Electric conductors are materials with movable electrically charged particles, referred to as "electrons" in metals. When an electric charge is applied to a metal at certain points the electrons will move and allow electricity to pass through. Materials with high electron mobility are good conductors and materials with low electron mobility are not good conductors, instead referred to as "insulators."
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 will normally be used when a large amount of conductive material is required.
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 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 then receives plating in another material to reduce manufacturing costs.
Steel and Brass
Steel is an alloy of iron, which is also a conductor, and is an inflexible metal which is highly corrosive when exposed to air. It is difficult to cast and is not used in small products or machines; instead, steel is used to encase other conductors or for large structure. Brass, which is also an alloy, is a tensile metal which makes it easy to bend and mold into different parts for smaller machines. It is less corrosive than steel, slightly more conductive, cheaper to purchase and still retains value after use, while steel alloy is only valuable when first bought.