by Ian Loft

Created on: December 11, 2007

It is easy to confuse voltage and current, testing is often only limited to voltage across two points or between wires. Testing for current is something else again and for those unfamiliar with the differences in terminology it can be easier to think of water flowing through a series of pipes to represent the behaviour and performance of an electrical circuit.

Water must have some kind of supply and this supply needs energy to move it. The energy in a water pipe can be thought of as pressure without which the water would remain static within a pipe. The water also has to move from point A to point B however if anything obstructs the pipe then flow will stop. We would use a tap to turn our water flow on or off and this is analogous to an electrical switch we use to turn power on or off.

If we think of voltage like water pressure we can also compare pipe diameters with the capacity of electrical wiring to handle various levels of voltage. Another way of painting a picture might be this: Think of an Olympic size swimming pool suspended 100 feet in the air. If we were to try and attach a small diameter hose and attempt to drain this pool there is a fair chance the pressure of water will overwhelm our small hose in much the same way 100 volts of electricity might simply melt a very fine wire. Clearly we would need something a little more heavy-duty to deal with this kind of energy.

Lets now assume we have a pipe of sufficient diameter through which we can easily turn the water on and off at will. We can direct the water flow where we like (that would be using our electric circuit to do whatever it is we have designed it for) and so long as water is in the pool we are going to continue doing this. Our pool would be more like a battery in that once the water is gone, that's it. But what about current and how are we to measure it?

Now we have managed to connect a pipe that seems to hold the pressure we can think about how fast the water is actually moving through the pipe. This is where it can get a little messy because if we change something a little anything might happen. For example, I change the pipe and increase the diameter then a great deal more water is going through the pipes while a smaller diameter will allow less water movement. This is in effect our current. We can change pressure by raising or lowering the height of our pool from above ground and we can change the current flow by either restricting with smaller pipes or allowing more through by using larger

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