Georg Simon Ohm (1787 - 1854) was born in Bavaria, Germany. He worked as a secondary mathematics teacher at the Jesuit College in Cologne, but wanted to teach at the university. To this end, he was required, as proof of admission, to undertake unpublished research work. He chose to experiment with electricity and built his own equipment, including wires.
Experimenting with different wire thicknesses and lengths, he discovered extremely simple mathematical relationships involving these dimensions and electrical quantities. Initially, it found that the current intensity was directly proportional to the area of the wire section and inversely proportional to its length. With this, Ohm was able to define a new concept: that of electrical resistance.
What does electrical resistance mean? The free electrons that flow along the electric wire or cable have to pass between the atoms that compose it, constantly colliding with them. In this way, the flow of electrons is impeded by the resistance that atoms oppose to their passage.
In 1827, Ohm was able to formulate a statement that involved, besides these quantities, the potential difference: "The intensity of the electric current that flows through a conductor is directly proportional to the potential difference and inversely proportional to the circuit resistance." This statement is still known today as Ohm's Law. Such relations had also been pointed out, half a century earlier, by the English Cavendish, who, however, did not disclose them.
Although these studies were an important collaboration in the theory of electrical circuits and their applications, Ohm's desired university post was denied him. His conclusions received negative criticism, in part because he tried to explain these phenomena based on a theory of heat flow. Ohm even had to resign from his high school job in Cologne, and lived in poverty for the next six years. In 1833, however, he reintegrated into scientific activities by accepting a post at the Nuremberg Polytechnic School.
As with so many other researchers, his work was first recognized abroad. In 1841, he would receive a medal from the Royal Society of London. Only in 1849 could Ohm become a professor at the University of Munich, a post in which he would remain for only five years, the last of his life.