PHY/VI/12 Student's Copy
2 0 1 8
6th Semester
PHYSICS
TWELFTH PAPER
Solid-state Physics—II
Pre-revised
Full Marks 55
Time 2½ hours
PART A—OBJECTIVE
Marks 20
The figures in the margin indicate full marks for the questions
SECTION—A
Marks 5
Tick the correct answer in the brackets provided 1×5=5
1. Quantum of elastic vibration is
phonon photon
graviton meson
2. Susceptibility of a diamagnetic material is
very large small but negative
small but positive zero
3. The process of producing electric dipoles inside the dielectric by an
external electric field is
dipole moment polarization
susceptibility magnetization
/494 1 Contd.
4. Separation between valence band and conduction band is measured in
volts metres
metre-1 electron volts
5. The superconducting state is perfectly in nature.
paramagnetic diamagnetic
ferromagnetic ferrimagnetic
SECTION—B
Marks 15
Answer the following questions 3×5=15
1. Compute the cut-off frequency for a linear diatomic lattice if the velocity of
sound and interatomic spacing in the lattice are 3 ´103 ms-1 and
3 ´10-10 m respectively.
2. Explain the domain theory of ferromagnetism.
3. Obtain an expression for London penetration depth.
4. Explain the origin of energy gap.
5. Explain what is meant by polarization in dielectrics.
PART B—DESCRIPTIVE
Marks 35
The figures in the margin indicate full marks for the questions
1. Show that the dispersion relation for the lattice waves in a monatomic
linear lattice of mass spacing a and the nearest neighbour interaction C
is w 2 1
2
C
M
sin ka
r
where w is the angular frequency and
r
k the wave
vector. Discuss the dispersion behaviour at low frequencies and high
frequencies. 4+1½+1½=7
PHY/VI/12 2 Contd.
OR
Discuss the vibrational modes of a diatomic linear lattice and also discuss
the two branches of the dispersion relation curve.
2. Using quantum theory, obtain an expression for paramagnetic
susceptibility. What is the difference with Langevin's classical theory?

OR
Discuss the formation and significance of the hysteresis loop. Show that the
area under the hysteresis loop denotes the energy dissipated per unit
volume of materials during each magnetizing cycle.
3. What is depolarization field? Obtain the expression for local electric field at
an atom in dielectric material.
OR
Write short notes on Lorentz field and Clausius-Mosotti relation.
3½+3½=7
4. What is the basic assumption of Kronig-Penney model? Discuss the results
of Kronig-Penney models for small barrier strength and
extremely large barrier strength 2+2½+2½=7
OR
Discuss the concept of effective mass of an electron. Explain how electron in
a crystal can behave dynamically like a particle with variable mass.
5. Give an elementary treatment of BCS theory of superconductivity. Explain
how the superconducting energy gap varies with temperature.
OR
Define superconductivity. What are type I and type II superconductors?

Explain briefly certain isotope effect of superconducting material. 2