Punjab Technical University 2005-4th Sem B.Tech Electrical and Electronics Engineering Electrical Engineering Materials (New) EE 208 - Question Paper

ELECTRICAL ENGINEERING MATERIALS (New) EE 208 fourth Sem May 2k5

Max Marks 60

Note: part A is compulsory. Attempt any 4 ques. from part B and 2 from part C. presume any missing data.

Section A Marks two every

1.
(a) Why do a few materials have high an others have low dielectric constants?
(b) What is the relationship ranging from the macroscopic measurable dielectric constant and the atomic structure of material?
(c) Why the resistivity of an impure metal is higher than that of a pure metal.
(d) Discuss the frequency dependence of ionic polarization.
(e) Derive the relationship ranging from orbital magnetic dipole moment and angular moment.
(f) List different applications of superconductors.
(g) Differentiate ranging from diamagnetism and perfect diamagnetism.
(h) Define transition temperature an how it cab e decreased.
(i) Define relaxation time, collision time and mean free path.

part B Marks five every

2. discuss spontaneous polarization id detail. Why does spontaneous polarization occur only beneath a certain temperature?

3. elaborate dielectric losses? Prove that the absorption of energy in dielectric is equal to the imaginary part of complex dielectric constant.

4. A solid contains five x 1023 identical atoms per m3, every with polarizability of two x 10-48 farad-m2. Assuming that the internal field is provided by the Lorentz formula, compute the ratio of internal field to the applied field.

5. The magnetic field strength on a piece of copper is 106 ampere m-1.Given the magnetic susceptibility of copper is -0.5 x 10-5, obtain the flux density and magnetization in copper.

6. Show that an electron with a velocity perpendicular to the direction of homogenous magnetic field of flux density B defines a circular path with angular velocity of rotation equal to eB/m.

part C Marks 10 every
7. explain in detail the different contributions to the permanent magnetic dipole moment of the atomic constituents of matter.

8.(a) for pure metals the theory predicts a thermal conductivity which is practically independent of temperature above Debye temperature. Why is this so?
(b) The electrical resistivities of copper and kanthal (an alloy of iron, chromium and aluminium) at room temperature are respectively 1.7 x 10-8 and 1.4 x 10-6 ohm-m. Assuming the Wiedemann-Franz legal regulations holds for these materials, obtain the electronic contributions to the thermal conductivities of these materials.

9. Write sort notes on the following:
(a) Ferromagnetic materials and their properties.
(b) Piezoelectricity
(c) Ferroelectric materials and their properties.

Earning:   Approval pending.