When the lights of an automobile are switched on, an ammeter in series with them
ID: 2194217 • Letter: W
Question
When the lights of an automobile are switched on, an ammeter in series with them reads 10.20 A and a voltmeter connected across them reads 12.10 V. When the electric starting motor is also turned on, the ammeter reading drops to 9.00 A and the lights dim somewhat. If the internal resistance of the battery is 42 m? and that of the ammeter is negligible, what is the emf of the battery?
What does the voltmeter read when the starting motor is turned on?
What is the current through the starting motor?
S Starting Lights Ill ge Lights motor RExplanation / Answer
i) Lights are connected in parallel to the battery thus the battery emf is 12.10 V ii)Voltage will be the same and current will be divided amongst the lights and starting motor so the voltmeter would read the same 12.10 V iii)the current will be divided among the lights and motor thus current through starting motor = 10.20 A - 9.00 A => I = 1.20 A
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