$$I=G\Dl V$$

where \(G\) is called the conductance. Conductance measures
how easy it is for current to flow: the larger the conductance, the
greater the current will be for a given potential difference. For a
wire, the conductance can be found from the formula
$$G=\sigma \frac{A}{L}$$

- The first parameter \(\sigma\) is the conductivity of the material that makes up the wire. (Notice the difference in endings: -ance vs -ivity!) In SI units (which we'll talk about later), metals have a conductivity of \(10^8\), while glass has a conductivity of \(10^{-12}\).
- The conductance is directly proportional to the
*cross-sectional area*\(A\) of the wire. A thicker wire carries current more easily than a thinner wire. - The conductance is inversely proportional to the
*length*\(L\) of the wire: shorter wires have less conductance.

Something to calculate conductance, how does conductivity change, what
is the current through the wire.