Electricity is associated with the accumulation or the flow of charged particles, particularly electrons, which are negatively-charged, subatomic particles. Charged particles will naturally flow from areas of high concentration to low concentration if a conductive path is available. The conductor is usually solid, like a copper wire, but can also be liquids such as salt water and mercury, or ionized gases.
Static electricity is caused by the accumulation of electrons, as might occur from rubbing hard rubber on a wool carpet. The resulting static charge can be released suddenly as a spark when you touch a metal object. During a thunderstorm, large quantities of charged particles build up in the clouds and are eventually released to the earth as lightning through ionized air.
In practical devices, the charged particles are made to flow in a controlled fashion through an electrical circuit to supply power to electrical loads, such as lights, motors, heating elements, electronic devices, etc. This flow of charged particles is called electrical current.
In this section we introduce some important concepts and vocabulary related to electricity, electric circuits, and electrical machines.
