有关磁场面积极小值的题目是磁偏转问题中常见的考查方向,也是各类考试和习题教学中常见的题目.但对学生来说,却较难.其难点在于带电粒子的运动轨迹不是完整的圆,且具体的磁场大小不明确给出,给学生制造一定的困难.下面讨论此类问题的基本解法. The problem of the minimum magnetic field area is a common test direction in the field of magnetic deflection, and is also a common problem in various examinations and exercises, but it is more difficult for the students.The difficulty is that the trajectories of the charged particles are not complete Of the circle, and the specific size of the magnetic field is not given, to create some difficulties for students below to discuss the basic solution to such problems.