# Ohms law??

#### Hotfingers

Joined Mar 29, 2015
2
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

#### Papabravo

Joined Feb 24, 2006
12,389
What is the csa?

#### Treeman

Joined May 22, 2014
157
What is the csa?
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

#### WBahn

Joined Mar 31, 2012
24,692
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
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
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?

#### Papabravo

Joined Feb 24, 2006
12,389
I missed the part about aluminum. Where did that come from?
Nevermind, it was just an example to show different materials have different resitivity.

#### Treeman

Joined May 22, 2014
157
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?
Treeman was being helpful as much as he could. I assumed there was more info to reveal - this seems to be the case often.

#### WBahn

Joined Mar 31, 2012
24,692
Treeman was being helpful as much as he could. I assumed there was more info to reveal - this seems to be the case often.
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