Electricity and Magnetism

For the modern day observer, electricity is often taken for granted. We have become so accustomed to using electricity that we seldom remember how long it took to understand, control, and apply its properties to benefit society. Such simple items as light bulbs have become so common and reliable that we hardly notice them, except for when they burnout. But such was not always the case. Rarely, if ever, do we consider the nine years Michael Faraday spent thinking of how to convert magnetism to electricity, or the hundreds of "failures" Edison had before successfully making a viable light bulb. We will begin this course with a brief history of electricity and magnetism, go over the differences between AC and DC, discuss electrical generation, and then conclude by making an electromagnet and an AC/DC demonstration device using a transformer.

The History of Electricity and Magnetism.

The fact that amber acquires the power to attract light objects when rubbed may have been known to the Greek philosopher Thales of Miletus, who lived about 600 BC. Another Greek philosopher, Theophrastus, in a treatise written about three centuries later, stated that this power is also possessed by other substances. Magnetism was also known to the ancients. The mineral magnetite, according to a legend written by Pliny, was so named because of a shepherd named Magnes, who first discovered the mineral on Mount Ida by noting that the nails of his shoes and the iron ferrule of his staff adhered to the ground. More likely, it acquired its name due to a prominent deposit of the mineral located in Magnesia along the Macedonian border. In either case, the mineral is highly magnetic and eventually found use in the mariner's compass (although such use was highly suspicious and often considered a device of the devil). The first scientific study of electrical and magnetic phenomena, however, did not appear until AD 1600, when the researches of the English physician William Gilbert were published. Gilbert was the first to apply the term electric (Greek elektron, "amber") to the force that such substances exert after rubbing. He also distinguished between magnetic and electric action.

The first machine for producing an electric charge was described in 1672 by the German physicist Otto von Guericke. It consisted of a sulfur sphere turned by a crank on which a charge was induced when the hand was held against it. The French scientist Charles François de Cisternay Du Fay was the first to make clear the two different types of electric charge: positive and negative. This he determined by noticing that there were differences in the "type" of electricity produced by rubbing amber and that produced by rubbing glass were not alike.

The earliest form of condenser, the Leyden jar, was developed in 1745. It consisted of a glass bottle with separate coatings of tinfoil on the inside and outside. If either tinfoil coating was charged from an electrostatic machine, a violent shock could be obtained by touching both foil coatings at the same time.

Benjamin Franklin was fascinated by the Leyden jar, but it just didn't have enough power for him. He connected several jars in series, which allowed him to store up more electricity, and subsequently, produce a larger flash and greater shock when he discharged it with his hand (though I suspect he also used other unsuspecting people's hands to discharge this apparatus). His famous kite experiment proved that the atmospheric electricity that causes the phenomena of lightning and thunder is identical with the electrostatic charge on a Leyden jar. Franklin developed a theory that electricity is a single "fluid" existing in all matter, and that its effects can be explained by excesses and shortages of this fluid.

The event that launched the world into the electric power age took place on October 17, 1831, when Michael Faraday moved a magnet inside a coil of wire to produce electricity. Long before this event Allesandro Volta had invented a battery to produce electricity, but such batteries were expensive and very cumbersome. With Faraday's discovery, the world was about to change. Instead of using copper, zinc, and acids to make batteries, the world would run on the generators developed under the simple concept of moving a magnet through a coil as described by Faraday. Electricity could now be produced efficiently and at low cost.