Because alternating current starts at zero, reaches a peak, and then returns to zero, there is always a variation in voltage and an effective value has to be determined.

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Alternating current (AC) indeed starts at zero, reaches a peak, and then returns to zero, completing a cycle. This results in a variation in voltage over time. The effective value, often referred to as the root mean square (RMS) value, is calculated to represent the equivalent direct current (DC) value that would deliver the same power to a load.

Because Alternating Current Starts at Zero, Reaches a Peak, and Then