There are two types of electrical current: direct current DC and alternating current AC.
The DC current is defined as an electron flow, are heading in one direction, usually through the action of a constant voltage, such as a battery that will always from negative to positive and has a constant voltage (1.5 volts for example).
The AC voltage is constantly changing and meaning. It goes from positive to negative and from negative to positive. For example it is from + 2V to 0V, 0V and -2V, 0V to -2V, 0V to 2V, and so on.
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