In order to compare the resistance of various pencils, the nature of this resistance, ohmic or otherwise, was first tested by graphing the voltage over current (Refer to Figure 5). The R2 values of the trend lines, which were close to 1, confirm that the pencils’ resistance is linear. As the graphs are linear, they can be said to be ohmic resistors. It was also noted that the trends became less accurate, indicated by lowered R2 values, as the resistance declined. This is because as the voltages and currents recorded became smaller, the uncertainty involved in the experiment became more influential, resulting in less accurate trends.
Figure 5: Ohmic resistance of pencils
The equations for the linear trend lines were ascertained, with the gradient denoting the resistance of the pencil. These trend lines were plotted with a set intercept at the origin given that theoretically when there is no current, there cannot be voltage. As all pencils were ohmic resistors, it was then possible to analyse the influence of carbon percentage by plotting this against the gradient resistances