Direct Current
One of two types of electrical flow, direct current (DC) predates alternating current. Unlike alternating current, direct current flows in only one direction. Current is measured in amperes, frequently shortened to "amps," which is the amount of electrical charge that flows over a given time span.
Benjamin Franklin, who first suggested the terms "positive" and "negative" electrical charges, believed the flow of current went from positive to negative. In fact the opposite is true, because current is carried by electrons, which are negatively-charged and so attracted to positive polarities. The electric battery that Alessandro Volta invented in 1800 produced direct current and was an immediate success. It, its successors, and direct current generators were used to operate a variety of electrical devices during the next eighty years.
Then, in 1881, serious competition arose in the form of a brilliant Croatian electrical engineer named Nikola Tesla. Employed by the Continental Edison Company in Paris, Tesla was a firm believer in the advantages of alternating current, but he had been unable to convince others. In 1884 he came to the United States to work with the great inventor Thomas Alva Edison, a major proponent of direct current.
The fact that direct current was prone to numerous problems was not in question. Direct current generators had carbon brushes that touched a rotating commutator to draw electrical power. This rotating contact point caused arcing, and the higher the voltage that was being generated, the greater the arcing. This effectively limited direct current to low levels. Another problem was due to resistance within the wires conducting the current. Resistance causes heat, and that resulted in reducing the current further. Raising the level of the current to compensate was ineffective; doubling the current caused heating loss to be squared, plus it worsened generator arcing. This meant that Edison's generating plants were limited to delivering power to customers within a few blocks. In addition, Tesla and Edison did not get along; each described the other's mentality as low, for example. Edison believed direct current was far safer than alternating current, which he thought was deadly, though Tesla disagreed. Edison argued that no one could switch from direct current because there were no successful alternating current motors. Tesla asserted the benefits of his alternating current polyphase system. Each man was determined his system was better and the arguments became more emotional. Eventually, Tesla left Edison in disgust in 1885.
The nail in direct current's coffin was delivered eight years later in 1893, and it was Tesla who held the hammer. He and George Westinghouse had underbid Edison for the contract to provide electricity to the Columbian Exposition in Chicago, and their alternating current was a spectacular triumph.
Direct current may have lost out as the primary source of the world's electric power, but it is still extremely vital. Batteries, both large and small, produce direct current for a variety of applications. Modern electronics, telephones, computers, and a host of other devices require direct current to operate. Ironically it is often Tesla's alternating current that is transformed into direct current to provide the power.
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