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Tuesday, 20 November 2012

Solid state physics-Model question paper for MSc/PhD

1(a) Outline Bohr’s theory of hydrogen atom and derive an expression for the radius of the first Bohr orbit for the normal hydrogen atom. (6 Marks)
(b) What are ionic crystals? Explain the formation of an ionic crystal and obtain an expression for its cohesive energy. (6 Marks)
(c) Calculate the potential energy of the system of Na+ and Cl- ions when they are 0.2 nm apart. (4 Marks)
(d) The atomic weights and densities of aluminium and copper are 26.98 and 63.54 and 2700 kg/m3 and 8960 kg/m3 respectively. Calculate the number of atoms present in unit volume of aluminium and copper. (4 Marks)
2(a) Write a note on various symmetry operations present in a crystal. (4 Marks)
(b) What are Miller indices? Illustrate with examples. Draw (112) and (232) planes. (6 Marks)
(c) Explain with neat sketches the different imperfections in a crystal. (6 Marks)
(d) The fraction of vacancy sites in a metal is 10-10 at 5000C. What will be the fraction of vacancy sires at 10000C.? (4 Marks)
3(a) Discuss a method of investigating the structure of a single crystal using X-rays. (6 Marks)
(b) Write a note on relaxation time. (4 marks)
(c) Explain quantum mechanical tunneling in solids and its significance. (6 Marks)
(d) A copper wire whose diameter is 0.16 cm carries a steady current of 10 amp. What is the current density in the wire? Also calculate the drift velocity of the electrons in copper. (4 Marks)
4(a) Discuss salient features of Debye’s theory of specific heat of solids. (4 Marks)
(b) Discuss the domain structure in ferromagnetic materials. Explain the reasons for the strong ferromagnetic property found in iron, cobalt and nickel. (6 Marks)
(c) Discuss Langevin’s theory for a paramagnetic gas and obtain an expression for the paramagnetic susceptibility of the gas. What are the main drawbacks of this theory? (6 Marks)
(d) Compute Debye temperature for diamond whose atomic weight and Young’s modulus are 12 and 1012 Nm2 respectively. Density of diamond is 3500 kg/m3. (4 Marks)
5(a) Derive the London equations and explain the term coherent length. Explain 1-2-3 superconductors. (6 Marks)
(b) Discuss d.c and a.c Josephson effect and explain their importance. (6 Marks)
(c) Explain the properties of Cooper pairs. (4 Marks)
(d) The London penetration depths for Pb at 3K and 7.1K are respectively 39.6nm and 173 nm. Calculate its transition temperature as well penetration depth at 0K. (4 Marks)
6(a) Distinguish between Zener breakdown and avalanche breakdown. (4 Marks)
(b) Derive an expression for the density of holes in an intrinsic semiconductor. Suggest a method for evaluating the energy gap of the semiconductor. (6 Maks)
(c) Discuss the physical origin and uses of Hall effect. (6 Marks)
(d) The room temperature electron mobility in GaAs is 0.08 m2V-1S-1. Calculate the diffusion constant of electrons. (4 Marks)
7(a) What is meant by dielectric loss? State its importance. (4 Marks)
(b) How does dielectric constant of a solid containing permanent dipole vary with temperature? Illustrate your answer with an example. (6 Marks)
(c) Discuss the salient features of optical absorption in the case of metals, semiconductors and insulators. (6 Marks)
(d) A fiber optic link is operated at a wavelength of 1.3 mm. Find the maximum bit-rate of a 25 km line made from a multimodal step-index fiber. Given n1=1.46 and n2=1.46. (4 Marks)
8(a) Write notes on gaseous insulating materials and liquid insulating materials. (6 Marks)
(b) Differentiate between thermosetting resins and thermoplastic resins. (6 Marks)
(c) Write a note on laminated composites. (4 Marks)
(d) Calculate the Young’s modulus of a composite with glass fibers reinforced in phenol formaldehyde plastics. The volume fraction of plastics is 33.3%. The modulus of glass fiber is 6.9×104 MPa and that of polymers 6.9×102 MPa.  (4 Marks)

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