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Eee 2203 Material Science Ii Question Paper

Eee 2203 Material Science Ii

Course:Bachelor Of Science In Electrical & Electronic Engineering.

Institution: Dedan Kimathi University Of Technology question papers

Exam Year:2011

EEE 2203 MATERIAL SCIENCE II
Page 1 of 3
KIMATHI UNIVERSITY COLLEGE OF TECHNOLOGY
University Examinations – 2011 / 2012
SECOND YEAR FIRST SEMESTER EXAMINATION FOR THE DEGREE OF
BACHELOR OF SCIENCE IN ELECTRICAL & ELECTRONIC ENGINEERING.
EEE 2203: MATERIAL SCIENCE II
DATE: AUGUST 2011 TIME: 2 Hours
INSTRUCTIONS
This paper consists of Five Questions
Question ONE is Compulsory. Answer Question one and any other two questions.
Take 12 7
0 0 ? 8.854 10 F /m, ? 4? 10 H /m ? ? ? ? ? ?
Electron mass 31 9.1 10 e m kg ? ? ? , electronic charge 19 e 1.6 10 C ? ? ?
Boltzmann’s Constant 23 1 k 1.38 10 JK ? ? ? ?
QUESTION ONE.
(a).
(i). Discuss three key parameters which are used to characterize magnetic materials for
engineering applications. [9 marks]
(ii). Using criteria (i) above list five classes of magnetic materials. [5 marks]
(b). State two reasons why copper is a good metallic conductor of electricity. Hence list and
discuss three causes of resistivity in metals. [10 marks]
(c). Define the key characteristics of the following materials;
(i). Adhesive material. [2 marks]
(ii). Ceramic material. [2 marks]
(iii). Substrate material for a circuit board. [2 marks]
EEE 2203 MATERIAL SCIENCE II
Page 2 of 3
QUESTION TWO.
(a). A 600 turns of a solenoid wire carrying a current of 100mA is wound on a cylindrical ferrite
core. The length of the core is 5cm with a diameter of1cm . If the relative permeability of
the material is 4 10 , calculate its;
(i). Magnetization (M) [2 marks]
(ii). Magnetic susceptibility [1 mark]
(iii). Total magnetic dipole moment [2 marks]
(iv). Magnetic flux density or induction (B) [2 marks]
(v) Permeability [1 mark]
(b).
(i). The conductivity of Nickel decreases when a small amount of Copper is added. This
is despite the fact that copper has a superior conductivity than Nickel. Explain why
the resistivity increases in the Nickel-Copper alloy. [4 marks]
(ii). A uniform silver wire has a resistivity of 18 1.2 10 m ? ? ? ? at room temperature. An
electric field of 100V/m exists along the length of the wire. If the number of free
conduction electrons is 5.8?1028 per cubic meter. Calculate the current density, the
drift velocity of electrons, their mobility and relaxation time. [8 marks]
QUESTION THREE
(a). Explain why power transformer or current transformer cores are made from cold rolled grain
oriented silicon steel (CRGOSS) alloy. [8 marks]
(b). Define the following terms as use in material science.
(i). Dielectric loss angle. [2 marks]
(ii). Magnetic anisotropy. [2 marks]
(iii). Super-ionic material [2 marks]
(c). Explain with the aid of diagrams how doping modulates the energy gap in a P-type and Ntype
semiconductor materials. [6 marks]
QUESTION FOUR.
(a). Discuss the following encapsulation methods as used in the electronic industry. Give typical
area where each is applied.
EEE 2203 MATERIAL SCIENCE II
Page 3 of 3
(i). Impregnation [3 marks]
(ii). Conformal coating [3 marks]
(b).
(i). Name four important characteristics of epoxy materials used for potting of electronic
devices and components. [4 marks]
(ii). Enumerate four non-electrical factors to be considered when selecting polymers or
polymeric composite materials used as printed circuit motherboard substrate
materials. [4 marks]
(c). A 10?F capacitor is connected across a 950V d.c power supply. If it contains titanium oxide
as the dielectric material having relative dielectric constant 50 r ? ? . Find;
(i). The energy stored in the capacitor. [1 mark]
(ii). The energy stored in polarizing the dielectric material. [2 marks]
(iii). The polarization (if the distance between capacitor plates is 50mm). [3 marks]
QUESTION FIVE
With two examples and two different engineering applications, discuss briefly the main properties
of the following engineering materials. [20 marks]
(i). electrical conducting materials
(ii). dielectric materials
(iii). magnetic materials
(iv). electrical superconductors
(v). electrical semiconductors

Eee 2203 Material Science Ii Question Paper

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