“带电粒子在磁场中的运动”是历年高考中的一个重要考点,而“带电粒子在有界磁场中的运动”则是此考点中的一个难点.其难点在于带电粒子进入设定的有界磁场后只运动一段圆弧就飞出磁场边界,其轨迹不是完整的圆,它要求考生根据带电粒子运动的几何图形去寻找几何关系,然后应用数学工具和相应物 “The motion of charged particles in a magnetic field” is an important test point in the college entrance examination over the years, and “movement of charged particles in a bounded magnetic field” is a difficult point in this test. The difficulty is that charged particles enter the bounded set. After the magnetic field moves only a circle, it flies out of the magnetic field boundary. Its trajectory is not a complete circle. It requires the examinee to find the geometric relationship according to the geometry of the charged particle motion, and then applies mathematical tools and corresponding objects.