Science 2023

## Table of contents:

One of the basic concepts used in physics is the magnetic field. It acts on moving electric charges. It is imperceptible and not felt by a person, but its presence can be detected using a magnet or iron. It is also quite easy to understand which magnetic field is called homogeneous and inhomogeneous.

## Definition and methods for detecting a magnetic field

When we encounter the concept of a magnetic field, we have a question about what kind of magnetic field it is, whether it is homogeneous or inhomogeneous. Before answering such a question, it is necessary to give initial definitions of terms.

The magnetic field is supposed to be considered a special kind of matter that exists near moving electric charges, especially near current-carrying conductors. Can be detected using a magnetic needle or iron filings.

## Uniform field

Occurs inside the bandmagnet and in the solenoid, when its length is much greater than the diameter. In this case, according to the gimlet rule, the contours of the magnetic field will be directed counterclockwise.

Magnetic lines are parallel and straight, the void between them is always the same, the force of influence on the magnetic needle does not differ at all points in its magnitude and direction.

## Heterogeneous field

In the case of an inhomogeneous field, the magnetic lines will be bent, the void between them will vary in size, the force of action on the magnetic needle will differ in magnitude and direction at different points in the field. Also, the force acting on an arrow placed in the field of a strip magnet acts at various points with forces that are different in magnitude and direction. This is called an inhomogeneous field. The lines of such a field are curved, the frequency varies from point to point.

It is possible to detect this kind of field near a straight conductor with current, a bar magnet and a solenoid.

## What are magnetic lines

First of all, when a problem arises, one should determine what kind of magnetic field, homogeneous or inhomogeneous, is formed, one should learn about magnetic lines, from the shape of which the field characteristic becomes clear.

To depict the magnetic field, began to use magnetic lines. They are imaginary stripes along a magnetic needle and placed in a magnetic field. It is possible to draw a magnetic line through anyfield point, it will have direction and always close.

## Direction

They leave the north pole of the magnet and head to the south. Inside the magnet itself, everything is strictly the opposite. The lines themselves have no beginning or end, are closed or go from infinity to infinity.

Outside of the magnet, the lines are located as densely as possible near the poles. From this it becomes clear that the effect of the field is strongest near the poles, and as you move away from the bottom, it weakens. Given that the magnetic stripes are curved, the direction of the force that acts on the magnetic needle also changes.

## How to portray

To understand how homogeneous magnetic fields differ from inhomogeneous ones, you need to learn how to depict them using magnetic lines.

One should consider the above example of the occurrence of a uniform magnetic field in the so-called solenoid, which is a cylindrical wire coil through which current is passed. Inside it, the magnetic field can be considered uniform, provided that the length is much greater than the diameter (outside the coil, the field will be non-uniform, the magnetic lines will be located in the same way as in a bar magnet).

The uniform field is also located in the center of the permanent bar magnet. In any limited area in space, it is also possible to reproduce a uniform magnetic field, in which the forces acting on the magnetized needle will be the same in magnitude and direction.

To depict a magnetic field, use the following example. If the lines are locatedperpendicular to the drawing plane and are directed from the viewer, then they are depicted with crosses, if on the viewer - with dots. As with the current, each cross is, as it were, the visible tail of an arrow flying from the beholder, and the point is sharper than the arrow that flies towards us.

Also, the requirement "Draw a uniform and non-uniform magnetic field" is easily fulfilled. Simply draw these magnetic lines, taking into account the characteristics of the field (uniformity and inhomogeneity).

However, the existence of inhomogeneous fields greatly complicates the task. In this case, obtaining any physical result using the general equation is unlikely.

## Differences

The answer to the question of how homogeneous magnetic fields differ from inhomogeneous ones is quite easy to give. First of all, it depends on the magnetic lines. In the case of a uniform field, the distance between them will be the same, and they will be evenly spaced, with the same force acting on the instruments at any point. For inhomogeneous fields, everything is strictly the opposite. The lines are unevenly located, in different places they act with unequal force on devices.

In practice, an inhomogeneous field is quite common, which should also be remembered, since uniform fields can only occur inside an object, such as a magnet or a solenoid. Outdoor observations will fix heterogeneity.

## Field detection

Having understood what uniform and inhomogeneous magnetic fields are, and defining themhaving disassembled, you should find out how you can find them.

The simplest for this is the experiment conducted by Oersted. It consists in using a magnetic needle, which helps to determine the existence of an electric current. As soon as the current moves along the conductor, the arrow located next to it will move, due to the fact that there are uniform and non-uniform magnetic fields.

## Interaction of conductors with current

Each conductor with current has its own magnetic field, which acts with a certain force on the nearest one. Depending on the direction of the current, the conductors will attract or repel each other. Fields originating from different sources will add up and form a single resulting field.

## How they are created and why

Examples of uniform and non-uniform magnetic fields used in cathode ray devices are created by coils that pass current. To obtain the required shape of the magnetic field, shelf tips and magnetic screens are used, made of materials with strong magnetic permeability.

The influence of inhomogeneous magnetic fields can change the course of irreversible physical and chemical phenomena, mostly a heterogeneous process. The appearance of turbulent diffusion leads to an increase by several orders of magnitude in the rate of gas movement from any liquid to the surface in the formmicrobubbles. The effect of local dehydration of ions and particles is due to the intensification of the microcrystallization process. In flowing media, high-energy reactions can create free radicals, atomic oxygen, peroxides, and nitrogenous compounds. Coagulation occurs, and products caused by erosive destruction appear in the liquid.

During hydrodynamic cavitation, the large size of the emerging bubbles and caverns complicates their entrainment by liquid from the area of ​​low pressure to the area of ​​higher pressure, where the bubbles collapse. During the collapse of a small bubble, there is a low air content and a strong chemical reaction occurs, similar to a plasma discharge. The presence of inhomogeneous magnetic fields leads to the instability of cavities, their disintegration and the appearance of small-scale vortices and bubbles. Given that the pressure at the center of such a vortex is reduced, it converts small gas bubbles.

When measuring induction in a non-uniform magnetic field, remember that the Hall voltage is proportional to the average value of the field induction within the area bounded by the surface of the transducer.

To focus paraxial beams, non-uniform magnetic fields are also used, formed by short coils, which are multilayer solenoids, the length of which is commensurate with their diameter. An electron entering such a field is subject to forces that change its direction. An electron under the influence of such a force approaches the axis of the lens, while the plane in which its trajectory is located isbends. The electron moves along a spiral segment that intersects the axis of the lens at a given point.

The spatial increase factor is caused by the spatial dispersal of inhomogeneous fields in the territory of a heterogeneous system washed down with liquid. To obtain the population inversion of the levels by the separation method, non-uniform fields created by a multiband magnet are used. The shape of the poles is similar to the rods in the quadrupole capacitor of an ammonia-based molecular generator.

## Uses

The magnetic-order method of flaw detection is based on the traction of magnetic particles by the forces of inhomogeneous fields that appear above the defects. By the accumulation of such a powder, the presence of a defect, its size and position on the part being checked is determined.

A significant disadvantage of the molecular beam method using strong inhomogeneous magnetic fields is considered to be a small splitting effect. There is a simple and seemingly implausible method to increase this effect. It consists in the application of a light external magnetic field. The latter will make it possible to increase the area of ​​use of nuclear precessional magnetometers towards non-uniform magnetic fields.

The advantage of this method is its high resolution, which makes it possible to detect non-uniform magnetic fields commensurate with the size of the particles of the magnetic layer of the tape, as well as the ability to find damage on complex surfaces and in tight openings.

The disadvantages arethe need for secondary processing of information, only particles of magnetic fields along the tape are recorded, the complexity of demagnetization and preservation of the tape, and it is necessary to prevent the influence of external magnetic fields.

Uniform and inhomogeneous magnetic fields are quite common, despite the fact that they are invisible to the average layman. Examples of uniform and non-uniform magnetic fields can be found in bar magnets and solenoids. At the same time, you can notice them using a simple magnetic needle or iron filings.