What does alternating current mean?

Answer 1

An alternating current (AC) is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant.

The word 'alternating' itself means "changing of direction of flow".

The usual waveform of an AC power circuit is very close to a sine wave because this is the way the electricity is generated in the power plants. It also allows us to efficiently transmit the energy by transforming it to higher and lower voltages.

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AC, or Alternating Current, does exactly what the name implies. In USA, Canada - and in other countries which use the same service frequency - the direction of the current changes 60 times a second (also called a frequency of 60 Hertz) within the 'Hot' wire (also known as the 'Live') - often colored Black - and the Return or Common wire (technically known as the 'Neutral'), which is usually colored White.

In Europe and many other areas of the world, the service frequency is 50 times a second (50 Hertz) within the 'Live' wire which is colored Brown (but on older systems it is colored Black) and the Return or Common wire (technically known as the 'Neutral'), which is colored Blue (but on older systems it is colored Black).

It is the service frequency which makes the typical "humming" sound you hear from Transformers or electric AC motors when they are running.

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During just one cycle of a single-phase alternating supply, the "live" or "hot" wire of an alternating voltage (or current) supply goes from zero to its positive peak, then back to zero, then continues on to its negative peak and back to zero again.

These positive- and negative-going parts of each cycle are always voltages (or currents) relative to the "neutral" wire. A neutral wire is necessary to allow the currents to return to the alternator.

In a 60 hertz supply there are 60 such cycles in each and every second. Similarly, there are 50 such cycles in each and every second in a 50 hertz supply.

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The good link below "AC, DC and Electrical Signals" gives a lot more information about the difference between alternating current and direct current.

Answer 2

Alternating Current means the current is positive and negative, cycling around zero, like a sine wave.