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ELECTRICITY AND ITS MEASUREMENT. Theory tells us that an electric current traveling through a wire is a movement of electrons-about 6.28 billion billion for each ampere.
So, if you're reading this by the light of a lamp with a pair of 60-watt bulbs, you have about 6,280,000,000,000,000,000 electrons hustling through the lamp cord every second.
You can't see them or weigh them as they do their work, but you can measure the current they produce. And you measure it much as you would measure water flowing through a pipe. Instead of figuring in gallons per minute, however, as with water, you calculate electricity in "coulombs" per second.
But you're not likely to hear that term often, as a current of 1 coulomb per second is called a current of 1 ampere. That is the more convenient term you see abbreviated to "amps." on the specification plates of the electric motors you use.
The pressure or "push" that moves the piped water along is measured in pounds per square inch. Similarly, the push behind an electric current is measured in volts. And here again, terms may be combined for convenience.
Multiply the number of amps. a device consumes by the number of volts in the power line and you have its rating in watts-the measuring units you see marked on light bulbs, toasters, and electric heaters.
(On alternating current, this simple mathematics doesn't apply to such things as motors and buzzers because of technical factors.) WHY POWER COMPANIES SUPPLY ALTERNATING CURRENT.
The type of current supplied to most American homes today is 60-cycle alternating current, commonly called AC. Unlike direct current (DC), as from a battery, which always flows in the same direction, AC reverses its direction of flow sixty times a second at 60 cycles.
Power companies use AC because the rapid reversal creates electrical effects that enable them to do essential things that can't be done with DC. For example, they can use a transformer (which won't work on ordinary DC) to "step up" voltage for long-distance transmission, while automatically lowering amperage proportionately.
(Transmission losses are much greater with high amperage and low voltage than with high voltage and low amperage.) At the destination point another transformer is used to "step down" the voltage and automatically raise the amperage to provide a usable combination.
There's a transformer on a utility pole not too far from your house to reduce the several thousand volts carried by the main power lines to the 120 volts required by your lamps and appliances. In most modern systems it also provides the 240 volts needed by heavier equipment.
In greatly simplified terms the transformer consists of two completely separate coils of wire wrapped around the same soft-iron core. When AC is fed into the primary (incoming) coil, the rapid magnetic changes in the iron core "induce" a separate AC in the secondary (outgoing) coil.
And the voltage in the separate coils is proportionate to their relative sizes. If the secondary coil has ten times the number of turns as the primary, it will have ten times the voltage, and you have a "step-up" transformer.
When the sizes are the other way around, the outgoing currerit is lower and you have a "step-down" transformer. This is the same principle used in the transformers that operate a toy train set.