When electrons move through a conductor, there's a chance that they will
bump into the large stationary atoms & particles inside it,
temporarily restricting its movement and creating a zone where more
electrons are lumped together.
The bumps that make electron flow harder give the conductor its Resistance.
Each material has a characteristic resistance to the flow of electrons.
In general, the more free electrons the material has, the less
resistance it will have. Materials such as the metals copper, silver and
gold have many free electrons in their structure, and are very good
conductors of current. Other materials such as carbon, have less free
electrons, but still enough to allow considerable current to flow.
The fact that carbon is very easy to mold into a particular shape make
it very useful in the making of resistive elements for electronic
circuits, since the thickness and length of the material help determine
the end resistance of the component, parameters easily changed to create
specific resistance values.
