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In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction. Most of the digital electronics that you build will use DC.
There were several technical factors that drove the adoption of alternating-current over direct-current. The direct-current system generated and distributed electrical power at the same voltage as used by the customer's lamps and motors.