AC vs DC: What’s the difference?

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Electricity involves the movement of electrons along a conductor. Direct current flows in one direction, while alternating current flows in both directions. Batteries produce DC, while power grids use AC. AC can transfer different amounts of energy and can be increased or decreased in strength by transformers.

Electricity is a type of energy that involves the movement of electrons along a conductor, such as a wire. The flow of electrons can occur in one direction or both directions along the wire. When electricity flows in one direction, it is referred to as direct current (DC). Alternating current (AC) is when electrons flow in both directions, one and then the other. Batteries produce direct current, and the power grids that supply electricity to homes and other buildings use alternating current.

Direct current

In nature, electricity occurs only rarely, in some animals or with lightning. In the quest to create electricity, scientists have discovered that electric and magnetic fields are interrelated. A magnetic field near a wire causes electrons to flow in only one direction along the wire because they are repelled and attracted by the poles of the magnet. This is how direct current from a battery was born, a development that is primarily attributed to the work and promotion of American inventor Thomas Edison during the 19th century.


In the late 19th century, another scientist, Serbian-American engineer Nikola Tesla worked on developing AC because it could transfer different amounts of energy. Instead of constantly applying magnetism along the wire, he used a spinning magnet. When the magnet was oriented in one direction, the electrons flowed towards the positive, but when the orientation of the magnet was flipped, the electrons also rotated.


Another difference between AC and DC pertains to the amount of energy each can carry. Each battery is designed to produce only one level of voltage, and that DC voltage can’t travel very far until it starts losing energy. The AC voltage from a generator in a power plant can be increased or decreased in strength by another mechanism, called a transformer.


Transformers are used wherever an electrical voltage needs to be increased or decreased. For example, they are commonly seen on electrical poles. A power plant produces very high voltage electricity so that it can travel great distances. The voltage must be reduced, however, before the electricity reaches the homes and other buildings that use it to power appliances, machinery and other devices. Alternating current can also be changed to direct current via an adapter, such as the type used to power a laptop computer battery.

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