For low-frequency currents(up to about 15, 000 cycles per second)an iron core, called a magnetic circuit; is placed.

对于低频率电流（约15，000周秒以内），置有一个叫作磁路的铁心。

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For low-frequency currents(up to about 15, 000 cycles per second)an iron core, called a magnetic circuit; is placed.

对于低频率电流（约15，000周秒以内），置有一个叫作磁路的铁心。

youdao