## Characteristics

AC electricity is described in terms of period, frequency, and amplitude.

• Period - Period is the amount of time that it takes the waveform to make one complete cycle.
• Frequency - Measured in hertz (`hz`), frequency is the number of times the waveform repeats itself in one second. This value is usually `60hz` in the United States and `50hz` in most of the rest of the world.
• Amplitude - This is the magnitude of the waveform and is usually measured in volts or amps.

## Other Waveforms

Alternating current is not always a perfect sine wave. In fact, alternating currents are often generated digitally by using triangle and square waves:

Sometimes, even more complex waveforms are generated, usually by adding other waveforms on top of an existing carrier wave, in what’s known as modulation:

In fact, this is how radio transmissions work! A message signal is added to a carrier signal, for instance `107.7Mhz`, then a radio receiver “tunes” into that particular frequency of carrier signal, and then subtracts it from the transmission, leaving only the message signal.

## Next - Review

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