Define drift velocity and derive an expression for it

Dreift velocity is the velocity attained by any particle such as electron when kept in an electric field
Let the electron have charge e,  mass m and kept in a electric field E inside a conductor.
The force experienced by the electron F = eE
Acceleration due to the force   = eE/m
Now displacement s due to the acceleration s = ½at2
Average velocity  vd  (drift velocity = Total displacement / total time taken
= s/t
vd = eE/2m