Consider again the ith electron at a given time t This
electron would have had its last collision some time
before t, and let ti be the time elapsed after its last
collision If vi was its velocity immediately after the last
collision, then its velocity Vi at time t is
 −
 
=
+  
 
 
 
E
V
v
i
i
i
e
t
m
(3 16)
since starting with its last collision it was accelerated
(Fig