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Electricity and magnetism

Electrical circuits

A simple electric circuitA simple electric circuit In current electricity, electrons are pushed along a conductor by a battery or generator. When the current is switched on, any electrons free to move in the wire all move in the same direction. They flow only if they have a complete pathway of conductors. This pathway is called a circuit. All parts of a circuit must conduct electricity and must be connected to one another. A circuit may have sections or components connected in a series or in parallel. Electrons flow from the negative terminal of a battery or generator towards the positive one, even though the electric current itself is said, by convention, to travel from positive to negative.

An electric circuitAn electric circuit

Series circuit (top) and parallel circuit (above)Series circuit (top) and parallel circuit (above)

Series or parallel

Components of an electrical circuit are connected in either a series or in parallel. In a series circuit—made up of, say, four light bulbs and a single 6-volt battery—a wire links the battery to the first bulb, from there to the second, then on to the next two in turn before returning to the battery in a continuous loop. In a parallel circuit, each bulb is wired to the battery in a separate loop. When the four light bulbs are connected in series, the same current flows through all of them but the voltage is divided into four: 1.5 V for each bulb. When the light bulbs are connected in parallel, each bulb receives a quarter of the current, but the full 6 V from the battery.

The conventional symbol for an electric current is I, which comes from the French phrase "intensité de courant" (current intensity). The I symbol was used by the French scientist André Marie Ampère (1775–1836) after whom the unit of electric current, the ampere, was named.

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