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Feb15-11, 07:56 AM
P: 310
The stepping up and stepping down is done by a transformer. The way a transformer works, whatever change is done to the voltage, the inverse is done to the current. Double the voltage, and the current is halved. Halve the voltage, and the current is doubled. This conserves power. There are some small power losses through eddy currents, hysteresis, flux leakage, wire resistance, etc, but overall transformers are very efficient. I believe around 95% or so.