An AC circuit is an alternating current circuit. Instead of a constant voltage supplied by a battery, the voltage oscillates in a sine wave patter varying with time.

V = V_0sin(wt)

Where

V_0 is the maximum voltage

W is the angular frequency

t is time

The first alternator to produce alternating current was a dynamo electric generator based on Michael Faraday’s principles. It was constructed by the French instrument maker Hippolyte Pixii in 1832.[1] The earliest recorded practical application of alternating current is Guillaume Duchenne, inventor and developer of electrotherapy. In 1855, it was announced that AC currents were superior to direct current for electrotherapeutic triggering of muscle contractions.

AV voltage may be increased or decreased with a transformer; use of a higher voltage leads to significantly more efficient transmissions of power. The power losses in a conductor are a product of the square of the current and the resistance of the conductor.

P_L = I^2R

The power transmitted is equal to the product of the current and the voltage

P_t = IV

Therefore the same amount of power can be transmitted with a lower current by increasing the voltage.

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