The pathway that allows electricity to flow from the positive terminal of a battery to the negative one is called an electric circuit. By connecting a battery to a metal wire, the electrons in a metal wire will start to move. Just like water through a pipe, the electrons flow in a current, so we call this an electric current.

Voltage

Electric current flowing around a circuit is like water flowing through pipes. In the same way that a pump is used to push the water along, a battery provides the pressure to push the electrons along the wire. This pressure is called voltage. The higher the voltage, the more energy each of the electrons carries. Voltage is measured in volts (we use the symbol V).

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Just as the flow of water is slowed down if the pipe it runs through becomes narrower, an electric current is reduced if the electrons have less space through which to flow. We say there is resistance to the flow. This may happen if the electrons are forced to squeeze along a thinner stretch of wire, for example. A thicker wire has a lower resistance to a thin one. Also, a shorter wire has less resistance than a longer one.
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Thin wires can be made to have an even higher resistance if they are coiled round and round to extend their length. The wires become hot as they resist the current flowing through them. Coils of fine wire are used as filaments in old-style light bulbs (called incandescent light bulbs). They glow white hot when the electric current is switched on, giving out light. Coils of thicker wire are used in electric fires, which glow red hot.
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Electric circuits that have electronic components connected to them are known as electronic circuits. In electronic circuits, resistance comes not from thinner wires but from something else. The electronic components are made from certain non-metallic materials that can conduct electricity—but not as well as metals. We call these materials semiconductors. Semiconductors provide some resistance to the flow of electric current.