Applied Physics 1 - Dec 2012

First Year Engineering (Semester 1)

TOTAL MARKS: 60
TOTAL TIME: 2 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Use suitable data wherever required.
(4) Figures to the right indicate full marks.

Attempt any FIVE.

1(a) Explain term lattice parameters of cubic crystal.(3 marks) 1(b) What is the probability of an electron being thermally excited to conduction band in silicon at 20^oC. The band gap energy is 1.12eV; Boltzmann constant is 1.38 x 10^-23 JIk.(3 marks) 1(c) Mobility of holes is 0.025 m² /V-sec What would be the resistivity of P-type silicon . if the Hall coefficient of the sample is 2.25 x 10^-5 m³ /C ?(3 marks) 1(d) Define dielectrics, electric dipole, polarizability.(3 marks) 1(e) Difference between soft and hard magnetic materials(3 marks) 1(f) Define Reverberation time. Write Sabine's formula and explain terms in it.(3 marks) 1(g) State the terms : magnetostriction effect; piezoelectric effect(3 marks) 2(a) Explain the formation of energy band in solids. With neat energy band diagram explain extrinsic semiconductors.(8 marks) 2(b) Draw the unit cell of HCP. What is its co-ordination number, atomic radius, effective number of atoms per unit cell. Also calculate its packing factor .(7 marks) 3(a) What is hysteresis? Draw a hysteris loop for ferromagnetic material and explain the various important points on it. What is the technical significance of the area enclosed under it. For a transformer which kind of material will you prefer-the one with small hysteresis area or the big one ?(8 marks) 3(b) Derive Bragg's law. Calculate the glancing angle on the plane (100) for a crystal of rock salt (a = 2.125 A⁰ .Consider the case of 2nd order maximum and A = 0.592 A⁰.(7 marks) 4(a) Calculate the number of atoms per unit cell of a metal having lattice parameter 2.9A⁰ and density 7.87 gm/cm3. Atomic weight of metal is 55.85, Avagadro number is 6.023 x 10²³ /gm-mole.(5 marks) 4(b) Prove that the Fermi level lies exactly at the centre of the forbidden energy gap in case of an intrinsic semiconductor.(5 marks) 4(c) Explain ionic polarization and obtain polarizability.(5 marks) 5(a) With neat diagram of a unit cell, explain the structure of BaTi0₃.(5 marks) 5(b) What is Hall effect ? Derive expression for Hall voltage.(5 marks) 5(c) Explain the absorption coeficient of a hall. Calculate the change in intensity level if the intensity of sound increases 1000 times its original intensity.(5 marks) 6(a) In what sense real crystals differ from ideal crystals? Explain the point defects in crystals.(5 marks) 6(b) Explain construction and working of a solar cell.(5 marks) 6(c) Find the natural frequency of vibration of quartz plate of thickness 2mm. Given Young's 5 modulus of quartz Y = 8 x 10¹⁰ N/m², density of quartz is 2650 kg/m³. Calculate the change in thickness required if the same plate is used to produce ultrasonic waves of frequency 3MHz.(5 marks)