RGU Question Paper Physics Semester VI 2021: Solid State Physics (Old)

 JUNE-2021

B. Sc. (VI Semester) Examination

PHYSICS

Paper: PHY-362 (Old Course)

(Solid State Physics)

Full Marks : 80

Pass Marks : 35%

Time : Three Hours

Note: 1. Answer any five questions. All questions have equal marks.

1. (a) What do you mean by packing fraction in crystals? Calculate the packing fraction of a body centred cubic lattice (BCC). 2+4= 6

(b) Explain the evolution of hexagonal closed pack structure. 4

(c) Define Miller indices. Find out the Miller indices of a plane that cuts x, y, z axes at 4, 2, 1 units and draw the corresponding plane. 2+2+2= 6

2. (a) Describe Bragg’s treatment for interpreting Xdiffraction from crystal planes. From Bragg’s condition prove that X-rays are suitable electromagnetic waves to observe diffraction pattern from crystals. 4+2= 6

(b) A beam of X-ray of wavelength 0.071 nm is diffracted by (110) plane of rock salt with lattice constant 0.28 nm. Find out the glancing angle for the 2nd order diffraction pattern. 4

(c) Define cohesive energy.Explain how van der Waal bonding can be formed in inert gases. 6

3. (a) Write four basic assumptions of free electron theory. Write two merits and demerits of this theory. 4+2+2= 8

(b) The density of Ag is 10.5 x ${10}^3$ kg/m3. The atomic weight of Ag is 107.9. Assuming each Ag atom provides one conduction electron, calculate the density of the electrons. Find out the mobility of the electrons in Ag if conductivity at 200 C is 6.8 x ${10}^7$ $oh{m}^{-1}{m}^{-1}$. 2+2= 4

(c) Plot the variation of energy and wave vector (E-k diagram) of an electron in periodic potential. How the velocity of such an electron varies compared to a free electron. 2+2= 4

4. (a) What is diamagnetism? Why diamagnetic materials negative susceptibility? 1+3= 4

(b) Discuss the origin of domain structure under the light of energy minimization concept. 4

(c) State two hypothesis of Weiss theory of ferromagnetism. 4

(d) $DY{3}^{+}$ has outer electronic configuration of $4f^{9}6s^0$ with 5 unpaired electrons. Calculate the magnetic susceptibility for a salt containing 1 kg.mole of $DY{3}^{+}$ ions at 300 K. 4

5. (a) Write any three main characteristics of superconductors. What are soft and hard superconductors? State the advantage of hard superconductors over soft one. 3+2+1= 6

(b) Plot the variation of specific heat with temperature for a superconductor. What do you mean by persistent current? 2+2= 4

(c) For a specimen of V3Ga, the critical fields are respectively 1.4 x ${10}^5$ and 4.2 x ${10}^5$ A/m for 14 K and 13 K. calculate the transition temperature and critical field at O K. 3+3= 6

6. (a) How Debye’s Model of specific heat is more acceptable over Einstein’s theory. 4

(b) Establish the dispersion relation for one dimension monoatomic lattice. 6

(c) What do you mean by acoustic and optical modes of vibration for one dimensional diatomic lattice vibration? What is the significance of the forbidden gap in the dispersion relation in this case? 4+2= 6

7. Write short notes on any four: 4x4= 16

(a) Wiedemann-Franz Law

(b) Extrinsic semiconductor

(c) Bohr magneton

(d) Coherence length

(e) Phonons