Aluminium is more expensive than iron. why is aluminium and not iron used for the central core in power cables?

One reason may be that iron is a much heavier metal, and a much better conductor of heat and electricity. Iron would lead to some issues after a while, and repairs may end up costing more than it would have cost to just buy aluminum in the first place. 
So, basically just because of each one's different ability to conduct heat and electricity.

Ibelieve it's celsius. hope this .

Olá. porque a reação na temperatura é muito rapida a do copo : )