You’ll need to learn a bit about alternating current (AC), if you want to use an AC power supply in your electronic circuits. One good way to get your mind around how AC works is to look at the device that's most often used to generate it: the alternator.

An alternator is a device that converts rotary motion, usually from a turbine driven by water, steam, or a windmill, into electric current. By its very nature, an alternator creates alternating current.

Here are a few other interesting tidbits about alternators:

• The term generator refers to any device that converts mechanical energy into electrical energy. An alternator is a specific type of generator, so it is common — and correct — to refer to an alternator as a generator.

• It's possible to generate direct current from rotating magnetic fields. A DC generator is more complex than an alternator, however, and contains additional components that can wear out over time.

• The frequency of the alternating current generated by an alternator is dictated by the rate at which the magnet rotates. The faster the magnet rotates, the higher the frequency of the resulting alternating current.

• If you place two sets of coils spaced evenly around the magnet, each forming its own complete circuit, alternating current will be induced in each set of coils. However, the polarities of the two voltages will be mirror-images of one another.

In other words, when the voltage is positive in one of the circuits, it will be negative in the other. The relationship between the polarity of the circuits is called a phase, and a power-generating system with two circuits arranged in this way is called a two-phase system. The two circuits are said to be 180º out of phase with one another.

• If three sets of coils are used, the system is called a three-phase system. In a three-phase system, the three circuits are 120º out of phase. Most public power-generation systems are three-phase systems because that results in the most efficient generation of power from the rotating magnetic fields.