A battery of e.m.f. $E$ and internal resistance $r$ is connected in series with a variable external resistor. The external resistance $R$ is gradually raised from zero. Which statement is correct? (Ignore any temperature effects.)
- AThe potential difference across the external resistance decreases.
- BThe potential difference across the internal resistance increases.
- CThe power dissipated in $r$ increases and then decreases.
- DThe power dissipated in $R$ increases and then decreases.