Question

Define drift velocity and relaxation time, with reference to the free electron theory of conductors.

Answer 1

The average time elapsed between two successive collisions is the relaxation of time of free electrons drifting in a conductor.
Relation between T and v is given by: V= -eE/m

Answer 2

The average velocity gained by particles such as electrons in any material due to the presence of an electric field  is termed as drift velocity.

Relaxation time is the time interval between two successive collisions of electrons inside a conducting material when a current is flowing through it.

Current flows in conductors due to the presence of free electrons. When the cuurent is flowing through it, the average speed of the electrons is the drift speed and the time interval between two successive collisions of these free electrons is the relaxation time.

The formulae for drift velocity is as follows-

Drift velocity :-

A. v = -(eEτ)/m

Where

1. e= charge on an electron
2. E= electic field intensity
3. τ= relaxation time
4. m= mass of electron

or

B. v = I/neA

Where

1. I= Current
2. n= number of electrons
3. A= Areas of cross section of conductor
4. e= Charge on electron