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Fundamentals of Electricity

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Alternating Current (AC)

Alternating current, or "AC" as it's often called, is the kind of power we are all familiar with. We rely on this kind of power in our homes, businesses, and industries. That's because AC power is much more economical to produce and use than DC power.

The first commercial AC power was set up by George Westinghouse in 1886. At that time, Edison was still providing DC current to homes, but the range of power transmission was about one mile from his plant in New Jersey. Because AC power was found to be much cheaper to distribute, it became the obvious preference.

The primary characteristic of AC power that makes it so economical is the ability to change the voltage levels by using transformers. The voltage can be stepped up or down as the need arises. This allows the power to be distributed as widely as needed.

Unlike DC voltage and current, which remain steady, AC voltage and current changes -- or cycles -- 60 times per second in North America. AC power in Europe cycles 50 times per second. This cycling has many advantages which we'll see in the next sections.