Ten Experiments that Shocked Physics

HERTZ AND ELECTROMAGNETIC WAVES

The initial problem

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In 1864, the English physicist Maxwell published a comprehensive work on electric and magnetic phenomena.

During the entire nineteenth century there had been numerous discoveries in this sector of physics which indicated a certain influence between the two types of phenomena.

Maxwell enunciated four equations, two for the electric field and two for the magnetic field, which took charge of all the experiments made up to that moment and which reflected the reciprocal influences.

The theoretical consequences of these equations were immediately very evident:

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1) First of all, the four equations represent a generalization of everything discovered up to then in electric and magnetic terms.

Maxwell's first equation is nothing but Gauss's electric law (and the third, Gauss's law magnetic), while the second is Faraday's law and the last is an extension of Ampére's law made by Maxwell himself.

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2) From Maxwell's third equation, the non-existence of isolated magnetic monopoles is determined which, stated in another way, means admitting lines of force of the magnetic field which are closed.

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3) From the first equation it can be seen that the lines of force of the electric field are, by definition, open, i.e. with a starting point and an arrival point determined by the electric charges of opposite sign which generate the field itself.

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4) Combining instead the first, the second and the fourth equation we obtain the already known conservation of the electric charge or continuity equation:

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5) In an electromagnetic field, the force to which a charge is subjected is given by the expression of the Lorentz force , which is an overcoming and generalization of the Colombian force.

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6) A further point of discussion arises from the fact that in the second and fourth equations the electric and magnetic fields are mutually bound to each other.

This evidence put an end to almost 50 years of misunderstandings between electrical and magnetic phenomena, simply by unifying them.

From 1864 onwards it was clear that there was a single field with a single force that described a single concept and since then all this took the adjective electromagnetic .

It is true that at times the electric or magnetic effects prevail, but in reality the two entities are never present only individually.

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7) Another aspect, closely linked to the previous one, is that of duality.

It is found that the equations are somehow specular with respect to the electric and magnetic fields, almost managing to exchange their roles.

Indeed, under a suitable rewriting of Maxwell's equations, this is possible in a natural and automatic way.

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8) Another consequence is the overcoming of Coulomb's theory of action at a distance with a local point-to-point interaction between electric phenomena and magnetic phenomena, so there was an extension of the notions much more than the Lorentz force can make