Define electric potential difference (p.d.) in terms of energy transferred and charge.
A battery with electromotive force (e.m.f.) $14\,\text{V}$ and negligible internal resistance is linked to a resistor network, as shown in Fig. 6.1. $R_1$ and $R_2$ are fixed resistors with resistances $6.0\,\Omega$ and $12\,\Omega$ respectively. $R_3$ is a variable resistor. Switch $S$ is closed. Calculate the current in the battery when the resistance of $R_3$ is adjusted to zero.
Calculate the current in the battery when the resistance of $R_3$ is set to $24\,\Omega$.
Use your results in (b)(i) to work out the change in the total power generated by the battery when $R_3$ is altered from zero to $24\,\Omega$.
Switch $S$ in Fig. 6.1 is now open. $R_1$ and $R_2$ are metal-wire resistors. Some data for these resistors are given in Fig. 6.2. Determine the ratio \[ \frac{\text{average drift speed of free electrons in } R_1}{\text{average drift speed of free electrons in } R_2}. \]