Then
because of the drift, in an infinitesimal amount of time
Dt, all electrons to the left of the area at distances upto
|vd|Dt would have crossed the area If n is the number
of free electrons per unit volume in the metal, then
there are n Dt |vd|A such electrons Since each
electron carries a charge –e, the total charge transported across this area
A to the right in time Dt is –ne A|vd|Dt E is directed towards the left and
hence the total charge transported along E across the area is negative of
this