State the condition under which the terminal potential difference across a battery and its emf are equal.

Explanation

To determine the condition under which the terminal potential difference across a battery (V) is equal to its electromotive force (EMF, E), we can analyze the behavior of the battery in different scenarios: charging and discharging.

### Step-by-Step Solution:

1. **Understanding EMF and Terminal Potential Difference**:
- The EMF (E) of a battery is the maximum potential difference between its terminals when no current is flowing.
- The terminal potential difference (V) is the voltage measured across the terminals of the battery when it is connected in a circuit and current is flowing.

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