Independent magnetic charges do not exist. All materials have some special magnetic effect due to the movement of electrons around the nucleus. However, in nature, materials such as iron, nickel, and cobalt exhibit strong magnetic properties, so Magnetics is also called ferroMagnetics.
Magnetics and electricity are directly related. Classical Magnetics believes that, just like electric charges, independent magnetic charges exist in nature. Identical magnetic charges repel each other, and different magnetic charges attract each other. Modern Magnetics believes that the ring current element is the fundamental cause of the generation of magnetic poles. The same magnetic poles repel each other, and different magnetic poles attract each other.
Ⅰ. Classical Magnetics and modern Magnetics
1. Classical Magnetics
After French physicist Coulomb established Coulomb's law, the law of interaction between electrostatic charges, in 1785, he conducted similar experiments on magnetic poles and proved that the same law also applies to the interaction between magnetic poles. . This is the classical theory of Magnetics.
Classical Magnetics explains that magnetic fields are generated by moving charged particles, especially electrons. The generation of a magnetic field by an electric current is a basic principle of classical electroMagnetics and the core content of Ampere's law. Classical Magnetics studies the properties of magnetic substances, including different types such as ferroMagnetics, paraMagnetics, and diaMagnetics. Magnetic moment is a physical quantity that describes the Magnetics of a substance. It can be the magnetic moment of atoms, molecules or electrons.
Positive and negative magnetic poles are generally referred to as magnetic north poles and magnetic south poles. To avoid this theoretical difficulty, classical magnetic field theory states that a pole in a very elongated magnet can be approximately viewed as a single pole. Based on such an assumption, it can be concluded that the force exerted by a single magnetic pole in the magnetic field is proportional to the strength of the magnetic pole itself and proportional to the strength of the magnetic field at the location of the magnetic pole.
In the classical theory of magnetic field, one of the most basic formulas is the formula of the force exerted by a single magnetic pole without any size in the magnetic field. But unlike the concept of charge in electric field theory, independent positive and negative charges in an electric field can exist alone, but independent positive and negative magnetic poles actually do not exist. Magnetic poles always appear in pairs.
Classical Magnetics can mathematically describe the distribution and shape of magnetic fields, such as the distribution of magnetic fields around different magnetic materials. Classical Magnetics studies the interaction between magnetic fields and matter, including the force of magnetic fields on moving charged particles and the effects of magnetic fields on magnetic matter.
2. Modern Magnetics
In the theory of electric and magnetic fields, the Lorentz formula is of great significance. This formula gives the magnitude and direction of the force exerted by a moving charge in the electric and magnetic fields.
Magnetic fields and electric fields have many similarities, but they are fundamentally different.
The difference between magnetic and electric fields:
Mode of action:
Electric Field: An electric field exerts an electric force on surrounding charges. Positive and negative charges experience forces in different directions in an electric field.
Magnetic field: A magnetic field exerts a magnetic force on moving charged particles such as electrons in an electric current. The effect of a magnetic field on a charge is a force perpendicular to the velocity of the charge and the direction of the magnetic field.
Electric Field: An electric field is a field of force created by electrical charges (both positive and negative). A charged body generates an electric field, and the interaction between charges is also transmitted through the electric field.
Magnetic field: A magnetic field is a field of force created by moving charged particles such as the spin and orbital motion of electrons. Electric currents and magnetic substances can also generate magnetic fields.
Electric Field: An electric field can exist around a charge at rest or it can propagate as the charge moves. Electric fields are invisible, but can be observed indirectly by measuring the force on the charges.
Magnetic field: Magnetic fields are usually produced by moving charged particles, or by electric currents and magnetic substances. Magnetic fields are also invisible, but can be observed by magnets attracting objects such as iron or by using magneto-sensing instruments.
Electric field: The strength of the electric field is related to the positive and negative of the charge. The electric field lines pointing to the positive charge start from the positive charge, and the electric field lines pointing to the negative charge point to the negative charge.
Magnetic field: The direction of the magnetic field is represented by the lines of force (lines of induction), which point from the magnetic north pole to the magnetic south pole, forming a closed loop.
(2) Electromagnetic theory
In the classical magnetic field theory, most of the formulas are correct and are still used today, but the most fundamental problem in the entire theory is that it adopts the assumption of a so-called separate magnetic pole that does not actually exist. This is a fatal weakness of the so-called Coulomb method in classical Magnetics theory.
Danish physicist Oersted discovered in 1820 that a wire passing an electric current would deflect a magnetic needle suspended nearby, showing that the electric current produced a magnetic field in the space around it, which proved that the phenomena of electricity and Magnetics are closely combined. the first experimental results. Immediately afterwards, experiments and theoretical analyzes by French physicist Ampere and others clarified the magnetic field generated by the coil carrying current and the magnetic force interacting between the current coils. By applying current elements to generate magnetic fields, many concepts in magnetic field theory are very similar to many concepts in electric field theory.
(3) Generation Magnetics covers the explanation of magnetic behavior at the microscopic scale by quantum mechanics. Quantum Magnetics studies the spin of electrons, spin-orbit coupling and exchange interactions between electrons, etc., thereby explaining the properties of magnetic materials. This is an important branch of the modern field of Magnetics, which studies the application of spin in electronics. Spintronics has potentially revolutionary applications in information storage, transmission and processing, such as spin transistors and spintronic devices.
Modern Magnetics studies different types of magnetic materials, including ferromagnetic, paramagnetic, diamagnetic, etc. Nanomagnets study magnetic phenomena at tiny scales, which has important implications for nanotechnology and information storage. Modern Magnetics studies the influence of different spin configurations on the Magnetics of materials, as well as the magnetic phase transition behavior under conditions such as temperature and pressure.
Ⅱ. Magnetic Theory
Key concepts in modern Magnetics theory include:
(1) Magnetic field strength
It is a physical quantity used to describe the strength of the magnetic field. It represents the magnetic force experienced by a unit positive charge in a magnetic field, usually represented by the symbol B, and the unit is Tesla (T). Magnetic field strength is a vector quantity because it has magnitude and direction. The magnetic field strength B at a given point is defined as the magnetic flux density caused by the magnetic force on a unit positive charge at that point. Mathematically, this can be expressed as B = F / (qv), where F is the magnetic force on the positive charge, q is the charge on the positive charge, and v is its velocity.
Ampere's law states that the magnetic field strength B generated by an electric current forms a closed loop around the current element, the size of which is proportional to the magnitude of the current. The direction of the magnetic field strength B is determined by the right-hand rule of force. When the right hand holds the direction of the current and points to the direction of the current, the direction pointed by the thumb of the right hand is the direction of the magnetic field strength.
(2) Magnetic induction
Also known as magnetic induction, magnetic induction intensity, magnetic induction magnetic field or magnetic sensitivity. It is a physical quantity that describes the degree of influence of a magnetic field on a substance. There is a certain relationship between the magnetic induction intensity and the magnetic field intensity, which can be expressed by the formula B = μ₀ * H.
The atoms or molecules inside a magnetic substance have magnetic moments that rearrange when placed in an external magnetic field, causing the substance to appear magnetic in the magnetic field. Magnetic induction describes the effect of a magnetic field on a magnetic substance and the arrangement of the magnetic moments inside the substance.
Flux is a physics concept used to describe the amount of a vector field passing through a surface. Magnetic flux, usually denoted by the symbol Φ, is the amount of magnetic field passing through a given surface. On a plane, the magnetic flux Φ is the product of the component of the magnetic field intensity B perpendicular to the plane and the plane area A, that is, Φ = B * A * cos(θ), where θ is the angle between the direction of the magnetic field and the normal to the plane.
Magnetization is a physical quantity related to the Magnetics of a substance, which is used to describe the distribution of the magnetic moment in the substance relative to the volume of the substance. Magnetization intensity is commonly represented by the symbol M, and the unit is A/m.
Magnetization is often related to the magnetic properties of a material, especially for ferromagnetic materials. When an external magnetic field acts on these materials, the internal magnetic moments rearrange, causing the material's magnetization to increase. Magnetization can also be used to describe the response of magnetic materials and the effects of electron spin and orbital motion in magnetic materials.
Magnetic moment is a physical quantity used to describe the response of an object to a magnetic field in a magnetic field, that is, the Magnetics of the object. The magnetic moment can be that of atoms, molecules, electrons, or microscopic current loops. Different types of magnetic materials exhibit different magnetic moment behaviors.
(6) Magnetic susceptibility coefficient
Magnetic susceptibility coefficient is a measure of a substance's ability to respond to a magnetic field and is related to the relationship between the generation of magnetic moment and the strength of the magnetic field. The magnetic susceptibility coefficient can be divided into bulk magnetic susceptibility, molar magnetic susceptibility, bulk relative magnetic susceptibility, and bulk absolute magnetic susceptibility.
It is another physical quantity that describes the magnetic field, similar to the electric potential that describes the electric field. The concept of magnetic potential is in some cases more convenient for analyzing and calculating the behavior of magnetic fields. Similar to electric potential, magnetic potential can also be defined based on different points in space. At each point, the choice of magnetic potential is not unique, because the magnetic field is a vector field, and the choice of magnetic potential can have a certain degree of freedom.
Magnetoresistance is a physical quantity used to describe the degree of obstruction of magnetic flux by objects in a magnetic field, similar to how resistance describes the obstruction of current in a circuit. The concept of magnetoresistance plays an important role in the research and application of magnetic materials.
It is a physical quantity that describes the magnetic conductivity of a material to a magnetic field, similar to electrical conductivity, which describes a material's ability to conduct electricity to an electric current. Magnetic permeability refers to the magnetic permeability of a substance relative to vacuum (or air) under a given magnetic field. Magnetization permeability refers to the response of a substance to magnetization.
A permanent magnet and another permanent magnet can exert force on each other without contact, which was once called action at a distance. Modern physicists introduced the concept of "field" in order to explain the interaction between charges and permanent magnets: there is a magnetic field in the space around a permanent magnet, which causes another person at any position in this space to move. One permanent magnet is subjected to a force exerted by a magnetic field, while the magnetic field generated by the second permanent magnet also exerts a counterforce on the first permanent magnet. Because forces are vector quantities, magnetic fields are vector fields. Many experimental facts have proved that the magnetic field is real.
After a piece of iron is attracted by a permanent magnet for a period of time, it is "magnetized" by the stronger magnetic field near the permanent magnet and becomes a permanent magnet. The force that magnetizes an object is sometimes called the "magnetizing force". A general iron block loses its magnetization state when it is moved from a place with a strong magnetic field to a place with a weak magnetic field, which is called "demagnetization" or "demagnetization".
Each permanent magnet has two magnetic poles with different properties. Permanent magnets are usually used to indicate the north-south direction. The pole pointing to the north is called the N pole, and the pole pointing to the guide is the S pole. Poles with the same name repel each other, and poles with different names attract each other.
A magnetic needle can be used to measure magnetic flux density. In a magnetic field, the period of the small swing (oscillation) of the magnetic needle around its equilibrium direction is inversely proportional to the square root of the magnetic flux. Therefore, the two magnetic flux values can be obtained by comparing the periods or frequencies of the magnetic needle oscillating in two magnetic fields. Ratio. If the magnetic moment and moment of inertia of the magnetic needle are known, the absolute value of the magnetic flux can be determined at one time.
The basic source of diaMagnetics is electromagnetic induction. Electromagnetic induction is Faraday's major discovery: around the magnetic flux that changes with time, an induced electromotive force (or electric field) is generated, so it can produce current in a wire circuit or eddy current in a large conductor. The magnetic field generated by the induced current here resists the changes in the magnetic field that induce them. This is Lenz's law.
Magnetic observations of ferromagnetic materials in the range of not very strong magnetic fields generally use induction methods instead of Faraday and Curie methods. Modern vibrating sample magnetometers are also induction methods in principle.
ParaMagnetics can be roughly divided into three types: strong, weak and very weak, each of which has different origins. Transition metals, that is, the crystals or solutions of compounds (mainly salts) of elements such as iron, palladium, rare earth platinum, and uranium in the periodic table, mostly exhibit strong paraMagnetics. Their obvious feature is that the magnetic susceptibility is strongly dependent on temperature.
Magnetostatics is the study of magnetic fields in systems where currents are stable (do not change with time). It is the magnetic analog of static electricity, where the charge is fixed. Magnetization does not have to be static; the magnetostatic equations can be used to predict rapid magnetic switching events that occur on time scales of nanoseconds or less. Magnetostatics is even a good approximation when the current is not static - as long as the current does not alternate rapidly.
Magnetostatics is widely used in micromagnetic applications, such as modeling of magnetic storage devices, such as computer memory. Magnetostatic focusing can be achieved with permanent magnets or by passing an electric current through a coil whose axis coincides with the axis of the beam.
Applications of magnetostatics:
Electromagnetic equipment design: Magnetostatics plays a key role in the design of electromagnetic equipment, such as transformers, inductors, electromagnetic relays, etc. Through the theory of magnetostatics, the distribution of magnetic fields, magnetic flux and induced electromotive force in electromagnetic equipment can be predicted, thereby optimizing the performance of the equipment.
Electromagnetic Induction: The theory of magnetostatics is used to explain electromagnetic induction phenomena such as generators, transformers, and induction heating. In these applications, energy conversion or transmission is achieved by generating an induced electromotive force through a changing magnetic field.
Magnetic materials: Magnetostatics helps us understand the behavior of magnetic materials, such as the magnetic permeability, saturation magnetic induction and hysteresis loops of ferromagnetic materials. This is of great significance for the selection and application of magnetic materials.
ElectroMagnetics is the branch of physics concerned with the study of the electromagnetic force, a physical interaction that occurs between charged particles. The electromagnetic force conducts electromagnetic fields through electric and magnetic fields, and it is responsible for electromagnetic radiation such as light. It is one of the four fundamental interactions (commonly known as forces) in nature, along with the strong interaction, weak interaction, and gravity. At high energies, the weak and electromagnetic forces are unified into a single electroweak force.
Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes electricity and Magnetics as different manifestations of the same phenomenon. Electromagnetic forces play an important role in determining the internal properties of most objects encountered in everyday life. The electromagnetic attraction between the nucleus and its orbiting electrons holds atoms together.
The electromagnetic forces are respectively responsible for chemical bonds which create molecules between atoms, and intermolecular forces. The electromagnetic forces govern all chemical processes resulting from the interaction between electrons of adjacent atoms. ElectroMagnetics is widely used in modern technology, and electromagnetic theory is the basis of power engineering and electronics including digital technology.
There are many mathematical descriptions of electromagnetic fields. Most prominently, Maxwell's equations describe how electric and magnetic fields generate and change each other, and how electric charges and currents generate and change.
Ⅵ.Applications of Magnetics
Electromagnetic equipment and electronic technology: Magnetics has important applications in the design and manufacture of electromagnetic equipment, including generators, motors, transformers, inductors, magnetic sensors, and magnetic storage devices (such as hard drives). Magnetics also plays a role in signal processing in electronics, magnetic cards, magnetic random access memory (MRAM), and more.
Materials Research and Manufacturing: Magnetics is used in the research and development of various magnetic materials, such as ferromagnetic materials, soft magnetic materials and hard magnetic materials, and in the manufacture of magnetic components and magnetic storage media.
Medical Imaging: Magnetic resonance imaging (MRI) is a key technology in the field of medical imaging, which uses strong static magnetic fields and changing gradient magnetic fields to generate detailed images of the internal structures of the human body. MRI plays an important role in diagnosis and research.