3.02 Resistivity.

The resistance of a component depends on an electrical property of the material that it is made from. This property is called resistivity.

Resistivities of various materials.

Conductors.


Copper 1.7 x 10-8 Ohm- metres.
Iron 1 x 10-7 Ohm- metres.

Semiconductors.


Graphite 10-5 Ohm- metres (very variable).
Silicon 105 Ohm- metres.

Insulators.


Paraffin wax 1015 Ohm- metres.
Porcelain 1020 Ohm- metres.

Resistance also depends on the physical dimensions of the component.

resistivity

Example 1.

What is the resistance of 100m of copper wire with a cross sectional area of 1.5mm2.

resistivity