Alternating current, or AC, power is a type of electrical current that alternates between a positive and negative charge and flow. AC power differs from the other main type of current, DC, which is a direct current that always flows in one direction between the positive and negative terminals.
DC power is the type of current used in batteries, which always have a constant positive and negative terminal. Alternating current electricity is produced by power plants, allowing the energy companies to change the voltage of the electricity. This is important, as it enables high voltages to travel across long distances. The high voltages are then reduced through a transformer before entering the local power grid.
Unlike AC power, the voltage of DC power is fixed, which means it would be nearly impossible to transport large voltages of DC electricity. In many cases, AC power is transformed to as high as 1 million volts, which is then reduced to around 1,000 volts when it enters the local power grid. This is then further reduced to 120 volts when it enters homes or other buildings.
In the United States, AC power alternates its flow 60 times per second, while it only alternates 50 times per second in Europe and many other places. Most standard U.S. power outlets provide 120-volt, 60-cycle AC power, while European outlets use 240-volt, 50-cycle electricity.