alleryStart learning →A battery of 12.0 V emf and 0.100 ohm internal resistance is connected to a 10.0 ohm load. What is its terminal voltage?
A11.9 V
B12.0 V
C10.0 V
D1.19 V
Answer & Solution
Correct answer: A. 11.9 V
1. The internal resistance sits in series with the load, so the current is I = emf / (Rload + r).
2. I = 12.0 V / (10.0 ohm + 0.100 ohm) = 12.0 V / 10.1 ohm = 1.188 A.
3. Terminal voltage follows from V = emf minus Ir.
4. V = 12.0 V minus (1.188 A)(0.100 ohm) = 12.0 V minus 0.119 V = 11.9 V.
5. The drop of only 0.1 V marks 10.0 ohm as a light load for this battery.
6. A reading of 12.0 V would need zero current, which is not the case once a load is attached.
_Source: OpenStax College Physics (CC BY 4.0), Ch 21 "Circuits and DC Instruments", section 21.2 Electromotive Force: Terminal Voltage_
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