带电粒子在有界磁场中的运动很难用实验让学生直观感受,学生往往通过作出的图像来认识其运动情景,对于复杂的问题需作出多幅图像进行动态思考如缩放圆法、旋转圆法等,特别是其中的几何关系对学生来说是一个难点,在以往的教学中往往让学生用硬币或圆形纸片旋转一下去辅助分析,但是硬币或圆形纸不能演示其中的几何关系。笔者制作了一个简易的演示教具,在铁圆环的基础上,加 The movement of charged particles in a bounded magnetic field is difficult to experiment with intuitive students feel that students often make the image to recognize their motion scenarios for complex issues need to make multiple images for dynamic thinking such as scaling circle method, Etc. In particular, the geometric relationship among them is a difficult problem for students. In the past teaching, students often used a coin or a round piece of paper to rotate for analysis. However, coins or round paper could not demonstrate the geometric relationship among them. The author produced a simple demonstration aids, based on the iron ring, plus