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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:2008
MOI UNIVERSITY
SCHOOL OF ENGINEERING
ECE 152; ELECTRICAL ENGINEERING MATERIALS
QUESTION ONE
a. Draw the equilibrium Boltzmann distribution and equilibrium probability curve for the scalar speed (4mks)
b. Drude supposed that moving electrons are scattered by random collisions with the ion cores , explain (4mks)
c. From the total electron transport equation show that s={(ne^2)t}/m. Indicate all the steps involved. (6mks)
QUESTION TWO
a. Differentiate between phonons and fermions (3mks)
b. Write down the expression of the total density of electrons per unit volume. Discuss it (5mks)
c. Explain the importance of Fermi level in band theory of solids. (6mks)
QUESTION THREE
a. Discuss the term semi-conductors (4mks)
b. With clear explanation show that E(F)=E(G)/2. (4mks)
c. In an n-type semiconductor, the Fermi level lies 0.3 eV below conduction band at 300 K. If the temperature is increased to 330 K, find the new position of the Fermi level. (6mks)
QUESTION FOUR
a. what is compensation doping (2mks)
b. With use of elaborate diagrams explain the difference between insulators, semi conductor and metal (6mks)
c. In a p-type semiconductor, the Fermi level lies 0.4 eV above the valence band. If the concentration of acceptor atoms is tripled, find the new position of the Fermi level. (Assume KT=0.03eV) (6mks)
QUESTION FIVE
a. State Pauli exclusion principle (2mks)
b. List dielectric properties of materials (6mks)
c. A semiconductor is said to be degenerate when, in the case of a donor doped semiconductor, the Fermi level is located at energy of 3KT or less from the conduction band. Calculate the minimum doping density for silicon at 300K to become degenerate if n=1.4*10^16 per square metre and the energy gap between the valence and conduction bands is 1.1 eV (K=1.38*10^-23 J/K) (6mks)
QUESTION SIX
a. Briefly explain the terms remanence and coercive field (4mks)
b. List three properties each for soft magnetic materials and hard magnetic materials. (6mks)
c. A 100 µm thick sample of silicon is doped with 10^23 phosphorus atoms per cubic meter. If its mobility is 0.07 square meters/v-sec, current I=1mA and flux density B=0.1 Wb/square meter, find the hall voltage (4mks)
QUESTION SEVEN
a. Differentiate between luminescence, fluorescence and phosphorescence (3mks)
b. What are optical properties (3.5mks)
c. What is photo conductivity (1.5mks)
d. Calculate the energy of photons of infrared (?=11500A), yellow (?=5800A) and ultraviolet (?=2000A) (6mks)
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