The Displacement of the Gravitating Needle in its Dependence on Atmospheric Temperatures

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The variations of temperature are found to be proportional to the strength of the current and not to the square of the strength of the current as in the case of heat due to the ordinary resistance of a conductor. This second law is the I 2 R law , discovered experimentally in by the English physicist Joule. In other words, this important law is that the heat generated in any part of an electric circuit is directly proportional to the product of the resistance R of this part of the circuit and to the square of the strength of current I flowing in the circuit.

In Johann Schweigger devised the first galvanometer. This instrument was subsequently much improved by Wilhelm Weber In William Sturgeon of Woolwich, England, invented the horseshoe and straight bar electromagnet, receiving therefor the silver medal of the Society of Arts. This was the forerunner of the Thomson reflecting and other exceedingly sensitive galvanometers once used in submarine signaling and still widely employed in electrical measurements.

Arago in made the important discovery that when a copper disc is rotated in its own plane, and if a magnetic needle be freely suspended on a pivot over the disc, the needle will rotate with the disc. If on the other hand the needle is fixed it will tend to retard the motion of the disc. This effect was termed Arago's rotations. The true explanation was reserved for Faraday, namely, that electric currents are induced in the copper disc by the cutting of the magnetic lines of force of the needle, which currents in turn react on the needle. Georg Simon Ohm did his work on resistance in the years and , and published his results in as the book Die galvanische Kette, mathematisch bearbeitet.

For experiments, he initially used voltaic piles , but later used a thermocouple as this provided a more stable voltage source in terms of internal resistance and constant potential difference. He used a galvanometer to measure current, and knew that the voltage between the thermocouple terminals was proportional to the junction temperature. He then added test wires of varying length, diameter, and material to complete the circuit.

He found that his data could be modeled through a simple equation with variable composed of the reading from a galvanometer, the length of the test conductor, thermocouple junction temperature, and a constant of the entire setup. From this, Ohm determined his law of proportionality and published his results. In , he announced the now famous law that bears his name , that is:. Ohm brought into order a host of puzzling facts connecting electromotive force and electric current in conductors, which all previous electricians had only succeeded in loosely binding together qualitatively under some rather vague statements.

Ohm found that the results could be summed up in such a simple law and by Ohm's discovery a large part of the domain of electricity became annexed to theory. The discovery of electromagnetic induction was made almost simultaneously, although independently, by Michael Faraday , who was first to make the discovery in , and Joseph Henry in In began the epoch-making researches of Michael Faraday , the famous pupil and successor of Humphry Davy at the head of the Royal Institution, London, relating to electric and electromagnetic induction.

The remarkable researches of Faraday, the prince of experimentalists , on electrostatics and electrodynamics and the induction of currents. These were rather long in being brought from the crude experimental state to a compact system, expressing the real essence. Faraday was not a competent mathematician, [78] [79] [80] but had he been one, he would have been greatly assisted in his researches, have saved himself much useless speculation, and would have anticipated much later work. He would, for instance, knowing Ampere's theory, by his own results have readily been led to Neumann's theory, and the connected work of Helmholtz and Thomson.

Faraday's studies and researches extended from to and a detailed description of his experiments, deductions and speculations are to be found in his compiled papers, entitled Experimental Researches in Electricity. He was not in the remotest degree a mathematician in the ordinary sense — indeed it is a question if in all his writings there is a single mathematical formula. The experiment which led Faraday to the discovery of electromagnetic induction was made as follows: He constructed what is now and was then termed an induction coil , the primary and secondary wires of which were wound on a wooden bobbin, side by side, and insulated from one another.

In the circuit of the primary wire he placed a battery of approximately cells. In the secondary wire he inserted a galvanometer. On making his first test he observed no results, the galvanometer remaining quiescent, but on increasing the length of the wires he noticed a deflection of the galvanometer in the secondary wire when the circuit of the primary wire was made and broken. This was the first observed instance of the development of electromotive force by electromagnetic induction. He also discovered that induced currents are established in a second closed circuit when the current strength is varied in the first wire, and that the direction of the current in the secondary circuit is opposite to that in the first circuit.

Also that a current is induced in a secondary circuit when another circuit carrying a current is moved to and from the first circuit, and that the approach or withdrawal of a magnet to or from a closed circuit induces momentary currents in the latter. In short, within the space of a few months Faraday discovered by experiment virtually all the laws and facts now known concerning electro-magnetic induction and magneto-electric induction. Upon these discoveries, with scarcely an exception, depends the operation of the telephone, the dynamo machine, and incidental to the dynamo electric machine practically all the gigantic electrical industries of the world, including electric lighting , electric traction, the operation of electric motors for power purposes, and electro-plating , electrotyping , etc.

In his investigations of the peculiar manner in which iron filings arrange themselves on a cardboard or glass in proximity to the poles of a magnet, Faraday conceived the idea of magnetic " lines of force " extending from pole to pole of the magnet and along which the filings tend to place themselves. On the discovery being made that magnetic effects accompany the passage of an electric current in a wire, it was also assumed that similar magnetic lines of force whirled around the wire.

For convenience and to account for induced electricity it was then assumed that when these lines of force are " cut " by a wire in passing across them or when the lines of force in rising and falling cut the wire, a current of electricity is developed, or to be more exact, an electromotive force is developed in the wire that sets up a current in a closed circuit.

Faraday advanced what has been termed the molecular theory of electricity [81] which assumes that electricity is the manifestation of a peculiar condition of the molecule of the body rubbed or the ether surrounding the body. Faraday also, by experiment, discovered paramagnetism and diamagnetism , namely, that all solids and liquids are either attracted or repelled by a magnet.

For example, iron, nickel, cobalt, manganese, chromium, etc. Brugans of Leyden in and Le Baillif and Becquerel in [83] had previously discovered diamagnetism in the case of bismuth and antimony.

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Faraday also rediscovered specific inductive capacity in , the results of the experiments by Cavendish not having been published at that time. He also predicted [84] the retardation of signals on long submarine cables due to the inductive effect of the insulation of the cable, in other words, the static capacity of the cable. The 25 years immediately following Faraday's discoveries of electromagnetic induction were fruitful in the promulgation of laws and facts relating to induced currents and to magnetism. In Heinrich Lenz and Moritz von Jacobi independently demonstrated the now familiar fact that the currents induced in a coil are proportional to the number of turns in the coil.

Lenz also announced at that time his important law that, in all cases of electromagnetic induction the induced currents have such a direction that their reaction tends to stop the motion that produces them, a law that was perhaps deducible from Faraday's explanation of Arago's rotations. The induction coil was first designed by Nicholas Callan in In Joseph Henry , the American physicist, published an account of his valuable and interesting experiments with induced currents of a high order, showing that currents could be induced from the secondary of an induction coil to the primary of a second coil, thence to its secondary wire, and so on to the primary of a third coil, etc.

Up to the middle of the 19th century, indeed up to about , electrical science was, it may be said, a sealed book to the majority of electrical workers.

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Prior to this time a number of handbooks had been published on electricity and magnetism, notably Auguste de La Rive 's exhaustive ' Treatise on Electricity ,' [94] in French and English ; August Beer 's Einleitung in die Elektrostatik, die Lehre vom Magnetismus und die Elektrodynamik , [95] Wiedemann 's ' Galvanismus ,' and Reiss' [96] ' Reibungsal-elektricitat.

Henry d'Abria [97] [98] published the results of some researches into the laws of induced currents, but owing to their complexity of the investigation it was not productive of very notable results. These books were departures from the beaten path. As Jenkin states in the preface to his work the science of the schools was so dissimilar from that of the practical electrician that it was quite impossible to give students sufficient, or even approximately sufficient, textbooks.

A student he said might have mastered de la Rive's large and valuable treatise and yet feel as if in an unknown country and listening to an unknown tongue in the company of practical men. As another writer has said, with the coming of Jenkin's and Maxwell's books all impediments in the way of electrical students were removed, " the full meaning of Ohm's law becomes clear; electromotive force, difference of potential, resistance, current, capacity, lines of force, magnetization and chemical affinity were measurable, and could be reasoned about, and calculations could be made about them with as much certainty as calculations in dynamics ".

About , Kirchhoff published his laws relating to branched or divided circuits. He also showed mathematically that according to the then prevailing electrodynamic theory, electricity would be propagated along a perfectly conducting wire with the velocity of light. Helmholtz investigated mathematically the effects of induction upon the strength of a current and deduced therefrom equations, which experiment confirmed, showing amongst other important points the retarding effect of self-induction under certain conditions of the circuit.

In , Sir William Thomson later Lord Kelvin predicted as a result of mathematical calculations the oscillatory nature of the electric discharge of a condenser circuit. To Henry, however, belongs the credit of discerning as a result of his experiments in the oscillatory nature of the Leyden jar discharge. He wrote: [] 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 the equilibrium is obtained. These oscillations were subsequently observed by B.

Feddersen [] [] who using a rotating concave mirror projected an image of the electric spark upon a sensitive plate, thereby obtaining a photograph of the spark which plainly indicated the alternating nature of the discharge. Sir William Thomson was also the discoverer of the electric convection of heat the "Thomson" effect. He designed for electrical measurements of precision his quadrant and absolute electrometers. The reflecting galvanometer and siphon recorder , as applied to submarine cable signaling, are also due to him. About the American physicist Henry Augustus Rowland of Baltimore demonstrated the important fact that a static charge carried around produces the same magnetic effects as an electric current.

After Faraday's discovery that electric currents could be developed in a wire by causing it to cut across the lines of force of a magnet, it was to be expected that attempts would be made to construct machines to avail of this fact in the development of voltaic currents. It consisted of two bobbins of iron wire, opposite which the poles of a horseshoe magnet were caused to rotate. As this produced in the coils of the wire an alternating current , Pixii arranged a commutating device commutator that converted the alternating current of the coils or armature into a direct current in the external circuit.

A notable advance in the art of dynamo construction was made by Samuel Alfred Varley in [] and by Siemens and Charles Wheatstone , [] who independently discovered that when a coil of wire, or armature, of the dynamo machine is rotated between the poles or in the "field" of an electromagnet, a weak current is set up in the coil due to residual magnetism in the iron of the electromagnet, and that if the circuit of the armature be connected with the circuit of the electromagnet, the weak current developed in the armature increases the magnetism in the field.

This further increases the magnetic lines of force in which the armature rotates, which still further increases the current in the electromagnet, thereby producing a corresponding increase in the field magnetism, and so on, until the maximum electromotive force which the machine is capable of developing is reached. By means of this principle the dynamo machine develops its own magnetic field , thereby much increasing its efficiency and economical operation. Not by any means, however, was the dynamo electric machine perfected at the time mentioned.

In an important improvement had been made by Dr. Antonio Pacinotti of Pisa who devised the first electric machine with a ring armature. This machine was first used as an electric motor, but afterward as a generator of electricity. In the drum armature was devised by Hefner-Alteneck. This machine in a modified form was subsequently known as the Siemens dynamo. These machines were presently followed by the Schuckert , Gulcher , [] Fein, [] [] [] Brush , Hochhausen , Edison and the dynamo machines of numerous other inventors.

Beginning about alternating current generators came into extensive operation and the commercial development of the transformer, by means of which currents of low voltage and high current strength are transformed to currents of high voltage and low current strength, and vice versa, in time revolutionized the transmission of electric power to long distances. Likewise the introduction of the rotary converter in connection with the "step-down" transformer which converts alternating currents into direct currents and vice versa has effected large economies in the operation of electric power systems.

Before the introduction of dynamo electric machines, voltaic, or primary, batteries were extensively used for electro-plating and in telegraphy. There are two distinct types of voltaic cells, namely, the "open" and the "closed", or "constant", type. The open type in brief is that type which operated on closed circuit becomes, after a short time, polarized; that is, gases are liberated in the cell which settle on the negative plate and establish a resistance that reduces the current strength.

After a brief interval of open circuit these gases are eliminated or absorbed and the cell is again ready for operation. Closed circuit cells are those in which the gases in the cells are absorbed as quickly as liberated and hence the output of the cell is practically uniform. Batteries of the Daniell or "gravity" type were employed almost generally in the United States and Canada as the source of electromotive force in telegraphy before the dynamo machine became available.

In the late 19th century, the term luminiferous aether , meaning light-bearing aether , was a conjectured medium for the propagation of light. It signifies the substance which was thought in ancient times to fill the upper regions of space, beyond the clouds. In James Clerk Maxwell of Edinburgh announced his electromagnetic theory of light, which was perhaps the greatest single step in the world's knowledge of electricity. The paper presented a simplified model of Faraday's work, and how the two phenomena were related. He reduced all of the current knowledge into a linked set of differential equations with 20 equations in 20 variables.

This rate of change will give us the force. The method of calculation which it is necessary to employ was first given by Lagrange , and afterwards developed, with some modifications, by Hamilton's equations. It is usually referred to as Hamilton's principle ; when the equations in the original form are used they are known as Lagrange's equations. Now Maxwell logically showed how these methods of calculation could be applied to the electro-magnetic field. Maxwell supposes that the magnetic energy of the field is kinetic energy , the electric energy potential.

Around , while lecturing at King's College, Maxwell calculated that the speed of propagation of an electromagnetic field is approximately that of the speed of light. He considered this to be more than just a coincidence, and commented " We can scarcely avoid the conclusion that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena.

In his paper A Dynamical Theory of the Electromagnetic Field , Maxwell wrote, The agreement of the results seems to show that light and magnetism are affections of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws. It was known by calculation and experiment that the velocity of electricity was approximately , miles per second; that is, equal to the velocity of light, which in itself suggests the idea of a relationship between -electricity and "light.


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Maxwell, following Faraday, contended that the seat of the phenomena was in the medium. The methods of the mathematicians in arriving at their results were synthetical while Faraday's methods were analytical. Faraday in his mind's eye saw lines of force traversing all space where the mathematicians saw centres of force attracting at a distance. Faraday sought the seat of the phenomena in real actions going on in the medium; they were satisfied that they had found it in a power of action at a distance on the electric fluids. Both of these methods, as Maxwell points out, had succeeded in explaining the propagation of light as an electromagnetic phenomenon while at the same time the fundamental conceptions of what the quantities concerned are, radically differed.

The mathematicians assumed that insulators were barriers to electric currents; that, for instance, in a Leyden jar or electric condenser the electricity was accumulated at one plate and that by some occult action at a distance electricity of an opposite kind was attracted to the other plate. Maxwell, looking further than Faraday, reasoned that if light is an electromagnetic phenomenon and is transmissible through dielectrics such as glass, the phenomenon must be in the nature of electromagnetic currents in the dielectrics.

He therefore contended that in the charging of a condenser, for instance, the action did not stop at the insulator, but that some "displacement" currents are set up in the insulating medium, which currents continue until the resisting force of the medium equals that of the charging force. In a closed conductor circuit, an electric current is also a displacement of electricity. The conductor offers a certain resistance, akin to friction, to the displacement of electricity, and heat is developed in the conductor, proportional to the square of the current as already stated herein , which current flows as long as the impelling electric force continues.

This resistance may be likened to that met with by a ship as it displaces in the water in its progress. The resistance of the dielectric is of a different nature and has been compared to the compression of multitudes of springs, which, under compression, yield with an increasing back pressure, up to a point where the total back pressure equals the initial pressure. When the initial pressure is withdrawn the energy expended in compressing the "springs" is returned to the circuit, concurrently with the return of the springs to their original condition, this producing a reaction in the opposite direction.

Consequently, the current due to the displacement of electricity in a conductor may be continuous, while the displacement currents in a dielectric are momentary and, in a circuit or medium which contains but little resistance compared with capacity or inductance reaction, the currents of discharge are of an oscillatory or alternating nature.

Maxwell extended this view of displacement currents in dielectrics to the ether of free space. Assuming light to be the manifestation of alterations of electric currents in the ether, and vibrating at the rate of light vibrations, these vibrations by induction set up corresponding vibrations in adjoining portions of the ether, and in this way the undulations corresponding to those of light are propagated as an electromagnetic effect in the ether.

Maxwell's electromagnetic theory of light obviously involved the existence of electric waves in free space, and his followers set themselves the task of experimentally demonstrating the truth of the theory. By , he presented the Remarks on the mathematical classification of physical quantities. In , the German physicist Heinrich Hertz in a series of experiments proved the actual existence of electromagnetic waves , showing that transverse free space electromagnetic waves can travel over some distance as predicted by Maxwell and Faraday.

Hertz published his work in a book titled: Electric waves: being researches on the propagation of electric action with finite velocity through space. The electron as a unit of charge in electrochemistry was posited by G. Johnstone Stoney in , who also coined the term electron in It has been noted herein that Dr.

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William Gilbert was termed the founder of electrical science. This must, however, be regarded as a comparative statement. Oliver Heaviside was a self-taught scholar who reformulated Maxwell's field equations in terms of electric and magnetic forces and energy flux, and independently co-formulated vector analysis. During the late s a number of physicists proposed that electricity, as observed in studies of electrical conduction in conductors, electrolytes, and cathode ray tubes , consisted of discrete units, which were given a variety of names, but the reality of these units had not been confirmed in a compelling way.

However, there were also indications that the cathode rays had wavelike properties. Faraday, Weber , Helmholtz , Clifford and others had glimpses of this view; and the experimental works of Zeeman , Goldstein , Crookes, J. Thomson and others had greatly strengthened this view. Weber predicted that electrical phenomena were due to the existence of electrical atoms, the influence of which on one another depended on their position and relative accelerations and velocities.

Helmholtz and others also contended that the existence of electrical atoms followed from Faraday's laws of electrolysis , and Johnstone Stoney, to whom is due the term "electron", showed that each chemical ion of the decomposed electrolyte carries a definite and constant quantity of electricity, and inasmuch as these charged ions are separated on the electrodes as neutral substances there must be an instant, however brief, when the charges must be capable of existing separately as electrical atoms; while in , Clifford wrote: "There is great reason to believe that every material atom carries upon it a small electric current, if it does not wholly consist of this current.

In , J. He made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called "corpuscles", had perhaps one thousandth of the mass of the least massive ion known hydrogen. He further showed that the negatively charged particles produced by radioactive materials, by heated materials, and by illuminated materials, were universal.

The nature of the Crookes tube " cathode ray " matter was identified by Thomson in In the late 19th century, the Michelson—Morley experiment was performed by Albert A. Michelson and Edward W. Morley at what is now Case Western Reserve University. It is generally considered to be the evidence against the theory of a luminiferous aether.

The experiment has also been referred to as "the kicking-off point for the theoretical aspects of the Second Scientific Revolution. Dayton Miller continued with experiments, conducting thousands of measurements and eventually developing the most accurate interferometer in the world at that time.

Miller and others, such as Morley, continue observations and experiments dealing with the concepts. By the end of the 19th century electrical engineers had become a distinct profession, separate from physicists and inventors. They created companies that investigated, developed and perfected the techniques of electricity transmission, and gained support from governments all over the world for starting the first worldwide electrical telecommunication network, the telegraph network. William Stanley made the first public demonstration of a transformer that enabled commercial delivery of alternating current in Gordon , [] [ non-primary source needed ] in Lord Kelvin and Sebastian Ferranti also developed early alternators, producing frequencies between and hertz.

After , polyphase alternators were introduced to supply currents of multiple differing phases. The possibility of obtaining the electric current in large quantities, and economically, by means of dynamo electric machines gave impetus to the development of incandescent and arc lighting. Until these machines had attained a commercial basis voltaic batteries were the only available source of current for electric lighting and power.

The cost of these batteries, however, and the difficulties of maintaining them in reliable operation were prohibitory of their use for practical lighting purposes. The date of the employment of arc and incandescent lamps may be set at about Even in , however, but little headway had been made toward the general use of these illuminants; the rapid subsequent growth of this industry is a matter of general knowledge. Such batteries are now utilized on a large scale as auxiliaries to the dynamo machine in electric power-houses and substations, in electric automobiles and in immense numbers in automobile ignition and starting systems, also in fire alarm telegraphy and other signal systems.

In , the World's Columbian International Exposition was held in a building which was devoted to electrical exhibits. General Electric Company backed by Edison and J. Morgan had proposed to power the electric exhibits with direct current at the cost of one million dollars. However, Westinghouse proposed to illuminate the Columbian Exposition in Chicago with alternating current for half that price, and Westinghouse won the bid.

It was an historical moment and the beginning of a revolution, as George Westinghouse introduced the public to electrical power by illuminating the Exposition. The Second Industrial Revolution, also known as the Technological Revolution, was a phase of rapid industrialization in the final third of the 19th century and the beginning of the 20th. Along with the expansion of railroads , iron and steel production, widespread use of machinery in manufacturing, greatly increased use of steam power and petroleum , the period saw expansion in the use electricity and the adaption of electromagnetic theory in developing various technologies.

The s saw the spread of large scale commercial electric power systems, first used for lighting and eventually for electro-motive power and heating. Systems early on used alternating current and direct current. Large centralized power generation became possible when it was recognized that alternating current electric power lines could use transformers to take advantage of the fact that each doubling of the voltage would allow the same size cable to transmit the same amount of power four times the distance.

Transformer were used to raise voltage at the point of generation a representative number is a generator voltage in the low kilovolt range to a much higher voltage tens of thousands to several hundred thousand volts for primary transmission, followed to several downward transformations, for commercial and residential domestic use. The International Electro-Technical Exhibition of featuring the long distance transmission of high-power, three-phase electric current. As a result of this successful field trial, three-phase current became established for electrical transmission networks throughout the world.

Much was done in the direction in the improvement of railroad terminal facilities, and it is difficult to find one steam railroad engineer who would have denied that all the important steam railroads of this country were not to be operated electrically. In other directions the progress of events as to the utilization of electric power was expected to be equally rapid. In every part of the world the power of falling water, nature's perpetual motion machine, which has been going to waste since the world began, is now being converted into electricity and transmitted by wire hundreds of miles to points where it is usefully and economically employed.

The first windmill for electricity production was built in Scotland in July by the Scottish electrical engineer James Blyth. Brush , [] [ non-primary source needed ] this was built by his engineering company at his home and operated from until The connected dynamo was used either to charge a bank of batteries or to operate up to incandescent light bulbs , three arc lamps, and various motors in Brush's laboratory. The machine fell into disuse after when electricity became available from Cleveland's central stations, and was abandoned in Various units of electricity and magnetism have been adopted and named by representatives of the electrical engineering institutes of the world, which units and names have been confirmed and legalized by the governments of the United States and other countries.

Thus the volt, from the Italian Volta, has been adopted as the practical unit of electromotive force, the ohm, from the enunciator of Ohm's law, as the practical unit of resistance; the ampere , after the eminent French scientist of that name, as the practical unit of current strength, the henry as the practical unit of inductance, after Joseph Henry and in recognition of his early and important experimental work in mutual induction.

Dewar and John Ambrose Fleming predicted that at absolute zero , pure metals would become perfect electromagnetic conductors though, later, Dewar altered his opinion on the disappearance of resistance believing that there would always be some resistance. Walther Hermann Nernst developed the third law of thermodynamics and stated that absolute zero was unattainable. Carl von Linde and William Hampson , both commercial researchers, nearly at the same time filed for patents on the Joule—Thomson effect.

Linde's patent was the climax of 20 years of systematic investigation of established facts, using a regenerative counterflow method. Hampson's design was also of a regenerative method. The combined process became known as the Linde—Hampson liquefaction process. Heike Kamerlingh Onnes purchased a Linde machine for his research.

Around , Karol Olszewski and Wroblewski predicted the electrical phenomena of dropping resistance levels at ultra-cold temperatures.

Olszewski and Wroblewski documented evidence of this in the s. A milestone was achieved on 10 July when Onnes at the Leiden University in Leiden produced, for the first time, liquified helium and achieved superconductivity. In , William Du Bois Duddell develops the Singing Arc and produced melodic sounds, from a low to a high-tone, from this arc lamp. Between and , many scientists like Wilhelm Wien , Max Abraham , Hermann Minkowski , or Gustav Mie believed that all forces of nature are of electromagnetic origin the so-called "electromagnetic world view".

This was connected with the electron theory developed between and by Hendrik Lorentz. Lorentz introduced a strict separation between matter electrons and the aether, whereby in his model the ether is completely motionless, and it won't be set in motion in the neighborhood of ponderable matter. Contrary to other electron models before, the electromagnetic field of the ether appears as a mediator between the electrons, and changes in this field can propagate not faster than the speed of light.

In , three years after submitting his thesis on the Kerr effect , Pieter Zeeman disobeyed the direct orders of his supervisor and used laboratory equipment to measure the splitting of spectral lines by a strong magnetic field. Lorentz theoretically explained the Zeeman effect on the basis of his theory, for which both received the Nobel Prize in Physics in This theorem states that a moving observer relative to the ether makes the same observations as a resting observer.

This theorem was extended for terms of all orders by Lorentz in Lorentz noticed, that it was necessary to change the space-time variables when changing frames and introduced concepts like physical length contraction to explain the Michelson—Morley experiment, and the mathematical concept of local time to explain the aberration of light and the Fizeau experiment. That resulted in the formulation of the so-called Lorentz transformation by Joseph Larmor , and Lorentz , He declared simultaneity only a convenient convention which depends on the speed of light, whereby the constancy of the speed of light would be a useful postulate for making the laws of nature as simple as possible.

And finally in June and July he declared the relativity principle a general law of nature, including gravitation. He corrected some mistakes of Lorentz and proved the Lorentz covariance of the electromagnetic equations. However, historians pointed out that he still used the notion of an ether and distinguished between "apparent" and "real" time and therefore didn't invent special relativity in its modern understanding.

In , while he was working in the patent office, Albert Einstein had four papers published in the Annalen der Physik , the leading German physics journal. These are the papers that history has come to call the Annus Mirabilis papers :. All four papers are today recognized as tremendous achievements—and hence is known as Einstein's " Wonderful Year ". At the time, however, they were not noticed by most physicists as being important, and many of those who did notice them rejected them outright. Some of this work—such as the theory of light quanta—remained controversial for years. The first formulation of a quantum theory describing radiation and matter interaction is due to Paul Dirac , who, during , was first able to compute the coefficient of spontaneous emission of an atom.

In the following years, with contributions from Wolfgang Pauli , Eugene Wigner , Pascual Jordan , Werner Heisenberg and an elegant formulation of quantum electrodynamics due to Enrico Fermi , [] physicists came to believe that, in principle, it would be possible to perform any computation for any physical process involving photons and charged particles.

However, further studies by Felix Bloch with Arnold Nordsieck , [] and Victor Weisskopf , [] in and , revealed that such computations were reliable only at a first order of perturbation theory , a problem already pointed out by Robert Oppenheimer. With no solution for this problem known at the time, it appeared that a fundamental incompatibility existed between special relativity and quantum mechanics. In December , the German chemists Otto Hahn and Fritz Strassmann sent a manuscript to Naturwissenschaften reporting they had detected the element barium after bombarding uranium with neutrons ; [] simultaneously, they communicated these results to Lise Meitner.

Meitner, and her nephew Otto Robert Frisch , correctly interpreted these results as being nuclear fission. Some historians who have documented the history of the discovery of nuclear fission believe Meitner should have been awarded the Nobel Prize with Hahn. Difficulties with the Quantum theory increased through the end of Improvements in microwave technology made it possible to take more precise measurements of the shift of the levels of a hydrogen atom , [] now known as the Lamb shift and magnetic moment of the electron.

With the invention of bubble chambers and spark chambers in the s, experimental particle physics discovered a large and ever-growing number of particles called hadrons. It seemed that such a large number of particles could not all be fundamental. Their assignment was to seek a solid-state alternative to fragile glass vacuum tube amplifiers.

Their first attempts were based on Shockley's ideas about using an external electrical field on a semiconductor to affect its conductivity. These experiments failed every time in all sorts of configurations and materials. The group was at a standstill until Bardeen suggested a theory that invoked surface states that prevented the field from penetrating the semiconductor. The group changed its focus to study these surface states and they met almost daily to discuss the work.

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The rapport of the group was excellent, and ideas were freely exchanged. As to the problems in the electron experiments, a path to a solution was given by Hans Bethe. In , while he was traveling by train to reach Schenectady from New York, [] after giving a talk at the conference at Shelter Island on the subject, Bethe completed the first non-relativistic computation of the shift of the lines of the hydrogen atom as measured by Lamb and Retherford. The idea was simply to attach infinities to corrections at mass and charge that were actually fixed to a finite value by experiments.

In this way, the infinities get absorbed in those constants and yield a finite result in good agreement with experiments. This procedure was named renormalization. Feynman's mathematical technique, based on his diagrams , initially seemed very different from the field-theoretic, operator -based approach of Schwinger and Tomonaga, but Freeman Dyson later showed that the two approaches were equivalent.

Even though renormalization works very well in practice, Feynman was never entirely comfortable with its mathematical validity, even referring to renormalization as a "shell game" and "hocus pocus". Peter Higgs , Jeffrey Goldstone , and others, Sheldon Glashow , Steven Weinberg and Abdus Salam independently showed how the weak nuclear force and quantum electrodynamics could be merged into a single electroweak force. Robert Noyce credited Kurt Lehovec for the principle of p—n junction isolation caused by the action of a biased p-n junction the diode as a key concept behind the integrated circuit.

Noyce's chip solved many practical problems that Kilby's had not. Noyce's chip, made at Fairchild Semiconductor , was made of silicon , whereas Kilby's chip was made of germanium. Philo Farnsworth developed the Farnsworth—Hirsch Fusor , or simply fusor, an apparatus designed by Farnsworth to create nuclear fusion.

History of electromagnetic theory

Unlike most controlled fusion systems, which slowly heat a magnetically confined plasma , the fusor injects high temperature ions directly into a reaction chamber, thereby avoiding a considerable amount of complexity. When the Farnsworth-Hirsch Fusor was first introduced to the fusion research world in the late s, the Fusor was the first device that could clearly demonstrate it was producing fusion reactions at all.

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Hopes at the time were high that it could be quickly developed into a practical power source. However, as with other fusion experiments, development into a power source has proven difficult. Nevertheless, the fusor has since become a practical neutron source and is produced commercially for this role.


  • The Kleiner Feldberg Cloud Experiment 1990: EUROTRAC Subproject Ground-Based Cloud Experiment (GCE).
  • Force - Wikipedia.
  • Archimedes’ Principle – College Physics?
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  • The mirror image of an electromagnet produces a field with the opposite polarity. Thus the north and south poles of a magnet have the same symmetry as left and right. Prior to , it was believed that this symmetry was perfect, and that a technician would be unable to distinguish the north and south poles of a magnet except by reference to left and right. In that year, T. Lee and C. Yang predicted the nonconservation of parity in the weak interaction.

    To the surprise of many physicists, in C. Wu and collaborators at the U. National Bureau of Standards demonstrated that under suitable conditions for polarization of nuclei, the beta decay of cobalt preferentially releases electrons toward the south pole of an external magnetic field, and a somewhat higher number of gamma rays toward the north pole. As a result, the experimental apparatus does not behave comparably with its mirror image. The first step towards the Standard Model was Sheldon Glashow 's discovery, in , of a way to combine the electromagnetic and weak interactions.

    The Higgs mechanism is believed to give rise to the masses of all the elementary particles in the Standard Model. This includes the masses of the W and Z bosons , and the masses of the fermions - i. After the neutral weak currents caused by Z boson exchange were discovered at CERN in , [] [] [] [] the electroweak theory became widely accepted and Glashow, Salam, and Weinberg shared the Nobel Prize in Physics for discovering it. The W and Z bosons were discovered experimentally in , and their masses were found to be as the Standard Model predicted.

    The theory of the strong interaction , to which many contributed, acquired its modern form around —74, when experiments confirmed that the hadrons were composed of fractionally charged quarks. With the establishment of quantum chromodynamics in the s finalized a set of fundamental and exchange particles, which allowed for the establishment of a " standard model " based on the mathematics of gauge invariance , which successfully described all forces except for gravity, and which remains generally accepted within the domain to which it is designed to be applied.

    The formulation of the unification of the electromagnetic and weak interactions in the standard model is due to Abdus Salam , Steven Weinberg and, subsequently, Sheldon Glashow. After the discovery, made at CERN , of the existence of neutral weak currents , [] [] [] [] mediated by the Z boson foreseen in the standard model, the physicists Salam, Glashow and Weinberg received the Nobel Prize in Physics for their electroweak theory.

    Because of its success in explaining a wide variety of experimental results. There are a range of emerging energy technologies. Also, the nanowire battery , a lithium-ion battery, was invented by a team led by Dr. Yi Cui in Reflecting the fundamental importance and applicability of Magnetic resonance imaging [] in medicine, Paul Lauterbur of the University of Illinois at Urbana—Champaign and Sir Peter Mansfield of the University of Nottingham were awarded the Nobel Prize in Physiology or Medicine for their "discoveries concerning magnetic resonance imaging". The Nobel citation acknowledged Lauterbur's insight of using magnetic field gradients to determine spatial localization , a discovery that allowed rapid acquisition of 2D images.

    Wireless electricity is a form of wireless energy transfer , [] the ability to provide electrical energy to remote objects without wires. Its aim is to reduce the dependence on batteries. Further applications for this technology include transmission of information —it would not interfere with radio waves and thus could be used as a cheap and efficient communication device without requiring a license or a government permit. A Grand Unified Theory GUT is a model in particle physics in which, at high energy, the electromagnetic force is merged with the other two gauge interactions of the Standard Model , the weak and strong nuclear forces.

    Many candidates have been proposed, but none is directly supported by experimental evidence. GUTs are often seen as intermediate steps towards a " Theory of Everything " TOE , a putative theory of theoretical physics that fully explains and links together all known physical phenomena, and, ideally, has predictive power for the outcome of any experiment that could be carried out in principle. No such theory has yet been accepted by the physics community.

    The magnetic monopole [] in the quantum theory of magnetic charge started with a paper by the physicist Paul A. Dirac in In some theoretical models , magnetic monopoles are unlikely to be observed, because they are too massive to be created in particle accelerators , and also too rare in the Universe to enter a particle detector with much probability.

    After more than twenty years of intensive research, the origin of high-temperature superconductivity is still not clear, but it seems that instead of electron-phonon attraction mechanisms , as in conventional superconductivity, one is dealing with genuine electronic mechanisms e. From Wikipedia, the free encyclopedia.

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