Current Density

$\vec{J}$ is a vector where the vector is along the direction of the motion of positive charge.

$\vec{J}=nq\vec{u}$ $\vec{J}={\rho }_v\vec{u}$

• The velocity $\vec{u}$ depends on the conductor properties and on the applied electric field

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

We call $\sigma$ the Conductivity.