The free
electrons in a metal are in constant random motion. As they move about they collide with each
other and with the atoms of the metal. If a potential difference is now applied across the metal the
electrons tend to move towards the positive connection. As they do so their progress is interrupted
by collisions. The ease with which the free electrons can move through the material is called its
conductance. If the temperature of the metal is raised the atoms vibrate more strongly and the
electrons make more violent collisions with them and so the conductance of the metal decreases.
The conductance of any conducting material depends on the following factors:
(a) the material itself (actually how many free electrons there are per metre cubed)
(b) its
length
(c) its cross-sectional area and (d) its temperature
The conductance of a given
piece of material is connected to the current flowing through it and the potential difference between
its ends by the equation: