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The resistance of a sample depends on:
(a) what it is - copper has a very low resistance and plastic a very high one. Materials that have a very high resistance are called INSULATORS and those that have a low resistance are called CONDUCTORS.
(b) how long it is - a long wire has a bigger resistance than a short one of the same material and diameter
(c) how thick it is - a thick wire has a lower resistance than a thin one of the same length and material

As the free electrons move through the material they collide with the atoms of the material and this affects their motion causing resistance.

© Keith Gibbs 2009