The average value of ti then is t
(known as relaxation time) Thus, averaging Eq (3 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