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History of Electricity

The discovery of electricity and the laws of physics governing its behavior are one of the greatest achievements of humanity. In scarcely 150 years we went from the most basic observations of the effects of electricity to its exploitation in computers and telecommunications.

Magnetism, which is related to electricity, was discovered long ago. The Greeks discovered magnetic materials about 900 BC. In 600 BC, the Greek,Thales of Miletos, recorded that rubbing amber against a cat’s fur (this generates static electricity) picked up feathers. Amber is a fossilized resin and the Greek word for amber is elektron (ἤλεκτρον), although our word electron was not coined until 1891.

Around 1600 William Gilbert, Queen Elizabeth’s physician, discovered that the Earth itself was a magnet and used this observation to explain how the compass worked.  He also described static electricity and regarded it as an electric fluid that was liberated by rubbing.

In 1729 Stephen Gray demonstrated that electrostatic charges reside on the surface of objects and can be transferred by means of wires (conductors).

In 1733 Charles Francois du Fay discovered that electrostatic charges could be positive or negative (he didn’t use those terms).

In 1747 Benjamin Franklin invented the theory that there was only one type of electric charge; the other type was simply an absence of the charge. Franklin proposed that the flowing charge was positive. It was, of course, negative and we’ve had to live with the consequences ever since.

In 1780 Luigi Galvani noticed that static electricity caused frogs’ legs to twitch. He also noticed that the same twitching occurred when the nerves were touched by two dissimilar metals. He had, of course, invented a means of generating electricity - the cell.

In 1793 Alessandro Volta created a cell by using discs of dissimilar metals separated by wet cardboard. By stacking pairs of discs he created the Voltaic pile or battery.

In 1807 Humphrey Davy made one of the great intellectual steps and realized that Volta’s pile generates electricity because of chemical action and therefore chemical effects are themselves electrical in nature.

In 1820 Hans Christian Oersted discovers that a current in a wire caused a compass needle to deflect. This effect is the basic of the electric motor and the loudspeaker.

In 1820 following Oersted’s discovery Andre Marie Ampere demonstrates that parallel currents flowing in two wires repel each other and that opposite currents attract each other.

In 1826 the German physicist Georg Simon Ohm realized that the electromagnetic potential or voltage was the driving force that caused current to flow in a conductor. Ohm realized that the flow of electricity was rather like the flow of heat (which is driven by temperature difference). Ohm’s work led to the formulation of Ohm’s Law, I = E/R.

In 1831 Michael Faraday investigated whether there was an inverse effect between electricity and magnetism. If electricity could create magnetism as Oersted demonstrated, could the inverse be true? Faraday discovered that when a magnet was moved inside a coil of wire, an electric current was induced in the coil. This is, of course, the basis of the generator and the magnetic disk itself.

In 1841 James Prescott Joule demonstrated that energy is conserved in circuits that involve heating and chemical transformations.

At this point many of the inventions and discoveries were related to refining mathematical models of the relationship between magnetism and electricity, and the nature of electromagnetic radiation. This led to the prophesying of electromagnetic radiation (Maxwell) and its discovery (Hertz).  

In 1897 Joseph John Thomson was working with cathode rays (streams of electrons given off from a heated surface and the basis of the thermionic vacuum tube). Thomson determined that the weight of electrons was far less than that of hydrogen atoms and that their characteristics were not determined by the metal of the cathode. He argued that they must be a new sub-atomic particle. Thomson also determined that electrons could be deflected by magnetic fields (the basis of the cathode ray tube used in TVs) and devised one of the great experiments of classic physics to measure the charge to mass ratio of an electron.

In 1904 John Ambrose Fleming invented the thermionic diode or rectifier. Surrounding a heated cathode giving off electrons in a vacuum tube with a wire mesh allowed electricity to flow one way only (electrons from cathode to anode). This device could be used to convert ac to dc and to demodulate radio waves; that is, turn high-frequency alternating current radio waves into a direct current that could be detected.

In 1912 Lee De Forest made the greatest ever step by inventing the device needed to establish electronics. Up to this point only passive devices (resistors, capacitors, and inductors) existed. There was no means of amplifying weak signals. By inserting a new electrode between the cathode and anode of a Fleming diode, Lee De Forest invented the Audion tube (now called the triode) that could amplify signals. By changing the voltage on the grid, it was possible to modulate the flow of electrons between the cathode and anode. A negative voltage on the grid would repel electrons and stop them reaching the cathode. Anything that we can do today with the transistor could be done with the triode.

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Electronic Circuits