A battery possesses an electromotive force (e.m.f.) $E$ and an internal resistance $r$. It supplies a current $I$ to a variable resistor, and the potential difference (p.d.) across the battery terminals is $V$. The variable resistor is then altered so that $I$ becomes larger. Why does $V$ fall?
- AThe e.m.f. $E$ decreases.
- BThe internal resistance $r$ increases.
- CThe p.d. across $r$ increases.
- DThe resistance of the variable resistor increases.