For electrons q = – e If j is normal to a cross-sectional area
A and is constant over the area, the magnitude of the current I through
the area is nevd A 8 Using E = V/l, I = nevd A, and Ohm’s law, one obtains
2
d
eE
ne v
m
ρm
=
The proportionality between the force eE on the electrons in a metal
due to the external field E and the drift velocity vd (not acceleration)
can be understood, if we assume that the electrons suffer collisions
with ions in the metal, which deflect them randomly