Explain why the terminal potential difference (p.d.) of a cell that has internal resistance can be smaller than the electromotive force (e.m.f.) of the cell.
A battery with e.m.f. $4.5\,\text{V}$ and internal resistance $r$ is connected in series to a resistor of $6.0\,\Omega$, as shown in Fig. 5.1. The current $I$ in the circuit is $0.65\,\text{A}$. Determine the internal resistance $r$ of the battery.
Determine the battery's terminal potential difference (p.d.).
Determine the amount of power dissipated in the resistor.
Determine the battery's efficiency.
A second resistor with resistance $20\,\Omega$ is connected in parallel with the $6.0\,\Omega$ resistor in Fig. 5.1. Describe and explain qualitatively how the heating effect inside the battery changes.