Electromagnetism [electromagnetics]

Electromagnetism is the branch of classical physics that studies electromagnetic interaction and constitutes a fundamental theory that allowed to explain natural phenomena such as electricity, magnetism, and light; it is the first example of unification of two different forces, the electric and the magnetic one.

In applied engineering, electromagnetics is the study of those aspects of electrical engineering in situations in which the electromagnetic properties of materials and the geometry in which those materials are arranged is important. This requires an understanding of electromagnetic fields and waves, which are of primary interest in some applications.

Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as different manifestations of the same phenomenon. The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life:

  • the electromagnetic attraction between atomic nuclei and their orbital electrons holds atoms together;
  • electromagnetic forces are responsible for the chemical bonds between atoms that create molecules, and intermolecular forces;
  • the electromagnetic force governs all chemical processes, which arise from interactions between the electrons of neighboring atoms.
  • other forces (e.g., friction, tension, and contact forces) are derived from electromagnetic forces (and the other fundamental forces).

From electromagnetic theory originate important theoretical and applicative branches concerning electric current through the circuit theory, electrical engineering, and electronics.

Usually, electromagnetism refers to classical theory, summarized in Maxwell’s equations. This theory accurately describes physical reality down to quantum dimensions: the extension of the theory also on a quantum scale is called quantum electrodynamics; the study of electromagnetism combined with special relativity leads instead to classical electrodynamics.

Historical notes

The foundations of electromagnetism are laid at the beginning of the nineteenth century. Its initiator is the Danish physicist H. C. Oersted that on July 20, 1820 announced in a memory the fundamental experiment that showed the deviation of the magnetic needle in the presence of a straight stretch of electric circuit. The result made a sensation and subsequent studies of J. B. Biot and F. Savart showed, among other things, that the acting force is not Newtonian and depends on the direction of the current. At the same time applied to these studies A.. M. Ampère, who discovered the electrodynamic actions between electric currents (to him we owe the term electrodynamics to indicate this area of physics), rejected the theory that tried to explain Oersted’s result, admitting that the circuit crossed by current turns into a magnet, and proposed instead to consider the magnet as composed of a multitude of small circuits all parallel to each other and whose currents move in the same direction.

The verification of this brilliant theory led Ampère to study various types of circuits including solenoids. We owe to Ampère also the mathematical formulation of the laws relating to the force that is exerted between two elements of current as a function of their intensity, distance and mutual position. The relation electricity-magnetism constitutes the fundamental problem in the work of M. Faraday, who laid the theoretical foundations and elaborated the fundamental laws of electromagnetism: in 1831 he came, in fact, to discover the phenomenon of electromagnetic induction by producing electric currents through variations of magnetic fields.

Faraday explained the phenomenon by introducing the fundamental concept of “lines of force”, lines of magnetic induction that are generated as concentric circles around a metal wire when it is crossed by electric currents and that are similar to those existing between the two poles of a natural magnet. From this he derived the fundamental law on the direction of the induced current depending on the variation of the lines of force concatenated with the circuit, law revised and made more rigorous by E. Lenz. From Faraday’s work started J. C. Maxwell.

In the fundamental Treatise on Electricity and Magnetism (1873) mathematically formulated the concept of line of force, introduced the concepts of electromagnetic field and displacement current, founded the electrodynamics of dielectrics, which allowed him then a general treatment of polarization, and finally condensed the whole theory in six equations that connected in a single building electricity, magnetism and optics. The mechanistic conception that dominated physics suffered a decisive blow. H. Hertz, later, verified Maxwell’s hypothesis and was able to produce electromagnetic waves that, like light, could be reflected, refracted and polarized, opening the way to the development of radiotelecommunications. Subsequent developments are related to the names of H. Poincaré, H. A. Lorentz, P. and M. Curie, M. Planck, A. Einstein, in whose works electromagnetism is totally merged in the new atomic and nuclear physics.

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