Electronics/History/Chapter 2

Electricity and Magnetism: 1600-1875 [1]

Luigi Galvani edit

Luigi Galvani (September 9, 1737 - December 4, 1798) was an Italian physician and physicist who lived and died in Bologna.

Dissecting a frog at a table where he had been conducting experiments with static electricity, Galvani touched an exposed sciatic nerve of the frog with his metal scalpel, which had picked up a charge. At that moment, he saw the dead frog's leg kick as if in life. The observation made Galvani the first investigator to appreciate the relationship between electricity and animation--or life. He is typically credited with the discovery of biological electricity.

Galvani coined the term animal electricity to describe whatever it was that activated the muscles of his specimens. Along with contemporaries, he regarded their activation as being generated by an electrical fluid that is carried to the muscles by the nerves. The phenomenon was dubbed "galvanism," after Galvani, on the suggestion of his peer and sometime intellectual adversary Alessandro Volta.

Galvani's investigations led shortly to the invention of an early battery, but not by Galvani, who did not perceive electricity as separable from biology. Galvani saw electricity instead as the essence or the stuff itself of life, which he regarded vitalistically. Thus it was Volta who built the first battery, which became known therefore as a voltaic pile. While, as Galvani believed, all life is indeed electrical--in that all living things are made of cells and every cell has a cell potential--biological electricity has the same chemical underpinnings as the flow of current between electrochemical cells, and thus can be recapitulated in a way outside the body. Volta's intuition was correct as well.

Galvani's name also survives in the Galvanic cell, the galvanometer and "galvanize".

Alessandro Volta edit

Alessandro Giuseppe Antonio Anastasio Volta (February 18, 1745 - March 5, 1827) was an Italian physicist known especially for the development of the electric battery. Late in life, he received the title of Count.

De vi attractiva ... Volta was born and educated in Como, Italy, where he became professor of physics at the Royal School in 1774.

His passion had always been the study of electricity, and still a young student he had even written a poem in Latin on this fascinating new discovery.De vi attractiva ignis electrici ac phaenomenis inde pendentibus is his first scientific paper. In 1775 he devised the electrophorus, a device that produced a static electric charge. In 1776-77 he studied the chemistry of gases, discovered methane, and devised experiments such as the ignition of gases by an electric spark in a closed vessel.

In 1779 he became professor of physics at the University of Pavia, a chair he occupied for 25 years. In 1794 Volta married Teresa Peregrini, daughter of Count Ludovico Peregrini; the couple had three sons.

In 1800, as the result of a professional disagreement over the galvanic response advocated by Luigi Galvani, he developed the so-called voltaic pile, a forerunner of the electric battery, which produced a steady electric current. Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc and silver. Initially he experimented with individual cells in series, each cell being a wine goblet filled with brine into which the two dissimilar electrodes were dipped. The electric pile replaced the goblets with cardboard soaked in brine. (The number of cells, and thus the voltage it could produce, was limited by the pressure, exerted by the upper cells, that would squeeze all of the brine out of the cardboard of the bottom cell.)

Templo Voltiano

In honor of his work in the field of electricity, Napoleon made him a count in 1810; in 1815 the Emperor of Austria named him a professor of philosophy at Padua.

Volta is buried in the city of Como in Italy; the Templo Voltiano near Lake Como is a museum devoted to explaining his work; his original instruments and papers are on display there. The building appeared, along with his portrait, on Italian currency before the introduction of the Euro.

An electrophorus is a simple plate capacitor used to collect static charge produced as a result of friction, devised in 18th century by Johannes Wilcke and Alessandro Volta.

The electrophorus consists of a dielectric plate on a metal surface and a metal plate with an insulating handle. First, the dielectric plate is triboelectrically charged, that is, by friction. Then, the metal plate is placed onto the dielectric plate. The metal plate charges by induction - the side facing the charged dielectric plate charges opposite to the charge of plate, while the side facing away from the dielectric charge attains the same sign of charge as the dielectric plate, thus making the metal plate electrically neutral as a whole. Then, the side facing away from the dielectric plate is momentarily grounded. Finally, the metal plate, now consisting only one sign of charge, is lifted.

The Voltaic Pile was invented by Alessandro Volta in 1800. He demonstrated that when certain metals and chemicals come into contact with each other they can produce an electrical current. He placed together several pairs of copper and zinc discs separated by paper soaked in salt water, and an electrical current was produced. This was the first chemical battery.

For his contributions to the study of electricity, the SI unit called the volt was named after Volta.

In 1881 an important electrical unit was named the volt was named in his honor.

Heinrich Hertz edit

Heinrich Rudolf Hertz (February 22, 1857 - January 1, 1894), was the German physicist for whom the hertz, the SI unit of frequency, is named. In 1888, he was the first to demonstrate the existence of electromagnetic radiation by building apparatus to produce radio waves.

Hertz was born in Hamburg, Germany, to a Jewish family that had converted to Christianity. His father was an advocate in Hamburg, his mother the daughter of a doctor. While at school, he showed an aptitude for sciences as well as languages, learning Arabic and Sanskrit. He studied sciences and engineering in the German cities of Dresden, Munich and Berlin. He was a student of Gustav R. Kirchhoff and Hermann von Helmholtz. He obtained his PhD in 1880, and remained a pupil of Helmholtz until 1883 when he took a post as a lecturer in theoretical physics at the University of Kiel. In 1885 he became a full professor at the University of Karlsruhe where he discovered electromagnetic waves.

Following Michelson's 1881 experiment (precursor to the 1887 Michelson-Morley experiment) which disproved the existence of Luminiferous aether he reformulated Maxwell's equations, to take the new discovery into account. Through experimentation, he proved that electric signals can travel through open air, as had been predicted by James Clerk Maxwell and Michael Faraday, and which is the basis for the invention of radio. He also discovered the photoelectric effect (which was later explained by Albert Einstein) when he noticed that a charged object loses its charge more readily when illuminated by ultraviolet light.

He died in Bonn, Germany.

His nephew Gustav Ludwig Hertz was a Nobel Prize winner, and Gustav's son Carl Hellmuth Hertz invented medical ultrasonography.

EM waves edit

The existence of electromagnetic waves, i.e. microwaves, was predicted by James Clerk Maxwell in 1864 from his famous Maxwell's equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building apparatus to produce radio waves.

spectrum edit

It was Sir Isaac Newton in 1666 who first used the word spectrum to refer to the celebrated Phenomenon of Colours which can be extracted from sunlight, by a glass prism.

Infared edit

History In 1800 the English astronomer William Herschel held a mercury thermometer in the spectrum produced by a glass prism to measure the heat content of different coloured lights. He found that the thermometer registered an increase in temperature even when held beyond the red end of the spectrum, where there was no visible light. This was the first experiment to show that heat could be transmitted by an invisible form of light.