# Mumbai University Previous year question papers

## I Year Examination June 2008

## Applied Physics

N.B.(1 ) Question No.1 is compulsory.

(2) Attempt any four questions from Question Nos. 2 to 7.

(3) Assume any suitable data wherever required.

(4) Figures to the right indicate full marks.

(5) Illustrate your answer with sketches wherever necessary.

1. (a) Explain various axes of quartz crystal.

(b) Define reverberation time. Write Sabine’s Formula and explain the terms used in it.

(c) Explain Schottky defect and Frenkel defect in ionic crystal.

(d) Find the resistivity of intrinsic Ge at 300oK. Given the density of carriers as 2.5 x 10-19 m- 3.

(Given J.le= 0.39 m2/volt-sec, J.lh= 0.19 m2 /volt-sec.

(e) Define superconductivity, critical temperature and critical magnetic field He’

2. (a) Describe NaCI structure and calculate the number of molecules per unit cell and packing factor assuming radius of Na+ is 0.98 A° and radius of CI- is 1.81 Ao.

(b) What is SONAR? Find the depth of sea water from a ship on the sea surface if the time interval of two seconds is required to receive the signal back. .Given that temperature of sea water is 20°C and salinity is 10 gm/lit.

3. (a) What is Hall effect? Derive the expression for Hall cofeficient (RH) and Hall voltage (VH) with proper diagram. .

(b) The volume of room is 600 m3. The wall area of the room is 220 m2, the floor area is 120 m2 and the ceiling area is 120 m2. The average sound absorption coefficient-

(i) For the wall is 0.03

(ii) For the ceiling is 0.8

(iii) The floor it is 0.06.

Calculate the average sound absorption coefficient and the reverberation time.

4. (a) What is Meissner effect? Explain the concept of MAGLEV trains.

(b) An X-ray machine has an accelerating potential of 25000 V. Find the shortest wavelength in the X-ray spectrum. Also evaluate its frequency as well as the energy of the photon. (Given Plank’s constant h = 6.63 x 10- 34 J.sec.)

5. (a) Explain the basic principle of magnetostaticfocussing. An electron travels with a velocity of 2.5 x 106 m/s in vacuum in a uniform magnetic field strength of 0.94 x 10- 4 wb/m2, such that velocity vector makes an angle of 30° with the field direction Determine the distance covered along the magnetic induction lines in five such revolution.

(b) What are continuous X-rays? The interplanar spacing of (110) plane is 2 AOfor a FCC crystal. Find the atomic radius.

6. (a) Explain functions of various important parts of a CRT with diagram.

(b) Derive packing factor for FCC: Cu has FCC structure and atomic radius 1.28 AO. Calculate its density if its atomic weight is 63.5. (Given Avogadro’s number = 6.023 x 1023in CGS).

7. (a)’ How does the Fermilevel change with increasing temperature in the extrinsic semiconductors (n-t~pe and p-type)? Sketch the diagram.

(b) Find the thickness of quartz plate needed to produce ultrasonic waves of frequency

(i) 3.8 MHz (ii) 300 KHz

(Density of quartz = 2650 kg/m3 Young’s modulus = 8 x 1010N/m2).