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# Resitivity Question

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1. A high voltage wire for transmission of electricity across the country is made of 10 aluminium wires (resistivity of 2.5×10−8Ωm) wound together with 15 copper wires (resistivity of 1.5×10−8Ωm). If all of the wires have a radius of 2.0mm, calculate the overall resistance of 20km of cable to two significant figures (The aluminium is there to give strength to the cable.)

Anyone know how to do this? Or give me a hint on how to solve it?
2. Work out the resistance of one aluminum wire and the resistance of one copper wire

treat the entire cable as if it was made of the appropriate numbers of wires of those resistances in a parallel circuit ... like this question http://www.thestudentroom.co.uk/show....php?t=4106261
3. (Original post by JustDynamite)
A high voltage wire for transmission of electricity across the country is made of 10 aluminium wires (resistivity of 2.5×10−8Ωm) wound together with 15 copper wires (resistivity of 1.5×10−8Ωm). If all of the wires have a radius of 2.0mm, calculate the overall resistance of 20km of cable to two significant figures (The aluminium is there to give strength to the cable.)

Anyone know how to do this? Or give me a hint on how to solve it?
Work out cross sectional area and the resistivity of eacha nd multiply by the number of those wires.

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