Ohm’s Law

Ohm’s law states that the current (I) through a conductor between two points is directly proportional to the potential difference (E) across the two points, and inversely proportional to the resistance (R) between them.

E=IR

I=\frac{E}{R}

R=\frac{E}{I}

More info: http://en.wikipedia.org/wiki/Ohm%27s_law