Define electric potential difference (p.d.)
A wire with cross-sectional area $A$ is made from metal of resistivity $\rho$. The wire is stretched. Assume that the volume $V$ of the wire stays constant as it stretches. Show that the resistance $R$ of the stretching wire is inversely proportional to $A^2$.
As shown in Fig. 6.1, a battery with electromotive force (e.m.f.) $E$ and internal resistance $r$ is connected to a variable resistor of resistance $R$. The current in the circuit is $I$. Use Kirchhoff’s second law to show that $R = \left(\frac{E}{I}\right) - r$.
An ammeter in the circuit in (c) measures the current $I$ while the resistance $R$ is changed. Fig. 6.2 shows a graph of $R$ against $\frac{1}{I}$. Use Fig. 6.2 to determine the power dissipated in the variable resistor when the circuit current is $2.0\,\text{A}$.
Use Fig. 6.2 and the equation from (c) to give the battery’s internal resistance $r$.
Use Fig. 6.2 and the equation from (c) to find the e.m.f. $E$ of the battery.
Use Fig. 6.2 and the equation from (c) to state the battery’s internal resistance $r$.
Use Fig. 6.2 together with the equation from (c) to determine the battery’s e.m.f. $E$.