Graph
Plot a graph of resistance, R, in 惟 on the y-axis against length, l, in cm on the x-axis). Draw the line of best fit.
Conclusion
We can see from the graph that as the length of the wire, l, increases, the resistance, R, also increases.
This agrees with our prediction.
In fact, since the line of best fit is a straight line through the origin, we can be even more precise.
We can say that, for a metal wire at constant temperature, the resistance is directly proportional to the length of the wire.
If you double the length of the wire you double its resistance.
Resistance and cross section area
A second experiment can be carried out to investigate experimentally how the resistance of a metallic conductor at constant temperature depends on the area of cross section.
The above experiment is repeated but with six, equal lengths of constantan wire, of different thickness.
Record voltage, current and diameter of the wire, d (supplied by the manufacture). Calculate resistance and cross section area, A, in mm2 (A = \(\frac{{\Pi d}^2}{4}\)).
Plot a graph of resistance, R, in 惟 on the y-axis against cross section area, A, in mm2 on the x-axis). Draw the line of best fit.
We can see from the graph that as the cross section area, A, increases, the resistance, R, decreases.
A thicker wire has a smaller resistance than a thin wire.
A more detailed investigation shows that resistance and cross section area are inversely proportional.
If you double the cross section area you half the resistance of the wire.
Resistance and material of conductor
A final experiment can be carried out to investigate experimentally how the resistance of a metallic conductor at constant temperature depends on the material of the conductor.
The experiment is repeated again but with six, equal lengths and thicknesses of wire of different materials.
Record voltage, current and calculate resistance.
A comparison of results in the table shows that wires of different material have different resistance.