A long time magnetic field causes many questions from a person, but now remains a little-known phenomenon. Its characteristics and properties tried to explore many scientists, because the benefits and potential from the use of the field were indisputable facts.
Let's disassemble everything in order. So, how does any magnetic field act and forms? That's right, from electric current. And the current, if you believe textbooks in physics, is the direction of the flow of charged particles, isn't it? So, when the current passes through any conductor, a certain variety of matter begins to act near him - a magnetic field. The magnetic field can be created by a current of charged particles or 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 affect the flow of charged particles, and they change the initial direction of movement perpendicular to the field itself.
Another magnetic field can be called electrodynamic, because it is formed about moving and acts only on moving particles. Well, it is dynamic due to the fact that it has a special structure in rotating bions on the area of \u200b\u200bspace. Make them rotate and move can ordinary electric moving charge. Biions transmit any possible interactions in this area of \u200b\u200bspace. Therefore, the moving charge attracts one pole of all bions and makes them rotate. Only he can bring them out of the state of rest, nothing else, because other forces will not be able to influence them.
The electric field contains charged particles that are very quickly moving and can overcome 300,000 km in just a second. The same speed also has light. The magnetic field does not happen without an electric charge. This means that the particles are incredibly closely related to each other and exist in the general electromagnetic field. That is, if there are any changes in the magnetic field, then the changes will be in the electric. This law is also addressed.
We speak a lot about the magnetic field here, but how can I imagine it? We cannot see it with our human naked eye. Moreover, due to the incredibly rapid spread of the field, we do not have time to fix it using various devices. But to study something, you need to have at least some idea about it. It also often has to portray the magnetic field in the schemes. In order to be easier to understand it, the conditional power lines of the field are carried out. Where did they take them? They came up with no accident.
Let's try to see a magnetic field with small metal sawdust and an ordinary magnet. Matter on a flat surface these sawdust and enter them into action magnetic field. Then we will see that they will move, rotate and line in drawing or scheme. The resulting image will show the approximate action of forces in the magnetic field. All forces and, accordingly, the power lines are continuous and closed in this place.
The magnetic arrow has similar characteristics and properties with a compass, and it is used to determine the direction of power lines. If it falls into the zone of action of the magnetic field, in its north pole we see the direction of the forces. Then we highlight a few conclusions: the top of an ordinary permanent magnet, from which the power lines proceed are denoted by the North Pole of the magnet. Then as the southern pole denote the point where the forces are closed. Well, the power lines inside the magnet in the diagram are not allocated.
Magnetic field, its properties and characteristics are pretty great applicationbecause in many tasks it has to take into account and explore. This is the most important phenomenon in the science of physics. It is inextricably linked with more complex things, such as magnetic permeability and induction. To clarify all the reasons for the appearance of a magnetic field, you need to rely on real scientific facts and confirmation. Otherwise, in more complex tasks, the wrong approach may disrupt the integrity of the theory.
And now we give examples. We all know our planet. Do you say that it does not have a magnetic field? Maybe you are right, but scientists say that processes and interactions within the Earth's core give rise to a huge magnetic field, which stretches for thousands of kilometers. But in any magnetic field should be his pole. And they exist, simply arranged a little away from the geographical pole. How do we feel it? For example, birds are developed by navigation abilities, and they are oriented, in particular, in a magnetic field. So, with his help, Geei safely arrive in Lapland. Special navigation devices also use this phenomenon.
To understand the origin of the field and its characteristics, it is necessary to have an idea of \u200b\u200bmany natural phenomena. If it is simple, then this phenomenon is a special form of matter created by magnets. Moreover, the sources of the magnetic field can be relays, current generators, electric motors, etc.
A bit of history
Before driving deep into the story, it is worth find out the definition of a magnetic field: MP is a power field that affects moving electrical charges and bodies. As for the phenomenon of magnetism, it is rooted in a deep past, by the heyday of the civilizations of Malaya Asia. It is on their territory, in Magnesia, the rocks were found, which attracted each other. They were called in honor of the terrain, from where they occurred.
Definitely it is difficult to say who discovered the concept of a magnetic field. However B. early XIX. A century H. Erst has conducted an experiment and revealed that if the magnetic arrow is located near the conductor and put the current on it, then the boom will begin to deviate. If a frame is taken with a current, then its field affects the external field.
Regarding modern options, magnets that are used in the production of various products can affect the operation of electronic heart stimulants and other devices in cardiology.
Standard iron and ferrite magnets almost do not cause problems, as they are characterized by a small force. However, more stronger magnets appeared relatively recently - neodymium, boron and iron alloys. They are bright silver and their field very much. They are used in such industries:
- Sewing.
- Food.
- Machine-tool.
- Space, etc.
Definition of concept and graphic display
Magnets that are presented in the form of horseshoes have two ends - two poles. It is in these places that the most pronounced attracting properties are manifested. If the magnet is suspended on the rope, then one end will always reach the north. In this principle, the work of the compass is founded.
Magnetic poles can interact with each other: the same is repelled, the variepetes are attracted. Around these magnets there is a corresponding field, which looks like electric. It is worth mentioning that it is impossible to determine the magnetic field of human senses.
The magnetic field and its characteristics are often displayed as graphs, with induction lines. The term means that there are lines, whose tangents converge with the magnetic induction vector. This parameter consists in the properties of MP and serves as the determining factor in its power and direction.
If the field is superimensional, then the lines will be much larger.
The concept of a magnetic field as an image:
In direct conductors with electric shock there are lines in the form of a concentric circle. Their central part will be placed on the axial line of the conductor. Magnetic lines are sent according to the line of the reel: the cutting element is screwed in such a way that it is specified towards the current, and the handle would point to the direction of lines.
The field that is created by one source may have different power in various environments. All due to the magnetic parameters of the medium, and more specifically, the absolute magnetic permeability, which is measured in Henry per meter (g / m). Other field parameters are a magnetic constant - complete vacuum permeability, and relative constant.
Permeability, tension and induction
Permeability - dimensionless meaning. Environments that have permeability less than units are referred to in diamagnetic. They are not more powerful in them than in vacuum. Such elements include water, table salt, bismuth, hydrogen. Substances with permeability above units are called paramagnetic. These include:
- Air.
- Lithium.
- Magnesium.
- Sodium.
The magnetic permeability indicator of diamagnetics and paramagnetics does not depend on such a factor as the outdoor field voltage. Simply put, this value is constant for a specific environment.
Ferromagnets are counted for a separate group. Their magnetic permeability can be equal to several thousand. Such substances are able to actively magnify and increase the field. Ferromagnets are widespread in electrical engineering.
Experts depict the interconnectedness of the outdoor field tension and the magnetic induction of ferromagnets using the magnetization curve, i.e. graphs. Where the curve graph befits, the increase in induction increases. After the bend, when the determined indicator is reached, saturation and the curve is slightly lifted, approaching the values \u200b\u200bof the line. In this place there is an increase in induction, but rather small. Summing up, it can be said that a graph of induction intensity relationship is a non-permeable, and that the permeability of the element depends on the external field.
Field tensions
Another important characteristic of MP is called tension that is used along with an induction vector. This definition is the vector parameter. It defines the intensity of the external field. You can explain the powerful fields in ferromagnets with small elements in them, which are submitted by small magnets.
If the ferromagnetic component does not have a magnetic field, then it may not have magnetic properties, because the domain fields will have different orientation. Considering the characteristics, you can put a ferromagnet in an external MP, for example, in a coil with a current, at this time the domains will change their position in the direction of the field. But if the outer MP is too weak, then only a small number of domains is turned over, which is close to it.
As the external field will increase their strength, all more Domains will start turning in its direction. Once all the domains turn, a new definition will appear - magnetic saturation.
Change of field
The magnetization curve does not converge with the clarification curve at the moment when the current increases until its saturation in the coil with a ferromagnet. Other occurs with zero tension, i.e. magnetic induction will contain other indicators that are referred to as residual induction. If induction is lagging behind the magnetizing force, then this is called hysteresis.
To achieve the absolute demagnetization of the core of the ferromagnet in the coil, it is necessary to give a reverse direction, creating the desired tension.
Various ferromagnetic elements need different segments. What he is more such a segment, the greater the energy is necessary for demagnetization. When the component is completely modified, it will reaches a state, which is called the coercive force.
If you continue to increase the current in the coil, then at one moment the induction will reaches the saturation state, but with another position of the lines. When demaging, residual induction appears in the other side. This can be useful in the production of a permanent magnet. Details that have good lubricating ability are used in mechanical engineering.
Lenza Rules, Left and Right Hand
By the law of the left hand, you can see the direction of current without any problems. So, when installing a hand, when magnetic lines and 4 fingers are admitted to the palm, shown on the current direction in the conductor, the thumb will show the direction of force. Such force will be directed perpendicular to the current and the induction vector.
The conductor moving in the MP is called the prototype of an electric motor when electricity turns into mechanical. When the conductor moves to the MP, an electromotive force is caused inside it, which has indicators, proportional induction used by the length and speed of movement. This ratio is referred to as electromagnetic induction.
To determine the direction of EDC, use the right hand rule: It is also placed in such a way that the line penetrate the palm, while the fingers will show where the induced EMF is directed, and the thumb point will send to the movement of the conductor. The conductor, which moves into the MP under the influence of mechanical force, is considered a simplified version of the electric generator, where the mechanical energy turns into an electric.
When a magnet is entered into the coil, an increase in the magnetic flux in the circuit, and the MP, which is created by the current induced, is directed to an increase in the growth of the magnetic flux. To determine the direction, you need to look at the magnet from the northern field.
If the conductor is able to create the clutch of flows when electricity passes through it, this is called the conductor inductance. This characteristic refers to the main one when the electrical circuits mention.
Field of land
Planet Earth itself is one big magnet. It is surrounded by a sphere where magnetic power is dominated. A consistent part of scientific researchers argues that the magnetic field of the Earth arose due to the kernel. It has a liquid sheath and solid internal composition. Since the planet rotates, endless flows appear in the liquid part, and the movement of electric charges creates a field around the planet, which serves as a protective barrier from harmful cosmic particles, for example, from solar wind. The field changes the direction of particles by sending them along the lines.
Earth is called a magnetic dipolem. The South Pole is located on the geographical northern, and the northern MP, on the contrary, on the southern geographical. In reality, the pole does not coincide not only by location. The fact is that the magnetic axis leans towards the rotational axis of the planet by 11.6 degrees. Because of such a small difference, it is possible to use a compass. The arrow of the device exactly indicates the southern magnetic pole and a little bit with a distortion - to the northern geographical. If the compass existed 730 thousand years ago, he would guide the magnetic, and the usual North Pole.
Subject: Magnetic field
Prepared: Baigarashev D.M.
Checked: Gabdullina A.T.
A magnetic field
If two parallel conductor are connected to a current source so that they passed electricity, depending on the direction of the current in them, the conductors are either repel, or attract.
An explanation of this phenomenon is possible from the position of the occurrence around the conductors of a special type of matter - a magnetic field.
The forces with which the conductors interact with the current are called magnetic.
A magnetic field - This is a special type of matter, a specific feature of which is an action on a moving electrical charge, conductors with a current, bodies with a magnetic moment, with force, depending on the charge velocity vector, the direction of the current in the explorer and on the direction of the magnetic moment of the body.
The history of magnetism is rooted in deep antiquity, to the ancient civilizations of small Asia. It is on the territory of Malaya Asia, in Magnesia, they found a rock formation, the samples of which were attracted to each other. By the name of the terrain, such samples began to be called "magnets". Any magnet in the form of a rod or horseshoe has two butts, which are called poles; It is at this place that its magnetic properties are most strongest. If you hang a magnet on the thread, one pole will always point to the north. In this principle, a compass was founded. The north pole addressed to the north of a free hanging magnet is called the northern pole of the magnet (N). The opposite pole is called the Southern Pole (S).
Magnetic poles interact with each other: the poles of the same name are repelled, and the variepetes are attracted. Similarly, the concept of the electric field surrounding the electrical charge is introduced an idea of \u200b\u200ba magnetic field around the magnet.
In 1820, Ersted (1777-1851) found that the magnetic arrow located next to the electric conductor deviates when the conductor flows the current, i.e., a magnetic field is created around the conductor with a current. If you take a frame with a current, then the outer magnetic field interacts with the magnetic field of the frame and has an orienting action on it, i.e. there is a position of the frame, in which the external magnetic field has a maximum rotating action on it, and there is a position when the torque Forces equal to zero.
Magnetic field at any point can be characterized by a vector in which is called vector magnetic induction or magnetic induction At point.
Magnetic induction B is a vector physical quantity that is the power characteristic of the magnetic field at the point. It is equal to the ratio of the maximum mechanical moment of forces acting on the frame with the current placed in a homogeneous field, to the product of the current in the frame on its area:
For the direction of the magnetic induction vector, the direction of positive standards is taken to the frame, which is associated with the current in the frame of the rule of the right screw, during the mechanical moment equal to zero.
In the same way, as the electric field strength lines depict the magnetic field induction lines. Line of the magnetic field induction is an imaginary line, the tangent to which coincides with the direction at the point.
The directions of the magnetic field at this point can be defined as a direction that indicates
north Pole Compass Arrow placed at this point. It is believed that the induction lines of the magnetic field are directed from the North Pole to the South.
The direction of the magnetic induction lines of the magnetic field created by the electric current, which flows through the straight conductor is determined by the rule of the bouwn or the right screw. For the direction of magnetic induction lines, the direction of rotation of the screw head is taken, which would ensure the transmitted movement in the direction of the electric current (Fig. 59).
where N 01 \u003d 4 P. 10 -7 in C / (A M). - Magnetic constant, R - distance, I - current power in the conductor.
Unlike the tension lines of the electrostatic field, which begin with a positive charge and ends on a negative, the magnetic field induction line is always closed. The magnetic charge is similar to the electrical charge not detected.
The unit of induction takes one Tesla (1 TL) - the induction of such a homogeneous magnetic field, in which the frame of 1 m 2, which flows in 1 A, the maximum torque mechanical moment is valid equal to 1 n m.
The induction of the magnetic field can also be determined by strength acting on the conductor with a current in the magnetic field.
The ampere force of the ampere, the value of which is determined by the following expression on the conductor with a current, placed in a magnetic field.
where I is the current in the conductor, l -the length of the conductor, B - the module of the magnetic induction vector, and the angle between the vector and the direction of the current.
Ampere's force can be determined by the rule of the left hand: the palm of the left hand is in such a way that the magnetic induction lines are in the palm, we have four fingers in the current direction in the conductor, then the bent thumb shows the direction of the ampere force.
Considering that I \u003d Q 0 NSV, and substituting this expression in (3.21), we obtain F \u003d Q 0 NSH / B Sin a.. The number of particles (n) in a predetermined volume of the conductor is N \u003d NSL, then F \u003d Q 0 NVB SIN a..
We define the force acting from the magnetic field to a separate charged particle moving in a magnetic field:
This force is called Lorentz's force (1853-1928). The direction of Lorentz's power can be determined by the rule of the left hand: the palm of the left hand is located so that the lines of magnetic induction enter the palm, four fingers showed the direction of movement of a positive charge, a large bent finger will show the direction of Lorentz's power.
The strength of the interaction between two parallel conductors for which the currents of the I 1 and I 2 flow are equal to:
where l -part of the conductor in a magnetic field. If currents of one direction, then the conductors are attracted (Fig. 60), if the opposite direction is repelled. Forces acting on each conductor are equal to the module, opposite to the direction. Formula (3.22) is the main to determine the unit of current 1 amper (1 A).
Magnetic properties of the substance characterizes the scalar physical size - magnetic permeability, showing how many times the induction in the magnetic field in a substance, fully filling the field, differs in the module from the induction in 0 magnetic field in vacuo:
In 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 substances are moving in various orbits. To simplify, we consider these orbits with circular, and each electron, applying around the atomic nucleus, can be considered as a circular electric current. Each electron, like a circular current, creates a magnetic field that is called orbital. In addition, the electron in the atom has its own magnetic field, called spin.
If, when introducing into an external magnetic field with induction in 0 inside the substance, induction is created in< В 0 , то такие вещества называются диамагнитными (N.< 1).
IN diamagnetic The materials in the absence of an external magnetic field magnetic fields of electrons are compensated, and when they are making them into a magnetic field, the induction of the magnetic field of the atom becomes directed against the external field. The diamagnet is pushed out of the external magnetic field.
W. paramagnetic Materials The magnetic induction of electrons in atoms is fully compensated, and the atom generally turns out to be similar to a small permanent magnet. Usually in substance, all these small magnets are oriented arbitrarily, and the total magnetic induction of all their fields is zero. If you put a paramagnet into an external magnetic field, then all small magnets - atoms will turn in an external magnetic field like the compass arrows and the magnetic field in the substance is enhanced ( n. >= 1).
Ferromagnetic are called such materials in which n. "1. So-called domains, macroscopic areas of spontaneous magnetization are created in ferromagnetic materials.
In various domains of induction of magnetic fields, there are various directions (Fig. 61) and in a large crystal
mutually compensate each other. When the ferromagnetic sample is introduced into the outer magnetic field, the boundaries of individual domains occur so that the volume of domains oriented over the external field increases.
With an increase in the induction of the external field, the magnetic induction of the magnetized substance increases. In some values \u200b\u200bin 0 induction ceases sharp growth. This phenomenon is called magnetic saturation.
The characteristic feature of ferromagnetic materials is the phenomenon of hysteresis, which consists in the ambiguous dependence of the induction in the material from the induction of the external magnetic field during its change.
The magnetic hysteresis loop is a closed curve (CDC`s), expressing the dependence of induction in the material from the amplitude of the induction of the external field with a periodic slow down change in the latter (Fig. 62).
The hysteresis loop is characterized by the following values \u200b\u200bB S, B R, B C. B s - the maximum induction value of the material at 0s; In R - residual induction equal to the value of induction in the material with a decrease in the induction of an external magnetic field from b 0s to zero; - C and in C - coercive force - the value equal to the induction of the external magnetic field needed to change the induction in the material from the residual to zero.
For each ferromagnet, there is such a temperature (Curie point (J. Curi, 1859-1906), above which the ferromagnet loses its ferromagnetic properties.
There are two ways to bring the magnetized ferromagnet into a demagnetic state: a) heat higher than the point of Curie and cool; b) magnetize the material by a variable magnetic field with slowly decreasing amplitude.
Ferromagnets with low residual induction and coercive force are called magnetic. They are used in devices where ferromagnets have often rejected (cores of transformers, generators, etc.).
Cericant ferromagnets, which have a large coercive force, are used for the manufacture of permanent magnets.
Magnetic field It is called a special, different substance, the type of matter through which the magnet action to other bodies is transmitted.
A magnetic field It occurs in space surrounding moving electrical charges and permanent magnets. It affects only moving charges. Under the influence of electromagnetic forces, moving charged particles are rejected
From its initial path in the direction perpendicular to the field.
Magnetic and electric fields are inseparable and form a joint electromagnetic field. Any change electric fieldleads to the appearance of a magnetic field, and, on the contrary, any change in the magnetic field is accompanied by the occurrence of the electric field. The electromagnetic field spreads at the speed of light, i.e. 300 LLC km / s.
It is well known for the action of permanent magnets and electromagnets for ferromagnetic bodies, the existence and inseparable unity of the poles of magnets and their interaction (the variance poles are attracted, the same is repelled). Similarly
with magnetic poles of land poles magnets call northern and South.
The magnetic field is clearly depicted by magnetic power lines, which set the direction of the magnetic field in space (Fig. 1.1). These lines have no beginning, no end, i.e. are closed.
The power lines of the magnetic field of the rectilinear conductor are concentric circles covering the wire. The stronger the current, the stronger the magnetic field around the wire. When removing from the wire with a current, the magnetic field is weakening.
In space surrounding the magnet or electromagnet, for the positive direction of magnetic power lines conditionally, the direction from north Pole to South. The more intense the magnetic field, the higher the density of the power lines.
The direction of magnetic power lines is determined rule Braschik:.
Fig. 1. Magnetic field of magnets:
a - straight; b - horseshoe-like
Fig. 2. Magnetic field:
a - straight wire; b - inductive coil
If screwing the screw in the direction of current, then magnetic magnetic power lines will be directed along the screw (Fig. 2 a)
To obtain a stronger magnetic field, inductive coils with wire winding are used. In this case, the magnetic fields of the individual turns of the inductive coil are also addressed and their power lines merge into a common magnetic flux.
Magnetic power lines come out of inductive coil
at the end, where the current is directed against the course of the clockwise, i.e. this end is the northern magnetic pole (Fig. 2, b).
When the direction of current changes in the inductive coil, the direction of the magnetic field will change.
Well known to the wide use of the magnetic field in everyday life, in production and in scientific research. It is enough to name the devices such as alternating current generators, electric motors, relays, elementary particle accelerators and various sensors. Consider in more detail what is the magnetic field and how it is formed.
What is a magnetic field - definition
The magnetic field is a power field acting on moving charged particles. The size of the magnetic field is grieved on the speed of its change. According to this feature, two types of magnetic field are distinguished: dynamic and gravitational.
The gravitational magnetic field occurs only near the elementary particles and is formed depending on the characteristics of their structure. Sources of dynamic magnetic field are moving electrical charges or charged bodies, conductor with current, as well as magnetized substances.
Properties of magnetic field
The great French scientist Andre Amper managed to find out the two fundamental properties of the magnetic field:
- The main difference between the magnetic field from the electric and its primary property is that it is wearing relative nature. If you take a charged body, leave it stationary in any reference system and place a magnetic arrow, then it will, as usual, point to the north. That is, it will not detect any field except the earth. If you start moving this charged body relative to the arrow, it will start rotating - this suggests that when the charged body moves, the magnetic field is also occurring other than electric. Thus, the magnetic field appears then and only if there is a moving charge.
- The magnetic field acts on another electric current. So, you can detect it by tracing the movement of charged particles, - in the magnetic field they will deviate, the conductors with the current will move, the frame with the current to turn the magnetized substances to shift. Here you should remember the magnetic arrow of the compass, usually painted in blue, because it is just a piece of magnetized iron. It is always oriented to the north, because the earth has a magnetic field. Our entire planet is a huge magnet: there is a southern magnetic belt on the North Pole, and the Northern Magnetic Pole is located on the southern geographical pole.
In addition, the properties of the magnetic field include the following characteristics:
- The power of the magnetic field is described by magnetic induction - this is a vector value that determines which force magnetic field affects moving charges.
- Magnetic field can be permanent and aC type. The first is generated by an electric field that does not change over time, the induction of such a field is also unchanged. The second most frequently generated by inductors feeding with alternating current.
- The magnetic field cannot be perceived by human senses and is fixed only by special sensors.
