Now almost everyone knows that the electric and magnetic fields are directly interconnected. There is even a special branch of physics that studies electromagnetic phenomena. But back in the 19th century, until Maxwell's electromagnetic theory was formulated, everything was completely different. It was believed, for example, that electric fields are inherent only in particles and bodies with an electric charge, and magnetic properties are a completely different field of science.
In 1864, the famous British physicist D.K. Maxwell points to the direct relationship of electrical and magnetic phenomena. The discovery was called "Maxwell's electromagnetic field theory." Thanks to her, it was possible to solve a number of insoluble issues, from the point of view of the electrodynamics of that time.
Most high-profile discoveries are always based on the results of previous researchers. Maxwell's theory is no exception. A distinctive feature is that Maxwell significantly expanded the results obtained by his predecessors. For example, he pointed out that in the Faraday experiment , not only a closed loop of conductive material can be used, but consisting of any material. In this case, the circuit is an indicator of the vortex electric field, which affects not only the crystal lattice of metals. With this point of view, when a dielectric material is in the field, it is more correct to speak of polarization currents. They also perform work, which consists in heating the material to a certain temperature.
The first suspicion of the connection of electrical and magnetic phenomena appeared in 1819. H. Oersted noted that if a compass is placed near the current conductor, the direction of the arrow deviates from the north pole.
In 1824, A. Ampere formulated the law of interaction of conductors, which later became known as the “Ampere Law”.
And finally, in 1831, Faraday recorded the appearance of a current in a circuit located in a changing magnetic field.
Maxwell's theory is designed to solve the basic problem of electrodynamics: with the known spatial distribution of electric charges (currents), one can determine some characteristics of the generated magnetic and electric fields. This theory does not consider the mechanisms themselves that underlie the occurring phenomena.
Maxwell's theory is intended for nearby charges, since in the system of equations it is believed that electromagnetic interactions occur at the speed of light, regardless of the medium. An important feature of the theory is the fact that on its basis such fields are considered that:
- generated by relatively large currents and charges distributed in a large volume (many times the size of an atom or molecule);
- alternating magnetic and electric fields change faster than the period of processes inside the molecules;
- the distance between the calculated point in space and the field source exceeds the size of atoms (molecules).
All this suggests that Maxwell's theory is applicable primarily to the phenomena of the macrocosm. Modern physics explains more and more processes from the point of view of quantum theory. In Maxwell's formulas, quantum manifestations are not taken into account. Nevertheless, the use of Maxwell systems of equations allows us to successfully solve a certain range of problems. It is interesting that since the densities of electric currents and charges are taken into account, it is theoretically possible for them to exist, but of a magnetic nature. This was indicated in 1831 by Dirac, denoting them as magnetic monopolies. In general, the basic postulates of the theory are as follows:
- the magnetic field is created by an alternating electric field;
- an alternating magnetic field generates an electric field of a vortex nature.