Magnetic field intensity H
Magnetic field intensity H is actually a physical quantity without practical meaning. When people defined it before, they assumed that there was such a thing as magnetic charge, but later they found that this thing did not exist. It was just the other side of the electric current. In the distant 1820s, scientists made a series of revolutionary discoveries, which opened up the modern theory of magnetism. In July 1820, Danish physicist Hans Oersted discovered that the current in the current-carrying wire would exert a force on the magnetic needle, causing the magnetic needle to deflect in direction. (Oersted experiment-magnetic effect of electric current) In September, just one week after the news arrived at the French Academy of Sciences, Ampere successfully conducted an experiment to show that if the currents carried flow in the same direction, two parallel current-carrying wires would attract each other; otherwise, if the flow directions are opposite, they will repel each other. In 1825, Ampere published Ampere's law, which is a rule about the relationship between the direction of the current and the magnetic flux lines of the magnetic field excited by the current.
Through mechanical measurements, it can be concluded that the "magnetic field" strength felt by the magnetic needle is the same for points with equal distances from the long straight wire, and the "magnetic field" strength of points with different distances is inversely proportional to the distance. In this way, we define the physical quantity of magnetic field strength H through mechanical measurements and current intensity. Its unit is ampere/meter A/m. In the Gaussian unit system, the unit of H is Oe Oersted, 1A/m=4π×10-3Oe. There are many explanations for the magnetic field strength H. We can understand H as an external magnetic field (analogous to the electric field strength, for example, using current I to apply a magnetic field H to an object). Magnetic induction intensity B Magnetic field strength is just a magnetic field given by an external current. For ferromagnetic materials in the magnetic field, in addition to being affected by the external magnetic field H, the particles inside the material will also generate an induced magnetic field under the action of the external magnetic field.
Magnetic induction intensity B
Magnetic induction intensity B indicates that a particle "feels" the total magnetic field, which is the sum of the external magnetic field H and the induced magnetic field M at this time. In a vacuum, the magnetic induction intensity is proportional to the external magnetic field, that is, B=μ0H, where μ0 is the magnetic permeability of the vacuum. The magnetic induction intensity inside the ferromagnetic material is B=μ0(H+M), that is, the total magnetic field is equal to μ0 multiplied by the sum of "the magnetic field H generated by the current" plus "the magnetic field M generated by the medium being magnetized by H". The unit of B is Tesla T, and the unit in the Gaussian unit system is Gauss Gs, 1T=10KGs. The magnetic induction intensity is the real "magnetic field intensity" of the magnet. Still, because H has been called magnetic field intensity in history, B can only be given another name called magnetic induction intensity. B and H both refer to "magnetic field intensity", but due to different definitions and derivation methods, their units are different (in the Gaussian system, the unit of B is Gauss Gs, and the unit of H is Oersted Oe, 1Oe＝1×10-4Wb·m-2＝1×10-4T＝1Gs). The magnetic field intensity H is the magnetic field of the virtual space. It does not take into account the matter in the space. It focuses on the relationship between the magnetic field and the current that generates the magnetic field. The magnetic induction intensity B considers the strength of the final magnetic field after adding actual matter to the virtual space magnetic field H. It focuses on the actual magnetic field strength of the matter.
Magnetic intensity M
We have just mentioned the magnetic intensity M, which is an induced magnetic field generated by the particles inside the material under the action of the external magnetic field. Modern physics has proved that each electron in the atom is orbiting and spinning around the nucleus, and both of these movements produce magnetic effects. If the molecule is regarded as a whole, the sum of the magnetic effects generated by each electron in the molecule can be expressed by an equivalent circular current. This equivalent circular current is called the molecular current.
