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The speed of the light
===Faraday's Law===
===Faraday's Law===
The third equation contains the result of Faraday's experiments with "electromagnetic induction"—a changing magnetic field creates an electric field, and that electric field circulates around the area experiencing the change in total magnetic flux. (Remember that the curl operator measures the extent to which a vector field runs in circles.) We won't go into the details of his experiments, except to note that he discovered that moving a coil of wire (a loop to pick up a circulating electric field) through a magnetic field (for example, by putting it on a shaft and turning it) led to the invention of electric generators, and hence made a major contribution to the industrialization of the world. Not bad for a theoretician.
The third equation contains the result of Faraday's experiments with "electromagnetic induction"—a changing magnetic field creates an electric field, and that electric field circulates around the area experiencing the change in total magnetic flux. (Remember that the curl operator measures the extent to which a vector field runs in circles.) We won't go into the details of his experiments, except to note that he discovered that moving a coil of wire (a loop to pick up a circulating electric field) through a magnetic field (for example, by putting it on a shaft and turning it) led to the invention of electric generators, and hence made a major contribution to the industrialization of the world. Not bad for a theoretician.
===The Unification of Light with the Theory of Electromagnetism===
It is possible, by means of experiments with electrical charges and currents, to find such a figure c<sup>2</sup> that has turned out to be the square of the velocity of propagation of electromagnetic effects. It could be demonstrated from static measurements of forces between two "unite" charges and between two "unit" currents that c ≈ 3.00 x 10 <sup>8</sup>ms<sup>-1</sup>. When Maxwell had performed this calculation with his equations for the first time, he could conclude that the system of electric and magnetic field will be propagated by this velocity and he pointed out the intriguing equivalence of this constant with the already experimentally determined speed of the light. Thus, he suggested that the light is the wave motion of the same medium that causes electric and magnetic phenomena. Electricity and magnetism had been unified by experimental works of [[Faraday]], [[Hans Christian Oersted|Ørsted]] and [[Ampère]]. After them, Maxwell carried out one of the greatest unifications in the physical sciences, the light ceased to be "something different" and have become electricity and magnetism in a new form - electromagnetic field propagated across the space.<ref>{{cite book |title=The Feynman Lectures on Physics, Volume 2 |author=Richard Phillips Feynman, Robert B. Leighton, Matthew Linzee Sands |publisher=Addison-Wesley |year=1966 |edition=2 |pages=18-9|url=http://books.google.com/books?ei=wJjyUe3-CsbMPYSegKgL&hl=sk&id=haXvAAAAMAAJ&dq=the+feynman+lectures+on+physics&q=electricity+and+magnetism+unified#search_anchor}}</ref>
==Other Formulations==
==Other Formulations==