Determination of r for a Metallic Conductor
             To determine the resistivity (r) of a given sample of wire
             Physical factors that affect the resistance of a conductor are length, cross sectional area and a constant that depends upon the material called the resistivity. The resistance per unit length is the same all along a uniform wire so if the resistance of different lengths of a wire is found out, the resistivity can be calculated.
             Resistance of a material, R = Voltage Current
             Resistance of a conductor, R = r × Length Cross sectional area
             - given sample of wire (» 5 m)
             - variable resistor – is used to alter the resistance to change the current and voltage for each length
             - ammeter – the 5 ampere outlet was used since the current was generally over 1 amperes
             - voltmeter – the 5 volt outlet was used because voltage was always below 5 volts
             - meter stick – more appropriate than a 30 cm ruler because the length is changed by 50 cm each time
             - micrometer – since the wire is very thin an accurate measurement of the diameter can be obtained by using a micrometer with an uncertainty of ± 0.0005mm.
             1. Set up the apparatus as shown on the diagram.
             2. Make sure the voltmeter outlet is at 5 volts and the ammeter outlet is at 1 amp.
             3. Measure 50 cm of the wire using the meter stick.
             4. Connect this part of the wire to the circuit using the crocodile clips.
             5. Make sure the wire is not touching other parts of the wire.
             6. Turn the power supply on, record the voltage and current.
             7. Using the variable resistor, alter the resistance and take 4 more different readings of voltage and current for this length.
             8. Repeat steps 4 to 6 for 5 more times, each time increase the length of wire by 50 cm using the meter s
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