Science 2023

To understand what is a characteristic of a magnetic field, many phenomena should be defined. At the same time, you need to remember in advance how and why it appears. Find out what is the power characteristic of a magnetic field. It is also important that such a field can occur not only in magnets. In this regard, it does not hurt to mention the characteristics of the earth's magnetic field.

## Field Emergence

First, we should describe the appearance of the field. After that, you can describe the magnetic field and its characteristics. It appears during the movement of charged particles. Can affect moving electrical charges, especially on conductive conductors. The interaction between a magnetic field and moving charges, or conductors through which current flows, occurs due to forces called electromagnetic.

Intensity or power characteristic of the magnetic field ina certain spatial point are determined using magnetic induction. The latter is denoted by the symbol B.

## Graphic representation of the field

The magnetic field and its characteristics can be represented graphically using induction lines. This definition is called lines, the tangents to which at any point will coincide with the direction of the vector y of the magnetic induction.

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 data lines will be drawn.

## What are magnetic lines

Magnetic lines in straight conductors with current have the shape of a concentric circle, the center of which is located on the axis of this conductor. The direction of the magnetic lines near conductors with current is determined by the gimlet rule, which sounds like this: if the gimlet is located so that it will be 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 turns of the solenoid. The direction of the lines of magnetic induction will correspond to the direction of the translational movement of the gimlet.

The definition of uniformity and inhomogeneity is the main characteristic of the magnetic field.

Created by one current, under equal conditions, the fieldwill differ in its intensity in different media due to different magnetic properties in these substances. The magnetic properties of the medium are characterized by absolute magnetic permeability. Measured in henries 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 the 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 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.

Ferromagnets belong to a special group. For these substances, the magnetic permeability will reach several thousand or more. These substances, which have the property of being magnetized and amplifying the magnetic field, are widely used 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 the 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 of randomly magnetized small parts in them, which can be represented as small magnets.

With no magnetic field, a 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 characteristics 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 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 part of all domains whose magnetic fields approach the direction of the external field will flip over. 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 rotated so that the magnetic fields are located in the direction of the external field.This state is called magnetic saturation.

## Relationship between magnetic induction and intensity

The relationship between the magnetic induction of a ferromagnetic substance and the strength of an external field can be depicted 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 level, saturation occurs, and the curve rises slightly, gradually acquiring the shape of a straight line. In this section, the induction is still growing, but rather slowly and only due to an increase in the strength of the external field.

The graphical dependence of the data of the indicator 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 increasing the current to full saturation in a coil with a ferromagnetic core and then decreasing it, 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 some indicator called the residual magnetic induction. The situation with the lagging of magnetic induction from the magnetizing force is called hysteresis.

To completely demagnetize the ferromagnetic core in the coil, it is required to give a reverse current, which will create the necessary tension. For various ferromagneticsubstances, a segment of various lengths is needed. The larger it is, the more energy is needed for demagnetization. The value at which the material is completely demagnetized is called the coercive force.

With a further increase in the current in the coil, the induction will again increase to the 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 high residual magnetism. Materials with the ability to remagnetize are used to create cores for electrical machines and devices.

## Left hand rule

The force that affects a conductor with current has a direction determined by the rule of the left hand: when the palm of the virgin hand is located 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 indicates 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 the speed of its movement. This dependence is called electromagnetic induction. Atdetermining the direction of the induced EMF in the conductor, the right hand rule is used: when the right hand is located in the same way as in the example from the left, the magnetic lines enter the palm, and the thumb indicates the direction of movement of the conductor, the outstretched 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 electrical generator in which mechanical energy is converted into electrical energy.

The law of electromagnetic induction can be formulated differently: in a closed circuit, an EMF is induced, with any change in the magnetic flux covered by this circuit, the EFE in the circuit is numerically equal to the rate of change of the magnetic flux that covers this circuit.

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 by a change in the magnetic field passing through the circuit, its magnetic field prevents this change. If the turns of the coil are pierced by magnetic fluxes of different magnitudes, then the EMF induced on the whole coil is equal to the sum of the EMF in different turns. The sum of the magnetic fluxes of different turns of the coil is called flux linkage. The unit of measurement of this quantity, as well as the magnetic flux, is weber.

When the electric current in the circuit changes, the magnetic flux created by it also changes. At the same time, according to the law of electromagnetic induction, insideconductor, an EMF is induced. 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 the strength of the current, but also on the size and shape of a given conductor, and the magnetic permeability of the surrounding substance.

## Conductor inductance

The coefficient of proportionality 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 of electrical circuits. For certain circuits, inductance is a constant. It will depend on the size of the contour, 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 give an explanation of what is a magnetic field. The main characteristics of the magnetic field are also given, with the help of which it is possible to define this phenomenon.