## 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 BaTiO_{3} (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 0.2cm^{2}. 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/m^{3}/(5 marks)
**4(c) ** If a gas contains 1.2×10^{27} atoms/m^{3} 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 cm^{2} 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)