交流电是其方向周期地变化的电流。
Alternating current is the current whose direction changes periodically.
可控硅控制的一半施加到其的交流电流的正周期。
The SCR controls half of the positive cycle of alternating current applied to it.
完成一次循环的时间称为周期，每秒循环的次数称为频率，任一方向的最大值称为交流电的振幅。
The time taken to complete one cycle is called the period, and the number of cycles per second is the frequency; the maximum value in either direction is the current's amplitude.
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