A fixed resistor and a variable resistor are joined in series to a cell with internal resistance, as illustrated. The graph plots how a quantity $X$ changes with the resistance $R$ of the variable resistor as $R$ is raised from zero to its greatest value. What might $X$ stand for?
- Athe current in the circuit
- Bthe electromotive force of the cell
- Cthe potential difference across the internal resistance
- Dthe terminal potential difference across the cell