A relay needs to be switched on from a point $800\,\text{m}$ away from its power supply. The power supply has negligible internal resistance. To operate, the relay needs $16.0\,\text{V}$ and a current of $0.60\,\text{A}$. A cable runs between the relay and the power supply, and two of the wires in the cable are used to deliver power to the relay. Each of these wires has a resistance of $0.0050\,\Omega$ per metre. What is the minimum output e.m.f. of the power supply?
- A$16.6\,\text{V}$
- B$18.4\,\text{V}$
- C$20.8\,\text{V}$
- D$29.3\,\text{V}$