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Internal Resistance?
When switch S in the figure is open, the voltmeter V of the battery reads 3.07V . When the switch is closed, the voltmeter reading drops to 2.97V , and the ammeter A reads 1.62 A. Assume that the two meters are ideal, so they do not affect the circuit.
Find the internal resistance r of the battery.
Express your answer in ohms to four significant digits.
In the first case the voltmeter measures the electromotive force of the battery E=3.07 V.
In the second case the voltmeter measures the potential difference of the battery U=2.97 V and the ammeter measures a current I=162 A.
Kirchhoff's law tells us that
E=U+rI (1)
where r is the internal resistance of the battery supposed to be in series with the external one.
From (1)
r=(E-U)/I=(3.07-2.97)/1.62=6.17283x10^-4
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