Ohm’s law states that a steady current (I) flowing through a material of a given resistance is directly proportional to the applied voltage (V) and inversely proportional to the resistance (R). The law is commonly expressed as I=V/R. Most, but not all, materials abide by Ohm’s law. Those that do not are usually described as nonohmic conductors. In slightly modified form, Ohm’s law can be extended to alternating current circuits as well as magnetic circuits.
The son of a locksmith, Ohm was born on March 16, 1789 in Erlangen, Bavaria (now part of Germany). He was initially educated by his father, who had considerable knowledge of a variety of subjects despite his lack of a formal education, and later entered the Erlangen Gymnasium. By the time he began studies at the University of Erlangen in 1805, Ohm possessed an excellent understanding of advanced mathematics. Yet he did not dedicate enough time to his education to please his father, preferring to partake in various diversions rather than apply himself to his books. Paternal displeasure resulted in Ohm dropping out of school after three semesters and relocating to Switzerland, where he became a teacher of mathematics.
Though no longer enrolled in a university, Ohm studied the works of important mathematicians during his free time. In 1809 he decided to leave his teaching post to tutor privately, all the while continuing his own studies. Eventually he re-enrolled at the University of Erlangen, receiving a doctorate a year later. Following graduation, Ohm began lecturing at his alma mater. But he was unhappy with the position, which paid poorly, as he would be with most of the teaching posts he held throughout his life. He resigned after a few semesters and accepted another post in Bamberg.
In an attempt to improve his prospects, Ohm penned a geometry textbook and began experimental work that he hoped would lead to publishable treatises. The positive reception of the geometry text led to an offer for him to teach at a school in Cologne. The physics laboratory there provided Ohm with the space and instruments he needed to carry out studies of electricity and magnetism, phenomena that were being heavily investigated in the early 1820s following the discovery by Hans Christian Ørsted that the two were related. Ohm’s work ultimately resulted in his publication of Die galvanische Kette, mathematisch bearbeitet (The Galvanic Circuit Investigated Mathematically) in 1827. The treatise contained an account of his electromagnetic theories and included all of the components of Ohm’s law.
Unlike most German scientists at the time, Ohm took a mathematical approach in his considerations of electricity and magnetism. This may have been partly responsible for the treatise’s initial poor reception among many of his contemporaries. In the years following the publication, Ohm’s standing among fellow scientists gradually improved, especially in other countries. He finally found the success he had been longing for throughout much of his life in the 1840s. In 1841 he received the prestigious Copley Medal from the Royal Society in England, and the following year was honored with foreign membership by the same association. Additional memberships in other scientific organizations soon followed. Perhaps most significant to Ohm was his appointment as a professor at the University of Munich in 1849, which finally put to an end his long stream of moves to unsatisfactory teaching positions. Shortly before his death he was awarded the physics chair at the university, a final marker of the considerable success Ohm had become.
In modern times, Ohm’s name is so familiar it is hard to believe the difficulties he faced during his lifetime. In addition to Ohm’s law, his name is associated with the international unit of electrical resistance. One ohm of resistance is present in a circuit when a single volt generates one ampere of current.