A cell with a constant electromotive force (e.m.f.) and internal resistance is joined to a fixed resistor $R$ by means of a potentiometer. A voltmeter is used to measure the potential difference (p.d.) across the terminals of the cell. Which statement accounts for how the voltmeter reading changes as contact Z is moved closer to end X of the potentiometer?
- AThe voltmeter reading decreases because the current through the cell decreases.
- BThe voltmeter reading decreases because the current through the cell increases.
- CThe voltmeter reading increases because the current through the cell decreases.
- DThe voltmeter reading increases because the current through the cell increases.