Visvesvaraya Technological University (VTU) 2005 B.E Engineering Physics - Question Paper
First Semester B.E Degree Examination, July/August 2005
Common to all Branches
Engineering Physics
Full ques. Paper in attachment
Page No,., 1 PHY12/22
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First/Second Semester B.E Degree Examination, July/August 2005
[Max. Marks : 100
Time: 3 hrs.]
Note: 1. Answer any FIVE full questions.
2. All questions carry eqla marks.
3. Answers must be specific and precise.
4- Draw neat sketches wherever necessary.
Electron mass m = 9.11 x 10-31fc
Electron charge e = 1.6 x 10
Velocity of light c = 3 x 10Sm/s;
Plancks constant h = 6.63 x 1034 J.S Permitivity of vacuum, 8.85 x 1012 F/M Avagadros number, ~ 6.025 x 1026/Kmole Boltzmann constantf K = 1.38 x 10-23 JjK ,
1. {a) What are matter waves ? Show that the electron accelerated by a potential
difference V volts is A = 1.22$ j'/Vnm for non- relativistic case.
fb) Explain phase velocity and group velocity. Derive the expression for de Braglie wave length using the concept of group velocity.
(c) The speed of electron is measured to within an uncertainty of 2.2 x lOm/s in one dimension. What is the minimum width required by the electron to be confined in an atom. (6+10+4 Marks)
2. (a) What is a wave function ? Give its significance. Assuming a particle of mass
m is confined in a field free region between impenetrable walls at x = 0 and x = a, show that the stationary energy levels of the particle are given by E?a = n2h2 /8ma2
(b) Explain the BCS theory of super conductity.
(c) A quantum particle confined to one-dimensional box of width a' is known to be in its first excited state. What is the probability of the particle in central
half? * (10+5+5 Marks)
3. (a) How does the electrical resistance of the metal change with impurity and
temperature? - *
(b) Derive the expression for eiectrical conductivity in metals interms of relaxation time and explain any three draw backs of classical theory of free electrons.
(cl Find the probability with which an energy level 0.2 eV below fermilevel being occupied at room temperature of 300if and 1000K. (5+10+5 Marks)
4. (a) Explain the properties of Ferrites and mention its two uses.
fb) Explain with theory how static dielectric constant of a dielectric material is determined and explain its frequency dependance.
(c) The dielectric constant of He gas at NTP is 1.0000684. Calculate the electronic polarisability of He atoms if the gas contains 2.7 x 1025 atoms per m3.
(5+10+5 Marks)
5. (si) Explain the terms stimulated emission and population inversion. Obtain an
expression for energy density of photons in terms of Einstein's co-fficients.
(b) Explain the construction and working of Ruby Laser
(c) Write a note on measurement of polJutents in atmosphere using laser,
(10+6+4 Marks)
6. (a) Explain the origin of characteristic X-rays.
(b) Derive Braggs law.
(c) Explain the principle of light propagation in an optical fibre. Derive the expression for numerical aperture in terms of refractive indices of core and cladding.
(d) Calculate the number of modes that can be propagated inside an optical fibre, given ncore ~ 1.53, nrj0j = 1.50, core radians 50im, X = 1 fim.
nCore = 1.53, = 1.50, core radians 50im A = Ifirn (5+5+6+4 Marks)
7. (a) Explain the structure of NaCl and calculate the packing fraction for a bcc
structure.
(bl Obtain the expression for inter planar distance in terms of Miller indices.
(c) Sketch the following planes in a cubie-unit celVKH), (121),(010)
(10+5+5 Marks)
8. (a) Explain the term MEMS. Discuss different materials used for MEMS.
(b) Explain the advatages and disadvantages of composite materials.
(c) Discuss the different types of nano scale systems. (6+6+8 Marks)
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