Timeline History 600 BC Thales of Miletus writes about amber becoming charged by rubbing - he was describing what we now call static electricity. 600 BC Thales of Miletos rubs amber (elektron in Greek) with cat fur and picks up bits of feathers. 1660 William Gilbert, court physician to Queen Elizabeth, first coined the term electricity from the Greek word for amber. Gilbert wrote about the electrification of many substances in his De magnete, magneticisique corporibus. He also first used the terms electric force, magnetic pole, and electric attraction. He also discusses static electricity and invents an electric fluid which is liberated by rubbing. 1660 Otto von Guericke invented a machine that produced static electricity. 1666-1713 Francis Hauksbee later made improvements on Guerickes electricity-generating machine and these improved machines provided experimenters with a ready source of static electricity. 1675 Robert Boyle discovered that electric attraction and repulsion can act across a vacuum and does not depend upon the air as a medium. He also added resin to the then-known list of electrics. 1729 Stephen Gray shows that electricity doesnt have to be made in place by rubbing but can also be transferred from place to place with conducting wires. He also shows that the charge on electrified objects resides on their surfaces. 1733 Charles Francois du Fay discovers that electricity comes in two kinds which he calledresinous(-) and vitreous(+). 1747 Benjamin Franklin and Ebenezer Kinnersley later renamed the two forms as positive and negative. 1745 Georg Von Kleist(L) discovered that electricity was controllable. Dutch physicist, Pieter van Musschenbroek (R) invented the Leyden Jar the first electrical capacitor. Leyden jars store static electricity. 1745 Pieter van Musschenbroek invents the Leyden jar, or capacitor, and nearly kills his friend Cunaeus. 1747 Benjamin Franklin invents the theory of one-fluid electricity in which one of Nollets fluids exists and the other is just the absence of the first. He proposes the principle of conservation of charge and calls the fluid that exists and flows ``positive. This educated guess ensures that undergraduates will always be confused about the direction of current flow. He also discovers that electricity can act at a distance in situations where fluid flow makes no sense. 1748 Sir William Watson uses an electrostatic machine and a vacuum pump to make the first glow discharge. His glass vessel is three feet long and three inches in diameter: the first fluorescent light bulb.Sir William Watson uses an electrostatic machine and a vacuum pump to make the first glow discharge. His glass vessel is three feet long and three inches in diameter: the first fluorescent light bulb. Ca. 1775 Henry Cavendish invents the idea of capacitance and resistance (the latter without any way of measuring current other than the level of personal discomfort). But being indifferent to fame he is content to wait for his work to be published by Lord Kelvin in 1879. 1785 Charles Augustin Coulomb uses a torsion balance to verify that the electric force law is inverse square. He also proposes a combined fluid/action-at-a-distance theory like that of Aepinus but with two conducting fluids instead of one. Fighting breaks out between single and double fluid partisans. He also discovers that the electric force near a conductor is proportional to its surface charge density and makes contributions to the two-fluid theory of magnetism. Ca. 1786 Italian physician, Luigi Galvani demonstrated what we now understand to be the electrical basis of nerve impulses when he made frog muscles twitch by jolting them with a spark from an electrostatic machine. 1793 Alessandro Volta makes the first batteries and argues that animal electricity is just ordinary electricity flowing through the frog legs under the impetus of the force produced by the contact of dissimilar metals. He discovers the importance of ``completing the circuit. In 1800 he discovers the Voltaic pile (dissimilar metals separated by wet cardboard) which greatly increases the magnitude of the effect. 1811 Arago shows that some crystals alter the polarization of light passing through them. 1812 Michael Faraday, a bookbinders apprentice, writes to Sir Humphrey Davy asking for a job as a scientific assistant. Davy interviews Faraday and finds that he has educated himself by reading the books he was supposed to be binding. He gets the job. 1819 Hans Christian Oersted discovered that electric currents create magnetic fields, an important aspect of electromagnetism. 1820 Andre Marie Ampere, one week after hearing of Oersteds discovery, shows that parallel currents attract each other and that opposite currents attract. 1821 Faraday begins electrical work by repeating Oersteds experiments. First electric motor (Faraday). 1821 Arago developed on it and invented the electro-magnet. 1825 Ampere publishes his collected results on magnetism. His expression for the magnetic field produced by a small segment of current is different from that which follows naturally from the Biot-Savart law by an additive term which integrates to zero around closed circuit. It is unfortunate that electrodynamics and relativity decide in favor of Biot and Savart rather than for the much more sophisticated Ampere, whose memoir contains both mathematical analysis and experimentation, artfully blended together. In this memoir are given some special instances of the result we now call Stokes theorem or as we usually write it. Maxwell describes this work as ``one of the most brilliant achievements in science. The whole, theory and experiment, seems as if it had leaped, full-grown and full-armed, from the brain of the `Newton of electricity. 1826 Georg Simon Ohm establishes the result now known as Ohms law. V=IR seems a pretty simple law to name after someone, but the importance of Ohms work does not lie in this simple proportionality. What Ohm did was develop the idea of voltage as the driver of electric current. He reasoned by making an analogy between Fouriers theory of heat flow and electricity. In his scheme temperature and voltage correspond as do heat flow and electrical current. It was not until some years later that Ohms electroscopic force (V in his law) and Poissons electrostatic potential were shown to be identical. 1827 Georg Simon Ohm published Ohm’s law. 1833 Faraday begins work on the relation of electricity to chemistry. In one of his notebooks he concludes after a series of experiments, ``...there is a certain absolute quantity of the electric power associated with each atom of matter. 1834 Faraday discovers self inductance. 1837 Faraday discovers the idea of the dielectric constant. 1837 Faraday discovers self inductance. 1838 Faraday shows that the effects of induced electricity in insulators are analogous to induced magnetism in magnetic materials. Those more mathematically inclined immediately appropriate Poissons theory of induced magnetism 1838 Faraday discovers Faradays dark space, a dark region in a glow discharge near the negative electrode. 1841 Michael Faraday is completely exhausted by his efforts of the previous 2 decades, so he rests for 4 years. 1841 James Prescott Joule shows that energy is conserved in electrical circuits involving current flow, thermal heating, and chemical transformations. 1842 Joseph Henry rediscovers the result of F. Savery about the oscillation of the electric current in a capacitive discharge and states, ``The phenomena require us to admit the existence of a principal discharge in one direction, and then several reflex actions backward and forward, each more feeble than the preceding, until equilibrium is restored. 1842 Michael Faraday is completely exhausted by his efforts of the previous 2 decades, so he rests for 4 years. 1846 Wilhelm Weber combines Amperes analysis, Faradays experiments, and the assumption of Fechner that currents consist of equal amounts of positive and negative electricity moving opposite to each other at the same speed to derive an electromagnetic theory based on forces between moving charged particles. This theory has a velocity-dependent potential energy and is wrong, but it stimulates much work on electromagnetic theory which eventually leads to the work of Maxwell and Lorenz. It also inspires a new look at gravitation by William Thomson to see if a velocity-dependent correction to the gravitational energy could account for the precession of Mercurys perihelion. 1847 Weber proposes that diamagnetism is just Faradays law acting on molecular circuits. In answering the objection that this would mean that everything should be diamagnetic he correctly guesses that diamagnetism is masked in paramagnetic and ferromagnetic materials because they have relatively strong permanent molecular currents. This work rids the world of magnetic fluids. 1847 Hermann von Helmholtz writes a memoir ``On the Conservation of Force which emphatically states the principle of conservation of energy: ``Conservation of energy is a universal principle of nature. Kinetic and potential energy of dynamical systems may be converted into heat according to definite quantitative laws as taught by Rumford, Mayer, and Joule. Any of these forms of energy may be converted into chemical, electrostatic, voltaic, and magnetic forms. He reads it before the Physical Society of Berlin whose older members regard it as too speculative and reject it for publication in Annalen der Physik. 1848-9 Gustav Kirchoff extends Ohms work to conduction in three dimensions, gives his laws for circuit networks, and finally shows that Ohms ``electroscopic force which drives current through resistors and the old electrostatic potential of Lagrange, Laplace, and Poisson are the same. He also shows that in steady state electrical currents distribute themselves so as to minimize the amount of Joule heating 1851 Thomson gives a general theory of thermoelectric phenomena, describing the effects seen by Seebeck and Peltier. 1853 Thomson uses Poissons magnetic theory to derive the correct formula for magnetic energy: He also gives the formula and gives the world the powerful, but confusing, analysis where the forces on circuits are obtained by taking either the positive or negative gradient of the magnetic energy. Knowing which sign to use is, of course, the confusing part. 1853 Thomson gives the theory of the RLC circuit providing a mathematical description for the observations of Henry and Savery. 1854 Faraday clears up the problem of disagreements in the measured speeds of signals along transmission lines by showing that it is crucial to include the effect of capacitance. 1854 Thomson, in a letter to Stokes, gives the equation of telegraphy ignoring the inductance: where R is the cable resistance and where C is the capacitance per unit length. Since this is the diffusion equation, the signal does not travel at a definite speed. 1855 Faraday retires, living quietly in a house provided by the Queen until his death in 1867. 1855 James Clerk Maxwell writes a memoir in which he attempts to marry Faradays intuitive field line ideas with Thomsons mathematical analogies. In this memoir the physical importance of the divergence and curl operators for electromagnetism first become evident. 1864 Maxwell reads a memoir before the Royal Society in which the mechanical model is stripped away and just the equations remain. He also discusses the vector and scalar potentials, using the Coulomb gauge. He attributes physical significance to both of these potentials. He wants to present the predictions of his theory on the subjects of reflection and refraction, but the requirements of his mechanical model keep him from finding the correct boundary conditions, so he never does this calculation. 1868 Maxwell decides that giving physical significance to the scalar and vector potentials is a bad idea and bases his further work on light. 1869 Maxwell presents the first calculation in which a dispersive medium is made up of atoms with natural frequencies. This makes possible detailed modeling of dispersion with refractive indices having resonant denominators. 1870-1890 The hunt is on for physical models of the aether which are natural and from which Maxwells equations can be derived. The physicists who work on this problem include Maxwell, Thomson, Kirchoff, Bjerknes, Leahy, Fitz Gerald, Helmholtz, and Hicks. 1872 E. Mascart looks for the motion of the earth through the aether by measuring the rotation of the plane of polarization of light propagated along the axis of a quartz crystal. 1873 Maxwell publishes his Treatise on Electricity and Magnetism, which discusses everything known at the time about electromagnetism from the viewpoint of Faraday. His own theory is not very thoroughly discussed, but he does introduce his electromagnetic stress tensor in this work, including the accompanying idea of electromagnetic momentum. 1880 Rowland shows that Faraday rotation can be obtained by combining Maxwells equations and the Hall term in Ohms law, assuming that displacement currents are affected in the same way as conduction currents. 1881 J. J. Thomson attempts to verify the existence of the displacement current by looking for magnetic effects produced by the changing electric field made by a moving charged sphere. 1881 George Fitz Gerald points out that J. J. Thomsons analysis is incorrect because he left out the effects of the conduction current of the moving sphere. Including both currents makes the separate effect of the displacement current disappear. 1883 Fitz Gerald proposes testing Maxwells theory by using oscillating currents in what we would now call a magnetic dipole antenna (loop of wire). He performs the analysis and discovers that very high frequencies are required to make the test. Later that year he proposes obtaining the required high frequencies by discharging a capacitor into a circuit. 1883-5 Horace Lamb (R)and Oliver Heaviside(L) analyze the interaction of oscillating electromagnetic fields with conductors and discover the effect of skin depth. 1884 Heinrich Hertz asserts that made by charges and made by a changing magnetic field are identical. Working from dynamical ideas based on this assumption and some of Maxwells equations, Hertz is able to derive the rest of them. 1887 Hertz finds that ultraviolet light falling on the negative electrode in a spark gap facilitates conduction by the gas in the gap. 1888 Hertz discovers that oscillating sparks can be produced in an open secondary circuit if the frequency of the primary is resonant with the secondary. He uses this radiator to show that electrical signals are propagated along wires and through the air at about the same speed, both about the speed of light. He also shows that his electric radiations, when passed through a slit in a screen, exhibit diffraction effects. Polarization effects using a grating of parallel metal wires are also observed. 1888 Roentgen shows that when an uncharged dielectric is moved at right angles to a magnetic field is produced. 1889 Hertz gives the theory of radiation from his oscillating spark gap. 1889 Oliver Heaviside finds the correct form for the electric and magnetic fields of a moving charged particle, valid for all speeds v < c. 1889 J. J. Thomson shows that Cantons effect (1762) in which a red hot poker can neutralize the electrification of a small charged body is due to electron emission causing the air between the poker and the body to become conducting. 1894 J. J. Thomson measures the speed of cathode rays and shows that they travel much more slowly than the speed of light. The aether model of cathode rays begins to die. 1895 Marconi built a wireless system capable of transmitting signals at long distances (1.5 mi./ 2.4 km). From Marconis experiments, the phenomenon that transmission range is proportional to the square of antenna height is known as Marconis law.This formula represents a physical law that radio devices use. 1896 J. J. Thomson discovers that materials through which X-rays pass are rendered conducting. 1897 J. J. Thomson deflects cathode rays by crossed electric and magnetic fields and measurese/m. 1899 Ernest Rutherford discovers that the rays from uranium come in two types, which he calls alpha and beta radiation. 1904 John Ambrose Fleming invented the two-electrode vacuum-tube rectifier, which he called the oscillation valve, for which he received a patent on 16 November. It was also called a thermionic valve, vacuum diode, kenotron, thermionic tube, or Fleming valve. The Supreme Court of the United States later invalidated the patent because of an improper disclaimer and, additionally, maintained the technology in the patent was known art when filed.[ 1907 Lee De Forest invented the electric amplifier. 1910 Ernest R. Rutherford measured the distribution of an electric charge within the atom. 1913 Electric refrigerator. Robert Millikan measured the electric charge on a single electron.
Posted on: Thu, 05 Dec 2013 00:29:16 +0000
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