Free electron theory

Electrons travel at the speed of light. However the speed is slowed down heavily in a conductor and they travel with an average velocity called drift velocity due to the combination of electric field and collisions.

The Fermi level is the surface level at the lowest available energy states where no electrons will have enough energy to rise above the surface. Only those electrons very close to the Fermi energy can participate in ordinary electrical conduction. The conductivity of a material depends on the drift speed and the fermi speed.

Also learn 

Matthiessans rule

Wiedmann Franz law

The contents given below are just scribbling notes

From Ohms law



I=EA/r -------1

Current Density, J=nevd

I=nevdA  ------------2

From 1 and 2

r=E/(nevd)       ------------3

Acceleration experienced by free e-s is =vd/t


vd=eE.t/me ---------------4

From 3

r=me/(ne2t)              ------------5

Mean free path, l=vav.t --------------6

From 5 and 6