当导体的自由电子只以一个方向运动时，这样产生的电流叫做直流电，常缩写为。
When the free electrons in a conductor move in one direction only. The current thus established is called a direct current, which is often abbreviated to DC.
当导体的自由电子只以一个方向运动时，这样产生的电流叫做直流电，常缩写为。
When the free electrons in a conductor move in one direction only. The current thus established is called a direct current, which is often abbreviated to DC.
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