Imagine a copper wire 10 km long that needs to supply a city with 10 Mwatts of power--say from a waterfall. If the city ran on DC power, with voltages of 100 V, how much current would run through that wire? If you were willing to lose 1% of your power as heat in the wire, how thick would such a wire have to be? The resistivity of copper is 1.7 x 10-8 ohm-m.