The terminal voltage of a cell is greater than its emf, when it is

Options

A. being charged
B. an open circuit
C. being discharged
D. it never happens

Answer

To determine when the terminal voltage of a cell is greater than its electromotive force (emf), we can analyze the situation step by step.

### Step-by-Step Solution:

1. **Understanding Terminal Voltage and EMF**:
- The emf (E) of a cell is the maximum potential difference when no current is flowing.
- The terminal voltage (V) is the potential difference across the terminals of the cell when it is connected to a circuit and current is flowing.

2. **Internal Resistance**:
- Every cell has some internal resistance (r). When current (I) flows through the cell, there is a voltage drop across this internal resistance given by the formula \( IR \), where R is the internal resistance.

3. **Discharging the Cell**:
- When a cell is discharging (supplying power to a circuit), the terminal voltage is given by:
\[ V = E - IR \]
- In this case, the terminal voltage (V) is less than the emf (E) because the term \( IR \) is subtracted from E.

4. **Charging the Cell**:
- When a cell is being charged, the current flows into the cell. In this case, the terminal voltage is given by:
\[ V = E + IR \]
- Here, the terminal voltage (V) is greater than the emf (E) because the term \( IR \) is added to E.

5. **Conclusion**:
- The terminal voltage of a cell is greater than its emf when it is being charged. Therefore, the correct answer is that the terminal voltage is greater than its emf when the cell is charging.

### Final Answer:
The terminal voltage of a cell is greater than its emf when it is **charging**.

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