To understand what is characteristicmagnetic field, it is necessary to give definitions to many phenomena. In this case, you need to remember in advance how and why it appears. Learn what is the power characteristic of a magnetic field. It is important that a similar field can occur not only in magnets. In this regard, it does not hurt to mention the characteristics of the earth's magnetic field.
First, describe the occurrence of the field.After that, you can describe the magnetic field and its characteristics. It appears during the movement of charged particles. Can affect the moving electrical charges, especially conductive conductors. The interaction between a magnetic field and moving charges, or conductors through which a current flows, is due to forces called electromagnetic ones.
The intensity or force characteristic of a magnetic field at a certain spatial point is determined by magnetic induction. The latter is denoted by B.
The magnetic field and its characteristics can beare represented in graphical form by means of induction lines. This definition refers to the lines tangent to which at any point will coincide with the direction of the vector in the magnetic induction.
These lines enter into the characteristic of the magnetic field and are used to determine its direction and intensity. The higher the intensity of the magnetic field, the more these lines will be drawn.
Magnetic lines for rectilinear conductors withcurrent have the form of a concentric circle, the center of which is located on the axis of a given conductor. The direction of the magnetic lines near the conductors with current is determined by the rule of the borer, which sounds like this: if the bore 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.
At the coil with current the direction of the magnetic fieldwill also be determined by the rule of the drill. It is also required to rotate the handle in the direction of the current in the turns of the solenoid. The direction of the lines of magnetic induction will correspond to the direction of the translational movement of the drill.
The definition of homogeneity and inhomogeneity is the main characteristic of the magnetic field.
Created by one current, under equal conditions,the field will differ in its intensity in different media because of the different magnetic properties in these substances. The magnetic properties of the medium are characterized by absolute magnetic permeability. Measured in Henry per meter (g / m).
The characteristic of the magnetic field isabsolute magnetic permeability of vacuum, called the magnetic constant. The value that determines how many times the absolute magnetic permeability of the medium will be different from the constant is called the relative magnetic permeability.
This is a dimensionless quantity.Substances having 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 exceedingunit, are called paramagnetic. In these substances, the field will be stronger than in a vacuum. These media and substances include air, aluminum, oxygen, platinum.
В случае с парамагнитными и диамагнитными substances the value of the magnetic permeability will not depend on the voltage of the external, magnetizing field. This means that the value is constant for a certain substance.
The special group includes ferromagnets.For these substances, the magnetic permeability will be several thousand or more. For these substances, which have the property of magnetizing and amplifying the magnetic field, there is widespread use in electrical engineering.
To determine the characteristics of the magnetic fieldTogether with the magnetic induction vector, a value called the magnetic field strength can be applied. This term is a vector quantity that defines the intensity of an external magnetic field. The direction of the magnetic field in a medium with the same properties in all directions of the intensity vector will coincide with the vector of magnetic induction at the field point.
Strong magnetic properties of ferromagnets are explained by the presence of arbitrarily magnetized small parts in them, which can be represented as small magnets.
With an absent magnetic field, the ferromagnetic substance may not have pronounced magnetic properties, since the domain fields acquire different orientations, and their total magnetic field is zero.
According to the main characteristic of the magnetic field, ifIf the ferromagnet is placed in an external magnetic field, for example, in a current coil, then under the influence of the external field the domains will turn in the direction of the external field. Moreover, the magnetic field at the coil will increase, and the magnetic induction will increase. If the external field is sufficiently weak, then only a fraction of all the domains will turn, the magnetic fields of which are in the direction close to the direction of the external field. During the increase in the strength of the external field, the number of rotated domains will increase, and at a certain value of the external field voltage, almost all parts will be turned so that the magnetic fields will be located in the direction of the external field. This state is called magnetic saturation.
Interconnection of magnetic inductionthe ferromagnetic substance and the intensity of the external field can be represented using a graph called the magnetization curve. In place of the curve of the curve of the curve, the rate of increase of magnetic induction decreases. After bending, where the tension reaches a certain index, saturation occurs, and the curve rises slightly, gradually acquiring the shape of a straight line. In this area, induction is still growing, but rather slowly and only due to an increase in the strength of the external field.
Graphic dependence of the indicator data is notis direct, it means that their relationship is not constant, and the magnetic permeability of the material is not a constant indicator, but depends on the external field.
With increasing current to full saturation incoil with a ferromagnetic core and its subsequent reduction of the magnetization curve will not coincide with the demagnetization curve. With zero intensity, magnetic induction will not have the same value, but will acquire some indicator, called residual magnetic induction. The situation with the lag of magnetic induction from the magnetizing force is called hysteresis.
For the complete demagnetization of the ferromagneticthe core in the coil is required to give a reverse current, which will create the necessary tension. For different ferromagnetic substances a segment of various lengths is required. The larger it is, the more energy is needed for demagnetization. The value at which the material is fully demagnetized is called the coercive force.
With further increase of the current in the coil inductionwill increase again to the saturation index, but with a different direction of magnetic lines. When demagnetized in the opposite direction, residual induction will be obtained. The phenomenon of residual magnetism is used to create permanent magnets from substances with a large amount of residual magnetism. From substances that have the ability to magnetization reversal, are the cores for electrical machines and appliances.
The force affecting a conductor with current hasthe direction determined by the rule of the left hand: when the palm of the Virgin hand is placed in such a way that the magnetic lines enter it, and four fingers are extended in the direction of the current in the conductor, the bent thumb will indicate the direction of the force. This force is perpendicular to the vector of induction and current.
A conductor moving in a magnetic field with a current is considered the prototype of an electric motor that changes electrical energy into mechanical energy.
During the movement of the conductor in a magnetic fieldAn electromotive force is induced inside it, which has a value that is proportional to the magnetic induction, the effective length of the conductor and the speed of its movement. This relationship is called electromagnetic induction. When determining the direction of induced EMF in a conductor, the right-hand rule is used: when placing the right hand in the same way as in the example from the left, magnetic lines enter the palm, and the thumb indicates the direction of movement of the conductor, elongated fingers will indicate the direction of the induced EMF. A conductor moving in a magnetic flux under the influence of an external mechanical force is the simplest example of an electric generator in which mechanical energy is converted into electrical energy.
The law of electromagnetic induction can beformulated differently: in a closed loop, EMF is induced; for any change in the magnetic flux covered by a given circuit, the EDT in the circuit is numerically equal to the rate of change of the magnetic flux that covers the given circuit.
This form provides the average EMF index and indicates the dependence of the EMF not on the magnetic flux, but on the rate of its change.
You also need to remember the law Lenz:the current induced by a change in the magnetic field passing through the circuit, its magnetic field prevents this change. If the coils at the coil are penetrated by different magnetic fluxes, then the emf induced over the whole coil is equal to the sum of the ede in different coils. The sum of the magnetic fluxes of different turns of a coil is called flux linking. The unit of measurement of this quantity, like the magnetic flux, is Weber.
When changing the electric current in the circuitthere is a change and the magnetic flux created by it. In this case, according to the law of electromagnetic induction, EMF is induced inside the conductor. It appears in connection with the change of current in the conductor, because this phenomenon is called self-induction, and the EMF induced in the conductor is called the EMF of self-induction.
Flow coupling and magnetic flux depend not only on the strength of the current, but also on the size and shape of the conductor, and the magnetic permeability of the surrounding substance.
The proportionality coefficient is calledconductor inductance. It denotes the ability of a conductor to create a flux linkage when electricity passes through it. This is one of the basic parameters of electrical circuits. For certain circuits, inductance is a constant indicator. It will depend on the size of the contour, its configuration and the magnetic permeability of the medium. The current in the circuit and the magnetic flux will not matter.
The above definitions and phenomena givean explanation for what is a magnetic field. It also presents the main characteristics of the magnetic field, which can be used to define this phenomenon.
