(1789-1854) Bavarian Theoretical and Experimental Physicist (Classical Electromagnetism)
Georg Simon Ohm’s formulation of the relationship between current, electromotive force (voltage), and resistance, known as Ohm’s law, was a seminal contribution to the understanding of electricity and opened the door to an era of invention in which scientists could design electric circuits for specific functions. Although his name would later be synonymous with the unit of resistance (the ohm), he was underappreciated in his lifetime and frustrated in his academic ambitions.
Ohm was born in Erlangen, Bavaria (now Germany), on March 16, 1789. His Protestant parents had no formal education, but Ohm was fortunate in his father, a self-educated master locksmith who gave his children a solid education in mathematics, physics, chemistry, and philosophy. Young Georg gained far more from this home schooling than he did from the uninspiring, learning-by-rote methods used at the Erlangen Gymnasium, where he was sent at age 11 for his secondary education.
On entering the University of Erlangen in 1803, the future pioneer of the theory of electricity dissipated his opportunity for higher education in a nonstop round of social pleasures, which included dancing, ice-skating, and playing billiards. His irate father demanded that he drop out after three semesters and sent him to earn his living as a schoolteacher and private tutor in Switzerland. During his years in Switzerland, Ohm, guided by a former professor, carried out an exhaustive program of independent mathematical study, reading the works of Euler, Laplace, and Lacroix, among others. The fact that he was awarded his Ph.D. in October 1811, after returning to the University of Erlangen in April of that same year, gives some idea of how well he succeeded in mastering the material independently.
Although the university immediately engaged him as an unpaid lecturer, an unimpeded path to the scholarly career he desired was not to be. Ohm was forced to take on a paying job as a teacher in a mediocre school in Bamberg. In 1817, he found a somewhat better position in Cologne, teaching mathematics and physics at the Jesuit Gymnasium. Ohm doggedly pursued his self-education, reading the work of the French mathematicians and acquainting himself with current work on electricity. In 1820, when the Danish physicist hans christian 0rsted announced his groundbreaking discovery that an electric current can generate a magnetic force, Ohm began using the gymnasium’s well-equipped physics laboratory to perform his own experiments.
His work would culminate in 1825, when, at age 36, Ohm published his first paper, examining the decrease in the magnetic force produced by a current flowing in a wire as the length of the wire increases. He used a voltaic pile (electric battery) to produce a current and connected different lengths of wire to it; he then measured the magnetic force that was generated by the current, using the magnetic needle of a galvanometer. In this way, that is, by measuring the magnetic force, he was, in fact, measuring the electric current flowing in the wire. The results confirmed his expectations: a longer wire produced a greater loss in the magnetic force. This implied that a longer wire had a smaller current flowing in it and, therefore, had greater resistance, the term coined by Ohm to designate the opposition of the material to the flow of charge.
In 1826, he repeated this experiment, this time generating the current by using a thermocouple (a pair of wires of different conductors, welded or soldered at one end, used to measure temperature). This technique had the advantage of producing a constant electric current, as distinct from the fluctuating current produced by the voltaic pile. He found that the magnetic force was equal to the electromotive force produced by the thermocouple divided by the length of the wire plus the resistance of the remainder of the circuit, including the thermocouple itself. He expressed his findings in terms known today as Ohm’s law, which states that the current is equal to the electromotive force divided by the overall resistance of the circuit.
In the context of this experiment, Ohm pointed out that an electric current flows through a conductor of varying resistance to produce a potential difference, just as heat flows through a conductor of varying conductivity from one temperature to another to produce a temperature difference. In 1827, Ohm published his results and his complete theory of electricity in his great work, Die Galvanische Kett, mahtem-atisch bearbeitet (The Galvanic circuit, investigated mathematically).
Despite the immense importance of Ohm’s work, recognition by the scientific community continued to elude him. Few of his peers were capable of understanding his mathematics, and those few German physicists who could appreciate the rigor of Ohm’s formulations doubted the correctness of his approach. Ohm remained a schoolteacher, in Berlin, until 1833, when he moved to Nuremberg and became a professor of physics at the respectable but undistinguished Polytechnic Institute.
Recognition, when it was finally given him, began in England. In 1841, Ohm was awarded the Royal Society’s Copley Medal. In 1849, he began to lecture at the University of Munich. He finally became a professor of physics at the university in 1852 but died only two years later in Munich on July 6, 1854.
Ohm’s law, together with the laws of electrodynamics discovered by andre-marie ampere at about the same time, pioneered the way to future theoretical investigation of electricity. His name is remembered in both the unit of resistance, the ohm, and its inverse, the unit of conductivity, the mho, Ohm spelled backward, also called the siemens.
Using Ohm’s law, scientists could for the first time calculate the amounts of current, voltage, and resistance in electric currents, measuring changes in one of these variables through changes in the others.
