Density of current and intensity in steady-state
In a steady-state (independent of time) :
Thus, it can be deduced that :
The total intensity exiting a given closed surface is equal to zero in steady-state :
In steady-state, the intensity has the same value through any section of a given field tube :
Let us consider a closed surface formed by one field tube (called current tube) and two surfaces and .
These two surfaces are based on two loops of and have the same orientation.
Let and be the intensities, or respectively the flux of the density of current through and :
(We can notive that the two vectors and are perpendicular).
In steady-state, the intensity of the electric current has the same value through any section of a circuit branch.
We can easily deduce Kirchhoff's circuit laws (flux or current density vector conservation).