把大头外放入蹄形磁体两极之间，上下各放4～6根。先让学生观察分析大头针与磁场分布（磁感线）的关系（拿出蹄形磁体磁场分布挂图或幻灯片作比较），得出大头针的位置就是该处磁场分布（磁感线），然后将闭合电路的一部分导体放人磁场（附图人导体上下运动，方向与大头针平行 Put the big head out between the two poles of the shoe magnets and place 4 to 6 rods up and down. First, let the students observe and analyze the relationship between the pin and the magnetic field distribution (magnetic induction line) (take out the magnet magnetic field wall map or slide for comparison), get the position of the pin is the magnetic field distribution (magnetic induction line), and then A part of the conductors of the closed circuit put a magnetic field (the figure’s conductor moves up and down, and the direction is parallel to the pins)