Ohm's law states that, in an electrical circuit, the current passing through most materials is directly proportional to the potential difference applied across them. In mathematical terms, this is written as:
i = V/R
where i is the current, V (or E in the diagram) is the potential difference, and R is a proportionality constant known as the resistance. Ohm's law holds well for most materials and objects, including solutions, provided that the passage of the current does not heat the conductor, but electron tubes and semiconductor devices show a much more complicated behavior. The statement is due to the Bavarian-born German physicist Georg Simon Ohm (1789–1854) who formulated it in 1827.