For explanatory purposes consider an electrophoretic particle moving (driven) in an electric field. Let:
and
denote an electric field and the velocity of the particle in such a field. If  is constant the time average of .
If  is not constant as a function of time and if  has a frequency component proportional to  the time average of  need not be zero.
Consider the following example:
Substituting (3) in (2) and computing the time average, , we obtain:
Thus, it is possible to have the particle experience a non-zero time average velocity, in other words, a net electrophoretic drift, even when the time average of the applied electric field is zero.