Today, we learn early on that visible light is just one chunk of the wide electromagnetic spectrum, whose radiation is made up of oscillating electric and magnetic fields. And we learn that electricity and magnetism are inextricably linked; a changing magnetic field creates an electric field, and current and changing electric fields give rise to magnetic fields.
We have Maxwell to thank for these basic insights. But they didn’t occur to him suddenly and out of nowhere. The evidence he needed arrived in bits and pieces, over the course of more than 50 years.
You could start the clock in 1800, when physicist Alessandro Volta reported the invention of a battery, which allowed experimenters to begin working with continuous direct current. Some 20 years later, Hans Christian Ørsted obtained the first evidence of a link between electricity and magnetism, by demonstrating that the needle of a compass would move when brought close to a current-carrying wire. Soon after, André-Marie Ampère showed that two parallel current-carrying wires could be made to exhibit a mutual attraction or repulsion depending on the relative direction of the currents. And by the early 1830s, Michael Faraday had shown that just as electricity could influence the behavior of a magnet, a magnet could affect electricity, when he showed that drawing a magnet through a loop of wire could generate current.
These observations were piecemeal evidence of behavior that no one really understood in a systematic or comprehensive way. What was electric current really? How did a current-carrying wire reach out and twist a magnet? And how did a moving magnet create current?
A major seed was planted by Faraday, who envisioned a mysterious, invisible “electrotonic state” surrounding the magnet—what we would today call a field. He posited that changes in this electrotonic state are what cause electromagnetic phenomena. And Faraday hypothesized that light itself was an electromagnetic wave. But shaping these ideas into a complete theory was beyond his mathematical abilities. That was the state of affairs when Maxwell came on the scene.
In the 1850s, after graduating from the University of Cambridge, in England, Maxwell set about trying to make mathematical sense of Faraday’s observations and theories. In his initial attempt, an 1855 paper called “On Faraday’s Lines of Force,” Maxwell devised a model by analogy, showing that equations that describe incompressible fluid flow could also be used to solve problems with unchanging electric or magnetic fields.
Full story read here http://spectrum.ieee.org/telecom/wirele ... -equations
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