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The key functions of a battery and bulb in a circuit are explained. A battery is a source of energy which provides a push – a voltage – of energy to get the current flowing in a circuit. A bulb uses the electrical energy provided by the battery, but does not use current. When the energy in the battery is used up there is no current and the bulb does not light up.

To demonstrate this, a model of a water circuit, with a water wheel, is shown. The turning water wheel represents a lit bulb in an electrical circuit. The moving water represents the current flowing around the circuit. A pump represents a battery providing the energy to move the water. When the water (current) stops flowing, the water wheel (the lightbulb) stops turning.