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Stuck on Isaac Physics Work

Hi guys, really struggling on question C1.9 which is as follows:
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.)
Can someone tell me how to do it? Thanks.
Original post by NomTheDestroyer
Hi guys, really struggling on question C1.9 which is as follows:
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.)
Can someone tell me how to do it? Thanks.


A critical question that you need to answer is: are the wires connected in parallel or series? I believe once you know the answer to this question, the rest are just "normal" calculations where you can calculate the resistance of each wire using the resistivity, cross-sectional area and length. Just make sure the units match.
Original post by Eimmanuel
A critical question that you need to answer is: are the wires connected in parallel or series? I believe once you know the answer to this question, the rest are just "normal" calculations where you can calculate the resistance of each wire using the resistivity, cross-sectional area and length. Just make sure the units match.

That's not a question to ask - they are obviously in parallel.
Original post by NomTheDestroyer
Hi guys, really struggling on question C1.9 which is as follows:
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.)
Can someone tell me how to do it? Thanks.

You can treat all the wires of the same material as a single one with the combined cross sectional area.

Calculate the resistance of each material, and then calculate their resistance in parallel
Original post by RogerOxon
That's not a question to ask - they are obviously in parallel.


Actually, what you think is obvious, may not be some students in the beginning.
Original post by Eimmanuel
A critical question that you need to answer is: are the wires connected in parallel or series? I believe once you know the answer to this question, the rest are just "normal" calculations where you can calculate the resistance of each wire using the resistivity, cross-sectional area and length. Just make sure the units match.

Thanks, I guess I just couldn't spot that (the thing about the strengthening threw me off). I've managed to complete it now.

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