Download King Abdulaziz University, Department of Physics, Jeddah

King Abdulaziz University, Department of Physics, Jeddah
HOMEWORK ASSIGNMENT #7, PHYSICS 471, SPRING, 2013
Deadline: 9 AM, Saturday, (Jumaada II 24, 1434) May 4, 2013
Name:…………………………………..……... ID:……………….. Signature:………………..
1- What are achievements of the quantum Fermi gas model?
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Successful prediction of basic thermal properties of metals
Successful prediction of conductivity
2- What are failures of the quantum Fermi gas model?
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Failure to predict a positive Hall coefficient
No understanding whatever of insulators
3- What is the major assumption of classical free electron model (Drude)?
Metal is an array of positive ions with electrons that are free to roam through the ionic array.
4- What is the major assumption of quqntum mechanical free electron model (Sommerfeld)?
Electrons are in a potential well with infinite barriers: They do not leave metal, but free to roam
inside.
5- Regarding electrons, what is the assumption of classical free electron model (Drude)?
Electrons are treated as an ideal neutral gas, and their total energy depends on the temperature
and applied field.
6- Regarding electrons, what is the major assumption of quqntum mechanical free electron
model (Sommerfeld)?
Electron energy levels are quantized and well defined, so average energy of electron is not equal
to (3/2)kBT.
7- In classical model, in the absence of an electrical field, what will happen to the electrons?
In the absence of an electrical field, electrons move with randomly distributed thermal velocities.
8- In quantum mechanical model, according to what electrons occupy energy?
Electrons occupy energy levels according to Pauli’s exclusion principle.
9- In brief, write the limitations of the FEG model of Drude?
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The positive ions act only as scattering centers and is assumed to have no effect on the
motion of electrons between collisions
Interactions between electrons are ignored
10- Describe the movement of electrons in the two models (Drude & Sommerfeld)?
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For Drude: Large number of particles moving slowly.
For Sommerfeld: Small effective number of particles moving very fast, due to special
quantum mechanical constraints