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Ece 152: Electrical Engineering Materials Question Paper

Ece 152: Electrical Engineering Materials

Course:Bachelor Of Engineering In Electrical And Electronics Engineering

Institution: Moi University question papers

Exam Year:2010

ECE 152: ELECTRICAL ENGINEERING MATERIALS.

REVIEW QUESTIONS.

1. Both copper and sodium chloride (common table salt) are crystalline solids; yet, copper is a good conductor of electricity and NaCl is an insulator. What distinction in the bonding process accounts for this difference?

2. Given energy-band diagrams for copper and sodium chloride, how do you identify which is an electric conductor and which is an insulator?

3. Why does the energy-band diagram for an electric conductor show energy levels in the conduction band dipping down to the same energy leve as some of the energy levels in the valence band?

4. In the energy-band diagram for a theoretical insulator, all energy levels in the valence band are occupied and all energy levels in the conduction band are unoccupied. Explain this in terms of a covalent-bonded material.

5. Why is the term ionization potential appropriate in describing the energy level which an electron must possess to escape the attraction of its parent nucleus?

6. What relationship is there between the width of the forbidden energy gap in an energy-band diagram and the performance of the material as an electric insulator? Explain this relationship.

7. Valence bonds in an insulator are broken by heat energy possessed by the insulator. They can also be broken by applying a large electric potential difference across a layer of insulating material. What is the observable difference in the behavior of the material under there two conditions?

8. Why could electric current not pass through the solution of an ionic compound if dissociation of the ions did not occur?

9. What is the difference between the process of electric conduction in a liquid and in a metallic conductor?

10. As in incandescent lamps, the heater of a vacuum tube gradually becomes thinner due to vaporization of the metal and finally burns out. What effect does the burning out of the heater have on the operation of a vacuum-tube rectifier?

11. At room temperature, there are as many electrons in the conduction band of a pure semiconductor crystal as there are positive holds in the valence band. Explain the source of these charge carriers.

12. Explain the mechanism of hole flow in a semiconductor.

13. When electric current flows in an intrinsic semianduator or in an insulator, equal number of electrons and positive holds flow in opposite directions. How does this compare with electric charge flow in an electrolyte?

14. In a crystal of n-type germanium at room temperature, electrons are the majority carriers and positive holds are the minority carriers. Why are there more electrons than holes?

15. As a mercury bell is discharged, the zinc electrode is oxidized into zinc oxide by combination with negative oxygen ions from the electrolyte. The positive potassium ions reduce the mercuric oxide electrode to mercury, thus maintaining the concetration of the solution. Explain, with a sketch, how this chemical action generates a voltage between the terminals of the cell.

16. Describe the various energy conversions that take place from the time some of the chemical energy of an automobile storage battery is used to start the engine of the car until this energy is restored to the battery by the car''s electric generator.

Ece 152: Electrical Engineering Materials Question Paper

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