Let's understand together what a magnetic field is. After all, many people live in this field all their lives and do not even think about it. It's time to fix it!
A magnetic field
A magnetic field- a special kind of matter. It manifests itself in action on moving electric charges and bodies that have their own magnetic moment (permanent magnets).
Important: the magnetic field does not affect stationary charges! A magnetic field is also created by moving electric charges, or by a time-varying electric field, or by the magnetic moments of electrons in atoms. That is, any wire through which current flows also becomes a magnet!
A body with its own magnetic field.
A magnet has poles called north and south. The designations "north" and "south" are given for convenience only (like "plus" and "minus" in electricity).
The magnetic field is depicted by magnetic field lines... The lines of force are continuous and closed, and their direction always coincides with the direction of the action of the field forces. If you scatter around the permanent magnet metal shavings, metal particles will show a visual picture of field lines magnetic field leaving the north and entering the South Pole... Graphical characteristic of the magnetic field - lines of force.
Magnetic field characteristics
The main characteristics of the magnetic field are magnetic induction, magnetic flux and magnetic permeability... But let's talk about everything in order.
Immediately, we note that all units of measurement are given in the system SI.
Magnetic induction B - vector physical quantity, which is the main force characteristic of the magnetic field. Denoted by a letter B ... Measurement unit of magnetic induction - Tesla (T).
Magnetic induction shows how strong a field is by determining the force with which it acts on a charge. Given power called by the Lorentz force.
Here q - charge, v - its speed in a magnetic field, B - induction, F is the Lorentz force with which the field acts on the charge.
F- a physical quantity equal to the product of the magnetic induction by the area of the circuit and the cosine between the induction vector and the normal to the plane of the circuit through which the flow passes. Magnetic flux- scalar characteristic of the magnetic field.
We can say that the magnetic flux characterizes the number of lines of magnetic induction permeating a unit area. The magnetic flux is measured in Weberch (Wb).
Magnetic permeability- coefficient determining magnetic properties Wednesday. One of the parameters on which the magnetic induction of the field depends is the magnetic permeability.
Our planet has been a huge magnet for several billion years. The induction of the earth's magnetic field changes depending on the coordinates. At the equator, it is approximately 3.1 times 10 to the minus fifth power of Tesla. In addition, there are magnetic anomalies, where the value and direction of the field differ significantly from the neighboring regions. Some of the largest magnetic anomalies on the planet are Kursk and Brazilian magnetic anomalies.
The origin of the Earth's magnetic field is still a mystery to scientists. It is assumed that the source of the field is the liquid metal core of the Earth. The core is moving, which means that the molten iron-nickel alloy is moving, and the movement of charged particles is the electric current that generates a magnetic field. The problem is that this theory ( geodynamo) does not explain how the field is kept stable.
The earth is a huge magnetic dipole. The magnetic poles do not coincide with the geographic ones, although they are in close proximity. Moreover, the earth's magnetic poles are moving. Their displacement has been recorded since 1885. For example, over the past hundred years, the magnetic pole in the Southern Hemisphere has shifted by almost 900 kilometers and is now in the Southern Ocean. The pole of the arctic hemisphere moves across the north Arctic Ocean to the East Siberian magnetic anomaly, the speed of its movement (according to 2004 data) was about 60 kilometers per year. Now there is an acceleration of the movement of the poles - on average, the speed is growing by 3 kilometers per year.
What is the significance of the Earth's magnetic field for us? First of all, the Earth's magnetic field protects the planet from cosmic rays and the solar wind. Charged particles from distant space do not fall directly onto the earth, but are deflected by a giant magnet and move along its lines of force. Thus, all living things are protected from harmful radiation.
During the history of the Earth, there have been several inversions(changes) of magnetic poles. Pole inversion- this is when they change places. Last time this phenomenon occurred about 800 thousand years ago, and there were more than 400 geomagnetic reversals in the history of the Earth. Some scientists believe that, given the observed acceleration of the magnetic poles, the next reversal of the poles should be expected in the next couple of thousand years.
Fortunately, no polarity reversal is expected in our century. This means that you can think about the pleasant and enjoy life in the good old constant field of the Earth, having considered the basic properties and characteristics of the magnetic field. And so that you can do this, there are our authors, whom you can confidently entrust with part of the educational efforts! and other types of work you can order at the link.
In the last century, various scientists have put forward several assumptions about the Earth's magnetic field. According to one of them, the field appears as a result of the rotation of the planet around its axis.
It is based on the curious Barnett-Einstein effect, which is that when any body rotates, a magnetic field arises. The atoms in this effect have their own magnetic moment, as they rotate around their axis. This is how the Earth's magnetic field appears. However, this hypothesis did not stand up to experimental tests. It turned out that the magnetic field obtained in such a nontrivial way is several million times weaker than the real one.
Another hypothesis is based on the appearance of a magnetic field due to the circular motion of charged particles (electrons) on the planet's surface. It also turned out to be untenable. The movement of electrons can cause the appearance of a very weak field, moreover, this hypothesis does not explain the inversion of the Earth's magnetic field. It is known that the north magnetic pole does not coincide with the geographic north.
Solar wind and mantle currents
The mechanism of formation of the magnetic field of the Earth and other planets Solar system not fully studied and so far remains a mystery to scientists. Nevertheless, one proposed hypothesis explains quite well the inversion and the magnitude of the induction of the real field. It is based on the work of the internal currents of the Earth and the solar wind.
Internal currents of the Earth flow in the mantle, which consists of substances with very good conductivity. The core is the current source. Energy is transferred from the core to the surface of the earth by convection. Thus, in the mantle there is constant movement substance, which forms a magnetic field according to the well-known law of motion of charged particles. If we associate its appearance only with internal currents, it turns out that all planets whose direction of rotation coincides with the direction of rotation of the Earth must have an identical magnetic field. However, it is not. Jupiter's geographic north pole coincides with the north magnetic pole.
Not only internal currents are involved in the formation of the Earth's magnetic field. It has long been known to react to the solar wind, a stream of high-energy particles emanating from the Sun as a result of reactions occurring on its surface.
The solar wind is by its nature an electric current (movement of charged particles). Being carried away by the rotation of the Earth, it creates a circular current, which leads to the appearance of the Earth's magnetic field.
The widespread use of magnetic fields in everyday life, at work and in scientific research... Suffice it to name devices such as alternators, electric motors, relays, accelerators elementary particles and various sensors. Let us consider in more detail what a magnetic field is and how it is formed.
What is a magnetic field - definition
A magnetic field is a force field acting on moving charged particles. The size of the magnetic field depends on the rate at which it changes. According to this feature, two types of magnetic fields are distinguished: dynamic and gravitational.
A gravitational magnetic field arises only near elementary particles and is formed depending on the features of their structure. Sources of a dynamic magnetic field are moving electric charges or charged bodies, conductors with current, as well as magnetized substances.
Magnetic field properties
The great French scientist André Ampere managed to find out two fundamental properties of the magnetic field:
- The main difference between a magnetic field and an electric field and its main property is that it is relative. If you take a charged body, leave it motionless in any frame of reference and place a magnetic needle next to it, then it will, as usual, point to the north. That is, it will not detect any field other than the earthly one. If you begin to move this charged body relative to the arrow, then it will begin to turn - this indicates that when the charged body moves, a magnetic field also arises, in addition to an electric one. Thus, a magnetic field appears if and only if there is a moving charge.
- The magnetic field acts on another electric current. So, it can be detected by tracing the movement of charged particles - in a magnetic field they will deflect, conductors with a current will move, a frame with a current will turn, magnetized substances will shift. Here we should recall the magnetic compass needle, usually colored in blue color, - it's just a piece of magnetized iron. He is always oriented to the north, because the Earth has a magnetic field. Our entire planet is a huge magnet: at the North Pole is the southern magnetic belt, and at the South geographic pole is the north magnetic pole.
In addition, the following characteristics are referred to the properties of the magnetic field:
- The strength of a magnetic field is described by magnetic induction - it is a vector quantity that determines the strength with which a magnetic field affects moving charges.
- The magnetic field can be of constant and variable type. The first is generated by an electric field that does not change in time; the induction of such a field is also unchanged. The second is most often generated using inductors powered by alternating current.
- The magnetic field cannot be perceived by the human senses and is recorded only by special sensors.
We still remember about the magnetic field from school, that's just what it is, “pops up” in the memories of not everyone. Let's refresh what we have passed, and perhaps tell you something new, useful and interesting.
Determination of the magnetic field
A magnetic field is a force field that acts on moving electric charges (particles). Thanks to this force field, objects are attracted to each other. There are two types of magnetic fields:
- Gravitational - is formed exclusively near elementary particles and varies in its strength based on the characteristics and structure of these particles.
- Dynamic, generated in objects with moving electric charges (current transmitters, magnetized substances).
For the first time, the designation for the magnetic field was introduced by M. Faraday in 1845, although its meaning was a little erroneous, since it was believed that both electric and magnetic effects and interactions are carried out proceeding from the same material field. Later in 1873, D. Maxwell "presented" quantum theory, in which these concepts began to be separated, and the previously derived force field was called the electromagnetic field.
How does a magnetic field appear?
Magnetic fields are not perceived by the human eye different subjects, and only special sensors can fix it. The source of the appearance of a magnetic force field on a microscopic scale is the movement of magnetized (charged) microparticles, which are:
- ions;
- electrons;
- protons.
Their movement occurs due to the spin magnetic moment, which is present in each microparticle.
Magnetic field, where can you find it?
As strange as it may sound, almost all objects around us have their own magnetic field. Although in the concept of many, only a pebble called a magnet has a magnetic field, which attracts iron objects to itself. In fact, the force of attraction is in all objects, only it manifests itself in a lesser valence.
It should also be clarified that a force field, called magnetic, appears only under the condition that electric charges or bodies are moving.
Immovable charges have an electric force field (it can also be present in moving charges). It turns out that the sources of the magnetic field are:
- permanent magnets;
- mobile charges.
A magnetic field this is the matter that arises around the sources electric current as well as around permanent magnets. In space, a magnetic field is displayed as a combination of forces that can affect magnetized bodies. This action is due to the presence of motive discharges at the molecular level.
The magnetic field only forms around electric charges that are in motion. That is why magnetic and electric fields are integral and together form electromagnetic field... The components of the magnetic field are interconnected and affect each other, changing their properties.
Magnetic field properties:
1. The magnetic field arises under the influence of driving charges of electric current.
2. At any point, the magnetic field is characterized by the vector physical quantity entitled magnetic induction, which is the force characteristic of the magnetic field.
3. The magnetic field can only act on magnets, conductive conductors and moving charges.
4. The magnetic field can be of constant and variable type.
5. The magnetic field is measured only by special devices and cannot be perceived by the human senses.
6. The magnetic field is electrodynamic, since it is generated only during the movement of charged particles and affects only the charges that are in motion.
7. Charged particles move along a perpendicular trajectory.
The size of the magnetic field depends on the rate of change of the magnetic field. According to this feature, there are two types of magnetic field: dynamic magnetic field and gravitational magnetic field. Gravitational magnetic field arises only near elementary particles and is formed depending on the structural features of these particles.
Magnetic moment occurs when a magnetic field acts on a conductive frame. In other words, the magnetic moment is a vector that is located on the line that runs perpendicular to the frame.
The magnetic field can be displayed graphically with the help of magnetic lines of force. These lines are drawn in such a direction that the direction of the field forces coincides with the direction of the line of force itself. Magnetic lines of force are continuous and closed at the same time.
The direction of the magnetic field is determined using a magnetic needle. The lines of force also determine the polarity of the magnet, the end with the output of the lines of force is North Pole and the end, with the entrance of these lines, is the south pole.
It is very convenient to visually evaluate the magnetic field using ordinary iron filings and a piece of paper.
If we put a sheet of paper on a permanent magnet, and pour sawdust on top, then the iron particles will line up according to the lines of force of the magnetic field.
The direction of the lines of force for the conductor is conveniently determined by the famous gimlet rule or rule right hand
... If we put our hand around the conductor so that thumb looked in the direction of the current (from minus to plus), then the 4 remaining fingers will show us the direction of the magnetic field lines. 
And the direction of the Lorentz force - the force with which the magnetic field acts on a charged particle or conductor with current, along left hand rule.
If we locate left hand in a magnetic field so that 4 fingers looked in the direction of the current in the conductor, and the lines of force entered the palm, then the thumb will indicate the direction of the Lorentz force, the force acting on the conductor placed in the magnetic field. 
That's all there is to it. Be sure to ask your questions in the comments.
