Ohm's law

Ohm's law states that resistance and current are proportional to voltage by the equation
:V = IR
by dividing by area, this becomes
:\vec{\mathbf{J}} = \sigma \vec{\mathbf{E}}
where J is current density, σ is conductivity, and E is the electric field strength in the wire.
For AC circuits, this becomes
:V_{rms} = I_{rms} \cdot Z
with Z representing impedance. This is a more general form of Ohm's law.
Ohm's law is not always followed. All materials will experience an electrical breakdown (a spark) given a high enough voltage, and some materials, such as diodes, do not follow Ohm's law even at low voltages.
Category:Electric circuits