USN 10PHY12/22

First/Second Semester B.E. Degree Examination, January 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 = 3×10^{8} m/s, m_{e} = 9.1×10^{-31} kg,

k = 1.38×10^{-23} J/K, ε_{0} = 8.854×10^{-12} F/m

**PART-A**

**1 a. i) Electrons behaves as a wave because they can be **

** A) Diffracted by a crystal B) Deflected by magnetic field **

** C) Deflected by electric field D) Ionise a gas**

** ii) Blackbody radiation spectrum, maximum intensity is shifting towards **

** A) shorter wavelength B) longer wavelength C) no change D) none of these**

** ii) We do not observe wave nature of macroparticles because**

** A) their wavelengths are very large B) their wavelengths are very negligibly small**

** C) their velocities are smaller D) their velocities are larger**

** iv) de-Broglie wavelength of an electron accelerated by a potential of 60 V is **

** A) 1.85 Å B) 1.58 Å C) 1.589 Å D) 1.57 Å (04 marks)**

** b. Describe Davisson-Germer experiment to prove the dual nature of matter waves. (08marks)**

** c. Define phase velocity and group velocity. Show that group velocity is equal to particle velocity. (08 marks)**

**2** a. i) If E_{1} is the energy of the lowest state of a one dimensional potential box of length ‘a’ and E_{2} is the

energy of the lowest state when the length of the box is halved, then

A) E_{2} = E_{1} B) E_{2} = 2E_{2} C) E_{2} = E_{1}/2 D) E_{2} = 4E_{1}

ii) The wavefunction is acceptable if it is

A) Finite everywhere B) Continuous everywhere

C) Single valued everywhere D) All of these

iii) For a particle in an infinite potential well in its 1^{st} excited state, the probability of finding the particle

at the center of box is

A) 0 B) 0.25 C) 0.5 D) 0.1

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. State and explain Heisenberg’s uncertainty principle and prove that nuclei do not contain electron.

(06 Marks)

c. Set up time independent one dimensional Schrödinger wave equation. (06 Marks)

d. An electron is bound in one dimensional potential well of width 0.18 nm. Find the energy value in eV of

the second excited state. (04 Marks)

**3 a. i) The value of Fermi distribution function at absolute zero (T= 0 K) is 1, under the condition**

** A) E = E _{F} B) E > E_{F} C) E >> E_{F} D) E < E_{F}**

** ii) Mobility of electron is **

** A) Reciprocal of conductivity B) Flow of electrons per unit**

** C) Reciprocal of resistivity D) Average electron drift velocity per unit electric field**

** iii) According to quantum free electron theory, the energy level in a metal are**

** A) Continuous B) Discrete C) Overlapping D) None**

** iv) For ordinary metals, the resistivity versus temperature curve at T = 0, **

** A) has a positive intercept B) has a negative intercept **

** C) goes through the origin D) none of these (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. A uniform silver wire has resistivity 1.54×10 ^{-8} ohm-m at room temperature for an electric field 2 v/m. Calculate relaxation time and drift velocity of the electrons, assuming that there are 5.8×10^{22} conduction electrons per cm^{3 }of the material. (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) Ultrasonic waves can be produced by

A) Photoelectric effect method B) Inverse piezoelectric effect method

C) Dielectric heating method D) High energy ball milling method

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. What is meant by polarization mechanism in dielectrics? Discuss any three different polarization mechanisms in dielectrics and their frequency dependence. (08 Marks)

c. What are soft magnetic materials? Discuss their properties. (04 Marks)

d. The relative permittivity of sulphur is 4. Calculate its atomic polarizability. Given that sulphur is in cubic form and has a density of 20180 kg/cubic meter and atomic weight of 32. (04 Marks)

**PART-B**

**5 a. i) The life time of an atom in the excited state is of the order of**

** A) Millisecond B) Few seconds C) Nano seconds D) Unlimited**

** ii) Pumping process used in diode laser is **

** A) Optical pumping B) Forward bias C) Electric discharge D) None of these**

** iii) Emission of a photon by an excited atom due to interaction of external energy is called**

** A) Spontaneous emission B) Stimulated emission C) Induced absorption D) Light amplification**

** iv) In He-Ne laser, the ratio of He-Ne gas molecules in the order**

** A) 1:10 B) 10:1 C) 1:1 D) 1:2 (04 Marks)**

**b. Obtain an expression for energy density of radiation under equilibrium condition in terms of Einstein **

** coefficient. (07 Marks)**

**c. Describe the recording and reconstruction processes in holography, with the help of suitable diagrams. (05 Marks)**

**d. Calculate on the basis of Einstein’s theory the number of photons emitted per second by He-Ne laser **

** source emitting light of wavelength 6328Å with an optical power 10 mW. (04 Marks)**

**6** a. i) The critical temperature of mercury is

A) 4.2 K B) 6.2 K C) 7.8 K D) 20 K

ii) A superconducting material, on being subjected to the critical field, changes to

A) Critical conductivity B) Superconducting which is independent of temp

C) Normal state D) Remains uninfluenced

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 width of the energy gap of the superconductor is maximum at

A) T_{c} B) 0K C) T_{c}/2 D) T_{c}/3 (04 Marks)

b. Give a brief account of SQUID. (06 Marks)

c. What are the different types of attenuation losses in an optical fiber? (06 Marks)

d. An optical fiber has core R.I. 1.5 and R.I. of cladding 3% less than the core index. Calculate the numerical

aperture, angle of acceptance and internal critical acceptance angle. (04 Marks)

**7 a. i) Which one of the following Bravais lattices is not found in cubic crystal?**

** A) Simple cubic B) Face centered C) Body centered D) Base centered**

** ii) A plane intercepts at a, b/2, 2c in a simple cubic unit cell. The miller indices of the plane are**

** A) (214) B) (241) C) (421) D) (124)**

** iii) The coordination number for a face centered cubic lattice is**

** A) 12 B) 8 C) 6 D) 26**

** iv) Atomic packing fraction of diamond crystal structure is **

** A)0.68 B) 0.74 C) 0.52 D) 0.34 (04 Marks)**

**b. Derive an expression for inter planar spacing in terms of Miller indices. (06 Marks)**

**c. Derive Bragg’s law for X-ray diffraction. State one of the applications of X-ray diffraction technique. (06 Marks)**

**d. Calculate the glancing angle for incidence of X-rays of wavelength 0.58Å on the plane (132) of NaCl which results in second order diffraction maxima taking the lattice as 3.81Å (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 bulk material reduced in two directions is known as

A) Quantum wire B) Quantum dot C) Quantum well D) Thin film

iii) Ultrasonic waves are used in

A) LIDAR B) RADAR C) SONAR D) LASER

iv) Which one is not the property of ultrasonic waves

A) Produce heat while passing through a medium. B) Can penetrate large distances through matter

C) Require a material medium for propagation D) Undergo polarization like light waves. (04 Marks)

b. Explain density of states for various quantum structures. (08 Marks)

c. Explain the principle and method of nondestructive testing of material using ultrasonics. (08 Marks)

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