# Mumbai University Previous year question papers

## I Year Examination Dec 2007

## Applied Physics

N.H. : (1) Question No. 1 is compulsory.

(2) Attempt any four questions out of remaining six questions.

(3) Assume suitable data if required.

1. Attempt any five :-

(a) Find the Miller Indices for a plane with the following set of intercepts (a/2, b, 00). Draw the plane for the same.

{b) What is mobility and conductivity of charge carriers? Which has the greater mobility, electron or hole and why?

(c) Calculate the change in intensity level when the intensity of sound increases 1000 times its original intensity.

.(d) Explain the significance of critical temperature in a superconductor.

(e) Find the echo time of ultrasonic pulse which is traveling with the velocity 5.9 x 103m/sec in mild steel. The correct thickness measured by gauge meter is 18 mm.

(f) Explain how the phase difference between two frequencies is measured, Using C.R.a.

(g) Calculate the distance between two atoms of a basis of the diamond structure, if the lattice constant of structure is 5 A

(h) Explain the different phases of Liquid Crystals.

2.(a) What is magnetostriction effect? Draw the diagram of maghetostriction Oscillator. Explain its working.

(b) What is the importance of Hall Effect in a semiconductor? In a Hall effect experimental set up, a sample of n type Ge has an donor pensity of 102 11m3.Find the Hall voltage developed if the magnetic field used is 0.6 T. Given J is 500 A/m2 and the thickness of sample is 5 mm.

3. (a) Describe the hcp structure. What is its coordination number, atomic radius and number of atoms owned by the unit cell? Also find its packing factor.

(b) Find the natural frequency of vibration of a Quartz plate of thickness 1.8 mm. Given Young’s modulus for quartz is 8 x 1010N/m2. D.ensity of quartz is 2650 kg/m3. Calculate the change in the thickness required if the same plate is used to produce ultrasonic waves of frequency 2MHz.

4.(a) What are Type I and Type II superconductors? Which type of superconductor does not follow the meissner effect strictly?

(b) An X-Ra~ beam of wavelength 0.71A .is diffracted by a Fcc crystal of density 1.99 x 10 kg/m3. Calculate the interplanar spacing for (2 0 0) planes and the glancing angle for the second order reflection from these planes. Given mol. wt of the crystal is 74.6 and Avagadros no. is 6.023 x 1026/kg mole. .

5. (a) Explain in detail the conditions necessary for good acoustical design of an auditorium.

(b) Ni has FCC structure. Its lattice constant is 3.52A, atomic wt. of Ni is 58.71. Given Avagadros no. is 6.023 x 1026/kgmole. Calculate its radius, A P F and density.

6. (a) Explain the basic principles of electrostatic and magnetostatic focusing..

(b) The resistivity of Cu is 1.72 x1 0-8 ohm m. Calculate the mobility of electrons in Cu. Given that the number of electrons per unit volume is 10-41 x 1028/m3.

7. (a) Show that for an intrinsic semiconductor, the Fermi level lies half way between conduction and valence band. With the help of energy band diagram, show the Fermi level positions for nand p type semiconductors at aK and tK.

(b) State Sabine’s Formula explaining the terms involved in it. A hall of length 20m, breadth 15m and ht 10m has a reverberation time of 2 sees. Calculate the average coefficient of absorption.