电磁感应知识与实际问题的联系非常紧密,电磁感应现象随处可见,从下面的几例中就可略见一斑.例1普通磁带录音机是用一个磁头来录音和放音的,磁头结构如图1所示.在一环形铁芯上绕一个线圈b,铁芯有个缝隙, The electromagnetic induction knowledge is closely related to practical problems. The phenomenon of electromagnetic induction can be seen everywhere. It can be seen from the following examples. Example 1 An ordinary tape recorder uses a magnetic head to record and play sounds. The magnetic head structure is shown in Figure 1. As shown, a coil b is wound around a toroidal core, and the core has a gap.