Visvesvaraya Technological University (VTU) 2007-2nd Sem B.E Electrical and Electronics Engineering Firstester .rtf - Question Paper

First/Second Semester B.E. Degree exam
Common to All Branches
Engineering Physics

Time:3 hrs.] [Max.Marks:100

ans 5 full ques. choosing at lowest 2 ques. in every part

Electron mass=m=9.11x10-31kg, Electron charge=e=1.6x10-19C, Velocity of light=c=3x108m/s,
Planck’s constant=h=6.63x10-34J-s, Permittivity of vacuum= e
o=8.85x-12F/m,
Avogadro Number=NA=6.025x1026/K.mole, Boltzman Constant=K=1.38x10-23J/K.

Part-I
1 a) discuss Compton effect and provide its significance.
b) describe the term a) phase velocity, b) group velocity. How are they related.
c) Derive an expression for de Broglie wave length using the concept of group velocity.
d) compute the de Broglie wave length of a neutron moving with kinetic energy 54 eV
provided the mass of the neutron = 1.675 x 10-27 Kg.
[Marks 5+5+5+5]

2 a) A wave function ? = A sin(npx/a) for motion of a particle in a zero potential well of
width ‘a’. compute the wave amplitude where ‘x’ is the position of the particle
along ‘a’.
b) What is a wave function? Set up time independent Schrodinger’s wave formula for
one dimensional motion.
c) The position and momentum of two keV electron are simultaneously determined and if its
position is located within 0.12nm, what is the percentage of uncertainty in its momentum?
[Marks 5+10+5]

3 a) describe the terms relaxation time, mobility and drift velocity.
b) What is density of energy states? Derive the expression for density of states for free
electron.
c) compute the probability of an electron occupying an energy level 0.02 eV above the
fermi level at 200K and 400K.
[Marks 5+10+5]

4 a) discuss internal field and derive the expression for internal field in 1 dimensional solids
and liquids.
b) Distinguish ranging from dia, para and ferromagnetic materials based on Langevin’s and
Wiess theory.
c) Dielectric constant of He gas at NTP is 1.0000684. compute the electronic
polarizability of He atoms if the gas contains 2.7x1025 atoms per m3 and hence the
radius of the Helium atoms.
[Marks 10+5+5]

Part-II

5 a) discuss stimulated emission and derive the expression for energy density of photons using
Einstein’s A & B co-efficients.
b) define the principle, and working of a semiconductor laser.
c) The power of a He-Ne laser is 1mW. compute the number of photons emitted per second
if the wavelength of the emitted light is 632.8nm.
[Marks 10+5+5]

6 a) discuss the propagation of light in optical fiber and derive the expression for angle of
acceptance and NA.
b) Distinguish ranging from Type-I and Type-II super conductors.
c) The attenuation of an optical fiber is -2.3 dB/km. compute the length of the optic
fiber that retains 20% of the initial intensity.
[Marks 10+5+5]

7 a) discuss 7 crystal systems.
b) discuss how Bragg’s spectrometer can be used to determine the wavelength of x-rays.
c) Sketch the planes (100), (010), (001) and (111) in a cubic unit cell.
[Marks 5+10+5]

8 a) discuss the method of fabrication of nano materials.
b) explain the various kinds of nano scale systems.
c) define ultrasonic velocity measurement in liquids.
[Marks 5+5+10]

Earning:   Approval pending.