# Conductance

Positive charge moves from higher potential to lower potential, so in a wire, current always flows "downhill"; and the steeper the slope (that is, the greater potential difference between the ends of the wire), the larger the current will be:
$$I=G\Dl V$$
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.