History of Electromagnetism

 The history of electromagnetism dates back over several thousand years. In the history of electromagnetic theory, the ancients would have been acquainted with the effects of atmospheric electricity, in particular lightning  as thunderstorms in most southern latitudes are common. They however had little understanding of electricity, and were unable to scientifically explain those phenomena. Electricity is treated jointly with magnetism, because both generally appear together; wherever electricity is in motion, magnetism is also present. The phenomenon of magnetism was observed early in the history of magnetism, but was not explained in contemporary understanding until the idea of magnetic induction was developed.  The phenomenon of electricity was observed early in the history of electricity, but was not fully explained in contemporary understanding until the idea of electric charge was fully developed.

  The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behaviour and often confused with magnetism. The ancients were acquainted with rather curious properties possessed by two minerals,  and magnetic iron ore. Amber, when rubbed, attracts light bodies; magnetic iron ore has the power of attracting iron.

Iron fillings on the  pole of a bar  magnet

   Magnets were first found in a natural state; certain iron oxides were discovered in various parts  of the world, notably in Magnesia in Asia Minor, that had the property of attracting small pieces of iron. The discovery of amber and other similar substances  in the ancient times suggests the possible perception of it by pre-historic man.  The accidental rubbing against the skins with which he clothed himself may have caused an attraction by the resin,thus electrified, of the light fur in sufficiently marked degree to arrest his attention.  Between such a mere observation of the fact, however and the making of any deduction from it, vast periods may have elapsed; but there came a time at last, when the amber was looked upon as a strange inanimate substance which could influence or even draw to itself other things; and this by its own apparent capacity and not through any mechanical bond or connection extending from it to them; when it was recognized,in brief, that nature held a lifeless thing showing an attribute of life.                                          

                                              

    Long before any knowledge of electromagnetism existed, people were indirectly aware of the effects of electricity. Lightning and certain other manifestations of electricity were known in ancient times, but it was not understood that these phenomena had a common origin. Ancient Egyptians were aware of shocks when interacting with electric fish (such as the electric catfish) or other animals (such as electric eels).^] The shocks from animals were apparent to observers since pre-history by a variety of peoples that came into contact with them.

 Originally electricity and magnetism were thought of as two separate forces. This view changed, however, with the publication of James Clerk Maxwell's 1873 Treatise on Electricity and Magnetism in which the interactions of positive and negative charges were shown to be regulated by one force. There are four main effects resulting from these interactions, all of which have been clearly demonstrated by experiments:

James Clerk Maxwell

1.    Electric charges attract or repel one another with a force inversely proportional to the square

      of the distance between them: unlike charges attract, like ones repel.

2.    Magnetic poles (or states of polarization at individual points) attract or repel one another in

      a similar way and always come in pairs: every north pole is yoked to a south pole.

3.    An electric current in a wire creates a circular magnetic field around the wire, its direction

      (clockwise or counter-clockwise) depending on that of the current.

4.    A current is induced in a loop of wire when it is moved towards or away from a magnetic 

      field, or a magnet is moved towards or away from it, the direction of current depending on

      that of the movement.

 While preparing for an evening lecture on 21 April 1820, Hans Christian Ørsted made a surprising observation. As he was setting up his materials, he noticed a compass needle deflected from magnetic north when the electric current from the battery he was using was switched on and off. This deflection convinced him that magnetic fields radiate from all sides of a wire carrying an electric current, just as light and heat do, and that it confirmed a direct relationship between electricity and magnetism.

Hans Christian Orsted

     At the time of discovery, Ørsted did not suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework. However, three months later he began more intensive investigations. Soon thereafter he published his findings, proving that an electric current produces a magnetic field as it flows through a wire. The CGS unit of magnetic induction (oersted) is named in honor of his contributions to the field of electromagnetism.

 His findings resulted in intensive research throughout the scientific community in electrodynamics. They influenced French physicist André-Marie Ampère's developments of a single mathematical form to represent the magnetic forces between current-carrying conductors. Ørsted's discovery also represented a major step toward a unified concept of energy.

 This unification, which was observed by Michael Faraday, extended by James Clerk Maxwell, and partially reformulated by Oliver Heaviside and Heinrich Hertz, is one of the key accomplishments of 19th century mathematical physics. It had far-reaching consequences, one of which was the understanding of the nature of light. Light and other electromagnetic waves take the form of quantized, self-propagating oscillatory electromagnetic field disturbances calledphotons. Different frequencies of oscillation give rise to the different forms of electromagnetic radiation, from radio waves at the lowest frequencies, to visible light at intermediate frequencies, to gamma rays at the highest frequencies.

  One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with classical mechanics, but it is compatible with special relativity. According to Maxwell's equations, the speed of light in a vacuum is a universal constant, dependent only on the electrical permittivity and magnetic permeability of free space. This violates Galilean invariance, a long-standing cornerstone of classical mechanics. One way to reconcile the two theories is to assume the existence of a luminiferous aether through which the light propagates. However, subsequent experimental efforts failed to detect the presence of the aether. After important contributions of Hendrik Lorentz and Henri Poincaré, in 1905, Albert Einstein solved the problem with the introduction of special relativity, which replaces classical kinematics with a new theory of kinematics that is compatible with classical electromagnetism.

 In addition, relativity theory shows that in moving frames of reference a magnetic field transforms to a field with a nonzero electric component and vice versa; thus firmly showing that they are two sides of the same coin, and thus the term "electromagnetism".

  Electromagnetism is the force that causes the interaction between electrically charged particles; the areas in which this happens are calledelectromagnetic fields. It is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interactionand gravitation.

 Electromagnetism is the interaction responsible for practically all the phenomena encountered in daily life, with the exception of gravity. Ordinary matter takes its form as a result of intermolecular forces between individual molecules in matter. Electrons are bound by electromagnetic wave mechanics into orbitals around atomic nuclei to form atoms, which are the building blocks of molecules. This governs the processes involved in chemistry, which arise from interactions between the electrons of neighbouring atoms, which are in turn determined by the interaction between electromagnetic force and the momentum of the electrons.

 Electromagnetism manifests as both electric fields and magnetic fields. Both fields are simply different aspects of electromagnetism, and hence are intrinsically related. Thus, a changing electric field generates a magnetic field; conversely a changing magnetic field generates an electric field. This effect is called electromagnetic induction, and is the basis of operation for electrical generators, induction motors, and transformers.