7 a]Mention any four assumptions of Drude-Lorentz model and discuss the success of Quantum free electron theory.
four major assumption of Drude-Lorentz model
- Free electrons in a metal resemble molecules of a gas. Therefore, Laws of kinetic theory of gases are applicable to free electrons also. Thus free electrons can be assigned with “average velocity (\overline{c})”, “Mean free path (\lambda)” and “mean collision time (\tau)”.
- The motion of an electron is completely random. In the absence of electric field, number of electrons crossing any cross section of a conductor in one direction is equal to number of electrons crossing the same cross section in opposite direction. Therefore net electric current is Zero.
- Electric current in the conductor is due to the drift velocity acquired by the electrons in the presence of the applied electric field.
- Electric field produced by lattice ions is assumed to be uniform throughout the metal.
- The force of repulsion between the electrons and force of attraction between electrons and lattice ions is neglected.
Success of quantum free electron theory of metals
The quantum free electron theory of metals is successful in explaining the certain experimentally observed facts which the classical free electron theory failed to explain. These are the merits of QFT.
Temperature dependence of electrical conductivity
