2 A little electricity
A little basic grounding in electricity will help in understanding why artificial lights are rated in watts. A voltage, from the mains or a battery, supplies the pressure to cause electrons, in the form of an electric current, to move around. How many electrons move is dependent on how much resistance is offered to their movement. All metals have a resistance which can be controlled by altering their length or diameter (Figure 2.1). The metal in a bulb is in the form of a piece of wire – the element – which may be straight or coiled to achieve the required length to fit within the glass bulb.
Figure 2.1 The resistance of a piece of wire is determined by the material it is made from, the cross-sectional area of the material, ...
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