Halliday, Resnick & Walker — Circuits: Problem 24

24 When the lights of a car are switched on, an ammeter in series with them reads 10.0 A and a voltmeter connected across them reads 12.0 V (Fig. 27-34). When the electric starting motor is turned on, the ammeter reading drops to 8.50 A and the lights dim somewhat. If the internal resistance of the battery is 0.0500 \(\Omega\) and that of the ammeter is negligible, what are (a) the emf of the battery and (b) the current through the starting motor when the lights are on?