U.S.N.
B.M.S. College of Engineering, Bengaluru-560019
Autonomous Institute Affiliated to VTU
December 2019 / January 2020 Semester End Main Examinations
Programme: B.E. Semester: I
Branch: Common to all Branches Duration: 3 hrs.
Course Code: 18PY1BSPHY Max Marks: 100
Course: APPLIED PHYSICS Date: 18.12.2019
Instructions: Answer five full questions, choosing one full question from each unit
Physical constants:
Mass of electron, me = 9.1x10-31 kg Speed of light, c = 3x108 m/s
Electronic charge, e = 1.602x10-19 C Planck constant, h = 6.626x10-34 Js
Boltzmann constant, kB = 1.38x10-23 J/K Mass of proton/neutron, m = 1.67x10-27 kg
Avogadro number, NA=6.023x1026/k.mol Permittivity of free space εo =8.85x10-12 F/m
UNIT-1
Important Note: Completing your answers, compulsorily draw diagonal cross lines on the
1 a) Define group velocity. Derive an expression for group velocity on the basis of 8
remaining blank pages. Revealing of identification, appeal to evaluator will be treated as
superposition of waves.
b) State Heisenberg’s uncertainty principle. Prove that an electron does not exist 8
inside the nucleus, using this principle.
c) Calculate the de-Broglie wavelength associated with 400 gm cricket ball 4
traversing with a speed of 90 km/hr.
OR
2 a) State de-Broglie hypothesis of matter waves. Derive an expression for 8
de-Broglie wavelength using the concept of group velocity.
b) Using Schrodinger wave equation, derive a normalized eigen function for a 8
particle in one dimensional potential well of infinite height by applying
boundary conditions.
c) An electron is trapped in one dimensional potential well of width 1 Å and 4
infinite height. Find the amount of energy required to excite the electron to its
fifth excited state.
UNIT - II
3 a) State Wiedemann-Franz law. Deduce the classical expression for thermal 8
conductivity of a conductor.
b) Mention the assumptions of quantum free electron theory and explain any 8
two of its merits.
c) Evaluate the relaxation time of electrons in copper having resistivity of 4
1.73 x 10-8 Ω-m, atomic weight of 63.5 and density of 8.92 g/cm3.
UNIT-III
malpractice.
4 a) Derive an expression for internal field in case of one-dimensional array of 8
atoms in dielectric solids.
b) Obtain an expression for the concentration of electrons in conduction band of 8
an intrinsic semiconductor.
c) The dielectric constant of sulphur is 3.4. Assuming the internal field as 4
Lorentz field, calculate the electronic polarizability of sulphur. Given, density
of sulphur is 2.07x103kg/m3 and its atomic weight is 32.07.
UNIT-IV
5 a) Elucidate the construction and working of semiconductor laser with an energy 8
band diagram.
b) Discuss the different types of optical fibers with suitable diagrams. 8
c) A laser beam with power per pulse 1 mW lasts 10 ns. If the number of photons 4
emitted per pulse is 3.941 x 107, calculate the wavelength of laser.
OR
6 a) Define numerical aperture. Derive an expression for numerical aperture of an 8
optical fiber and hence mention the condition for the ray propagation.
b) Describe the recording of a hologram and reconstruction of an image from it 8
with the help of suitable diagrams.
c) Calculate the number of modes an optical fiber can support for propagation 4
with core diameter of 50 µm and refractive indices of 1.5 and 1.48, respectively
for core and cladding, when the wavelength of the propagating wave is 1 µm.
UNIT-V
7 a) What is damped oscillation? Give the theory and discuss the case of critical 10
damping.
b) Define resonance. Explain in brief Nuclear Magnetic Resonance and list two 06
applications.
c) The Q factor of a spring loaded with 0.3 kg is 60. It vibrates with a frequency 04
of 2 Hz. Calculate the force constant and mechanical resistance.
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