600 före Kristus – Magnetit

De magnetiska egenskaperna hos naturlig ferriferrit (fe₃O₄) stenar (lodestones) beskrevs av grekiska filosofer.

600 före Kristus – Elektrisk laddning

Bärnsten är en gulaktig, genomskinlig mineral. Så tidigt som 600 BC den grekiske filosofen, Aristofanes var medveten om dess säregna egendom: när den gnuggas med en bit päls, bärnsten utvecklar förmågan att attrahera små materialbitar som fjädrar. I århundraden detta konstigt, oförklarlig egendom ansågs vara unik för bärnsten. Denna märkliga effekt förblev ett mysterium för länge sedan 2000 år, tills, omkring AD 1600, Dr William Gilbert undersökte reaktionerna av bärnsten och magneter och spelade först in ordet 'Elektrisk’ i en rapport om teorin om magnetism.

Senare in, i 1895, HA. Lorentz utvecklade Elektronteori. Vi vet nu att det finns tre sätt att generera el: Statisk, Elektrokemisk och elektromagnetisk induktion.

1175 – Första referens till en kompass

Alexander Neckem en engelsk munk av St. Albans beskriver hur en kompass fungerar.

1269 – Första detaljerade beskrivningen av en kompass

Peter Peregrine från Marincourt, en fransk korsfarare, beskriver en flytande kompass och en kompass med vridpunkt.

1600 – Statisk elektricitet (Av Magnete)

På 1500-talet, William Gilbert(1544-1603), hovläkaren till drottning Elizabeth I, bevisat att många andra ämnen är elektrisk (från det grekiska ordet för bärnsten, elektron) och att de har två elektriska effekter. När gnids med päls, bärnsten får hartsliknande elektricitet; glas, dock, när den gnides med siden, får glasaktig elektricitet. Elektricitet stöter bort samma sort och drar till sig motsatt sorts elektricitet. Forskare trodde att friktionen faktiskt skapade elektriciteten (deras ord för laddning). De insåg inte att lika mycket motsatt elektricitet fanns kvar på pälsen eller siden. Dr. William Gilbert, insåg att en kraft skapades, när en bit bärnsten (harts) gnuggades med ull och drog till sig lätta föremål. I beskrivningen av denna fastighet idag, vi säger att bärnsten är “elektrifierad” eller besitter och “elektrisk laddning”. Dessa termer kommer från det grekiska ordet “elektron” betyder bärnsten och från detta, termen “elektricitet” utvecklades. Det var först i slutet av 1800-talet som detta “något” visade sig bestå av negativ elektricitet, idag kallas elektroner.

Gilbert studerade också magnetism och in 1600 skrev “Av magnet” som gav den första rationella förklaringen till kompassnålens mystiska förmåga att peka nord-sydlig: jorden själv var magnetisk. “Av Magnete” öppnade eran av modern fysik och astronomi och startade ett sekel präglat av Galileos stora landvinningar, Kepler, Newton och andra.

Gilbert registrerade tre sätt att magnetisera en stålnål: genom beröring med en laststen; genom kalldragning i nord-sydlig riktning; och genom att under lång tid utsättas för jordens magnetfält i en nord-sydlig orientering.

1660 – Generator för statisk elektricitet

Otto von Guericke uppfinner en rå maskin för att producera statisk elektricitet.

1729 – Konduktörer och icke-konduktörer

Stephen Gray beskriver att kraft som en elektrifierad kropp besitter kunde överföras till en annan genom att koppla dem.

1734 – Elektrisk attraktion och avstötning

Charles Francois de Cisternay Du Fay först att känna igen två typer av elektricitet.

1730 – Sammansatt magnet

Servigton Savery producerar den första sammansatta magneten genom att binda ihop ett antal konstgjorda magneter med en gemensam polbit i varje ände.

1740 – Första kommersiella magneten

Gowen Knight producerar de första konstgjorda magneterna för försäljning till vetenskapliga utredare och markbundna navigatörer.

1745 – Elektrisk kraft, Kondensator

Leyden Jar är en av de tidigaste och enklaste formerna av elektriska kondensatorer, uppfunnit självständigt om 1745 av den nederländska fysikern Pieter van Musschenbroek vid universitetet i Leyden och Ewald Georg von Kleist från Pommern. Den ursprungliga Leyden-burken var en glasburk med propp som innehöll vatten, med en tråd eller spik som sträcker sig genom proppen i vattnet. Burken laddades genom att hålla den i ena handen och bringa den exponerade änden av tråden i kontakt med en elektrisk anordning. Om kontakten bröts mellan ledningen och elkällan, och tråden berördes med den andra handen, skedde en flytning som upplevdes som en våldsam chock.

Om en avgift Q placeras på metallplattorna, spänningen stiger till V. Måttet på en kondensators förmåga att lagra laddning är kapacitans C, där C = Q/V. Laddningen flödar från en kondensator precis som den flödar från ett batteri, men med en betydande skillnad. När laddningen lämnar en kondensators plattor, inget mer kan erhållas utan omladdning. Detta händer eftersom elektrisk kraft är konservativ. Den energi som frigörs kan inte överstiga den lagrade energin. Förmågan att utföra arbete kallas elektrisk potential.

En typ av bevarande av energi är också förknippad med emf. Den elektriska energin som kan erhållas från ett batteri begränsas av energin som lagras i kemiska molekylbindningar. Både emf och elektrisk potential mäts i volt, och, tyvärr, termerna spänning, potential, och emf används ganska löst. Till exempel, termen batteripotential används ofta istället för emf.

1747 – Glasaktig elektricitet, Bevarande av laddning

Benjamin Franklin (1706-90) var en amerikansk tryckare, författare, filosof, diplomat, forskare, och uppfinnare.

Efter Gilberts upptäckt att en kraft av elektrisk laddning skapas av friktion av olika material, Benjamin Franklin in 1747, förbättrat detta genom att meddela att detta elektrisk laddning består av två typer av elektriska krafter, en attraktionskraft och en frånstötande kraft. (William Watson (1715-87) i England självständigt kommit fram till samma slutsats.) För att identifiera dessa två krafter, han gav namnen, positiva och negativa laddningar och att symbolisera dem, han använde + och – undertecknar + vara för positiva och – för negativt. Benjamin Franklin insåg att alla material har en enda typ av elektrisk “vätska” som kan penetrera materia fritt men som varken kan skapas eller förstöras. Åtgärden av att gnugga överför bara vätskan från en kropp till en annan, elektrifierar båda. Franklin och Watson skapade principen om bevarande av laddning: den totala mängden el i ett isolerat system är konstant. Franklin definierade vätskan, som motsvarade glasaktig elektricitet, lika positivt och bristen på vätska som negativ. Därför, enligt Franklin, Flödesriktningen var från positiv till negativ–motsatsen till vad man nu vet är sant. En efterföljande tvåvätsketeori utvecklades, enligt vilka prover av samma typ attraherar, medan de av motsatta slag stöter bort.

Franklin var bekant med Leyden burk (en glasburk belagd in- och utsida med stanniol), hur den kunde lagra en laddning och hur den orsakade en chock när den laddades ur. Franklin undrade om blixtar och åska också var ett resultat av elektriska urladdningar. Under ett åskväder in 1752, Franklin flög en drake som hade en metallspets. I slutet av det våta, ledande hamplina som draken flög på fäste han en metallnyckel, till vilken han band ett icke-ledande sidensnöre som han höll i handen. Experimentet var extremt farligt, men resultaten var omisskännliga: när han höll knogarna nära nyckeln, han kunde dra gnistor från den. De nästa två som provade detta extremt farliga experiment dödades.

1750 – Första boken om magnettillverkning

John Mitchell ger ut den första boken om att tillverka stålmagneter.

1757 – Driva, Ångmaskin

James Watt(1736-1819) gjorde inga elektriska experiment. Han var instrumenttillverkare av yrke och startade en reparationsverkstad i Glasgow i 1757. Watt mätte arbetshastigheten för en häst som drog skräp upp i ett gammalt gruvschakt och fann att det uppgick till ca. 22,000 ft-lbs per minut. Han lade till en marginal på 50% anländer kl 33,000 ft-lbs är lika med en hästkraft.

James Watt, uppfann också ångkondenseringsmotorn. Hans förbättringar av ångmaskiner patenterades under en period av 15 år, börjar i 1769 och hans namn gavs till den elektriska kraftenheten, de Watt. När Edisons generator kopplades ihop med Watts ångmaskin, storskalig elproduktion blev ett praktiskt förslag.

1767 – Elektrisk kraft

Det var känt så tidigt som 1600 att attraktionskraft eller frånstötande kraft minskar när laddningarna separeras. Detta förhållande placerades först på en numeriskt korrekt, eller kvantitativa, stiftelse av Joseph Priestley, en vän till Benjamin Franklin. I 1767, Priestley drog indirekt slutsatsen att när avståndet mellan två små, laddade kroppar ökar med någon faktor, the forces between the bodies is reduced by the square of the factor. Till exempel, if the distance between charges is tripled, the force decreases to one-ninth its former value. Although rigorous, Priestley’s proof was so simple that he did not strongly advocate it. The matter was not considered settled until 18 years later, when John Robinson of Scotland made more direct measurements of the electrical force involved.

1780 – Electric Current

Because of an accident the 18th-century Italian scientist Luigi Galvani started a chain of events that culminated in the development of the concept of voltage and the invention of the battery. I 1780 one of Galvani’s assistants noticed that a dissected frog leg twitched when he touched its nerve with a scalpel. En annan assistent trodde att han samtidigt hade sett en gnista från en närliggande laddad elgenerator. Galvani resonerade att elektriciteten var orsaken till muskelsammandragningarna. tänkte han av misstag, dock, att effekten berodde på överföringen av en speciell vätska, eller “djurelektricitet,” snarare än till konventionell el.

Experiment som detta, där benen på en groda eller fågel stimulerades av kontakt med olika typer av metaller, ledde in Luigi Galvani 1791 att föreslå sin teori om att djurvävnader genererar elektricitet. I att experimentera med vad han kallade atmosfärisk elektricitet, Galvani fann att en grodmuskel skulle rycka när den hängdes i en mässingskrok på ett järngaller.

1792 – Elektrokemi, Voltaisk cell

Av 1792 en annan italiensk vetenskapsman, Alessandro Volta, höll inte med: he realized that the main factors in Galvani’s discovery were the two different metals – the steel knife and the tin plate – upon which the frog was lying. the different metals, separated by the moist tissue of the frog, were generating electricity. The frog’s leg was simply a detector.

I 1800,Volta showed that when moisture comes between two different metals, electricity is created. This led him to invent the first electric battery, de voltaic pile, which he made from thin sheets of copper and zinc separated by moist pasteboard (felt soaked in brine).

In this way, a new kind of electricity was discovered, electricity that flowed steadily like a current of water instead of discharging itself in a single spark or shock. Volta showed that electricity could be made to travel from one place to another by wire, thereby making an important contribution to the science of electricity.

1820 – Electromagnetism, Current

I 1820, a physicist Hans Christian Oersted, learned that a current flowing through a wire would move a compass needle placed beside it. This showed that an electric current produced a magnetic field.

Andre Marie Ampere, a French mathematician who devoted himself to the study of electricity and magnetism, was the first to explain the electro-dynamic theory. He showed that two parallel wires, carrying current, attracted each other if the currents flowed in the same direction and opposed each other if the currents flowed in opposite directions. He formulated in mathematical terms, the laws that govern the interaction of currents with magnetic fields in a circuit and as a result of this the unit of electric current, de amp, was derived from his name. An electric charge in motion is called electric current. The strength of a current is the amount of charge passing a given point per second, or I = Q/t, where Q coulombs of charge passing in t seconds. De unit for measuring current is the ampere eller amp, where 1 amp = 1 coulomb/sec. Because it is the source of magnetism as well, current is the link between electricity and magnetism.

1822 – Fourier Transforms

Baron Joseph Fourier (1768-1830) was a French mathematician. His method of analyzing waves, published in 1822, was a spinoff of his work on the flow of heat. It shows how any wave can be built up from simpler waves. This powerful branch of mathematics, Fourier Transforms has contributed to important modern developments like electronic speech recognition.

1826 – Resistance – Currents Causing Heat

I 1826, the German Physicist Georg Simon Ohm, examined Volta’s Principle of the electric battery och Ampere’s relationship of currents in a circuit. He noted that when there was a current in a circuit, there was at times, heat, and the amount of heat was related to different metals. He discovered that there was a relationship between current and heat, there was some “resistance” to the flow of current, in the circuit. By discovering this, he found out that if the potential difference (volt), remained constant, de current was in proportion to the resistance. Detta unit of electrical resistance – de ohm – was named after him. He also formulated a law, showing the relationship between volts, amps and resistance and this law was called “Ohm’s Law” also named after him. This law as we know it today, is the basis of electricity.

1830 – Inductance

I 1830, Joseph Henry (1797-1878), discovered that a change in magnetism can make currents flow, but he failed to publish this. I 1832 he described self-inductance – the basic property of inductor. In recognition of his work, inductance is measured in henries. The stage was then set for the encompassing electromagnetic theory of James Clerk Maxwell. The variation of actual currents is enormous. A modern electrometer can detect currents as low as 1/100,000,000,000,000,000 amp, which is a mere 63 electrons per second. The current in a nerve impulse is approximately 1/100,000 amp; a 100-watt light bulb carries 1 amp; a lightning bolt peaks at about 20,000 amps; and a 1,200-megawatt nuclear power plant can deliver 10,000,000 amps at 115 V.

1836 – Daniell Cell

I 1836, John Daniell (1790-1845) proposed an improved electric cell that supplied an even current during continuous operation. The Daniell cell gave new impetus to electric research and found many commercial applications. I 1837 Daniell was presented the highest award of the Royal Society, the Copley Medal, for the invention of the Daniell cell.

1837 – Telegraph, elektromagnet

After the electric battery and the electromagnet were discovered, Samuel Morse(1791-1872) introduced the electric telegraph. Coded messages were sent over wires, by means of electrical impulses (identified as dots and dashes) known as Morse code. This was really the beginning of commercially used electricity. The electric telegraph is known as the first practical use of electricity and the first system of electrical communication. It is interesting to note here, that the Post Office in Australia, played an important part at that time, in the organizing of the communication.

1840 – Mechanical Computer

Charles Babbage (1791-1871), a British mathematician, designed several machines to generate error-free tables for navigation. The mechanical devices would serve as models for the later electronic computers.

1850 – Thermoelectricity

Thomas Seebeck a German physicist was the discover of the “Seebeck effect“. He twisted two wires made of different metals and heated a junction where the two wires met, producing a small current. The current is the result of a flow of heat from the hot to the cold junction. This is called thermoelectricity. Thermo is a Greek word meaning heat.

1854 – Boolean Algebra

George Boole was entirely self taught. He published a way of using symbols that perfectly expresses the rules of logic. Using this system, complicated rules can be written clearly and often simplified.

1855 – Electromagnetic Induction

Michael Faraday (1791-1867) an Englishman, made one of the most significant discoveries in the history of electricity: Electromagnetic induction. His pioneering work dealt with how electric currents work. Many inventions would come from his experiments, but they would come fifty to one hundred years later. Failures never discouraged Faraday. He would say; “the failures are just as important as the successes.” He felt failures also teach. De farad, de unit of capacitance is named in the honor of Michael Faraday.

Faraday was greatly interested in the invention of the electromagnet, but his brilliant mind took earlier experiments still further. If electricity could produce magnetism, why couldn’t magnetism produce electricity. I 1831, Faraday found the solution. Electricity could be produced through magnetism by motion. He discovered that when a magnet was moved inside a coil of copper wire, a tiny electric current flows through the wire. H.C. Oersted, i 1820, demonstrated that electric currents produce a magnetic field. Faraday noted this and in 1821, he experimented on the theory that, if electric currents in a wire can produce magnetic fields, then magnetic fields should produce electricity. Av 1831, he was able to prove this and through his experiment, was able to explain, that these magnetic fields were lines of force. Dessa lines of force would cause a currentto flow in a coil of wire, when the coil is rotated between the poles of a magnet. This action then shows that the coils of wire being cut by lines of magnetic force, in some strange way, produces electricity. These experiments, convincingly demonstrated the discovery of electromagnetic induction in the production of electric current, by a change in magnetic intensity.

1860 – Arc Lights

As the practical use of electricity became evident and the electric telegraph was in operation, it was not long before scientists were looking towards making further use of this electricity. The next advance of great importance, was the introduction of the electric carbon arc light, which was exhibited in experimental form in 1808, by Sir Humphry Davey. He used a large battery to provide current for his demonstration, as these arc lights require a heavy current and no means of mechanically generating electricity had as yet been developed. The principle of these arc lights, is that when two carbon rods in a circuit are brought together, an arc is created. This arc, which gives off a brilliant incandescence, is maintained as long as the rods are just separated and keep mechanically fed this way, to maintain the arc. As the arc lights took a heavy current from these batteries, it was not until about 1860, that practical use was made of them. By this time adequate generating sources were developed and then they were only used mainly for street lighting and in picture theaters. Although arc lighting was still used until the early 1900’s they were eventually superseded by the incandescent light, except that most picture theaters use them in their projectors even today.

1860 – DC Motor

The history of the electric motor begins with Hans Christian Oersted, who discovered in 1820, that electricity produced a magnetic field, as mentioned before. Faraday followed up this in 1821, by devising the principle of the electric motor of his own design. Some of those worth mentioning are Jacobi i 1834, Elias i 1842, Froment i 1844 och Pacinotti i 1860. Pacinottiused a ring wound armature which was used in 1860 and was an outstanding advance on any previous attempts. Most of these motors were in the experimental stage but it was not until 1871, that Zenobe Theophile Gramme introduced his motor, which was really a development of Pacinotti’s machine. This motor was said to be the first electric motor of commercial significance. During this period the scientists concentrated on the “motor”, but meanwhile, experiments with machines producing electricity dynamically were under way.

1866 – LeClanche Cell

Leclanche (1839-1882) is a French engineer who in about 1866 invented the battery that bears his name. In slightly modified form, the Leclanché battery, now called a dry cell, is produced in great quantities and is widely used in devices such as flashlights and portable radios. This cell consists of a zinc case filled with a moist paste containing ammonium sulfate. In the center of this electrolyte paste is a carbon rod coated with manganese dioxide, which is a strong oxidizing agent.

1871 – DC Generator

With the development of the carbon filament lamp av Edison i 1879, de DC generator then became one of the essential components of the constant-potential lighting systems. Previous to this only arc lights were used for street lighting. Then commercial lighting and residential lighting, as the inventors were aiming at, became practical and so the electric light and power industry was born. When H. C. Oersted i 1820, discovered that an electric current produces magnetic fields, the DC motor was developed. I 1831, Michael Faraday discovered the principle of electromagnetic induction. He found that moving a magnet through a coil of wire, caused an electric current to flow in the wire, thus the electric generator could now be developed. But it was not until 1871, when Gramme introduced his motor and generator, that the electric generator was used commercially. Av 1872, Siemens och Halske of Berlin improved on Gramme’s generator, by producing the drum armature. Other improvements were made, such as the slotted armature in 1880 but by 1882, Edison had completed the design of the system we still use to distribute electricity from power stations.

1876 – Telephone

Since the telegraph was invented by Samual Morse in 1837, great advances had been made in its utilization, but it continued as a telegraph system using Morse Code for its communication. Alexander Graham Bell i 1875, was interested in telegraphy and realized that in using Morse Code over telegraph wires there should be other ways to this form of communication using electricity. He was also interested in acoustic and sound and worked on the principle that if Morse Code created electrical impulses in an electrical circuit, some means of sound causing vibration in the air, could also create electrical impulses in a circuit. In an experiment he use a “diaphragm” associated with an electrical circuit and any sound reaching the diaphragm, would cause electrical impulses and these were carried on to the other end of the circuit. These then would cause vibrations to another diaphragm at this end and would be in relation to the first diaphragm, hence the sound was electrically transmitted from one end of the circuit to the other end. He continued working on these experiments and on March 7th, 1876 his telephone was officially patented and a successful demonstration was made at an Exhibition Hall in Philadelphia. Graham Bell was just in time to patent his telephone, as another inventor Elisha Gray, was experimenting also on a similar invention. Later, Edison improved on the diaphragm – then called transmitters – but Bell won the day, by being given the honor of inventing the “telephone”.

Alexander Graham Bell (1847-1922) born in Scotland, was raised in a family that was interested and involved in the science of sound. Bell’s father and grandfather both taught speech to the deaf. en unit of sound level is called a bel in his honor. Sound levels are measured in tenths of a bel, eller decibels. The abbreviation for decibel is dB.

1879 – DC Generation, Incandescent Light

Thomas Alva Edison, (1847-1931)was one of the most well known inventors of all time with 1093 patents. Self-educated, Edison was interested in chemistry and electronics. During the whole of his life, Edison received only three months of formal schooling, and was dismissed from school as being retarded, though in fact a childhood attack of scarlet fever had left him partially deaf.

Nearly 40 years went by before a really practical DC (Direct Current) generator was built by Thomas Edison. Edison’s many inventions included the phonograph and an improved printing telegraph. I 1878 Joseph Swan, a British scientist, invented the incandescent filament lamp and within twelve months Edison made a similar discovery in America. Swan and Edison later set up a joint company to produce the first practical filament lamp. Prior to this, electric lighting had been my crude arc lamps.

Edison used his DC generator to provide electricity to light his laboratory and later to illuminate the first New York street to be lit by electric lamps, in September 1882. Edison’s successes were not without controversy, dock – although he was convinced of the merits of DC for generating electricity, other scientists in Europe and America recognized that DC brought major disadvantages.

1880 – Heaviside Layer

Oliver Heaviside (1850-1925) The British mathematician realized that information travels along a cable as a wave in the space between the conductors, rather than through the conductors themselves. His concepts made it possible to design long-distance telephone cables. He also discovered why radio waves bend around the Earth. This led to long-range radio reception.

1880 – Absolute Temperatures, Kirchoff’s Laws, Coulomb’s Laws, magnetisk Flux, Microphone

William Thomson, Lord Kelvin (1824-1907) was best known in his invention of a new temperature scale based on the concept of an absolute zero of temperature at -273°C (-460° F). To the end of his life, Thomson maintained fierce opposition to the idea that energy emitted by radioactivity came from within the atom. One of the greatest scientific discoveries of the 19th century, Thomson died opposing one of the most vital innovations in the history of science.

Moskowitz, L. R.: Permanent Magnet Design and Application Handbook, Cahners Books International, Inc. (1976)