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|I = .||(1)|
One can relate the current I in a material to properties of
the atomic charges.
Suppose in the material there are n charges per unit volume, each carrying
a charge q . When acted upon by an electric field these charges begin to
move; let us associate an average drift velocity vd with each individual
charge. Consider now a section of the material with cross-sectional area A ,
as in Fig. 17.1.
In a time t a charge Q has moved a distance x . Since Q = (nAx)q , we have for the current
|I = = nAq = nAqvd.||(2)|