June 13 is the birthday of James Maxwell, a British physicist, the creator of classical electrodynamics
June 13 is the birthday of James Maxwell, a British physicist, the creator of classical electrodynamics. Very few people do not remember the name of James Maxwell, mentioned many times in school physics textbooks. The British scientist had an amazingly broad range of interests: from theory of electromagnetic phenomena, through kinetic theory of gases and optics to theory of elasticity, and more. He is known as a prominent physicist, the creator of classical electrodynamics, one of the founders of statistical physics, and the author of ideas on displacement current and Maxwell’s equations, Maxwell distribution, Maxwell's demon, and the principle of color photography.
It would seem that the history of photography began with that photo view from Niépce's window. But Maxwell the physicist contributed to this branch of science as well. His first scientific works, which he started in 1852, focused on physiology and physics of color vision and colorimetry.
In 1861, James Maxwell produced the first color photograph. To achieve that, he projected three transparencies – red, green and blue – on a screen simultaneously. In his experiments, Maxwell used a rotating disk with color sectors (Maxwell disk). Rapid rotation made the colors merge: if the color sequence in the disk was the same as in spectral colors, the resulting color looked white; a red-and-yellow disk produced orange color; the mixing of blue and yellow produced an impression of the color green. The three-component theory was proven, opening the path to color photography.
What do Saturn’s rings consist of? No-one had been able to find the answer since Galileo. But James Maxwell did. He proved that, to be stable, the Rings of Saturn must consist of unconnected particles (bodies).
He published the following articles: · “On Faraday's lines of force” (1855), · “On physical lines of force” (1861), · “A Dynamical Theory of the Electromagnetic Field” (1869). His monograph A Treatise on Electricity and Magnetism (1873) in two volumes became a symbolic summary.
However, many things had been known by the time Maxwell began investigating electrical and magnetic phenomena: the laws of interaction between stationary electric charges (Coulomb's law) and between currents (Ampere's Law) had been established, and the fact that magnetic interactions are interactions of moving electric charges had been proven. At that time, scientists believed that interaction is transmitted instantaneously through void (theory of long-range action). Michael Faraday made a decisive pivot to theory of short-range action in the 1930s.
According to his concept, an electric charge produces an electric field in the surrounding space. And such fields affect each other. The field of one charge affects that of the other and vice versa. The currents interact through a magnetic field. Faraday used lines of force to describe their propagation through space. He believed them to be similar to normal elastic lines in a hypothetical medium — the world ether.
These ideas of the reality of processes in a space surrounding charges and currents were fully accepted by Maxwell who believed that a body could not act where it does not exist. He also gave these concepts a new, mathematical, form. With the concept of a field introduced, Coulomb’s and Ampere’s laws began to be expressed in a fuller, deeper and more elegant way. Moreover, Maxwell noticed a new property of fields in the phenomenon of electromagnetic induction: a changing magnetic field in an empty space generates an electric field with closed lines of force (the so called eddy electric field).
But there was another discovery concerning properties of an electromagnetic field. No experiment was conducted that time. The physicist guessed that a changing electric field generated a magnetic field as well as a normal electric current does (the displacement current hypothesis). In 1869, the key behavior patterns of an electromagnetic field were fully established and expressed in a system of four equations.
Maxwell’s equations are the basic equations of classical macroscopic electrodynamics. They describe electromagnetic phenomena in arbitrary media and in a vacuum.
The conclusion following from those equations was the finite nature of the electromagnetic interactions propagation speed, which is the difference between the short-range action theory and the long-range action theory. The speed was found to equal the speed of light in a vacuum: 300,000 km/s, which led Maxwell to the conclusion that light was a form of electromagnetic waves.
Maxwell’s another fundamental contribution to science was the development and establishment of the kinetic theory of gases (statistical mechanics). The scientist was the first to claim that laws of nature were statistical. And in 1866, he discovered the first statistical law of molecule velocity distribution, which became known as Maxwell distribution.
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