Introduction:

An electrical conductor is a substance in which electrical charge carriers, usually electrons, move easily from atom to atom with the application of voltage. Conductivity, in general, is the capacity to transmit something, such as electricity or heat. Pure elemental silver is the best electrical conductor encountered in everyday life. Copper, steel, gold, aluminum, and brass are also good conductors. In electrical and electronic systems, all conductors comprise solid metals molded into wires or etched onto circuit boards. Some liquids are good electrical conductors. Mercury is an excellent example. A saturated salt-water solution acts as a fair conductor. Gases are normally poor conductors because the atoms are too far apart to allow a free exchange of electrons. However, if a sample of gas contains a significant number of ions, it can act as a fair conductor.

Insulators:

A substance that does not conduct electricity is called an insulator or dielectric material. Common examples include most gases, porcelain, glass, plastic, and distilled water. A material that conducts fairly well, but not very well, is known as a resistor. The most common example is a combination of carbon and clay, mixed together in a specific ratio to produce a constant and predictable opposition to electric current.

Copper and Silver:

Silver is the best conductor of electricity because it contains a higher number of movable atoms (free electrons). For a material to be a good conductor, the electricity passed through it must be able to move the electrons; the more free electrons in a metal, the greater its conductivity. However, silver is more expensive than other materials and is not normally used unless it is required for specialized equipment like satellites or circuit boards. Copper is less conductive than silver but is cheaper and commonly used as an effective conductor in household appliances. Most wires are copper-plated and electromagnet cores are normally wrapped with copper wire. Copper is also easy to solder and wrap into wires, so it is often used when a large amount of conductive material is required.

Aluminum works well, but risky:

Aluminum, when compared by unit weight, is actually more conductive than copper and costs less. Aluminum material is used in household products or in wiring but it is not a common choice because it has several structural flaws. For example, aluminum has the tendency to form an electrically resistant oxide surface in electrical connections, which may cause the connection to overheat. Aluminum is instead used for high-voltage transmission lines (such as overhead phone cables) which can be encased in steel for additional protection.

Gold works well but Expensive:

Gold is a good electric conductor and does not tarnish like other metals when exposed to the air -- for example, steel or copper may oxidize (corrode) when in prolonged conduct with oxygen. Gold is especially expensive and is only used for certain materials, such as circuit board components or small electrical connectors. Some materials may receive gold plating as an electric conductor, or use a small amount of gold which is then plated in another material to reduce manufacturing costs.