To understand what is characteristic magnetic field, many phenomena need to be defined. At the same time, you need to remember in advance how and why it appears. Find out what is power characteristic magnetic field. It is important that such a field can occur not only in magnets. In this regard, it would not hurt to mention the characteristics of the earth’s magnetic field.
Emergence of the field
First we need to describe the emergence of the field. Then you can describe the magnetic field and its characteristics. It appears during the movement of charged particles. May affect in particular live conductors. The interaction between a magnetic field and moving charges, or conductors through which current flows, occurs due to forces called electromagnetic.
The intensity or strength characteristic of a magnetic field at a certain spatial point is determined using magnetic induction. The latter is designated by the symbol B.
Graphical representation of the field
The magnetic field and its characteristics can be represented in graphical form using induction lines. This definition refers to lines whose tangents at any point will coincide with the direction of the magnetic induction vector.
These lines are included in the characteristics of the magnetic field and are used to determine its direction and intensity. The higher the intensity of the magnetic field, the more of these lines will be drawn.
What are magnetic lines
Magnetic lines in straight current-carrying conductors have the shape of a concentric circle, the center of which is located on the axis of the given conductor. The direction of magnetic lines near conductors carrying current is determined by the gimlet rule, which sounds like this: if the gimlet is positioned so that it is screwed into the conductor in the direction of the current, then the direction of rotation of the handle corresponds to the direction of the magnetic lines.
In a coil with current, the direction of the magnetic field will also be determined by the gimlet rule. It is also required to rotate the handle in the direction of the current in the solenoid turns. The direction of the magnetic induction lines will correspond to the direction of the translational movement of the gimlet.
It is the main characteristic of a magnetic field.
Created by a single current, under equal conditions, the field will vary in intensity in different media due to the different magnetic properties in these substances. The magnetic properties of the medium are characterized by absolute magnetic permeability. It is measured in henry per meter (g/m).
The characteristic of the magnetic field includes the absolute magnetic permeability of the vacuum, called the magnetic constant. The value that determines how many times the absolute magnetic permeability of the medium will differ from the constant is called relative magnetic permeability.
Magnetic permeability of substances
This is a dimensionless quantity. Substances with a permeability value of less than one are called diamagnetic. In these substances the field will be weaker than in a vacuum. These properties are present in hydrogen, water, quartz, silver, etc.
Media with a magnetic permeability exceeding unity are called paramagnetic. In these substances the field will be stronger than in a vacuum. These environments and substances include air, aluminum, oxygen, and platinum.
In the case of paramagnetic and diamagnetic substances, the value of magnetic permeability will not depend on the voltage of the external, magnetizing field. This means that the quantity is constant for a certain substance.
A special group includes ferromagnets. For these substances, the magnetic permeability will reach several thousand or more. These substances, which have the property of being magnetized and enhancing a magnetic field, are widely used in electrical engineering.
Field strength
To determine the characteristics of a magnetic field, a value called magnetic field strength can be used along with the magnetic induction vector. This term is determining the intensity of the external magnetic field. The direction of the magnetic field in a medium with identical properties in all directions, the intensity vector will coincide with the magnetic induction vector at the field point.
The strength of ferromagnets is explained by the presence in them of arbitrarily magnetized small parts, which can be represented in the form of small magnets.
With no magnetic field, a ferromagnetic substance may not have pronounced magnetic properties, since the fields of the domains acquire different orientations, and their total magnetic field is zero.
According to the main characteristic of the magnetic field, if a ferromagnet is placed in an external magnetic field, for example, in a coil with current, then under the influence of the external field the domains will turn in the direction external field. Moreover, the magnetic field at the coil will increase, and the magnetic induction will increase. If the external field is weak enough, then only a part of all domains will turn over, the magnetic fields of which are close in direction to the direction of the external field. As the external field strength increases, the number of rotated domains will increase, and with a certain value voltage of the external field, almost all parts will be rotated so that the magnetic fields will be located in the direction of the external field. This state is called magnetic saturation.
Relationship between magnetic induction and tension
The relationship between the magnetic induction of a ferromagnetic substance and the external field strength can be depicted using a graph called a magnetization curve. At the point where the curve graph bends, the rate of increase in magnetic induction decreases. After bending, where the tension reaches a certain value, saturation occurs, and the curve rises slightly, gradually taking on the shape of a straight line. In this area, the induction is still growing, but rather slowly and only due to an increase in the external field strength.
The graphical dependence of the indicator data is not direct, which means that their ratio is not constant, and the magnetic permeability of the material is not a constant indicator, but depends on the external field.
Changes in the magnetic properties of materials
When the current strength is increased to complete saturation in a coil with a ferromagnetic core and then decreased, the magnetization curve will not coincide with the demagnetization curve. With zero intensity, the magnetic induction will not have the same value, but will acquire a certain indicator called residual magnetic induction. The situation where magnetic induction lags behind the magnetizing force is called hysteresis.
To completely demagnetize the ferromagnetic core in the coil, it is necessary to give a reverse current, which will create the necessary voltage. Different ferromagnetic substances require a piece of different lengths. The larger it is, the greater the amount of energy required for demagnetization. The value at which complete demagnetization of the material occurs is called coercive force.
With a further increase in the current in the coil, the induction will again increase to saturation, but with a different direction of the magnetic lines. When demagnetizing in the opposite direction, residual induction will be obtained. The phenomenon of residual magnetism is used when creating permanent magnets from substances with a high index of residual magnetism. Cores are created from substances that have the ability to remagnetize electric machines and instruments.
Left hand rule
The force influencing a current-carrying conductor has a direction determined by the left-hand rule: when the palm of the virgin hand is positioned in such a way that the magnetic lines enter it, and four fingers are extended in the direction of the current in the conductor, bent thumb will indicate the direction of the force. This force is perpendicular to the induction vector and current.
A current-carrying conductor moving in a magnetic field is considered a prototype of an electric motor that changes electrical energy to mechanical.
Right hand rule
When a conductor moves in a magnetic field, an electromotive force is induced within it, which has a value proportional to the magnetic induction, the length of the conductor involved and the speed of its movement. This dependence is called electromagnetic induction. When determining the direction of the induced emf in a conductor, use the rule right hand: when the right hand is positioned in the same way as in the example with the left, the magnetic lines enter the palm, and the thumb indicates the direction of movement of the conductor, the extended fingers will indicate the direction of the induced EMF. Moving in a magnetic flux under the influence of an external mechanical force conductor is the simplest example electric generator, in which mechanical energy is converted into electrical energy.
It can be formulated differently: in a closed loop, an EMF is induced; with any change in the magnetic flux covered by this loop, the EMF in the loop is numerically equal to the rate of change of the magnetic flux that covers this loop.
This form provides an average EMF indicator and indicates the dependence of the EMF not on the magnetic flux, but on the rate of its change.
Lenz's Law
You also need to remember Lenz's law: the current induced when the magnetic field passing through the circuit changes, its magnetic field prevents this change. If the turns of a coil are penetrated by magnetic fluxes of different magnitudes, then the EMF induced throughout the whole coil is equal to the sum of the EDE in different turns. The sum of the magnetic fluxes of different turns of the coil is called flux linkage. The unit of measurement for this quantity, as well as for magnetic flux, is Weber.
When the electric current in the circuit changes, the magnetic flux it creates also changes. At the same time, according to the law electromagnetic induction, an EMF is induced inside the conductor. It appears in connection with a change in current in the conductor, therefore this phenomenon is called self-induction, and the EMF induced in the conductor is called self-induction EMF.
Flux linkage and magnetic flux depend not only on current strength, but also on the size and shape of a given conductor, and the magnetic permeability of the surrounding substance.
Conductor inductance
The proportionality factor is called the inductance of the conductor. It refers to the ability of a conductor to create flux linkage when electricity passes through it. This is one of the main parameters electrical circuits. For certain circuits, inductance is a constant value. It will depend on the size of the circuit, its configuration and the magnetic permeability of the medium. In this case, the current strength in the circuit and the magnetic flux will not matter.
The above definitions and phenomena provide an explanation of what a magnetic field is. The main characteristics of the magnetic field are also given, with the help of which this phenomenon can be defined.
When connecting two parallel conductors to electrical current, they will attract or repel, depending on the direction (polarity) of the connected current. This is explained by the phenomenon of the emergence of a special kind of matter around these conductors. This matter is called a magnetic field (MF). Magnetic force is the force with which conductors act on each other.
The theory of magnetism arose in ancient times, in the ancient civilization of Asia. In the mountains of Magnesia they found a special rock, pieces of which could be attracted to each other. Based on the name of the place, this rock was called “magnetic”. Bar magnet contains two poles. Its magnetic properties are especially pronounced at the poles.
A magnet hanging on a thread will show the sides of the horizon with its poles. Its poles will be turned north and south. The compass device operates on this principle. Opposite poles of two magnets attract, and like poles repel.
Scientists have discovered that a magnetized needle located near a conductor is deflected when an electric current passes through it. This indicates that an MP is formed around it.
The magnetic field affects:
Moving electric charges.
Substances called ferromagnets: iron, cast iron, their alloys.
Permanent magnets– bodies that have a common magnetic moment of charged particles (electrons).
1 - South pole of the magnet
2 - North pole of the magnet
3 - MP using the example of metal filings
4 - Magnetic field direction
Lines of force appear when a permanent magnet approaches paper sheet, on which a layer of iron filings is poured. The figure clearly shows the locations of the poles with oriented lines of force.
Magnetic field sources
- Electric field changing over time.
- Mobile charges.
- Permanent magnets.
We have been familiar with permanent magnets since childhood. They were used as toys that attracted various metal parts. They were attached to the refrigerator, they were built into various toys.
Electric charges that are in motion most often have more magnetic energy compared to permanent magnets.
Properties
- Main hallmark and the property of the magnetic field is relativity. If you leave a charged body motionless in a certain frame of reference, and place a magnetic needle nearby, then it will point to the north, and at the same time will not “feel” an extraneous field, except for the field of the earth. And if you start moving a charged body near the arrow, then an MP will appear around the body. As a result, it becomes clear that the MF is formed only when a certain charge moves.
- A magnetic field can influence and influence electric current. It can be detected by monitoring the movement of charged electrons. In a magnetic field, particles with a charge will be deflected, conductors with flowing current will move. The frame with the current supply connected will begin to rotate, and the magnetized materials will move a certain distance. The compass needle is most often colored Blue colour. It is a strip of magnetized steel. The compass always points north, since the Earth has a magnetic field. The entire planet is like a big magnet with its own poles.
The magnetic field is not perceived by human organs and can only be detected by special devices and sensors. It can be variable and permanent type. The alternating field is usually created by special inductors that operate from alternating current. A constant field is formed unchanged electric field.
Rules
Let's consider the basic rules for depicting the magnetic field for various conductors.
Gimlet rule
The line of force is depicted in a plane, which is located at an angle of 90 0 to the path of current flow so that at each point the force is directed tangentially to the line.
To determine the direction of magnetic forces, you need to remember the rule of a gimlet with a right-hand thread.
The gimlet must be positioned along the same axis with the current vector, the handle must be rotated so that the gimlet moves in the direction of its direction. In this case, the orientation of the lines is determined by rotating the gimlet handle.
Ring gimlet rule
The translational movement of the gimlet in a conductor made in the form of a ring shows how the induction is oriented; the rotation coincides with the flow of current.
The lines of force have their continuation inside the magnet and cannot be open.
The magnetic field of different sources is added to each other. In doing so, they create a common field.
Magnets with the same poles repel, and magnets with different poles attract. The value of the interaction strength depends on the distance between them. As the poles approach, the force increases.
Magnetic field parameters
- Flow coupling ( Ψ ).
- Magnetic induction vector ( IN).
- Magnetic flux (F).
The intensity of the magnetic field is calculated by the size of the magnetic induction vector, which depends on the force F, and is formed by the current I along a conductor having a length l: B = F / (I * l).
Magnetic induction is measured in Tesla (T), in honor of the scientist who studied the phenomena of magnetism and worked on their calculation methods. 1 T is equal to the magnetic flux induction force 1 N at length 1m straight conductor at an angle 90 0 to the direction of the field, with a flowing current of one ampere:
1 T = 1 x H / (A x m).
Left hand rule
The rule finds the direction of the magnetic induction vector.
If the palm of the left hand is placed in the field so that the magnetic field lines enter the palm from the north pole at 90 0, and 4 fingers are placed along the current flow, the thumb will show the direction of the magnetic force.
If the conductor is at a different angle, then the force will directly depend on the current and the projection of the conductor onto the plane at a right angle.
The force does not depend on the type of conductor material and its cross-section. If there is no conductor, and the charges move in a different medium, then the force will not change.
When the magnetic field vector is directed in one direction of one magnitude, the field is called uniform. Different environments affect the size of the induction vector.
Magnetic flux
Magnetic induction passing through a certain area S and limited by this area is a magnetic flux.
If the area is inclined at a certain angle α to the induction line, the magnetic flux is reduced by the size of the cosine of this angle. Its greatest value is formed when the area is at right angles to the magnetic induction:
F = B * S.
Magnetic flux is measured in a unit such as "weber", which is equal to the flow of induction of magnitude 1 T by area in 1 m2.
Flux linkage
This concept is used to create general meaning magnetic flux, which is created from a certain number of conductors located between magnetic poles.
In the case where the same current I flows through a winding with a number of turns n, the total magnetic flux formed by all turns is the flux linkage.
Flux linkage Ψ measured in Webers, and equals: Ψ = n * Ф.
Magnetic properties
Magnetic permeability determines how much the magnetic field in a certain medium is lower or higher than the field induction in a vacuum. A substance is called magnetized if it produces its own magnetic field. When a substance is placed in a magnetic field, it becomes magnetized.
Scientists have determined the reason why bodies acquire magnetic properties. According to scientists' hypothesis, there are microscopic electric currents inside substances. An electron has its own magnetic moment, which is of a quantum nature, and moves along a certain orbit in atoms. It is these small currents that determine magnetic properties.
If the currents move randomly, then the magnetic fields caused by them are self-compensating. The external field makes the currents ordered, so a magnetic field is formed. This is the magnetization of the substance.
Various substances can be divided according to the properties of their interaction with magnetic fields.
They are divided into groups:
Paramagnets– substances that have magnetization properties in the direction of an external field and have a low potential for magnetism. They have a positive field strength. Such substances include ferric chloride, manganese, platinum, etc.
Ferrimagnets– substances with magnetic moments unbalanced in direction and value. They are characterized by the presence of uncompensated antiferromagnetism. Field strength and temperature affect their magnetic susceptibility (various oxides).
Ferromagnets– substances with increased positive susceptibility, depending on tension and temperature (crystals of cobalt, nickel, etc.).
Diamagnets– have the property of magnetization in the opposite direction of the external field, that is, negative meaning magnetic susceptibility, independent of tension. In the absence of a field, this substance will not have magnetic properties. These substances include: silver, bismuth, nitrogen, zinc, hydrogen and other substances.
Antiferromagnets
– have a balanced magnetic moment, resulting in a low degree of magnetization of the substance. When heated, a phase transition of the substance occurs, during which paramagnetic properties appear. When the temperature drops below a certain limit, such properties will not appear (chromium, manganese).
The magnets considered are also classified into two more categories:
Soft magnetic materials
. They have low coercivity. In low-power magnetic fields they can become saturated. During the magnetization reversal process, they experience minor losses. As a result, such materials are used for the production of cores electrical devices operating on AC voltage( , generator, ).
Hard magnetic materials. They have an increased coercive force. To remagnetize them, a strong magnetic field is required. Such materials are used in the production of permanent magnets.
The magnetic properties of various substances are used in technical projects and inventions.
Magnetic circuits
A combination of several magnetic substances is called a magnetic circuit. They are similar and are determined by similar laws of mathematics.
Operate on the basis of magnetic circuits electrical devices, inductance, . In a functioning electromagnet, the flux flows through a magnetic circuit made of ferromagnetic material and air, which is not ferromagnetic. The combination of these components is a magnetic circuit. Many electrical devices contain magnetic circuits in their design.
1This article presents the results of studies of vector and scalar magnetic fields of permanent magnets and the determination of their distribution.
permanent magnet
electromagnet
vector magnetic field
scalar magnetic field.
2. Borisenko A.I., Tarapov I.E. Vector analysis and the beginnings of tensor calculus. – M.: Higher School, 1966.
3. Kumpyak D.E. Vector and tensor analysis: tutorial. – Tver: Tverskoy State University, 2007. – 158 p.
4. McConnell A.J. Introduction to tensor analysis with applications to geometry, mechanics and physics. – M.: Fizmatlit, 1963. – 411 p.
5. Borisenko A.I., Tarapov I.E. Vector analysis and the beginnings of tensor calculus. – 3rd ed. – M.: Higher School, 1966.
Permanent magnets. Constant magnetic field.
Magnet- these are bodies that have the ability to attract iron and steel objects and repel some others due to the action of their magnetic field. The magnetic field lines pass from the south pole of the magnet and exit from the north pole (Fig. 1).
Rice. 1. Magnet and magnetic field lines
A permanent magnet is a product made of a hard magnetic material with a high residual magnetic induction that maintains its magnetization state for a long time. Permanent magnets are manufactured various shapes and are used as autonomous (non-energy consuming) sources of magnetic field (Fig. 2).
An electromagnet is a device that creates a magnetic field when an electric current passes. Typically, an electromagnet consists of a winding of an ferromagnetic core, which acquires the properties of a magnet when an electric current passes through the winding.
Rice. 2. Permanent magnet
Electromagnets, designed primarily to create mechanical force, also contain an armature (a moving part of the magnetic circuit) that transmits force.
Permanent magnets made from magnetite have been used in medicine since ancient times. Queen Cleopatra of Egypt wore a magnetic amulet.
IN ancient China The “Imperial Book on Internal Medicine” addressed the issue of using magnetic stones to correct Qi energy in the body - “living force”.
The theory of magnetism was first developed by the French physicist Andre Marie Ampere. According to his theory, the magnetization of iron is explained by the existence electric currents, which circulate within the substance. Ampere made his first reports on the results of his experiments at a meeting of the Paris Academy of Sciences in the fall of 1820. The concept of “magnetic field” was introduced into physics by the English physicist Michael Faraday. Magnets interact through a magnetic field, he also introduced the concept of magnetic power lines.
Vector magnetic field
A vector field is a mapping that associates each point in the space under consideration with a vector with a beginning at that point. For example, the wind speed vector in this moment time varies from point to point and can be described by a vector field (Fig. 3).
Scalar magnetic field
If each point M of a given region of space (most often of dimension 2 or 3) is associated with a certain (usually real) number u, then they say that a scalar field is specified in this region. In other words, a scalar field is a function that maps Rn to R (scalar function of a point in space).
Gennady Vasilyevich Nikolaev tells in a simple way, shows and simple experiments proves the existence of a second type of magnetic field, which science for some strange reason has not found. Since the time of Ampere there has still been an assumption that it exists. He called the field discovered by Nikolaev scalar, but it is still often called by his name. Nikolaev brought electromagnetic waves to complete analogy with conventional mechanical waves. Now physics considers electromagnetic waves as exclusively transverse, but Nikolaev is confident and proves that they are also longitudinal or scalar and this is logical, how a wave can propagate forward without direct pressure is simply absurd. According to the scientist, the longitudinal field was hidden by science on purpose, possibly in the process of editing theories and textbooks. This was done with simple intent and was consistent with other cuts.
Rice. 3. Vector magnetic field
The first cut that was made was the lack of airtime. Why?! Because ether is energy, or a medium that is under pressure. And this pressure, if the process is organized correctly, can be used as a free source of energy!!! The second cut is the removal of the longitudinal wave, this is a consequence that if the ether is a source of pressure, that is, energy, then if you add only transverse waves, then no free or free energy can be obtained; a longitudinal wave is required.
Then the counter superposition of waves makes it possible to pump out the ether pressure. This technology is often called zero point, which is generally correct. It is at the border of the connection of plus and minus (high and low pressure), with counter-movement of waves, that you can get the so-called Bloch zone or simply a dip in the medium (ether), where additional energy of the medium will be attracted.
The work is an attempt to practically repeat some of the experiments described in the book by G.V. Nikolaev “Modern electrodynamics and the reasons for its paradoxical nature” and to reproduce the generator and motor of Stefan Marinov, as far as possible at home.
Experience G.V. Nikolaev with magnets: Two round magnets from speakers were used
Two flat magnets with opposite poles located on a plane. They attract each other (Fig. 4), whereas when they are perpendicular (regardless of the orientation of the poles), there is no force of attraction (only torque is present) (Fig. 5).
Now let’s cut the magnets in the middle and connect them in pairs with different poles, forming magnets of the original size (Fig. 6).
When these magnets are located in the same plane (Fig. 7), they will again, for example, be attracted to each other, while when positioned perpendicularly they will already repel (Fig. 8). In the latter case, the longitudinal forces acting along the cut line of one magnet are a reaction to the transverse forces acting on side surfaces another magnet, and vice versa. Existence longitudinal force contradicts the laws of electrodynamics. This force is the result of the scalar magnetic field present at the cut site of the magnets. Such a composite magnet is called siberian colia.
A magnetic well is a phenomenon when a vector magnetic field repels, and a scalar magnetic field attracts, and a distance is created between them.
Bibliographic link
Zhangisina G.D., Syzdykbekov N.T., Zhanbirov Zh.G., Sagyntai M., Mukhtarbek E.K. PERMANENT MAGNETS AND PERMANENT MAGNETIC FIELDS // Advances modern natural science. – 2015. – No. 1-8. – P. 1355-1357;URL: http://natural-sciences.ru/ru/article/view?id=35401 (access date: 04/05/2019). We bring to your attention magazines published by the publishing house "Academy of Natural Sciences"
Let's understand together what a magnetic field is. After all, many people live in this field all their lives and don’t even think about it. It's time to fix it!
A magnetic field
A magnetic field – special kind matter. It manifests itself in the 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, either 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 that has 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 represented by magnetic power lines. The lines of force are continuous and closed, and their direction always coincides with the direction of action of the field forces. If metal shavings are scattered around a permanent magnet, the metal particles will show a clear picture of the magnetic field lines coming out of the north pole and entering the south pole. Graphic characteristic of a magnetic field - lines of force.
Characteristics of the magnetic field
The main characteristics of the magnetic field are magnetic induction, magnetic flux And magnetic permeability. But let's talk about everything in order.
Let us immediately 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 the letter B . Unit of measurement of magnetic induction – Tesla (T).
Magnetic induction shows how strong the field is by determining the force it exerts on a charge. This force is called Lorentz force.
Here q - charge, v - its speed in a magnetic field, B - induction, F - Lorentz force with which the field acts on the charge.
F– a physical quantity equal to the product of 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 flux passes. Magnetic flux is a scalar characteristic of a magnetic field.
We can say that magnetic flux characterizes the number of magnetic induction lines penetrating a unit area. Magnetic flux is measured in Weberach (Wb).
Magnetic permeability– coefficient that determines the magnetic properties of the medium. One of the parameters on which the magnetic induction of a field depends is magnetic permeability.
Our planet has been a huge magnet for several billion years. The induction of the Earth's magnetic field varies 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 neighboring areas. Some of the largest magnetic anomalies on the planet - Kursk And Brazilian magnetic anomalies.
The origin of the Earth's magnetic field still remains 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 the molten iron-nickel alloy is moving, and the movement of charged particles is the electric current that generates the 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 move. Their displacement has been recorded since 1885. For example, over the past hundred years, the magnetic pole in the Southern Hemisphere has shifted almost 900 kilometers and is now located in the Southern Ocean. The pole of the Arctic hemisphere is moving through the Arctic Ocean to the East Siberian magnetic anomaly; its movement speed (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 solar wind. Charged particles from deep space do not fall directly to the ground, but are deflected by a giant magnet and move along its lines of force. Thus, all living things are protected from harmful radiation.
Several events have occurred over the course of Earth's history. inversions(changes) of magnetic poles. Pole inversion- this is when they change places. Last time this phenomenon occurred about 800 thousand years ago, and in total there were more than 400 geomagnetic inversions in the history of the Earth. Some scientists believe that, given the observed acceleration of the movement of the magnetic poles, the next pole inversion should be expected in the next couple of thousand years.
Fortunately, a pole change is not yet expected in our century. This means that you can think about pleasant things 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, to whom you can confidently entrust some of the educational troubles with confidence! and other types of work you can order using the link.
If you insert a hardened steel rod into a current coil, then, unlike an iron rod, it does not demagnetize after switches off the current, and retains magnetization for a long time.
Bodies that retain magnetization for a long time are called permanent magnets or simply magnets.
The French scientist Ampere explained the magnetization of iron and steel electric currents, which circulate inside each molecule these substances. At the time of Ampere, nothing was known about the structure of the atom, so the nature of molecular currents remained unknown. Now we know that in every atom there are negatively charged electron particles, which, when moving, create magnetic fields, they cause the magnetization of iron and. become.
Magnets can have a wide variety of shapes. Figure 290 shows an arc and strip magnets.
Those places of the magnet where the strongest are found magnetic actions are called magnet poles(Fig. 291). Every magnet, like the magnetic needle we know, necessarily has two poles; northern (N) and southern (S).
By holding a magnet close to objects made from various materials, it can be established that very few of them are attracted by a magnet. Fine attracted by magnet cast iron, steel, iron and some alloys that are much weaker - nickel and cobalt.
Natural magnets are found in nature (Fig. 292) - iron ore (the so-called magnetic iron ore). Rich deposits We have magnetic iron ore in the Urals, in Ukraine, in the Karelian Autonomous Soviet Socialist Republic, Kursk region and in many other places.
Iron, steel, nickel, cobalt and some other alloys acquire magnetic properties in the presence of magnetic iron ore. Magnetic iron ore allowed people to become familiar with the magnetic properties of bodies for the first time.
If a magnetic needle is brought closer to another similar needle, they will turn and set opposite poles against each other (Fig. 293). The arrow interacts with any magnet in the same way. By bringing a magnet close to the poles of a magnetic needle, you will notice that the north pole of the needle is repelled by the north pole of the magnet and attracted to the south pole. The south pole of the arrow is repelled by the south pole of the magnet and attracted by the north pole.
Based on the experiments described, it is possible draw the following conclusion; different names Magnetic poles attract, like poles repel.
The interaction of magnets is explained by the fact that there is a magnetic field around every magnet. The magnetic field of one magnet acts on another magnet, and, conversely, the magnetic field of the second magnet acts on the first magnet.
Using iron filings you can get an idea of the magnetic field of permanent magnets. Figure 294 gives an idea of the magnetic field of a bar magnet. Both the magnetic lines of the magnetic field of the current and the magnetic lines of the magnetic field of the magnet are closed lines. Outside the magnet, magnetic lines leave the north pole of the magnet and enter the south pole, closing inside the magnet.
Figure 295a shows magnetic magnetic field lines of two magnets, facing each other with like poles, and in Figure 295, b - two magnets facing each other with opposite poles. Figure 296 shows the magnetic field lines of an arc-shaped magnet.
All these pictures are easy to obtain through experience.
Questions. 1. What is the difference in magnetizing a piece of iron and a piece of steel using current? 2, What bodies are called permanent magnets? 3. How did Ampere explain the magnetization of iron? 4. How can we now explain Ampere’s molecular currents? 5. What are the magnetic poles of a magnet called? 6. Which substances do you know that are attracted by a magnet? 7. How do the poles of magnets interact with each other? 8. How can you use a magnetic needle to determine the poles of a magnetized steel rod? 9. How can you get an idea of the magnetic field of a magnet? 10. What are the magnetic field lines of a magnet?