# Resistance and fabrication

1. Sep 19, 2010

### J89

1. The problem statement, all variables and given/known data
Suppose that you wish to fabricate a uniform wire out of 1.00 g of copper. Assume the wire has a resistance R = 0.600 , and all of the copper is used.

What will be the diameter of the wire?

2. Relevant equations
A = V/l
R = sqrt(A/pi)

3. The attempt at a solution
For the volume I have gotten 1.12e-7 ( (1*10e-3)/8.92e3)=8.92e3 is the density of copper and it's 1 g of copper. and for the length, I have gotten 1.988.

For the diameter..
I divided the volume/length to get the area = 1.12e-7/1.988 = 5.63e-8
Then I used the formula r = sqrt(A/pi) = sqrt(5.63e-8/pi) = 1.34e-4
so diameter = 2 *r = 1.34e-4*2 = 2.68e-4, but I keep getting it wrong! Can someone explain what I'm doing wrong??

2. Sep 19, 2010

### Gokul43201

Staff Emeritus
How did you get that?

3. Sep 19, 2010

### J89

The resistivity of copper is 1.7e-8. The resistance is .600 ohms. The volume of copper is 1.12e-7 (1 kg copper/density of copper) = 1e-3/8.92e3 = 1.12e-7. So..

I/A = R/P =

.600/(1.7e-8) = 3.53e7 m..then multiply it by the volume of copper = 3.53e7 * (1.12e-7) = 3.9525 and then take the sqrt of that to get the length = 1.988, which is correct according to the problem I'm doing.

Last edited: Sep 19, 2010
4. Sep 19, 2010

### Gokul43201

Staff Emeritus
That looks good, as does the rest of it. Could it be that you need more sig figs? How do you know you answer is wrong?

5. Sep 20, 2010

### J89

The length is right. I know my diameter is wrong because everytime I put it in the hw box, it keeps marking it wrong, and I think this is the correct way to do it..I did a similar problem to this one, and that was marked right..don't know, what I am doing wrong for the diameter..can someone help me?