Define the electromotive force (e.m.f.) of a source.

1. (a)Define the electromotive force (e.m.f.) of a source.[2]
2. (b)The circuit shown in Fig. 5.1 contains a battery of e.m.f. E that has internal resistance r, a variable resistor, a voltmeter and an ammeter. [Figure 5.1] Readings from the two meters are taken for different settings of the variable resistor. The variation with current I of the potential difference (p.d.) V across the terminals XY of the battery is shown in Fig. 5.2. [Figure 5.2] Explain why V is not constant.[3]
3. (c)For the battery in (b), use Fig. 5.2 to determine:
4. (c)(i)the e.m.f. E E = ............................................................ V[1]
5. (c)(ii)the maximum current that the battery can supply maximum current = ............................................................ A[1]
6. (c)(iii)the internal resistance r. r = ............................................................ Ω[2]
7. (d)On Fig. 5.2, sketch a line to show a possible variation with I of V 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 range of currents as the original line.[2]

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