# Ohms law??

Discussion in 'Homework Help' started by Hotfingers, Mar 29, 2015.

1. ### Hotfingers Thread Starter New Member

Mar 29, 2015
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Hi I'm new to this site and would be grateful for a bit help with some home work exam to follow shortly...if I have the resistance and the csa how do I work out the length?... Thanks guys

2. ### Papabravo Expert

Feb 24, 2006
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What is the csa?

3. ### Treeman Member

May 22, 2014
158
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Cross sectional area PB. I guess we talkin wire diameters. My answer would be find the equations that use these known measurements and substitute where required.
R=(resistivity x length) / csa

4. ### Papabravo Expert

Feb 24, 2006
10,145
1,791
Last edited: Mar 29, 2015
5. ### WBahn Moderator

Mar 31, 2012
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So to use that equation you need three of the four parameters. You apparently only have two. You also need to know the resistivity. Doesn't it make sense that the length of aluminum wire is going to different than length of copper or the length of steel?

@Hotfingers : Do you have either the resistivity or at least the material that the wire is made out of?

6. ### Papabravo Expert

Feb 24, 2006
10,145
1,791
I missed the part about aluminum. Where did that come from?
Nevermind, it was just an example to show different materials have different resitivity.

7. ### Treeman Member

May 22, 2014
158
15
Treeman was being helpful as much as he could. I assumed there was more info to reveal - this seems to be the case often.

8. ### WBahn Moderator

Mar 31, 2012
17,748
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No problem there. I didn't realize until after I had posted that the two quotes in my response were from different people, so I went back and added the note to the TS.

Treeman likes this.
9. ### Hotfingers Thread Starter New Member

Mar 29, 2015
2
0
Thanks for reply,s guys will continue with the homework,cheers