Mean Free Path of Electrons
Although an iron rod in your hand looks stationary, a lot of electrons are moving inside it continuously.
This is because it is a conductor. Conductor are full of free electron as well as positive charges.
In the conductor, negative charges are quite mobile compared to positive ions and they move randomly everywhere in the conductor like a gas particles.
This movement of free electrons is due to thermal agitation
While moving randomly, they suffer successive collisions inside the conductor with positive ions.
These free electrons inside the conductor move with an average velocity of about
The mean free path and relaxation time
Since, the electrons are continuously moving and successive collisions are occuring, these electrons travel some distances between two such collisions.
This average distance travelled by a free electron between two such successive collisions is called its mean free path
The time interval between the two successive collisions is called Relaxation Time
Let's see what happens, when a battery is connected to this conductor
Due to the battery, an electric field will be developed inside the conductor.
And the electrons will start drifting towards the positive terminal in presence of this electric field.
Now, the motion will no longer be random as they will always try to drift towards positive terminal of the battery.
Electrons (negative charges) are moving inside conductor randomly due to thermal agitation and collide with positive ions continuously.
The average distance travelled by the free electrons between two successive collision s is called its mean free path.
And the time taken between the two successive collisions of the electrons is called the relaxation time.