Define drift velocity of free electron . If relaxation time is r then write a vector relation b etween drift velocity and electric field.

Explanation

Due to commulative effect of collision with the ions and electric force, free electrons acquires a constant velocity in a particular direction which is known as drift velocity.
or we can say:
it is the average velocity of free electrons in the presence of electric field.
Relation `vecv_(d)=-((er)/(m))vecE`