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Multiple-choice questions: (70 points) write the letter of statement that is not true:
1.
A.B.U
The Drude Model: (a) It is a classical approach using concepts from the kinetic theory
of gases. (b) A relaxation-time approximation is used where the probability of collision
is l/t. (c) No forces act on the electrons in between collisions. (d) It predicts accurately
the electronic heat capacity of metals.
2.
The Sommerfeld Model: (a) The crystal potential is replaced by an average Coulomb
potential. (b) The separation of states is so close that a continuum model can be applied.
(c) The electrons are highly localized due to a strong crystal potential. (Q) The energy of
the highest occupied state at 0 K is the Fermi energy.
3. Density of states in k-space, N(k): (a) N(k) is determined by the boundary value
conditions. (b) For lattices in any dimensions, N(k) is constant in k-space. (C) N(k)
depends on the direction and magnitude of k. (d) It is directly proportional to the
volume of the crystal.
E影響,
c
4. The Fermi surface of a metal: (a) is responsible for many of the transport properties of
the metal, (b) depends on the nature of the chemical bonds, (c) is always a sphere, (d) can
involve mixing of electron orbitals.
✓
5.
The conductivity of a material () increases with the mobility of its carriers, (b)
increases with the density of carriers, (C) it is inversely proportional to the energy gap. cogu
changes with temperature.
6.
BID
Plasmons: (a) They are an important characteristic of the Sommerfeld electron gas
model. (b) Plasmons occur spontaneously in metals. (c) They are related to charge
density oscillations. (d) The Plasmon energy is typically of the order of 10 eV.
The Fermi energy Ef in intrinsic semiconductors 8) is usually close to y E, at OK (b) it
ACiD.
can increase or decrease with temperature depending on the ratio of hole and electron
effective masses, (c) it represents the point at which the probability of occupation is 12,
even though there may not been any states with that energy, (d) its value relative to the
electronic bands must remain unaffected in the presence of defects or interfaces.
