Question Paper: Applied Physics 1 : Question Paper Dec 2014 - First Year Engineering (Semester 1) | Mumbai University (MU)
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## Applied Physics 1 - Dec 2014

### 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.

### Solve any five of the following.

1(a) Identify the type of lattice and number of atoms per unit cell for CsCl and BaTiO3 (above 120°C) crystal strcuture.(3 marks) 1(b) Fermi Energy for Silver is 5.5 eV. Find out the energy for which the probability of occupancy at 300K is 0.9.(3 marks) 1(c) Explain the formation of depletion region in an unbiased p-n junction.(3 marks) 1(d) Write three distinct differences between ionic and oriental polarization. (3 marks) 1(e) Draw the variation of permeability against external magnetic field for a paramagnetic and ferromagnetic material (below Curie temperature)(3 marks) 1(f) Mention only one solution for each of the following acoustical problems in a hall. (i) Echo (ii) Dead spot and (iii) Inadequate loudness(3 marks) 1(g) What is piezoelectric effect? Why ferro-electrics are prefferred than quartz for the production of ultrasonic waves?(3 marks) 2(a)(i) What is effective mass? Why the effective mass of holes is more than the effective mass of electrons?(4 marks) 2(a)(ii) Draw the diagrams only (fully labelled and self explanatory) to show the variation of Fermi energy with (i) Temperature and (ii) Impurity concentration at high level, for an n-type semiconductor.(4 marks) 2(b) Define space lattice and basis. A metal crystallizes with a density of 2.7gm/cc and has a packing fraction of 0.74. Determine the mass of one atom if the nearest neighbour distance is 2.86Å.(7 marks) 3(a) Explain the variation in magnetic induction with magnetic field for a ferromagnetic material, using the domain theory and with the help of a graph. A magnetic field of 1800 Amp/m produces a magnetic flux of 3×10-4 Wb in an iron bar of cross-sectional area of 0.2cm2. Calculate the susceptibility and the permeability.(8 marks) 3(b)(i) How the variation in glancing angle is achieved while determining the crystal structure using (i) Rotating crystal method and (ii) Powder method?(3 marks) 3(b)(ii) Calculate Bragg angle if (200) planes of a BCC crystal with lattice parameter 2.814Å give second order reflection with X-rays of wavelength 0.71Å.(4 marks) 4(a) Calculate the critical radius ratio of an ionic crystal in ligancy 4 configuration.(5 marks) 4(b) Determine the concentration of conduction electron in a sample of Silicon if one in every million Silicon atom is replaced by a Phosphorous atom. Assume every Phosphorous atom to be singly ionized. Si has a molar mass of 0.028 kg/mole and density of 2300 kg/m3/(5 marks) 4(c) If a gas contains 1.2×1027 atoms/m3 and radius of atom is 0.53Å, then calculate electronic polarizability and dielectric constant. Find the capacitance of a parallel plate capacitor having this gas inside, with plate area 1 cm2 and plate separation 0.12 cm.(5 marks) 5(a) Find Miller Indices of a plane whose intercepts are a, 4a and a, where a is the lattice constant. Draw (102), (201] and (040) in a cubic unit cell.(5 marks) 5(b) In a semiconductor with Hall co-efficient 145cc/C having width of 2 cm and thickness 0.2 cm with a magnetic field induction of 2T along the smaller dimensions, a current of 150mA is passing. Calculate the current density and Hall voltage.(5 marks) 5(c) Write Sabine's formula explaining each term. Explain how this formula can be used for the determination of absorption co-efficient of a given material.(5 marks) 6(a) Write five distinct differences between Frenkel and Schottky defect.(5 marks) 6(b) Explain how a voltage difference is generated in a p- junction when it is used in a photovoltaic solar cell.(5 marks) 6(c) Explain the principle, construction and working of a magnetostriction oscillator to produce ultrasonic waves.(5 marks)

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