Why do they say that copper wires are more conductor than aluminium wires?
Copper conducts electricity better than Aluminium, it has a lower resistance - that is less energy is converted into heat when passing the same amount of electricity through a Copper than Al wire.
1 dm^3 of copper has less resistance than 1 dm^2 of Al.
1 Kg of Cu has more resistance than 1 Kg of Al.
1 $ of Cu has about the same resistance than 1 $ of Al. ( at prices when the books I read were written )
The quantity you need to pay attention to is resistivity. As mgb points out it gives you a lower resistance for copper when compared to the same quantity of aluminum. I don't have the numbers in front of me, but aluminum wire requires about 50% more cross-sectional area to carry the same current as copper. If you are familiar with wire gauges, aluminum must be 2 gauges larger than copper. The great problem is that wire heats up when carrying current (I^2R losses) and aluminum expands much more than copper, thus loosening connections. Furthermore, aluminum oxide forms quite easily and is very non-conducting. My house originally had aluminum wiring due to the high price of copper when the Chilean copper mines were shut down in the early 1970s. After 2 fires, I had the house rewired with copper.
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