September 22, 2008


Factors Affecting Resistance
As previously discussed, every material offers some resistance for opposition to the flow of current. Some conductors such as copper, silver, and aluminum offer very little resistance to current flow. Insulators such as glass, wood, and paper, offers high resistance to the flow of current.

The size and type of wire in an electric circuit are chosen to keep the electric resistance as low as possible. This allows the current to flow easily through the conductor. In an electrical circuit the larger the diameter of the wire, the lesser the opposition, electrical resistance, to the flow of current.

Temperature also affects the resistance of an electrical conductor. In most conductors (copper, silver, aluminum, and so on), resistance increases with temperature. Carbon is an exemption because the resistance decreases as temperature increases. Certain alloys of metals (manganin and constantan) have resistance that does not change with temperature.

The relative resistance of several conductors of the same length and cross section is shown below. Silver is used as a standard of 1 and the remaining metals are arranged in order of ascending resistance.