Atoms & Light

Part 4 - Electricity

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Our remote ancestors knew about shocks from electric fish. Egyptians from 2750 BCE referred to them as "Thunders of the Nile." The Greeks and Romans also reported the numbing effect of electric shocks delivered by electric catfish and knew that such shocks could travel along conducting objects. The Arabs described the electric ray using the Arabic word for lightning.

Around 600 BCE, Thales of Miletus created static electricity by rubbing rods of amber with cat's fur to attract light objects like feathers. He believed that friction made amber magnetic in contrast to minerals such as magnetite, which needed no rubbing.

In 1600, William Gilbert (Queen Elizabeth's physician) carefully studied electricity and magnetism. He wrote De Magnete, coined the word electricus (from elektron, the Greek word for "amber") which first appearance in print as 'electric' in Thomas Browne's Pseudodoxia Epidemica of 1646.

In 1663, Otto von Guericke built a friction machine that would continuously convert mechanical work into static electricity (electricity at high voltage and low continuous direct current (DC)). This was later known an electrostatic generator which typically generated a charge by transferring electrons from one electrode to another either the by friction (the triboelectric effect) or electrostatic induction.

However, it was 1729 before Stephen Gray identified electrical conductors and non conductors (insulators) and 1733 before C. F. du Fay showed the difference between positive and negative electricity.

The Leyden Jar was invented by Ewald Georg von Kleist and Pieter van Musschenbroek around 1746 as a way to temporarily store a high-voltage electric charge. It was the first condenser or capacitor and was used for many early experiments in electricity and electrostatics.

In 1752 in the USA, Benjamin Franklin was said to have flown a kite in a storm creating a succession of sparks from a key to the back of his hand and demonstrating that lightning was indeed electrical in nature. This led to the invention of the lightening conductor to protect buildings from lightening strikes.

John Canton invented an instrument to measure electricity that was standardized by Alessandro Volta and, in 1787, improved by Bennet as the gold leaf electroscope.

In 1791, Michael Faraday discovered the principles of electromagnetic induction, diamagnetism and electrolysis. In 1821, he discovered that a wire carrying an electric current rotated around a fixed magnet and also demonstrated a that a magnet, rotated around a conducting wire circuit, produced a current in the circuit. In 1831, he built the first electric motor and also the first electrical generator. (Also known as a dynamo). 

 He also demonstrated that the voltage of an alternating current could easily be changed by placing two coils of wire together; the voltage in one coil would create a voltage in the other in direct relationship to the number of windings in each coil. (This device is now known as an electrical transformer). The unit of capacitance, the farad, is named in his honour.

In March 1861, James Clerk Maxwell took the work of Faraday and others and summarized it in a set of equations which is accepted as the basis of all modern theories of electromagnetic phenomena.

Luigi Galvani's experiments with twitching frog legs prompted Alessandro Volta to discover that a source of electricity was created by two dissimilar metals in a liquid solution. In 1800, he developed the voltaic pile consisting of alternate plates of copper or silver and zinc separated by flannel soaked in brine. This was rapidly copied to provide a steady supply of electric current for experiments that revolutionized science. 

Humphrey Davy in London used electrolysis to isolate a range of new metals including potassium, sodium, barium, strontium and magnesium. Water was easily decomposed into hydrogen and oxygen thus confirming Lavoisier's discovery. 

In 1802 Davy also produced a brilliant light from a continuous spark (arc) between two carbon rods, the first arc lamp. In Denmark, in 1820, H.C. Oersted realized that a wire carrying an electric current was surrounded by a magnetic field. In 1799, Alessandro Volta developed the first electrical battery. Known as the Voltaic Cell, it consisted of two plates one of copper and another of zinc in a solution of sulphuric acid or brine. He also realized that the driving force of electrical potential (voltage) cause the current to flow. The electrical unit of potential is named Volt in his honour.

André-Marie Ampère, in Paris, founded the science of electrodynamics, after 1820, when Hans Christian Ørsted showed that a magnetic needle was deflected by an adjacent electric current. Ampère also demonstrated the connection between his discoveries and Charles Augustin de Coulomb's law of magnetic action. In 1827 Ampère published Memoir on the Mathematical Theory of Electrodynamic Phenomena, Uniquely Deduced from Experience.

Georg Simon Ohm discovered the direct relationship between current (Amperage) and electrical potential (Voltage) and also the resistance of various metals to conduct electricity (measured in Ohms).  

(Ohm's Law, E=IR, is the basic formula used to calculate the relationship between voltage (E), current (I) and resistance (R) in an electrical circuit. E (volts) = I (amps) x R (ohms)).

(The conductors with lowest resistance (best conductivity) are silver, copper, gold and aluminum, but, because of the cost, the most commonly used are copper and aluminum. Aluminum being used almost exclusively for high voltage transmission lines where it is supported by a steel wire cable).