Define the electromotive force (e.m.f.) produced by a source.
The circuit shown in Fig. 5.1 includes a battery of e.m.f. $E$ with internal resistance $r$, a variable resistor, a voltmeter and an ammeter. Readings from the two meters are recorded for different settings of the variable resistor. Fig. 5.2 shows how the potential difference (p.d.) $V$ across the terminals $XY$ of the battery varies with current $I$. Explain why $V$ is not constant.
For the battery in (b), use Fig. 5.2 to find the e.m.f. $E$.
For the battery in (b), use Fig. 5.2 to find the maximum current that the battery can supply.
For the battery in (b), use Fig. 5.2 to find the internal resistance $r$.
On Fig. 5.2, sketch a line to show one possible variation of $V$ with $I$ for a battery with a lower e.m.f. and a lower internal resistance than the battery in (b). Your line should extend over at least the same current range as the original line.
Explain why $V$ does not remain constant.