls into the zone of action of a magnetic field, we can see the direction of action of the forces from its north pole. Then let us highlight several conclusions from here: the top of an ordinary permanent magnet, from which the lines of force emanate, is designated 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 have a fairly wide application, 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 such as magnetic permeability and induction are inextricably linked with it. To explain all the reasons for the appearance of a magnetic field, we must rely on real scientific facts and confirmation. Otherwise in more complex tasks the wrong approach can destroy the integrity of the theory.
Now let's give examples. We all know our planet. Will you say that it has no magnetic field? You may be right, but scientists say that processes and interactions inside the Earth's core give rise to a huge magnetic field that stretches for thousands of kilometers. But in any magnetic field there must be its poles. And they exist, they are just located a little away from the geographic pole. How do we feel it? For example, birds have developed navigation abilities, and they navigate, in particular, by the magnetic field. So, with his help, the geese arrive safely in Lapland. Special navigation devices also use this phenomenon.
A MAGNETIC FIELD
A magnetic field is a special type of matter, invisible and intangible to humans,
existing independently of our consciousness.
Even in ancient times, scientific thinkers guessed that something existed around a magnet.
Magnetic needle.
A magnetic needle is a device necessary when studying the magnetic action of electric current.
It is a small magnet mounted on the tip of a needle and has two poles: north and south. The magnetic needle can rotate freely on the tip of the needle.
The northern end of the magnetic needle always points to "north".
The line connecting the poles of the magnetic needle is called the axis of the magnetic needle.
A similar magnetic needle is found in any compass - a device for orienting oneself.
Where does the magnetic field originate?
Oersted's experiment (1820) - shows how a conductor with current interacts with a magnetic needle.
When the electrical circuit is closed, the magnetic needle deviates from its original position; when the circuit is opened, the magnetic needle returns to its original position.
A magnetic field arises in the space around a conductor carrying current (and in the general case around any moving electric charge).
The magnetic forces of this field act on the needle and turn it.
In general, we can say
that a magnetic field arises around moving electric charges.
Electric current and magnetic field are inseparable from each other.
IT'S INTERESTING THAT...
Many celestial bodies - planets and stars - have their own magnetic fields.
However, our closest neighbors - the Moon, Venus and Mars - do not have a magnetic field,
similar to earthly.
___
Gilbert discovered that when a piece of iron is brought closer to one pole of a magnet, the other pole begins to attract more strongly. This idea was patented only 250 years after Gilbert's death.
In the first half of the 90s, when new Georgian coins appeared - lari,
local pickpockets have acquired magnets,
because the metal from which these coins were made was well attracted by a magnet!
If you take a dollar bill by the corner and hold it near a powerful magnet
(for example, horseshoe-shaped), creating a non-uniform magnetic field, piece of paper
will deviate towards one of the poles. It turns out that the ink on the dollar bill contains iron salts.
possessing magnetic properties, so the dollar is attracted to one of the poles of the magnet.
If you hold a large magnet close to a carpenter's bubble level, the bubble will move.
The fact is that the bubble level is filled with diamagnetic fluid. When such a liquid is placed in a magnetic field, a magnetic field in the opposite direction is created inside it, and it is pushed out of the field. Therefore, the bubble in the liquid approaches the magnet.
YOU NEED TO KNOW ABOUT THEM!
The organizer of the magnetic compass business in the Russian Navy was a famous deviator scientist,
captain of the 1st rank, author of scientific works on the theory of the compass I.P. Belavanets.
Participant trip around the world on the frigate "Pallada" and a participant in the Crimean War of 1853-56. He was the first in the world to demagnetize a ship (1863)
and solved the problem of installing compasses inside an iron submarine.
In 1865 he was appointed head of the country's first Compass Observatory in Kronstadt.
A magnetic field is a special form of matter that is created by magnets, conductors with current (moving charged particles) and which can be detected by the interaction of magnets, conductors with current (moving charged particles).
Oersted's experience
The first experiments (carried out in 1820) that showed that there is a deep connection between electrical and magnetic phenomena were the experiments of the Danish physicist H. Oersted.
A magnetic needle located near a conductor rotates through a certain angle when the current in the conductor is turned on. When the circuit is opened, the arrow returns to its original position.
From the experience of G. Oersted it follows that there is a magnetic field around this conductor.
Ampere's experience
Two parallel conductors, through which an electric current flows, interact with each other: they attract if the currents are in the same direction, and repel if the currents are in the opposite direction. This occurs due to the interaction of magnetic fields arising around the conductors.
Properties of magnetic field
1. Materially, i.e. exists independently of us and our knowledge about it.
2. Created by magnets, conductors with current (moving charged particles)
3. Detected by the interaction of magnets, conductors with current (moving charged particles)
4. Acts on magnets, current-carrying conductors (moving charged particles) with some force
5. There are no magnetic charges in nature. You cannot separate the north and south poles and get a body with one pole.
6. The reason why bodies have magnetic properties was found by the French scientist Ampere. Ampere put forward the conclusion that the magnetic properties of any body are determined by closed electric currents inside it.
These currents represent the movement of electrons around orbits in an atom.
If the planes in which these currents circulate are located randomly in relation to each other due to the thermal movement of the molecules that make up the body, then their interactions are mutually compensated and no magnetic properties the body is not detected.
And vice versa: if the planes in which the electrons rotate are parallel to each other and the directions of the normals to these planes coincide, then such substances enhance the external magnetic field.
7. Magnetic forces act in a magnetic field in certain directions, which are called magnetic lines of force. With their help, you can conveniently and clearly show the magnetic field in a particular case.
In order to more accurately depict the magnetic field, it was agreed that in those places where the field is stronger, the field lines should be shown denser, i.e. closer to each other. And vice versa, in places where the field is weaker, fewer field lines are shown, i.e. less frequently located.
8. The magnetic field is characterized by the magnetic induction vector.
The magnetic induction vector is a vector quantity characterizing the magnetic field.
The direction of the magnetic induction vector coincides with the direction of the north pole of the free magnetic needle at a given point.
The direction of the field induction vector and current strength I are related by the “right screw (gimlet) rule”:
if you screw in a gimlet in the direction of the current in the conductor, then the direction of the speed of movement of the end of its handle at a given point will coincide with the direction of the magnetic induction vector at that point.
Magnetic field and its characteristics
Lecture outline:
Magnetic field, its properties and characteristics.
A magnetic field- the form of existence of matter surrounding moving electric charges (current-carrying conductors, permanent magnets).
This name is due to the fact that, as the Danish physicist Hans Oersted discovered in 1820, it has an orienting effect on the magnetic needle. Oersted's experiment: a magnetic needle was placed under a current-carrying wire, rotating on a needle. When the current was turned on, it was installed perpendicular to the wire; when the direction of the current changed, it turned in the opposite direction.
Basic properties of the magnetic field:
generated by moving electric charges, current-carrying conductors, permanent magnets and an alternating electric field;
acts with force on moving electric charges, current-carrying conductors, and magnetized bodies;
an alternating magnetic field generates an alternating electric field.
From Oersted's experience it follows that the magnetic field is directional and must have a vector force characteristic. It is designated and called magnetic induction.
The magnetic field is represented graphically using magnetic field lines or magnetic induction lines. Magnetic power lines These are the lines along which iron filings or the axes of small magnetic needles are located in a magnetic field. At each point of such a line the vector is directed along a tangent.
Magnetic induction lines are always closed, which indicates the absence of magnetic charges in nature and the vortex nature of the magnetic field.
Conventionally, they leave the north pole of the magnet and enter the south. The density of the lines is chosen so that the number of lines per unit area perpendicular to the magnetic field is proportional to the magnitude of the magnetic induction.
N 
Magnetic solenoid with current
The direction of the lines is determined by the right screw rule. A solenoid is a coil with current, the turns of which are located close to each other, and the diameter of the turn is much less than the length of the coil.
The magnetic field inside the solenoid is uniform. A magnetic field is called uniform if the vector is constant at any point.
The magnetic field of a solenoid is similar to the magnetic field of a bar magnet.
WITH 
A current-carrying solenoid is an electromagnet.
Experience shows that for a magnetic field, as for an electric field, superposition principle: the induction of a magnetic field created by several currents or moving charges is equal to the vector sum of the induction of magnetic fields created by each current or charge:
The vector is entered in one of 3 ways:
a) from Ampere’s law;
b) by the effect of a magnetic field on a current-carrying frame;
c) from the expression for the Lorentz force.
A 
mpper experimentally established that the force with which a magnetic field acts on an element of a conductor with current I located in a magnetic field is directly proportional to the force
current I and the vector product of the element of length and magnetic induction:
- Ampere's law
N 
The direction of the vector can be found according to the general rules of the vector product, from which the rule of the left hand follows: if the palm of the left hand is positioned so that the magnetic lines of force enter it, and the 4 extended fingers are directed along the current, then the bent thumb will show the direction of the force.
The force acting on a wire of finite length can be found by integrating over the entire length.
When I = const, B=const, F = BIlsin
If =90 0, F = BIl
Magnetic field induction- vector physical quantity, numerically equal to strength, acting in a uniform magnetic field on a conductor of unit length with unit current strength, located perpendicular to the magnetic lines of force.
1T is the induction of a uniform magnetic field, in which a force of 1N acts on a conductor 1m long with a current of 1A, located perpendicular to the magnetic lines of force.
So far we have considered macrocurrents flowing in conductors. However, according to Ampere's assumption, in any body there are microscopic currents caused by the movement of electrons in atoms. These microscopic molecular currents create their own magnetic field and can rotate in the fields of macrocurrents, creating an additional magnetic field in the body. The vector characterizes the resulting magnetic field created by all macro- and microcurrents, i.e. at the same macrocurrent, the vector in different environments has different values.
The magnetic field of macrocurrents is described by the magnetic intensity vector.
For a homogeneous isotropic medium
,
0 = 410 -7 H/m - magnetic constant, 0 = 410 -7 N/A 2,
is the magnetic permeability of the medium, showing how many times the magnetic field of macrocurrents changes due to the field of microcurrents of the medium.
Magnetic flux. Gauss's theorem for magnetic flux.
Vector flow(magnetic flux) through the platform dS called a scalar quantity equal to
where is the projection onto the direction of the normal to the site;
is the angle between the vectors and.
Directional surface element,
Vector flux is an algebraic quantity,
If 
- when leaving the surface;
If 
- upon entering the surface.
The flux of the magnetic induction vector through an arbitrary surface S is equal to
For a uniform magnetic field =const,
1 Wb - magnetic flux passing through a flat surface with an area of 1 m 2 located perpendicular to a uniform magnetic field, the induction of which is 1 T.
The magnetic flux through the surface S is numerically equal to the number of magnetic field lines crossing this surface.
Since magnetic induction lines are always closed, for a closed surface the number of lines entering the surface (Ф 0), therefore, the total flux of magnetic induction through a closed surface is zero.
- Gauss's theorem: The flux of the magnetic induction vector through any closed surface is zero.
This theorem is a mathematical expression of the fact that in nature there are no magnetic charges on which magnetic induction lines begin or end.
The Biot-Savart-Laplace law and its application to the calculation of magnetic fields.
The magnetic field of direct currents of various shapes was studied in detail by Fr. scientists Biot and Savard. They found that in all cases, magnetic induction at an arbitrary point is proportional to the current strength and depends on the shape, size of the conductor, the location of this point in relation to the conductor and on the environment.
The results of these experiments were summarized by Fr. mathematician Laplace, who took into account the vector nature of magnetic induction and hypothesized that the induction at each point is, according to the principle of superposition, the vector sum of the inductions of elementary magnetic fields created by each section of this conductor.
Laplace formulated a law in 1820, which was called the Biot-Savart-Laplace law: each element of a current-carrying conductor creates a magnetic field, the induction vector of which at some arbitrary point K is determined by the formula:
- Biot-Savart-Laplace law.
From the Biot-Sauvar-Laplace law it follows that the direction of the vector coincides with the direction of the vector product. The same direction is given by the rule of the right screw (gimlet).
Considering that,
Conductor element co-directed with current;
Radius vector connecting to point K;
The Biot-Savart-Laplace law is of practical importance because allows you to find at a given point in space the induction of the magnetic field of a current flowing through a conductor of finite dimensions and arbitrary shape.
For a current of arbitrary shape, such a calculation is a complex mathematical problem. However, if the current distribution has a certain symmetry, then the application of the superposition principle together with the Biot-Savart-Laplace law makes it possible to calculate specific magnetic fields relatively simply.
Let's look at some examples.
A. Magnetic field of a straight conductor carrying current.
for a conductor of finite length:
for a conductor of infinite length: 1 = 0, 2 =
B. Magnetic field at the center of the circular current:
=90 0 , sin=1,
Oersted experimentally discovered in 1820 that circulation in a closed loop surrounding a system of macrocurrents is proportional to the algebraic sum of these currents. The proportionality coefficient depends on the choice of system of units and in SI is equal to 1.
C 
Circulation of a vector is called a closed loop integral.
This formula is called circulation theorem or total current law:
circulation of the magnetic field strength vector along an arbitrary closed circuit is equal to the algebraic sum of the macrocurrents (or total current) covered by this circuit. his characteristics In the space surrounding currents and permanent magnets, a force arises field, called magnetic. Availability magnetic fields is revealed...
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