# Circuits - Calculating resistance/conductance etc

1. Feb 19, 2014

1. The problem statement, all variables and given/known data
Source with voltage 4.25mV is ran along a 10cm long cylindrical copper conductor which has a cross sectional radius of 0.8mm. If the current was measured at 5A flowing through the conductor calculate: the resistance and conductance of the conductor and the resistivity and conductivity of the material the conductor is made from.

2. Relevant equations

The only equations we were given last week which is supposed to refer to this problem type are:
$$I=\frac{Q}{t} \\ Q=ne \\ I=\frac{ne}{t} \\ I=frac{neAl}{t}=neAv_d \\ v_d=\frac{I}{nAe} \\ J=\frac{I}{A}=nv_de \\ \rho=\frac{E}{J} \\ \rho=(\frac{V}{I})(\frac{A}{l}) \\ R=\frac{V}{I}=\frac{\rho l}{A} \\$$

3. The attempt at a solution

For the resistance i have done:
$$R=\frac{V}{I}=\frac{0.00425}{5}=0.00085Ω$$
For the conductance I looked it up that its the inverse so I just did
$$\frac{1}{0.00085}=1176.47Ω^{-1}\\$$
for the resistivity i have done
$$\rho=\frac{RA}{l} \\ \rho=\frac{(0.00085)(\pi 0.0088^2)}{0.1}=2.07\times 10^{-5} \\$$
It is the conductivty that is confusing the hell out of me, dont even know where to start.

Any help is really appreciated. Thanks.

Last edited: Feb 19, 2014
2. Feb 19, 2014

### ehild

3. Feb 19, 2014

Oh right OK thank you :)

Is what I have already done correct? Apart from the little typo mistake where I used 0.88mm for the radius as it should be just 0.8mm.

4. Feb 19, 2014

### ehild

It looks correct.

ehild