Solid State Physics — DU B.Sc. (Prog.) Physical Science courses pertaining to Electronics Previous Year Question Papers

Attempt four questions in all. (b) What are Brillouin Zones? Draw the first three Brillouin Zones for a two-dimensional square lattice. (8) (a) Consider a one-dimensional diatomic linear chain consisting of two types of atoms with masses mı and ma, arranged alternately and connected by identical springs of spring constant C. Derive the dispersion relation for lattice vibrations in the crystal Sketch the dispersion curves (o versus k) for acoustic and optical branches. (b) A dielectric material is placed in an external electric field of 2.0x105 V/m with polarization 3.0 × 10-3 C/m?. Calculate the local electric field acting at an atom. (3) Q. 4 (a) What is the effective mass of an electron? Derive the expression for the effective mass of an electron and explain how it differs from the mass of a free electron. Draw the variation of (i) Energy, (ii) velocity of electron and (iii) effective mass of electron with respect to the wave vector k. (10) (b) Copper has an FCC structure and the atomic radius is 1.245 Å. Determine the interplanar spacing for (111) planes. Q. 5 (a) Explain the Langevin theory of paramagnetism and derive the expression for the magnetic susceptibility of a paramagnetic substance. Explain its dependance on temperature. (12) (b) Define polarizability and state the Claussius-Massoti relation. (3)