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This section may seem rather theoretical, but I thought that I would throw it in anyway!
Electronic systems work with electrical voltage and current. What do I mean by ‘Voltage’? An electrical system requires a source of electrical ‘energy’ in order to produce a flow of current. A current flows when electrons in a conductive material (usually a metal) are ‘forced’ between the positive and negative of the source. The source is referred to as the ‘Electro Motive Force’ or ‘EMF’. The term ‘Force’ is rather a misnomer, because it implies a physical interaction - Newtons laws and all that! However, it is descriptive, because it, in effect, ‘pushes’ the electrons in the conductors, around the circuit. The ‘Voltage’ in a system is the equivalent of the EMF.
So what is this mysterious source? Well, in a battery, it is a chemical reaction. This can be self-generating, like the multi-purpose ‘AA’ cell, or it can be stimulated by passing an external current through chemicals, as in a rechargeable battery. A common mistake is to call a single cell a ‘battery’. A battery is multiple cells connected together in ‘Series’.
All electrical systems exhibit ‘Resistance’. This is a property that ‘resists’ the flow of current. A physical analogy could be a water tap. When the tap is off, there is no flow of water. This is equivalent to a resistance of infinity (which is pretty high!). As the tap is turned on, the water flow increases. This is equivalent to reducing the resistance. When the resistance reaches zero, there would be no restriction to the flow of current. In theory, at this point, there would be infinite current flowing! So why doesn’t it? Because there is always some resistance in an electrical system. The one place that ultimately restricts current flow, is the source (the EMF). This is referred to as the ’Internal Resistance’. You remember that chemical reaction in a battery? Well it can only supply a limited amount of current. If you can make a battery with no internal resistance...patent it, QUICK!
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