Question Paper: Applied Physics 1 : Question Paper May 2013 - First Year Engineering (Semester 1) | Mumbai University (MU)
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## Applied Physics 1 - May 2013

### 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) Draw unit cell showing position of the atoms for:
a) Monoatomic BCC crystal
b) Monoatomic SC crystal
c) CsCl crystal
(3 marks)
1(b) Fermi level in K is 2.1 eV. What are energies for which the probabilities of occupancy at 300K are 0.99 and 0.01 ?(3 marks) 1(c) Draw energy band diagram of an unbiased p-n junction and mark the barrier potential and depletion region.(3 marks) 1(d) Write the relation between polarization and dielectric susceptibility and the relation between dielectric susceptibility and dielectric constant.(3 marks) 1(e) Why soft magnetic materials are used in core of transformers?(3 marks) 1(f) Calculate the change in intensity level the intensity of sound increases 1000 times its original intensity.(3 marks) 1(g) Explain Cavitation effect.(3 marks) 2(a) Derive an expression for Fermi level for an intrinsic semiconductor. Draw the energy level diagram to show effect of
(1)Temperature
(2) impurity atom concentration in low range and
(3) impurity atom concentration in high range.
(8 marks)
2(b) An element crystal has a density of 8570 kg/m3 packing fraction is 0.68 . Determine mass of an atom if nearest neighbour distance is 2.86 Å(7 marks) 3(a) Prove that in a ferromagnetic material, power loss per unit volume in a hysteresis cycle is equal to area under hysteresis loop.
An iron ring of mean circumferential length 30 cm and cross section 1cm2, is wound around uniformly with 300 turns of wire. When a current of 0.032 Amp flows in it, the flux produced in the ring is 2 x 10-6 Wb. Find the flux density, magnetic field intensity and permeability of iron.
(8 marks)
3(b) Derive Bragg's law. Explain why x-rays and not ? rays are used for crystal structure analysis. What data about crystal structure can be obtained from the x-ray diffraction pattern of a crystal?(7 marks) 4(a) Find out critical radius ratio of an ionic crystal in ligacy 6 configuration. What is maximum size of cation in ligacy 6 configuration when radius of anion is 2.02 Å(5 marks) 4(b) In an n-type semiconductor the fermi level lies 0.4eV below conduction band. If concentration of donor atom is doubled, find the new position of the Fermi Level w.r.t. the conduction band.(5 marks) 4(c) Explain origin of electronic, ionic and oriental polarization and temperature dependence of respective polarizability.(5 marks) 5(a) Find out the intercepts made by the plane (1 0 1) and (4 1 4) in a cubic unit cell. Draw [1 2 1] and [1 2 4] in a cubic unit cell.(5 marks) 5(b) A bar of n type Ge of size 0.010m x 0.001m x 0.001m is mounted in magnetic field of 2*10-1T. The electron density in the bar is 7 x 1021/m3. If one millivolt is applied across long ends of the bar, determine the current through the bar and the voltage between Hall electrodes placed across the short dimensions of the bar. Assume ? e=0.39 m2/vs(5 marks) 5(c) Define reverberation time . Write sabine's formula explaining each term. What are the factors which determine average absorption co-efficient of a material(5 marks) 6(a) Explain difference between three liquid crystals w.r.t the order in arrangement of molecules with the help of diagram. Which property of liquid crystal is used for display?(5 marks) 6(b) How is a p-n junction diode used to generate a potential difference in photovoltaic solar cell ?(5 marks) 6(c) What is piezoelectric effect. Explain the working of piezoelectric Oscillator used to produce ultrasonic wave. (5 marks)

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