- AC stands for "alternating current." The polarity of the electric charge switches from positive to negative, or alternates, at a fixed rate. For typical household current in the United States, the alternation rate is 60 cycles per second.
- DC stands for "direct current." The polarity of the electric charge does not switch back and forth. This is why one end of a battery is positive, and the other end is negative. Current flows from the negative end of the battery, through the device being operated and back to the battery at the positive end.
- Devices designed to operate on DC current use batteries or a power supply device that converts household AC to DC at the correct voltage. The main advantage of DC is the device can be portable, operating off batteries rather than having to be plugged into a wall outlet.
- Devices designed to operate on AC current can use more energy because AC can be easily transmitted at high current levels (amperage). A typical home has a 200-amp electrical system. At the typical voltage of 120 volts, this permits consumption of up to 24,000 watts, more than enough for the many devices we use every day. Most batteries permit only a tiny fraction of this consumption, typically allowing loads in the milliampere range, or 200,000 times less than a home load center.
- Inventor Thomas Edison wanted to use DC power for the country's first electrical grid system. However, the high cost to transmit DC over long distances led utility companies to reject Edison's plan in favor of the cheaper AC system we have today.
