An old 9.0-V battery produces a potential difference of 9.0 V when checked with a voltmeter.A student is still suspicious of the battery and measures a voltage of 7.6 V when a 100-Ω resistor connects the battery leads.What is the internal resistance of this battery?

Question

Quizplus · Accepted Answer

We can use the formula V = EMF - Ir, where V is the voltage measured across the battery and resistor, EMF is the electromotive force or potential difference of the battery, I is the current flowing through the circuit, and r is the internal resistance of the battery.

Substituting the given values, we have 7.6 V = 9.0 V - I(100 Ω) 
Solving for I, we get I = 0.14 A

Substituting this in the same formula, we get 7.6 V = EMF - (0.14 A)(r) 
Solving for r, we get r = (EMF - 7.6 V)/0.14 A

Substituting EMF = 9.0 V, we get r = 18.4 Ω

Therefore, the internal resistance of the battery is 18.4 Ω. So, the correct answer is (C).

An Old 90-V Battery Produces a Potential Difference of 9