16) over the
N-electrons at any given time t gives us for the average velocity vd
(
)
(
)
( )
≡
=
−
E
v
V
v
d
i
i
i
average
average
average
e
t
m
0 –
τ
τ
=
= −
E
E
e
e
m
m
(3 17)
This last result is surprising It tells us that the
electrons move with an average velocity which is
independent of time, although electrons are
accelerated This is the phenomenon of drift and the
velocity vd in Eq