To understand what is a characteristic of a magnetic field, many phenomena must be defined. In this case, you must first remember how and why it appears. Find out what is the strength characteristic of a magnetic field. Moreover, it is important that such a field can be found not only in magnets. In this regard, it does not hurt to mention the characteristic of the magnetic field of the earth.
Field occurrence
First, describe the occurrence of the field. After you can describe the magnetic field and its characteristics. It appears during the movement of charged particles. May affect moving electrical charges, especially conductive 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 specific spatial point is determined by magnetic induction. The latter is indicated 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 vector at the magnetic induction.
The named lines are included in the characteristic of the magnetic field and are used to determine its direction and intensity. The higher the magnetic field intensity, the more data lines will be drawn.
What are magnetic lines
The magnetic lines of rectilinear conductors with current have the form of a concentric circle, the center of which is located on the axis of the conductor. The direction of the magnetic lines near the conductors with current is determined by the rule of the gimlet, 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 a current, the direction of the magnetic field will also be determined by the rule of the gimlet. 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 translational motion of the gimlet.
The definition of homogeneity and heterogeneity is the main characteristic of the magnetic field.
Created by a single current, under equal conditions, the field will vary in intensity in different media due to the differing 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 magnetic field characteristic 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 the relative magnetic permeability.
Magnetic permeability of substances
This is a dimensionless quantity. Substances with a permeability value of less than unity are called diamagnetic. In these substances, the field will be weaker than in vacuum. These properties are present in hydrogen, water, quartz, silver, etc.
Media with a magnetic permeability greater than unity are called paramagnetic. In these substances, the field will be stronger than in vacuum. These media and substances include air, aluminum, oxygen, 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 value is constant for a particular 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 magnetizing and amplifying a magnetic field, have widespread use in electrical engineering.
Field strength
To determine the characteristics of the magnetic field, together with the magnetic induction vector, a value called the magnetic field strength can be used. This term is a vector quantity that determines the intensity of an external magnetic field. The direction of the magnetic field in a medium with the same properties in all directions, the intensity vector will coincide with the magnetic induction vector at the field point.
The strong magnetic properties of ferromagnets are explained by the presence in them of arbitrarily magnetized small parts, which can be represented as small magnets.
With a missing magnetic field, the 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 the ferromagnet is placed in an external magnetic field, for example, in a coil with a current, then under the influence of an external field, the domains will unfold in the direction of the external field. Moreover, the magnetic field at the coil will increase, and magnetic induction will increase. If the external field is sufficiently weak, then only a fraction of all domains will turn over, the magnetic fields of which in the direction are close to the direction of the external field. As the strength of the external field increases, the number of rotated domains will increase, and at a certain value of the external field voltage, almost all parts will be deployed so that the magnetic fields are located in the direction of the external field. This condition is called magnetic saturation.
The relationship of magnetic induction and tension
The interconnectedness of the magnetic induction of the ferromagnetic substance and the intensity of the external field can be represented using a graph called the magnetization curve. At the bend of the curve graph, the rate of increase in magnetic induction decreases. After a bend, where the tension reaches a certain indicator, saturation occurs, and the curve rises slightly, gradually becoming 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
With an increase in the current strength to complete saturation in the coil with a ferromagnetic core and its subsequent decrease, the magnetization curve will not coincide with the demagnetization curve. With zero tension, 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 ferromagnetic core in the coil, it is necessary to give a reverse current, which will create the necessary tension. For different ferromagnetic substances, a length of various lengths is necessary. 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 a saturation index, 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 to create permanent magnets from substances with a large indicator of residual magnetism. From substances with the ability to magnetize, cores are created for electrical machines and devices.
Left hand rule
The force affecting the current conductor has a direction determined by the rule of the left hand: when the palm of the ninth hand is positioned so 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 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 into mechanical energy.
Right hand rule
During the movement of the conductor in a magnetic field, an electromotive force is induced inside it, which has a value proportional to the magnetic induction, the length of the conductor involved and its speed. This relationship is called electromagnetic induction. When determining the direction of the induced EMF in the conductor, the rule of the right hand is used: when the right hand is located, as in the example with the left, the magnetic lines enter the palm of the hand, and the thumb indicates the direction of movement of the conductor, extended fingers 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 be formulated differently: EMF is induced in a closed circuit, with any change in the magnetic flux covered by this circuit, the EDE in the circuit is numerically equal to the magnetic flux change rate that covers this circuit.
This form provides an averaged EMF indicator and indicates the dependence of the EMF not on the magnetic flux, but on its rate of change.
Lenz's Law
We also need to recall Lenz’s law: the current induced by a change in the magnetic field passing through the circuit prevents this change by its magnetic field. If the coils of a coil are penetrated by magnetic fluxes of different magnitude, then the EMF induced by a whole coil is equal to the sum of the EDE in different coils. The sum of the magnetic fluxes of different turns of the coil is called flux linkage. The unit of measurement for this quantity, like magnetic flux, is Weber.
When the electric current in the circuit changes, the magnetic flux created by it also changes. In this case, according to the law of electromagnetic induction, induction of EMF occurs inside the conductor. It appears in connection with a change in current in the conductor, therefore this phenomenon is called self-induction, and the induced EMF in the conductor is called the self-induction EMF.
Flux linkage and magnetic flux depend not only on the current strength, but also on the size and shape of the conductor, and the magnetic permeability of the surrounding substance.
Conductor inductance
The proportionality coefficient is called the inductance of the conductor. It denotes the ability of a conductor to create flux linkage when electricity passes through it. This is one of the main parameters of electrical circuits. For certain circuits, inductance is a constant indicator. 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 is a magnetic field. The main characteristics of the magnetic field are also given, with the help of which one can define this phenomenon.