法拉第电磁感应定律告诉我们,只要闭合电路的磁通量发生变化,就会有感应电动势产生.引起磁通量的变化的原因无非有以下三种情况:①B不随时间变化,但闭合电路的整体或局部在做切割磁感线的运动,这样产生的感应电动势叫动生电动势.②B随时间变化,但闭合电路的任一部分都不动,这样 Faraday’s law of electromagnetic induction tells us that as long as the magnetic flux of the closed circuit changes, there will be induced electromotive force generated. There are three reasons causing the magnetic flux change: ①B does not change with time, but the whole or part of the closed circuit is cutting Magnetic induction line of movement, the resulting induced electromotive force called dynamic electromotive force.②B changes with time, but closed any part of the circuit are not moving, so