| Definition: | at a given point within a volume element of quasi-infinitesimal volume V, vector quantity equal to the sum, for all free charge carriers within the volume element, of the products of electric charge and velocity, divided by the volume V:
J=1Vn∑i=1Qi vi
where n is the number of free carriers within the volume element, Qi the electric charge of the ith carrier and vi its velocity
NOTE – The flux of the electric current density J through any directed surface S is equal to the electric current I through that surface:
I=∫SJ⋅endA
where endA is the vector surface element.
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