English physicist and chemist Michael Faraday is known for his many experiments that contributed greatly to the understanding of electromagnetism. Faraday, who became one of the greatest scientists of the 19th century, began his career as a chemist. He wrote a manual of practical chemistry that reveals his mastery of the technical aspects of his art, discovered a number of new organic compounds, among them benzene, and was the first to liquefy a "permanent" gas (i.e., one that was believed to be
incapable of liquefaction).
His major contribution, however, was in the field of electricity and magnetism . He was the first to produce an electric current from a magnetic field, invented the first electric motor and dynamo, demonstrated the relation between electricity and chemical
bonding, discovered the effect of magnetism on light, and discovered and named diamagnetism, the peculiar behavior of certain substances in strong magnetic fields.
He provided the experimental, and a good deal of the theoretical, foundation upon which James Clerk Maxwell
erected classical electromagnetic field theory.
Michael Faraday's Early Career
Faraday began his scientific career as Sir Humphry
Davy's laboratory assistant. When Faraday joined Davy
in 1812, Davy was in the process of revolutionizing the
chemistry of the day. Davy's ideas were influenced by an
atomic theory that was also to have important consequences for Faraday's thought.
Faraday's work under Davy came to an end
in 1820. There followed a series of discoveries
that astonished the scientific world. . In 1820
he produced the first known compounds of carbon and chlorine , $C_2 Cl_6$ and $C_2 Cl_4$. These
compounds were produced by substituting chlorine for hydrogen in "olefiant gas" (ethylene),
the first substitution reactions induced.
In 1825, as a result of research on illuminating gases, Faraday isolated and described benzene . In the
1820s he also conducted investigations of steel
alloys, helping to lay the foundations for scientific metallurgy and metallography. While
completing an assignment from the Royal Society of London to improve the quality of
optical glass for telescopes, he produced a glass of very high refractive index that was to lead him, in 1845,
to the discovery of diamagnetism.
By the 1820s Andre-Marie Ampere had shown that
magnetic force apparently was a circular one, producing in
effect a cylinder of magnetism around a wire carrying an
electric current. No such circular force had ever before
been observed, and Faraday was the first to understand
what it implied. If a magnetic pole could be isolated, it
ought to move constantly in a circle around a current-carrying wire. Faraday's ingenuity and laboratory skill
enabled him to construct an apparatus that confirmed this
conclusion. This device, which transformed electrical energy into mechanical energy, was the first electric motor.
On Aug. 29, 1831, Faraday wound a thick iron ring on
one side with insulated wire that was connected to a battery. He then wound the opposite side with wire connected
to a galvanometer. What he expected was that a "wave"
would be produced when the battery circuit was closed
and that the wave would show up as a deflection of the
galvanometer in the second circuit. He closed the primary
circuit and, to his delight and satisfaction, saw the galvanometer needle jump. A current had been induced in the
secondary coil by one in the primary. When he opened the
circuit, however, he was astonished to see the galvanometer jump in the opposite direction. Somehow, turning off
the current also created an induced current in the secondary circuit, equal and opposite to the original current. This
phenomenon led Faraday to propose what he called the
"electrotonic" state of particles in the wire, which he considered a state of tension.
In the fall of 1831 Faraday attempted to determine just
how an induced current was produced. He discovered that
when a permanent magnet was moved in and out of a coil
of wire a current was induced in the coil. Magnets, he
knew, were surrounded by forces that could be made visible by the simple expedient of sprinkling iron filings on a
card held over them.
Faraday saw the "lines of force" thus revealed as lines of tension in the medium, namely air, surrounding the magnet, and he soon discovered the law determining the production of electric currents by magnets: the magnitude of the current was dependent upon the number of lines of force cut by the conductor in unit
time. He immediately realized that a continuous current could be produced by rotating a copper disk between the
poles of a powerful magnet and taking leads off the disk's rim and center. This was the first dynamo. It was also the
direct ancestor of electric motors, for it was only necessary to reverse the situation, to feed an electric current to
the disk, to make it rotate.
Since the very beginning of his scientific work, Faraday
had believed in what he called the unity of the forces of
nature. By this he meant that all the forces of nature were
but manifestations of a single universal force and ought,
therefore, to be convertible into one another. In 1846 he
made public some of his speculations in a lecture titled
"Thoughts on Ray Vibrations." Specifically referring to
point atoms and their infinite fields of force, he suggested
that the lines of electric and magnetic force associated
with these atoms might, in fact, serve as the medium by
which light waves were propagated.
In 1845 Faraday tackled the problem of his hypothetical electrotonic state. He passed a beam of plane-polarized
light through the optical glass of high refractive index and
then turned on an electromagnet so that its lines of force
ran parallel to the light ray. The plane of polarization was
rotated, indicating a strain in the molecules of the glass.
But Faraday again noted an unexpected result. When he
changed the direction of the ray of light, the rotation
remained in the same direction, a fact that Faraday correctly interpreted as meaning that the strain was not in
the molecules of the glass but in the magnetic lines of
force. The direction of rotation of the plane of polarization depended solely upon the polarity of the lines of
force; the glass served merely to detect the effect.
By 1850 Faraday had evolved a radically new view of
space and force. Space was not "nothing," the mere location of bodies and forces, but a medium capable of
supporting the strains of electric and magnetic forces. The
energies of the world were not localized in the particles
from which these forces arose but rather were to be found
in the space surrounding them. Thus was born field theory.
As Maxwell later freely admitted, the basic ideas for his
mathematical theory of electrical and magnetic fields
came from Faraday; his contribution was to mathematize
those ideas in the form of his classical field equations.
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