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A battery of emf E and internal resistance r is being charged: the battery's positive terminal is joined to charger terminal A and its negative terminal to charger terminal B. Which statement is correct?

1. The potential difference between A and B must be greater than E.
2. A must be at lower potential than B.
3. Inside the battery, current flows from the positive terminal to the negative terminal.
4. No current flows through the battery.

Correct answer: The potential difference between A and B must be greater than E.

Solution

To drive charging current into the battery, the charger's terminal voltage must overcome both the emf and the internal-resistance drop, so V_AB = E + I*r > E.

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