笔者通过对一道“电磁铁”题的一题多变, 将与“电磁铁”相关的“电与磁”的知识点融入其中,不仅系统了知识,培养了能力,还避免了“题海战术”,减轻了学生负担．题目如图1将电磁铁接入电路中,闭合开关．请标出电磁铁的N、S极．评析:考查电磁铁的极性判断,即右手螺旋法则(又叫安培定则)．答案如图2所示．变题1 在电磁铁旁边放一小磁针,请标出小磁针静止后的N、S极． By changing the subject of an “electromagnet” question, the author integrates the “electromagnet”-related “electrical and magnetic” knowledge points, not only the knowledge of the system, the ability to develop, but also the “sea tactics” "Reducing student burden. The problem is shown in Figure 1. The electromagnet is connected to the circuit and the switch is closed. Please mark the N and S poles of the electromagnet. Comment: Check the polarity of the electromagnet, that is right-handed spiral rule (also called Ampere’s rule). The answer is shown in Figure 2. Change the question 1 Put a small magnetic needle beside the electromagnet. Please mark the N and S poles after the small magnetic needle is stationary.