When Maxwell arrived on the scene, physicists had already learned that static electricity is created whenever they rubbed, say, a piece of amber with a rabbit fur. They had also discovered that a compass needle could be moved whenever a magnet is brought nearby. Given the very different nature of these effects, these two phenomena were assumed to be independent and unrelated.
However, at about the same time a few tantalizing observations hinted that electricity and magnetism may actually be linked. Following these leads, Maxwell derived a set of four simple equations that, to the astonishment of many, showed that electricity and magnetism were but two sides of the same coin. The two phenomena were forever linked by something he named the electromagnetic field.
Just as a gravitational field allows any mass to tug on any other, Maxwell’s electromagnetic field allows any positive charge to repel positive charges and attract negative charges. Maxwell also showed that a stream of moving electric charges would create an electromagnetic field that could move a compass needle. He even went on to show that if those moving charges were to increase in speed or change direction (both of which are forms of acceleration), they’d produce an electromagnetic wave that would travel through space. This wave is best understood as a disturbance in the electromagnetic field itself.
Maxwell’s classical electrodynamics, as his theory is now known, was immensely powerful. It proved capable of explaining nearly every electric or magnetic phenomenon known at the time. For instance, it could successfully explain why colors emerged from Newton’s prism, and why a diffraction pattern was formed by Young’s double slits. Physicists and engineers still use it every day to explain countless electric and magnetic phenomena with great accuracy.
DEFINITION
Classical electrodynamics is a classical (pre-quantum) theory that describes the behavior of electric and magnetic systems. It is governed by the four Maxwell equations, and accurately describes all electric and magnetic phenomena for macroscopic systems.
It could even be used to calculate the speed at which electromagnetic waves should travel through empty space. Remarkably, Maxwell found that these waves move at exactly the same speed physicists had previously estimated for rays of light! By the time Maxwell’s theory was confirmed by experiment several decades later, little doubt remained that light was indeed a wave phenomenon. Newton’s particles had not only hit the mat, they seemed down for the count, once and for all.
There’s more. Just as classical mechanics could predict future states of massive particles interacting via gravity, classical electrodynamics could predict the future states of electric charges. Provided, of course, that the initial states were known. Both of these branches of classical physics came complete with causal and predictive determinism.
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