A $110\,\text{V}$ supply with negligible internal resistance is linked to a heater via a fuse and a switch. The supply’s positive and negative terminals are $S^+$ and $S^-$. For fault-finding, points $C1$ and $C2$ on either side of the heater can be accessed. A voltmeter is placed between $S^-$ and $C1$. When the circuit operates correctly, the voltmeter reading is recorded while the switch is closed. A fault then develops, and the voltmeter is once more connected between $S^-$ and $C1$ with the switch still closed. Which fault would produce the same two voltmeter readings?
- Aa break in the wire of the heater
- Ba broken switch that cannot close correctly
- Ca melted fuse
- Da short circuit in the heater