HiSET Science: Electrical Properties of Materials

Common Means of Transferring Electrical Charge
Charge is transferred in three common ways: conduction, induction, and friction. Conduction, as the name implies, takes place between conductive materials. There must be a point of contact between the two materials and a potential difference, such as when a battery is connected to a circuit. Induction also requires conductive materials. It occurs due to one material encountering a varying magnetic field. This can be the result of a changing magnetic field or the material moving within a constant magnetic field. Charge transfer due to friction does not require conductive materials. When two materials are rubbed together, electrons may be transferred from one to the other, leaving the two materials with equal and opposite charges. This is observed when shoes are dragged across a carpeted floor.

Conductors, Insulators, and Semiconductors
In many materials, electrons are able to move freely; these are known as conductors. Due to their atomic structure and delocalized electrons, metals tend to be the best conductors, particularly copper and silver. Highly conductive wires are instrumental in creating low-resistance pathways for electrons to travel along within a circuit.
Other materials naturally inhibit the movement of charge and are known as insulators. Their electrons are tightly held by the individual constituent atoms. Glass, pure water, wood, and plastic are all insulators. Insulators are necessary in circuits to prevent charge from escaping to undesirable places, such as an operator's hand. For this reason, most highly conductive materials are covered by insulators.
Semiconductors, as the name suggests, are materials that only partially conduct electrical charge. The elements silicon and germanium are both common semiconductors, and are frequently used in microelectronic devices because they allow for tight control of the rate of conduction. In many cases, the conduction ability of semiconductors can be controlled by adjusting the temperature of the material.