Electric Current
A dry cell supplies direct current, or dc. This is electricity that flows in only one direction. Electron flow is always from the negative terminal of the battery through the circuit, and back to the positive terminal, though current is said to flow from positive to negative.
If we connect the lamp to a source of alternating current (ac), current will flow through the lamp in both directions (first one way and then the other). A source of ac acts like a battery that is rapidly reversed in its holder—current will flow first in one direction, then in the other through the wires and the lamp.
A flashlight cell, transistor radio battery, or automobile storage battery is a source of dc. The electricity which you get when you plug an appliance into your household electrical outlets is 60-cycle ac. Sixty-cycle ac is alternating current that changes from plus to minus and back to plus, 60 times per second. All house current in the United States is 60-oycle ac, but some foreign countries use 50-cycle ac, and military and some industrial generators often produce 400-cycle ac.
While technicians still often speak of cycles per second, modern terminology expresses frequency in hertz (Hz). The 60-cycle household current is 60 Hz.
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August 20, 2008