## A Brief History of Ideas About Electricity

Two and a half thousand years ago it was known by the Greeks that rubbing a piece of amber resin would make it attract tiny pieces of paper. The word electricity is derived from the Greek word for amber, 'elektron'.

Much later in 1680, Otto von Guericke design a machine to rub fur against glass that produced sparks. This machone enable experiments to be conducted and many similar machines were designed.

In 1752, the American Benjamin Franklin suggested that lightning was due to electricity. To prove it he flew a kite in a thunderstorm and found that electricity was conducted down the wet string. He later used his insight to invent the lightning conductor, used to protect buildings against lightning. He also suggested the existence of two types of charge – positive and negative.

In 1791 the Italian Luigi Galvani showed that a frogs leg twitched if couched by two different metals connected by a wire.

In 1800 Alessandro Volta built the first battery. He suggested that electric current was a fluid flowing through the wires. Andre Ampere suggested that current carried a positive charge from the positive terminal of a battery to the negative terminal. Ampere later turned out to be wrong, but his suggestion gave rise to the convention that current carries a positive charge and flows from positive to negative terminal.

In 1826 Georg Ohm, a German, discovered Ohm's Law. This law states that the current through a conductor is proportional to the voltage across it. The equation may be written as V=IR where V is the voltage, I is the current and R is a new quantity, called resistance.

The British scientist Joule later discovered that the passing of current had a heating effect on the conductor.

In 1897 JJ Thompson discovered the electron, which is negatively charged and showed that electric current was due to the movement of electrons.

In 1911, superconductivity was discovered, allowing current to flow forevery with no electrical resistance. Very low temperatures were required, close to absolute zero, until in 1987, a material was discovered that was superconducting at much higher temperatures. Since then scientists have been searching for materials that will superconduct at room temperature.