带电粒子以某一速度沿垂直于磁场方向射入有界的匀强磁场中后 ,要求粒子在运动中通过某个定点 ,以此作为题设条件的物理问题 ,我们暂且称为过定点问题 ,粒子过定点问题是高考物理试题中的热点问题之一 .此类问题之所以能成为热点 ,笔者认为有以下几种原因 :( 1 )此类问题所涉及 After a charged particle is injected into a bounded homogeneous magnetic field at a certain speed along a direction perpendicular to the magnetic field, the particle is required to pass through a fixed point in the motion. This is a physical problem with the condition of the question, which we will call the over-point problem for the time being. The problem of over-fixed particles is one of the hot issues in the physics test of college entrance examination. The reason why such problems can become hot spots, the author believes that there are several reasons: (1) This type of problem involves