Transformer
A transformer functions only with alternating current. That's why the power companies use AC in fact. Transformers simultaneously step up voltage and step down current, and vice versa. Why would this be advantageous? When current is high, a great deal of power is lost to heat. So power companies transmit power at very high voltages but low currents. Then using substations and small transformers outside your house (the gray cylindrical boxes) they can step up the current for practical home use.
flyatyou66, April 2014
