2015 academic year [PDF]

KABARAK

UNIVERSITY

UNIVERSITY EXAMINATIONS 2014/2015 ACADEMIC YEAR FOR THE DEGREE OF BACHELOR OF SCIENCE IN TELECOMMUNICATION TLCM 322 MATERIALS II DAY: WEDNESDAY

DATE: 20/4/2015

TIME: 11:00AM– 1:00PM

STREAM: Y3S2

INSTRUCTIONS:
Answer question 1 and any other TWO Question ONE (30 marks) a)

Differentiate between n and p type semiconductors.

b)

A 0.01 m long bar of tungsten (W) is placed in a laboratory furnace and heated from room temperature (25°C) to 500°C. What will be the length of the bar at 500°C? The coefficient of thermal expansion (α) for W at 27°C is 4.5 mm/(mm· °C) x10-6) while the value at 527°C is 4.8 mm/(mm· °C) x 10-6., 5 marks

c)

For each of the questions below, refer to the phase diagram for mysterious compound X.

Page 1 of 4

3 marks

d)

i.

If a bottle containing compound X is to be kept at room temperature, in what phase is it likely to be in? 2 mark

ii.

At what temperature and pressure will all three phases coexist?

iii.

If a bottle of compound X is at a pressure of 45 atm and temperature of 1000 C, what will happen if the temperature is raised to 4000 C? 2 mark

2 mark

Explain the following: (i) Permeability.

2 marks

(ii) Dielectric constant

2 marks

e)

List any 5 desirable properties of an insulation materials.

5 marks

f)

Explain how phonons and photons contribute to thermal conduction.

2 marks

g)

Explain the magnetization- curves of magnetic materials.

5 marks

Question 2 (20 marks) a)

Discuss 4 types of defects likely to be found in materials

b)

Determine the number of vacancies needed for a BCC iron crystal to have a density of 7.87 g/cm3. The lattice parameter of the iron is 2.866 × 10-8 cm. (take: atomic Page 2 of 4

8 marks

c)

mass of iron to be 55.847).

7 marks

Explain the usefulness of burgers’ vector.

5 marks

Question 3 (20 marks) a)

Describe the two classes of plastics and give two examples of each.8 marks

b)

i) ii)

c)

Give four examples of natural insulating materials.

Explain the functions of a fuse. Discuss the desirable properties of fuse materials.

2 marks 6 marks 2 marks

Question 4 (20 marks) a)

i) Explain the physical meaning of heat capacity Is the ability of a material to absorb heat ii) iii)

b)

2 marks

Discuss the dependence of Heat Capacity on Temperature 6 marks Estimate the amount of heat (in J) required to raise 2 kg of polypropylene from room temperature (i.e., 25°C) to 100°C. The specific heat for polypropylene is 1880 J/kg·K. Express your answer in kJ. 3 marks

With the help of energy bands explain how conduction takes place in conductors, semiconductors and insulators.

9 marks

Question 5 (20 marks) a)

Explain the steps involved in the polymerization process

b)

A cylindrical specimen of stainless steel having a diameter of 12.8 mm and a gauge length of 50.8 mm is pulled in tension. Use the load-elongation characteristics tabulated below to: i) Plot a graph of stress versus strain 9 marks ii) Determine Young’s Modulus of the specimen (steel) 3 marks iii) Determine the yield strength at a strain offset of 0.002 3 marks

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5 marks

Load (N) 0 12700 25400 38100 50800 76200 89100 92700 102500 107800 119400 128300 149700 159000 160400 159500 151500 124700

Length (mm) 50.8 50.825 50.851 50.876 50.902 50.952 51.003 51.054 51.181 51.308 51.562 51.816 52.832 53.848 54.356 54.864 55.88 56.642

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