On completion of this lesson you should be able to:

• identify properties which need to be considered when materials are considered for a particular purpose
• Determine property data from a variety of sources.

1. Select four components of a motor car and give two properties which should be considered when selecting a material for each component.

2. For the data given for iron on page 28, confirm the value of Poisson's ratio using the values of Young's modulus and the shear modulus.

3. Distinguish between ductility and malleability.

4. Tensile tests on aluminium specimens gave the following load/extension results:

Force    Specimen A    Specimen B     Specimen C    Specimen D
27 kN         0.51 mm          0.47 mm        0.53 mm      0.51 mm

Calculate the mean extension and the standard deviation of these readings.

Given that the specimens are 10 cm long and 1 cm diameter, calculate the value of Young's modulus for aluminium based on these results.

Compare this value to that from a source of materials data.

5. For electrical conductors, state three factors that affect conductivity. A copper wire of length 70 cm and diameter 0.8 mm carries a current of 50 mA when a potential difference of 1.2 mV is applied. Determine the resistivity of copper and compare the value to that given by a source of data.

6. Determine the dielectric contstant of polystyrene if, when used as the dielectric of a capacitor with square plates 1 cm long and separation 5 mm, the capacitance is 4.60 × 10^-13 F. (The permittivity of free space is ε₀ = 8.85 × 10^-12 F m^-1.)