The electromotive force of a battery is the voltage between its terminals when
Correct answer: B. The circuit is opened.
- A. The circuit is closed.
- B. The circuit is opened.
- C. Its circuit resistance is minimum.
- D. Its internal resistance is maximum.
Explanation
The electromotive force (emf) of a battery is defined as the potential difference across its terminals when no current is flowing through the circuit, which is when the circuit is open. This is because the emf represents the maximum potential difference provided by the battery, without any voltage drop due to the internal resistance. When the circuit is closed, current flows, and the measured voltage is reduced by the internal resistance. Therefore, option B is correct, while the other options describe conditions where the voltage is affected by the current and internal resistance.
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About Internal Resistance of Sources
Internal resistance is the opposition to current inside a cell or other source, causing terminal voltage to fall below its emf when current flows. Questions use E = V + Ir, current in complete circuits, lost volts, source combinations, and the difference between internal resistance and the external load resistance.
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