AC and DC current are the two primary methods of electrical transmission. DC most frequently finds a home in battery-powered objects as well as home electronics, while AC forms the basis for the most efficient long-range energy transmission. Appliances often have devices known as inverters for changing AC current, which is only usable by the simplest of devices, into DC current, which is usable in electronics thanks to its stability of flow. AC and DC technology were at one point competing technologies. DC technology is the elder technology by far and dates back as far as the Baghdad battery found in Khujut Rabu in 250 B.C., though scholars can only speculate as to what it was used for.
How AC and DC Differ
To the layman AC/DC may seem quite similar, as both are electricity; however the difference is in the waveform of the transmitted electricity. The DC waveform, when viewed in the form of a chart, is illustrated by a smooth and less varying line akin to the ripples in a pond, remaining almost entirely stable. The AC waveform alternates between periods of high and low voltage, giving the overall appearance of a square waveform changing quickly at right angles on a chart. Another important distinction is that direct current moves in only one direction, whereas alternating current moves in two. The frequency of that variation is known as a Hertz cycle. The variation between the two voltage levels serves to reduce collisions that cause energy loss during transmission, making AC the superior long-distance transmission format to DC, which suffers a high degree of energy loss during transmission.
DC in Electronics
Direct current is used in any device that has a circuit board because the chips within these devices require a steady, unidirectional flow of electrons to operate and store data. Every home PC has a DC inverter built into the system, which then provides DC style power to the rest of the devices inside the case. Laptops are another story, since they contain a battery that already gives power in the DC format. Anybody who has brought a laptop on the road is familiar with the bulky box located somewhere on the power cord, which is a DC converter as well. DC current is also required to run the majority of electric motors; these motors run everything from the optical disk drive and the spinning of its hard disk in a computer, to the movements of a robotic arm at a manufacturing plant.
DC in Power Generation
The most basic electrical generators create their energy in DC format, which is then changed via transformer into AC format for transmission. The reason for this is DC generators are far simpler to construct and they make the most of the rotary energy that they harness. Another reason that DC generators are more popular is that AC generators require extensive engineering and phase-synchronization equipment placed in series with one another, whereas DC easily lends itself to parallel circuitry.
- Aaron Graubart/Photodisc/Getty Images