History of electromagnetism
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William Gilbert: not only shown by amber. Electricus = “amber-like” Certain substance show the
effect after subjected to friction “effluvium” was removed.. 'electret' . Gilbert found
electroscope.
 Nicollo Cabeo, Robert Boyle:
Electricity repel as well as attract
 Joseph Priestly 1767 attraction of electricity follow the same law as gravitation: inverse square
law
 Gray: electric fluid
 Charles Franxois DuFay: two fluid: resinuous and Vitreous
 Benjamin Franklin one fluid theory. Surplus + vs deficit  Franklin's conservation of electric charges and Priestley's law of attrction bring electricity into an
exact science
 Henry Cavendish rediscover inv sq law. Electrostatic capacity, specific inductive capacity.
Virtually introduce the notion of electric potential
 Aepinus: effluvium around electrical bodies vs action at a distance (Franklin and others)
 Coulomb 1785 verified Priestley's law. Action at a distance prevailed... until Faraday. Coulomb
Did not accept one fluid theory but of Robert Symmer 1759: positive and negative
 Simeon Dennis Poisson accept two fluid theory. Materials in whic the fluids move freely are
called conductors. Inspired by Laplacian = 0 in the case of gravitation, Poisson replaced zero by
density of electric fluid.
 Green gave the name potential. Green connect surface integral and volume integral: the Green
theorem
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Petrus Peregrinus. Lodestone made spherical, small needles align like meridians.... Poles
Gilbert: north and south. Attraction and repulsion between different and like poles
John Michells 1750 : inverse sq law for magnetism.. earlier than the law for electric force
Franz Aepinus 1759 poles : where magnetic fluid concentrates
Anton Brugmans:two-fluids: boreal and austral
Coulomb: no magnetic monopole. Magnetization is separation of boreal and austral to opposite
ends in a molecule
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A tradesman of Wakefield dicovered that a number of knives and forks in a box struck hy
lightning can attract nails
Franklin 1751 magnetized sewing needle by means of discharge of a Leyden jar.
Hans Christiaan Oersted: connection between galvanism and magnetism. "Electric conflict"
around a wire.. a circle.. magnetic needle direct in opposite direction when placed above and
below wire.
Jean-Baptiste Biot and Felix Savart quantifed the magnetic field (originally called force)
Oersred thought a current-carrying wire should be moved by a magnet..he showed
experimentally
Andre Marie Ampere: two current carrying wires atrract or oppose each other. ..
electrodynamics . ponderomotive force. Ponderomotive force also exerted by magnet on such
currents. Weakness: force directed along the lines joining two current elements
Ampere: magnetism is really an electrical phenonemena. It is current rather than magnetic fluid
thas is the fundamental quantity.
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1822 Thomas Johann Seebeck: current generated by heat.
18 55: Faraday: Induksi elektromagnet
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Cavendish: conductance power of metal
Humphrey Davy: conductance inversely proportiinal to length, directly proportional to sectional
area.
Davy: conductance varies w temperature.
1826 George Simon Ohm compared elcteeic flow to caloric. The magnitude of flow is
proportional to difference in electroscopic forces, just as in the theory of heat the flow of caloric
proportional to temperature difference.