# Aluminium vs Copper in power lines

1. Jun 7, 2016

### Monosandalus

Hi,

I have a question concerning the use of aluminium in power lines. I know that it's lighter than copper and thus cheaper, which is the main reason we prefer it above copper. But in fact alumunium has a lower conductivity than copper. Why is it then that one kg of aluminium can carry twice as much electricity as one kg of copper ? This seems to be contradictory to me.

Thank you :)

2. Jun 7, 2016

### collinsmark

Here's some information that should be useful in the process of considering the question objectively:

Resistivity, $\rho_e, \mathrm{(\Omega \cdot m)}$:
Copper: $1.68 \times 10^{-8}$
Aluminum: $2.86 \times 10^{-8}$​

Conductivity, $\sigma, \mathrm{(S / m)}$:
Copper: $5.96 \times 10^{7}$
Aluminum: $3.50 \times 10^{7}$​

Density $\rho_m, \mathrm{(g/cm^3)}$ [Edit: corrected copy-paste error and a typo.]
Copper: 8.96
Aluminum: 2.70
By the way, resistivity and conductivity are not independent. They are merely reciprocals. $\rho_e = 1/\sigma$. Both resisitivity and conductivity are given in terms of spacial dimensions, such as unit cross-sectional area and unit length.

If $A$ is the cross sectional area of the conductor, $\ell$ is the conductor's length, then

Resistance, $r = \frac{\rho_e \ell}{A}$

Conductance, $G = \frac{1}{r} = \frac{\sigma A}{\ell}$

Mass, $m = A \ell \rho_m$

Last edited: Jun 8, 2016
3. Jun 7, 2016

### rbelli1

You got those swapped. Copper is the higher density material.

BoB

4. Jun 7, 2016

### Nidum

Think about two wires of equal length . One made from 1 kg of Copper and the other from 1 kg of Aluminium .

5. Jun 7, 2016

### collinsmark

And the price of metals depends on many factors besides just their densities (their weights). Lead is not cheaper than silver because it is lighter (it isn't: lead is heavier than silver); it's cheaper because it is more abundant and easier to extract.

6. Jun 7, 2016

### collinsmark

Thanks. It was a copy-paste error. Correction made.