# Resistivity Help

Discussion in 'Homework Help' started by RJElec, Jan 27, 2014.

1. ### RJElec Thread Starter New Member

Apr 28, 2013
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An aluminum wire 7.5m long connected in parallel with a copper wire 6m long. When a current of 5A is passed through this combination it is found that the current in the aluminum wire is 3A. If the diameter of the aluminum wire is 1mm determine the diameter of the copper wire.

ρCU = 0.17μΩmm and ρAL= 0.28μΩmm

Can anyone help me with the procedure for calculating this Ive found the resistance of the aluminum but am not entirely sure where to go next

Thanks

Oct 18, 2012
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3. ### RJElec Thread Starter New Member

Apr 28, 2013
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Is the resistance the same for both? I mean once i calculated the resistance for the AL can i use it to calc the CU?

4. ### tshuck Well-Known Member

Oct 18, 2012
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You would have to work out the math to prove they have the same resistance.

However, Ohm's Law tells you they aren't...

5. ### shteii01 AAC Fanatic!

Feb 19, 2010
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No, the resistances are different. How do you know that? Simple. 5 A is goes in, 3 A comes out of Al wire. Where did the other 2 A go? It went through Cu wire. Why did Al wire passed more current than Cu wire? Because Al wire has lower resistance.

Overall, you have a classic current divider circuit. In the current divider circuit you have two resistors in parallel. The branch with lower resistance conducts more current, the branch with higher resistance conducts less current.

6. ### shteii01 AAC Fanatic!

Feb 19, 2010
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The properties of the wire, like resistance for example, should be tabulated somewhere. Maybe even in your textbook, in one of the chapters or in appendix in the end of the book. Look them up and plug them into the tshuck formula.

7. ### RJElec Thread Starter New Member

Apr 28, 2013
7
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Ok i got it thanks i just didn't see it straight away but i have drawn out a parallel circuit and filled in the blanks.

Oct 18, 2012
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679