Solid State Physics

Set No.1

Code No: RR10201 I B.Tech.

Regular Examinations, June -2005 SOLID STATE PHYSICS ( Common to Electrical & Electronic Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, Electronics & Telematics, Electronics & Computer Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Explain the terms i. basis ii. space lattice and iii. unit cell. (b) Describe the seven crystal systems with diagrams. 2. (a) What are Miller indices? How are they obtained? (b) Explain Schottky and Frankel defects with the help of suitable figures. 3. (a) Show that the wavelength of an√electron accelerated by a potential difference ‘V’ volts, is λ = 1.227 × 10−10 / V m for non-relativistic case. (b) Describe an experiment to establish the wave nature of electrons. (c) Explain the difference between a matter wave and an electromagnetic wave. 4. (a) Explain the origin of energy bands in solids. (b) Assuming the electron - lattice interaction to be responsible for scattering of conduction electrons in a metal, obtain an expression for conductivity in terms of relaxation time and explain any three draw backs of classical theory of free electrons. (c) Find the temperature at which there is 1% probability of a state with an energy 0.5 eV above Fermi energy. 5. (a) Explain Clausius - Mosotti relation in dielectrics subjected to static fields. (b) What is orientational polarization. Derive an expression for the mean dipole moment when a polar material is subjected to an external field. (c) The relative dielectric constant of sulphur is 3.75 when measured at 27 o C Assuming the internal field constant γ = 1/3 calculate the electronic polarisability of sulphur if its density at this temperature is 2050 kg/m3 . The atomic weight of sulphur being 32. 6. (a) Draw the B-H curve for a ferro-magnetic material and identify the retentivity and the coersive field on the curve. 1 of 2

Set No.1

Code No: RR10201 (b) What are paramagnetic and diamagnetic materials.

(c) An atom contains 10 electrons revolving in a circular path of radius 10−11 m. Assuming homogeneous charge distribution, calculate the orbital dipole moment of the molecule in Bohr magneton. 7. (a) When donor impurities are added to a semiconductor, the concentration of holes decreases. Explain with reasons. (b) Show that the Fermi level is nearer to the conduction band in a n-type semiconductor. Discuss the variation of conductivity with temperature of an n-type semiconductor. 8. (a) Explain the terms ‘numerical aperture’ and ‘acceptance angle’. (b) With the help of a suitable diagram explain the principle, construction and working of an optical fiber as a waveguide. (c) An optical fiber has a core material of refractive index of 1.55 and cladding material of refractive index 1.50. The light is launched into it in air. Calculate its numerical aperture. ?????

2 of 2

Set No.2

Code No: RR10201 I B.Tech.

Regular Examinations, June -2005 SOLID STATE PHYSICS ( Common to Electrical & Electronic Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, Electronics & Telematics, Electronics & Computer Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Show that FCC is the most closely packed of the three cubic structures by working out the packing factors. (b) Describe the structure of NaCl. 2. (a) What are Miller indices? How are they obtained? (b) Explain Schottky and Frankel defects with the help of suitable figures. 3. (a) Explain the concept of matter waves. (b) Describe Davison and Germer’s experiment and explain how it enabled the verification of wave nature of matter. (c) Calculate the velocity and kinetic energy of an electron of wavelength 1.66 × 10−10 m. 4. (a) What is Fermi level? (b) Explain Fermi-Dirac distribution for electrons in a metal. Discuss its variation with temperature. (c) Calculate the free electron concentration, mobility and drift velocity of electrons in aluminum wire of length of 5 m and resistance 0.06 Ω carrying a current of 15 A, assuming that each aluminum atom contributes 3 free electrons for conduction. Given: Resistivity for aluminum = 2.7× 10−8 Ω-m. Atomic weight = 26.98 Density = 2.7 × 103 kg/ m3 Avagadro number = 6.025 × 1023 5. (a) Explain briefly the classification of ferro-electric materials. (b) What is meant by a local field in a solid dielectric. Derive an expression for the local field for structures possessing cubic symmetry. (c) There are 1.6× 1020 NaCl molecules / m3 in a vapour. Determine the orientational polarization at room temperature if the vapour is subjected to an electric field 5000 V/cm. Assume that the NaCl molecule consists of sodium and chlorine ions separated by 0.25 nm 1 of 2

Set No.2

Code No: RR10201

6. (a) Explain clearly the difference between hard and soft magnetic materials. What are mixed ferrites? Mention their uses. (b) How ferrites are superior to ferromagnetic materials? 7. (a) Distinguish between metals, semiconductors and insulators. (b) Explain the effect of temperature on resistivity of a semiconductor. (c) Derive an expression for the number of electrons per unit volume in the conduction band of an intrinsic semiconductor. 8. (a) Explain the characteristics of a laser beam. (b) Mention any two applications of laser, each in the field of scientific research, engineering and medicine. (c) Describe the construction and working of a Ruby laser. ?????

2 of 2

Set No.3

Code No: RR10201 I B.Tech.

Regular Examinations, June -2005 SOLID STATE PHYSICS ( Common to Electrical & Electronic Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, Electronics & Telematics, Electronics & Computer Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Explain the terms i. basis ii. space lattice and iii. unit cell. (b) Describe the seven crystal systems with diagrams. 2. (a) What are Miller indices? How are they obtained? (b) Explain Schottky and Frankel defects with the help of suitable figures. 3. (a) Explain the concept of matter waves. (b) Describe Davison and Germer’s experiment and explain how it enabled the verification of wave nature of matter. (c) Calculate the velocity and kinetic energy of an electron of wavelength 1.66 × 10−10 m. 4. (a) What is Fermi level? (b) Explain Fermi-Dirac distribution for electrons in a metal. Discuss its variation with temperature. (c) Calculate the free electron concentration, mobility and drift velocity of electrons in aluminum wire of length of 5 m and resistance 0.06 Ω carrying a current of 15 A, assuming that each aluminum atom contributes 3 free electrons for conduction. Given: Resistivity for aluminum = 2.7× 10−8 Ω-m. Atomic weight = 26.98 Density = 2.7 × 103 kg/ m3 Avagadro number = 6.025 × 1023 5. (a) Discuss the variation of spontaneous polarization of Roschelle salt with temperature. (b) Obtain an expression for the static dielectric constant of a monoatomic gas. (c) Explain the phenomenon of anomalous dielectric dispersion. 1 of 2

Set No.3

Code No: RR10201

6. (a) What are the characteristics of soft magnetic materials? (b) What is ferro-magnetic curie temperature? Discuss the behaviour of a ferromagnetic material below the curie temperature. (c) The magnetic field in the interior of a certain solenoid has the value of 6.5 × 10−4 T when the solenoid is empty. When it is filled with iron, the field becomes 1.4 T. Find the relative permeability of iron. 7. (a) Explain d.c. Josephson effect. (b) Describe the BCS theory of superconductivity. (c) Write applications of superconductivity. 8. (a) Describe the principle, construction and working of a semiconductor laser. (b) Write the applications of laser. ?????

2 of 2

Set No.4

Code No: RR10201 I B.Tech.

Regular Examinations, June -2005 SOLID STATE PHYSICS ( Common to Electrical & Electronic Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, Electronics & Telematics, Electronics & Computer Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Explain the formation of an ionic crystal. (b) Derive an expression for the cohesive energy of an ionic crystal. (c) Calculate the cohesive energy of NaCl from the following data: Equilibrium separation between the ion pair = 0.281 nm. Ionization energy of Na = 5.14 eV. Electron affinity of Cl = 3.61 eV. Born repulsive exponent = 9 Madelung constant = 1.748. 2. (a) What are Miller indices? How are they obtained? (b) Explain Schottky and Frankel defects with the help of suitable figures. 3. (a) Derive time independent Schrodinger’s wave equation for a free particle. (b) Explain the physical significance of wave function. (c) An electron is bound in a one-dimensional infinite well of width 1 × 10−10 m. Find the energy values in the ground state and first two excited states. 4. (a) Explain the origin of energy bands in solids. (b) Assuming the electron - lattice interaction to be responsible for scattering of conduction electrons in a metal, obtain an expression for conductivity in terms of relaxation time and explain any three draw backs of classical theory of free electrons. (c) Find the temperature at which there is 1% probability of a state with an energy 0.5 eV above Fermi energy. 5. (a) What are the important characteristics of ferro-electric materials? (b) Describe the possible mechanism of polarization in a dielectric material. (c) The dielectric constant of Helium gas at NTP is 1.0000684. Calculate the electronic polarisability of He atoms if the gas contains 2.7 × 1025 atoms / m3 . 1 of 2

Set No.4

Code No: RR10201

6. (a) Draw the B-H curve for a ferro-magnetic material and identify the retentivity and the coersive field on the curve. (b) What are paramagnetic and diamagnetic materials. (c) An atom contains 10 electrons revolving in a circular path of radius 10−11 m. Assuming homogeneous charge distribution, calculate the orbital dipole moment of the molecule in Bohr magneton. 7. (a) Derive the continuity equation for electrons. (b) What physical law is manifested in the continuity equation. (c) Find the diffusion coefficient of electrons in silicon at 300 K if µ is 0.19 m2 /V-S. 8. (a) Describe the construction of a typical optical fiber and give the dimensions of the various parts. (b) Define the acceptance angle and numerical aperture. Obtain an expression for the numerical aperture of an optical fiber. (c) Calculate the numerical aperture and acceptance angle for an optical fiber with core and cladding refractive indices being 1.48 and 1.45 respectively. ?????

2 of 2