From Wikipedia here: Ohm's law applies to electrical circuits; it states that the current passing through a conductor between two points is directly proportional to the potential difference (i.e. voltage drop or voltage) across the two points, and inversely proportional to the resistance between them. The mathematical equation that describes this relationship is: where I is the current in amperes, V is the potential difference between two points of interest in volts, and R is a circuit parameter, measured in ohmsresistance. (which is equivalent to volts per ampere), and is called the resistance. For all the various relationships, one can attempt to memorize the circle chart: http://www.ict4us.com/r.kuijt/en_ohm.htm But I think it's easier to remember just two mnemonic expressions: PIE in your EIR AND [IERP=AVOW or PIER=WAVO], then solve algebraically to reach the same results.

Actually thats wrong. Ohm's Law is J = σE where J is current density, E is the Electric Field present, and σ is a conductivity of the mater that power is traveling through. This is a general equation that applies to almost all matter. V = IR is all that we need to know for electronic circuits, but it wouldn't hold true if we weren't talking about highly conductive materials (ie. if we were talking about a block of wood), J = σE would. In short, the relation ship V = IR comes from the linear relationship between current density and an Electric field and that linear relationship is actually Ohm's law. That being said I don't do integral Calculus in my head very well (often required to find an electric field) so should I need to use Ohm's law at work I'd use V = IR. Just for a little educational trivia.