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Code No: R5100203
I B.Tech (R05) Supplementary Examinations, June 2009 APPLIED PHYSICS (Common to Electrical & Electronics Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, 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.
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[10]
2. (a) Explain Bragg’s law of X-ray diffraction. [6] (b) Describe Laue’s method for determination of crystal structure. [6] (c) A beam of X-rays is incident on a NaCl crystal with lattice spacing 0.282 nm. Calculate the wavelength of X-rays if the first order Bragg reflection takes place at a glancing angle of 8o 350 . Also calculate the maximum order of diffraction possible. [4] 3. (a) Distinguish between Frenkel and Schottkey defects. (b) Derive an expression for the energy change due to creation of vacancies inside a solid.
[8] [8]
4. (a) What is Fermi level? [2] (b) Explain Fermi-Dirac distribution for electrons in a metal. Discuss its variation with temperature. [8] (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 [6] 5. (a) What is Piezo-electricity? [4] (b) Obtain an expression for the internal field seen by an atom in an infinite array of atoms subjected to an external field. [8] (c) The dielectric constant of He gas at NTP is 1.0000684. Calculate the electronic polarizability of He atoms if the gas contains 2.7× 1025 atoms per m3 . [4] 6. (a) Name two superconducting materials with their transition temperatures. (b) Describe the effect of magnetic field and isotropic effect on superconductivity.
[6] [6]
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(c) For a specimen of V3 Ga, the critical fields are respectively 1.4 × and 4.2 × 105 amp/metre for 14 K and 13 K. Calculate the transition temperature and critical fields at 0 K and 4.2 K. [4] 7. (a) Describe the principle, construction and working of He-Ne laser. (b) Write the applications of laser.
[10] [6]
8. (a) Explain the terms ‘numerical aperture’ and ‘acceptance angle’. [6] (b) With the help of a suitable diagram explain the principle, construction and working of an optical fibre as a wave guide. [6] (c) An optical fibre 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. [4] ?????
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Code No: R5100203
I B.Tech (R05) Supplementary Examinations, June 2009 APPLIED PHYSICS (Common to Electrical & Electronics Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, Electronics & Computer Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Define crystal lattice, unit cell, lattice parameter and coordination number. (b) Consider a Body Centered Cubic lattice of identical atoms having radius R. Compute i. the number of atoms per unit cell ii. the coordination number and iii. the packing fraction. 2. (a) Explain how the X-ray diffraction can be employed to determine the crystal structure. (b) The distance between (110) planes in a Body-Centered Cubic structure is 0.203 nm. What is the size of the unit cell? What is the radius of the atom?
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3. (a) Derive time independent Schrodinger’s wave equation for a free particle. [8] (b) Explain the physical significance of wave function. [4] −10 (c) An electron is bound in a one-dimensional infinite well of width 1 × 10 m. Find the energy values in the ground state and first two excited states. [4] 4. (a) Explain the origin of energy bands in solids. (b)
(c) 5. (a) (b)
[6] 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. [6] Find the temperature at which there is 1% probability of a state with an energy 0.5 eV above Fermi energy. [4] ¡ ε +2 ¢ What is local field? Explain. Show that the local electrical field Eloc is given byEloc = E r3 where E is the applied electric field. [10] An air-filled capacitor has a capacitance of 1.3 pf. The separation of the plates is halved and a dielectric is inserted between them. The new capacitance is 3.9 pf. Find the dielectric constant of the dielectric. [6]
6. (a) Write a note on flux quantization. (b) Explain the principle of a SQUID. (c) The London penetration depths for Pb at 3 K and 7.1 K are respectively 39.6 nm and 173 nm. Calculate its transition temperature and penetration depth at 0 K.
[6] [6] [4]
[6] 7. (a) What do you understand by population inversion? How it is achieved? (b) Derive the relation between the probabilities of spontaneous emission and stimulated emission in terms of Einstein’s coefficients. [10] 8. (a) What is the principle of optical fibre communication? Explain. (b) Discuss various types of fibres for light wave communication. ?????
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Code No: R5100203
I B.Tech (R05) Supplementary Examinations, June 2009 APPLIED PHYSICS (Common to Electrical & Electronics Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, Electronics & Computer Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Define coordination number and packing factor of a crystal. (b) Describe the FCC crystal structure. (c) Obtain an expression for the packing factor of FCC structure.
[4] [6] [6]
2. (a) What are Miller indices? Draw (111) and (110) planes in a cubic lattice. [6] (b) Explain Bragg’s law of X-ray diffraction. [6] o (c) The Bragg’s angle for reflection from the (111) plane in a FCC crystal is 19.2 for an X-ray wavelength of 1.54 A.U. Compute the cube edge of the unit cell. [4] 3. (a) Explain the influence of point defects in crystals and how do they affect the properties of materials. (b) Obtain an expression for the energy required to create a vacancy in the crystal.
[8] [8]
4. (a) Explain the origin of energy bands in solids. [6] (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. [6] (c) Find the temperature at which there is 1% probability of a state with an energy 0.5 eV above Fermi energy. [4] 5. (a) Compare the relative merits of soft and hard magnetic materials. (b) Define coercivity and retentivity. (c) Explain the hysteresis curve and magnetic materials.
[6] [4] [6]
6. (a) Explain London penetration depth. (b) Describe the Superconducting Quantum Interference Device (SQUID). Mention their applications. (c) Estimate the London penetration depth from the following data: Critical temperature = 3.7 K Density = 7.3 × 103 kg/m3 Atomic weight = 118.7 Effective mass = 1.9 times the free electron rest mass.
[6] [6]
7. (a) Explain the terms: i. Absorption. ii. Spontaneous emission. iii. Stimulated emission. iv. Pumping mechanism. v. Population inversion. vi. Optical cavity. (b) Mention the medical applications of lasers.
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8. (a) Distinguish between light propagation in i. step index and ii. graded index optical fibres. [6] (b) Discuss the various advantages of communication with optical fibres over the conventional coaxial cables.[6] (c) Calculate the refractive indices of core and cladding of an optical fibre with a numerical aperture of 0.33 and their fractional difference of refractive indices being 0.02. [4] ?????
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Code No: R5100203
I B.Tech (R05) Supplementary Examinations, June 2009 APPLIED PHYSICS (Common to Electrical & Electronics Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, Electronics & Computer Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Define coordination number and packing factor of a crystal. (b) Describe the FCC crystal structure. (c) Obtain an expression for the packing factor of FCC structure.
[4] [6] [6]
2. (a) Draw the (112) and (120) planes, and the [112] and [120] directions of a simple cubic crystal. [4] (b) Derive an expression for the inter-planar spacing in the case of a cubic structure. [8] (c) Calculate the glancing angle at (110) plane of a cubic crystal having axial length 0.26 nm corresponding to the second order diffraction maximum for the X-rays of wavelength 0.065 nm. [4] 3. (a) Give an account on the effects of dislocations on the properties of solids. (b) Explain the significance of Burgers vector.
[10] [6]
4. (a) Explain the origin of energy bands in solids. [6] (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. [6] (c) Find the temperature at which there is 1% probability of a state with an energy 0.5 eV above Fermi energy. [4] 5. (a) Define the terms permeability (µ), susceptibility (χ ), magnetic induction (B), magnetic field (H), and magnetization (M) with reference to magnetism. Obtain a relation between magnetic susceptibility, magnetization, and magnetic field. [12] (b) A circular loop of copper having a diameter of 10 cm carries a current of 500 mA. Calculate the magnetic moment associated with the loop. [4] 6. (a) Explain the effect of temperature and dopent on the Fermi level in a semiconductor. [10] (b) i. Find the conductivity of intrinsic silicon at 300 K. It is given that ni at 300 K in silicon is 1.5 × 1016 /m3 and the mobilities of electrons and holes in silicon are 0.13 m2 /V-s and 0.05 m2 /V-s respectively. ii. If donor type impurity is added to the extent of one impurity atom in 108 silicon atoms, find the conductivity. iii. If acceptor type impurity is added to the extent of one impurity atom in 108 silicon atoms, find the conductivity. [6] 7. (a) Explain with a neat diagram i. absorption ii. spontaneous emission and iii. stimulated emission of radiation. (b) What is population inversion? How it is achieved by optical pumping?
[8] [8]
8. (a) Explain the principle behind the functioning of an optical fibre. [4] (b) Derive an expression for acceptance angle for an optical fibre. How it is related to numerical aperture? [8] (c) An optical fibre has a numerical aperture of 0.20 and a cladding refractive index of 1.59. Find the acceptance angle for the fibre in water which has a refractive index of 1.33. [4] ?????