Ohm's law

Ohm’s law is an empirical law that states that the electric current through a conductor between two points is directly proportional to the voltage across the two points.

Vector form

$$\mathbf{J}=\sigma \mathbf{E}$$

where
$\mathbf{J}$	current density vector field, measured in amperes per square meter, $\frac{\text{A}}{{\text{m}}^2}$
$\mathbf{x}$	position vector in three-dimensional space, typically expressed as $\mathbf{x}=(x,y,z)$ and measured in meters $\text{m}$
$t$	time, measured in seconds $\text{s}$
$\sigma$	conductivity, measured in siemens per meter $\frac{\text{S}}{\text{m}}$
$\mathbf{E}$	electric field, measured in volts per meter $\frac{\text{V}}{\text{m}}$