Define electrical resistance using potential difference and current.
A circuit is arranged to measure the resistance $R$ of a metal wire. The potential difference (p.d.) $V$ across the wire and the current $I$ in the wire are to be measured. Draw a circuit diagram of suitable apparatus for these measurements.
Measurements of p.d. $V$ and the matching current $I$ are taken. These are displayed in Fig. 2.1.
Explain how Fig. 2.1 shows that the readings suffer from a systematic uncertainty.
Explain how Fig. 2.1 shows that the readings suffer from random uncertainties.
Determine $R$ from the data in Fig. 2.1. Explain your working.
In another experiment, $R$ is found from these data: current $I = 0.64 \pm 0.01\,\text{A}$ and p.d. $V = 6.8 \pm 0.1\,\text{V}$. Calculate $R$ and its uncertainty. Give your answer to an appropriate number of significant figures.