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Chapter 2

# What you need to know about voltage, current, resistance and Ohm’s law

The time-honoured method of explaining voltage, current and resistance is to compare electricity with water in a hosepipe. The voltage corresponds with the pressure of water (in fact old text books speak of electricity being delivered at a pressure of so many volts) whilst the current corresponds to the rate at which the water travels through the pipe. The unit of pressure is the volt (abbreviated to V) and that of current is the ampere (abbreviated to amp or A). However, in electrical ratings and formulae current is referred to by the letter I, so you will find, for instance, I = 10 A, etc. At one time the letter E was used for voltage and although now rare, you may ...

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