ELECTRICITY & MAGNETISM

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VOLT'S PILE - Thousands of years ago man knew about electricity, but not enough to do anything positive with the curiosity. It would not be until electricity could be applied to lighting, that it would become commercially important, and traded, just as oil lamps made whalers rich, consigning candles to the emergency cupboard. Gas lamps too would be displaced, where electric lighting was safer and brighter.

The Greeks knew the magnetic properties of the mineral lodestone, sometimes called Magnetite, as early as 600 B.C. Thales Miletus (640 - 540 B.C.), an early Greek mathematician and astronomer, was aware of the properties of attraction and repulsion of lodestone with like pieces of lodestone. He too knew of an electrostatic effect called the amber effect, that is, the attraction of bits of straw to an amber rod that had been rubbed with wool.

ALESSANDRO VOLTA

In 1801 Alessandro Volta demonstrated his ‘Pile’ to Napoleon. The pile was a series of copper and zinc discs interleaved with moist cloth, to form an electric battery. Twenty years later in 1821 Michael Faraday invented a simple single-wire electric motor and then in October 1831 Faraday succeeded in generating an electric current mechanically. He had invented the dynamo using a bar magnet and a coil of copper wire. 

Volta’s ‘Pile’ was a primary cell. A primary cell is one where the metals are used up in a chemical exchange, which releases energy – generally they cannot be recharged. A secondary cell, uses a chemical reaction which is reversible. By putting electricity into a secondary cell at a higher voltage, the cell can store energy chemically, which can later be drawn out when needed. Secondary cells were called accumulators in the early days, because they accumulated a charge. The Lead-Acid cell is one of the most common accumulators or batteries generating just over two volts per cell, hence there are six cells in series in a twelve volt car battery. The term battery is now common for any cell, but in fact it denotes a number of cells joined in series to form one unit, after the batteries of artillery units formed of a number of cannons. 

These days we use lead-acid batteries in cars for starting petrol engines. After starting, the engine turns a generator to recharge the battery for the next time the engine needs starting. It is ironic that the invention of the electric starter motor for internal combustion engines saw the demise of the early electric cars in favour of petrol engines.

In early electricity generating, municipal, plants, electricity was not normally stored in banks of batteries, meaning that the steam or gas engines had to run noisily at night. Conversely, in rural plants and private houses, electricity would be supplied to houses for lighting at night, via battery banks of sufficient capacity to cope with demand, until the engines were started the next day to once again recharge the batteries, for the following night. The batteries also acted as a regulator to smooth the flow of electricity to some extent. Such as when the bakery in the village was baking, and the generator could not cope with peak demands.

Michael Faraday's experiment to show magnetic induction. A battery (right) is used to power a coil (A) to make an electro-magnet, that is inserted into another coil (B) that then generates a current, visible on the Galvonometer (C).

MICHAEL FARADAY

Michael Faraday discovered that when he moved a bar magnet inside a coil of copper wire, it produced a voltage and that by spinning a magnet inside a coil of copper wire a smooth electric current was generated. This is called direct current or DC from dynamos. Whereas alternating current or AC, is the kind of electricity we get from the plug sockets in our homes from alternators. The voltage generated in either kind of machine depends on the number of turns or coils of wire that the moving magnet passes across. The amperage depends on the thickness of the wire and the strength of the magnetic field or flux that the magnet makes. The distance between the magnet and copper wire is also important because the strength of a magnetic field rapidly diminishes with distance, the closer the fit the more efficient the machine.

Permanent magnets can be made of steel or a mixture of rare earth metals such as cobalt and neodymium. The alternative to permanent magnets is to generate a magnetic field by winding copper wire around silicon steel and pass an alternating current through the copper coils. This will turn the silicon steel into what is known as an electromagnet. It is exactly the reverse of using a bar magnet to create electricity. In the world of electric motors and generators, DC machines can sometimes operate as generators or motors. In theory an alternator could be made to operate as a synchronous motor by feeding it with the correct alternating electrical sinusoidal wave pattern. Once these discoveries had been made, engineers could put them to practical use in many ways.

Faraday's disc. The first electricity generator.

JAMES CLERK MAXWELL

The laws of electricity and magnetism were closely studied by James Clerk Maxwell (1831 –1879), a Scottish physicist. Maxwell wondered why the physical laws were not symmetric when expressed in mathematical form. By applying the concept of symmetry, he found an additional law, which completed the equations of electromagnetism in 1865.

Maxwell studied these equations and discovered that, according to the equation, light is made up of electromagnetic waves. The theoretical fact that electromagnetic waves of radio frequency, likely led to experiments in which radio waves were generated and detected. This discovery eventually opened up a new era of wireless communication and in due time brought us commercial radio and television and a host of other devices, including mobile phones.

PRACTICAL APPLICATIONS

Electric motors can turn impellor pumps to pump water uphill, and water can be fed through impellors to turn generators, such as in a hydroelectric dam. Once again, as with generators and motors, to greater or lesser degrees machinery can be reversible. This is the basis of regenerative braking on modern electric vehicles. The motors of which are remarkably efficient Direct Current synchronous machines, bearing little resemblance to Faraday's experiments.

Modern batteries can be very much larger that Volta's Pile, typically made of lithium, cobalt, and polymers. These batteries not only power EVs, but also store electrical energy in bulk, to stabilise the National Grid, to provide load levelling, just like at the Generating Works at Herstmonceux. The world's first stabilised municipal supply, and the only example remaining, anywhere in the world.

A hive of local activity, in the Sussex backwater of Herstmonceux. The driver from all of this was electric lighting, to replace candles and gas lighting.

The machinery at Herstmonceux Generating Works was gas powered in its final guise. The gas coming from heating coal. Hence, the sizeable brick built bunker, convenient to shed number three, where the (town) gas maker plant was installed. The complex is interesting because it not only generated electricity, but stored it in Shed number One, a room filled with large glass lead-acid batteries, with sufficient capacity to provide electric lighting and cooking to the village, in 1913.

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