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## Monday, April 30, 2012

### First/Second Semester B.E. Degree Examination, June/July 2012 Engineering Physics-Model Question Paper

USN                                                               10PHY12/22

First/Second Semester B.E. Degree Examination, June/July 2012
Engineering Physics
Time: 3 hrs.                                                                                                                 Max. Marks:100

Note: 1. Answer any FIVE full questions, choosing atleast two from each part.
2. Answer all objective type questions only in OMR sheet page 5 of the answer booklet.
3. Answer to objective type questions on sheets other than OMR will not be valued.
4. Physical constants: h = 6.626×10-34 Js, c = 3×108 m/s, me = 9.1×10-31 kg,
k = 1.38×10-23 J/K, ε0 = 8.854×10-12 F/m

PART-A
1 a.  i) Experimental evidence for the existence of matter waves was first provided by
A) de-Broglie     B) Davisson and Germer           C) G.P.Thomson                D) Max Planck
ii) Recoil electron in compton scattering carry maximum kinetic energy when x-ray scattering angle θ =
A) 1800                        B) 00               C) 900                      D) 650
iii) Ke,Kp and Ka are respective energy of an e-, a proton and aparticle of same de-Broglie wavelength. Then,
A) Ke>Kp>Ka        B) Ke>Kpa       C) Kepa       D) Ke=Kp= Ka
iv) de-Broglie wavelength associated with a moving particle is independent of its
A) mass       B) charge       C) velocity        D) momentum                                                              (04 marks)
b. Show that group velocity is equal to particle velocity.                                                      (04 Marks)
c. What is Planck’s radiation law?  Show how Wien’s law and Rayleigh-Jean’s law can be          derived from it.                                                                                                                            (08 Marks)
d. Calculate the momentum of the particle and de-Broglie wavelength associated with an electron with a kinetic energy of 1.5 keV.                                                                                                         (04 Marks)

2 a. i) The wavefunction for the motion of particles in one dimensional potential box of length ‘a’ is given by
yn = D sin npx/a where ‘D’ is normalization constant. The value of ‘D’ is
A)                                 B)                          C) a                        D)
ii) The ground state energy of an electron in an one dimensional infinite potential well of width 2Å is 16
eV. Its energy in third excited state is
A) 32 eV                           B) 64 eV                 C) 144 eV                 D) 256 eV
iii) According to Max Born approximation, |y|2 represents
A) Energy density                   B) Particle density          C) Probability density           D) Charge density
iv) Schrödinger’s wave equation is applicable for the particles with
A) Constant energy     B) Variable energy         C) Only constant potential energy
D) All of these                                                                                                                (04 Marks)
b. Solve the Schrödinger’s wave equation for allowed energy values in case of a particle in a potential box.                                                                                                                                 (08 Marks)
c. What is a wave function? Explain the properties of a wave function.                               (04 Marks)
d. Estimate the time spent by an atom in the excited state during the excitation and de-excitation processes, when a spectral line of wavelength 546 nm and width 10-14 m is emitted.          (04 Marks)
3 a. i) The mobility of electrons in a conductor is 4×10-3 m2V-1s-1. Then the drift velocity of the electron in the presence of applied electric field of strength 100 Vm-1 is
A) 4 ms-1         B) 10 ms-1        C) 0.4 ms-1       D) 0.04 ms-1
ii) Which one of the following is correct for current density?
A) J = neAvd   B) J = neA/vd C) J = nevd     D) J = 1/nevd
iii) The classical value of molar specific heat of a conductor is
A) 3/2 R            B) ½ R                        C) 3R              D) 5/2 R
iv) The Fermi energy of a metal at absolute zero temperature is proportional to
A) n1/3              B) n3/2              C) n2/3              D) n2                                                                         (04 Marks)
b. Define relaxation time and discuss the dependence of electrical resistivity of metals with temperature and impurity.                                                                                                          (06 Marks)
c. Explain how quantum free electron theory succeeds in overcoming the drawbacks of classical free electron theory.                                                                                                                         (06 marks)
d. lculate the probability of an electron occupying an energy level 0.02 eV above the Fermi level and 0.02 eV below the Fermi level at 200 K.                                                                                (04 marks)

4 a. i) Orientation polarization occurs
A) In all dielectrics     B) in polar dielectrics        C) in non-polar dielectrics
D) in ionic dielectrics
ii) The polarization produced in a dielectric medium in the frequency range 1013 to 1016 Hz is
A) electronic                     B) orientational      C) space charge                D) ionic
iii) The susceptibility of a diamagnetic material is
A) Infinity             B) positive       C) zero                        D) negative
iv) In a magnetic material, the major contributor to magnetism is
A) orbital motion of electrons                    B) nuclear spin
C) spin motion of electrons                        D) none of these                                             (04 Marks)
b. Derive the expression for internal field in solids.                                                               (08 Marks)
c. What are ferromagnetic materials? Discuss the hysteresis of a ferromagnetic material.     (04 Marks)
d. A solid dielectric material has electronic polarizability 7×10-40 Fm2. If it is a cubic structure, calculate the relative permittivity of the material. It has 3× 1028 atoms/m3.                         (04 Marks)

PART-B
i) Quartz plates are fixed at the ends of the discharge tube in a He-Ne laser so that
A) there won’t be leakage of gas                       B) the tube can withstand high electric voltage
C) the loses light can pass out without any loss      D) the emergency light is polarized
ii) The required condition to achieve laser action in a system is
A) state of population inversion         B) existence of metastable state
C) a resonant cavity                            D) all the three
iii) 3D image of an object constructed by hologram is the process of
A) Intensity recording                                    B) Phase information recording
C) Both phase and intensity information recording
D) Transmission and reflection recording
iv) The method used for the measurement of pollutants in the atmosphere is
A) Holography            B) Lidar          C) stimulated emission            D) coherence               (04 Marks)
b. Describe the construction and working of semiconductor laser.                                        (06 Marks)
c. Obtain an expression for energy density of radiation under equilibrium condition in terms of Einstein coefficient.                                                                                                                        (06 Marks)
d. A ruby laser emits pulse of 20 ns duration with average power per pulse being 100 kW. If the number of photons in each pulse is 6.981 × 1015, calculate the wavelength of photons.   (04 Marks)
6 a. i) The temperature of a superconductor kept in a weak magnetic field is reduced below critical
temperature, then
A) R=0;B≠0                   B) R≠0;B=0                           C) R≠0;B≠0                D) R=0;B=0
ii) Meissner effect will take place in
A) Solid                       B) Super conducting magnet          C) Maglev vehicle             D) MRI.
iii) In a single mode fiber, the diameter of the core is nearly equal to
A) 125 mm                        B) 100 mm                   C) 50 mm                         D) 10 mm
iv) The numerical aperture of an optical fiber in air is 0.32. The numerical aperture in water (nw = 4/3) is
A) 0.43                          B) 0.24                          C) 0.64                    D) 0.96              (04 Marks)
b. Explain BCS theory of superconductivity. Give a brief account of SQUID.                    (07 Marks)
c. Describe the point to point communication system, with the help of block diagram.        (05 Marks)
d. A fiber 500m long has an input power of 8.6 mw and output power 7.5 mw. What is the loss specification in cable?                                                                                                              (04 Marks)

7 a. i) The relation for angles between axes of a triclinic crystal is
A) a = β = γ = 900          B) a ≠ β ≠ γ = 900       C) a ≠ β ≠ γ ≠ 900       D) a = β = γ ≠ 900
ii) The coordination number in case of simple cubic crystal structure is
A) 12                         B) 8                                  C) 2                                       D) 6
iii) The packing fraction of diamond crystal structure is
A) 34%                     B) 52%                      C) 68%                    D) 74%
iv) In a simple cubic lattice the ratio d100:d110:d111 is
A) 6:3:1                    B) √3:√6:1              C) 6:3:√2                    D) √6:√3:√2                 (04 Marks)
b. Derive an expression for inter planar spacing in terms of Miller indices.                           (06 Marks)
c. With neat fig, explain crystal structure of NaCl.                                                                (06 Marks)
d. The minimum order of Bragg’s reflection occurs at an angle 200 in the plane . Find the wavelength of X-ray if lattice constant is 3.615 Å.                                                              (04 Marks)

8 a. i) In a carbon nanotube, the bond between the carbon atoms is
A) Metallic      B) ionic           C) covalent      D) hydrogen
ii) A constant testing of product without causing any damage is called
A) minute testing   B) destructive testing    C) non-destructive testing    D) random testing
iii) Ultrasonic waves are used in
A) LIDAR      B) RADAR     C) SONAR     D) LASER
iv) The typical size of nanomaterial is between
A) 1-10 nm      B) 10-50 nm    C) 1-100 nm    D) 1-1000 nm                                                  (04 Marks)
b. Explain density of states for various quantum structures.                                                  (04 Marks)
c. Write a note on carbon nanotube.                                                                                       (04 Marks)
d. Explain the principle and method of nondestructive testing of material using ultrasonics.
(08 Marks)