Using the last equation, Ohm’s law reads
I l
V
I
R
ρA
=
×
=
(3 10)
Current per unit area (taken normal to the current), I/A, is called
current density and is denoted by j The SI units of the current density
are A/m2 Further, if E is the magnitude of uniform electric field in the
conductor whose length is l, then the potential difference V across its
ends is El