Among the most practically useful mathematical formulas, Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points.

Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship (see formula above) where **I** is the current through the conductor in units of amperes, **V** is the potential difference measured across the conductor in units of volts, and **R** is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the **R** in this relation is constant, independent of the current.

More info can be found here: **http://en.wikipedia.org/wiki/Ohms_Law**