## Applied Physics 1 - May 2015

### 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 from the following:

** 1 (a) ** Draw the following in a cubic unit cell (0 1 2), (1 2 3), [1 2 1] (3 marks)

** 1 (b) ** Define the term space lattice, unit cell and lattice parameter. (3 marks)

** 1 (c) ** Determine the lattice constant for FCC lead crystal of radius 1.746 Å and also find the spacing of (2 2 0) plane. (3 marks)

** 1 (d) ** Define: drift current, diffusion current and mobility of charge carriers. (3 marks)

** 1 (e) ** What is the probability of an electron being thermally promoted to conduction band in diamond at 27°C, if bandgap is 5.6 eV wide. (3 marks)

** 1 (f) ** Why soft magnetic materials are used in core of transformers? (3 marks)

** 1 (g) ** Calculate the electronic polarizability of A_{1}. Given number of Air atoms at NTP=2.7×10^{25}/m^{3} and dielectric constant of Ar=1.0024. (3 marks)

** 2 (a) ** Show that for intrinsic semiconductors the Fermin level lies midway between the conduction band and the valence band. Draw the energy level diagram a function of temperature for n-type of semi-conductor. (8 marks)

** 2 (b) ** Cu has FCC structure. If the interplanar spacing d is 2.08 A° for the set of (111) planes. Find the density and diameter of Cu atom. Give atomic weight of Cu is 63.54. (7 marks)

** 3 (a) ** What is hysteresis? Draw a hysteresis loop for ferromagnetic material and explain the various important points on it. For a transformer which kind of material will you prefer-the one with small hysteresis area or the big one? (8 marks)

** 3 (b) ** Derive Bragg's law. X-ray of unknown wavelength give first order Bragg's reflection at glancing angle of 20° with (2 1 2) planes of cooper having FCC structure. Find the wavelength of X-rays, if the lattice constant for cooper is 3.615 A°. (7 marks)

** 4 (a) ** Discuss Diamond structure with neat diagram and also determine the effective number of atoms / unit cell, co-ordination number and atomic radius in tems of lattice constant. (5 marks)

** 4 (b) ** Classify solids on the basis of energy band diagram. (5 marks)

** 4 (c) ** Explain orientational polarization with suitable diagram and write the mathematical expression of orientational polarizability. (5 marks)

** 5 (a) ** Calculate the number of atoms per unit cell of a metal having the lattice parameter 2.9 A° and density 7.87 gm/cm^{3}. Atomic weight of metal is 55.85. Avogadro number is 6.023×10^{23}/gm mole. (5 marks)

** 5 (b) ** What is Hall effect? Mention its significance. How mobility can be determined by using Hall effect? (5 marks)

** 5 (c) ** The reverberation time is found to be 1.5 second, for an empty Hall and it is found to be 1.0 second when a curtain cloth of 20m^{2} is suspended at the centre of the Hall. If the dimensions of the hall are 10×8×6m^{3}, calculate the coefficient of absorption of curtain cloth. (5 marks)

** 6 (a) ** Describe principle, construction and working of magnetostriction oscillator to produce ultrasonic waves. (5 marks)

** 6 (b) ** Briefly explain the different types of point defects.(5 marks)

** 6 (c) ** Explain how a voltage difference is generated in a p-n junction when it is used in a photovoltaic solar cell. (5 marks)