04-11-2012, 07:44 PM
B.E/B.TECH DEGREE EXAMINATION,MAY/JUNE 2009
PH 2161-ENGINEERING PHYSICS-II
PART A( 10X2=20 MARKS )
1.define the terms.
2. What are the main drawbacks of classical free electron theory of metals?.
3. What is meant by Fermi energy? What is physical significance?
4. What is meant by Hall Effect? Write an expression for the hall coefficient
5. Distinguish between intrinsic and extrinsic semiconductors.
6. What do you understand by the terms "critical temperature" and "critical field" of a superconductor?
7. Distinguish between soft and hard magnets.
8. Mention four types of polarization mechanisms that can take place in the presence of an electric field in dielectric materials.
9. What are shape memory alloys? What are their properties?
10. What are the applications of carbon nano tubes?.
PART B-(5 X 16=80)
i. state the assumption of the classical free electron model.
ii. Obtain an expression for the electrical conductivity of a metal on the basis of classical free electron theory.
iii. The mobility of electron in copper is 3 x 10^-3 m^2/Vs assuming e=1.6 x 10^-19 C and me=9.1 x 10^-31 kg , calculate the mean free time.
i. explain the meaning of 'density of states'. Derive an expression for the number of allowed states per unit volume of a solid
ii. Write an expression for the Fermi energy distribution function, fFD(E) and discuss its behavior with change in temperature. Plot fFD(E) versus E for T=0k and T>0k.
i. describe the energy band theory of solids with the help of neat band diagrams. Distinguish between metals, insulators and semiconductors on the basis of band theory.
ii. Derive an expression for the charge density in terms of hall voltage and further explain how the mobility of the charge carriers can be evaluated by knowing the conductivity.
i. derive an expression for the electrical conductivity of an intrinsic semiconductor
ii. The electron mobility and hole mobility in silicon are 0.315m^2/Vs.and 0048m^2/Vs.
if the carrier concentrations is 1.5 x 10^16 m?^-3, calculate the resistivity of silicon at room temperature
iii.a sample of silicon doped with 10^23 phosphorus atoms/m^3.find the hall voltage in a sample with thickness =100UM,current, IX=1 mA and magnetic field, BZ=o.1 Wb/m2.(assume electron mobility Ue=0.07 m^2/Vs)
i. distinguish between type I and type II superconductors.
ii. What are cooper pairs? Give an outline of BCS theory of superconductivity.
iii .write a short note on SQUIDs.
i. give the classification of magnetic materials on the basis of magnetic susceptibility. Briefly discuss the domain theory of ferromagnetism.
ii. Calculate the energy loss per hour in the iron core of an transformer, if the area of the B-H loop is 250 J/m^3 and the frequency of the alternating current is 50 Hz.the density of the iron core is 7.5 x 10^3 kg/m^3.
iii. A magnetic field of 2000 A/m is applied to a material which has susceptibility of 1000.calculate the
1. Intensity of magnetization and
2. Flux density.
i. Derive an expression for the internal field in a dielectric material.
ii. The dielectric constant of a helium has at NTP is 1.0000684.calculate the electronic polarizablity of He atoms if the gas contains 2.7 x 10^26 atoms/m^3 and hence evaluate the radius of the helium atom.(E0=8.85 x 10^-12 F/m).
iii. Calculate the polarization produced in a dielectric medium of dielectric constant 6 when it is subjected to an electric field of 100 V/m(E0=8.85 x 10^-12 F/m).
i. what is ferroelectricity? Explain the hysteresis curve exhibited by a ferroelectric material with a suitable sketch.Give example for ferroelectric materials
ii. A capacitor consists of two conducting plates of area 200 cm^2 each sepearated by a dielectric constant E=3.7 of thickness 1mm.find the capacitance and the electric flux density when a potential of 300V is applied (E0=8.854 x 10^-12 F/m)
iii. Write a short note on uses of dielectric materials
i. what are nanotubes? Describe their synthesis and properties
ii. Write a short note on pulsed laser deposition
i. describe the preparation and properties of metallc glasses.
ii. Write short notes on nano particles and their applications
“Work hard in silence, let your success be your noise...”