1原题及解析如图1,在0≤x≤3~(1/2)a区域内存在与xy平面垂直的匀强磁场,磁感应强度的大小为B.在t=0时刻,一位于坐标原点的粒子源在xy平面内发射出大量同种带电粒子,所有粒子的初速度大小相同,方向与y轴正方向的夹角分布在0～180°范围内.已知沿y轴正方向发射的粒子在t=t_0时刻刚好从磁场边界上P(3~(1/2)a,a)点离开 1 original title and analysis shown in Figure 1, in 0 ≤ x ≤ 3 ~ (1/2) a region and the xy plane perpendicular to the uniform magnetic field, the size of the magnetic flux density B. At t = 0, a coordinate The particle source of the origin emits a large amount of the same kind of charged particles in the xy plane, and the initial velocities of all the particles are the same, and the angle between the direction and the positive direction of the y-axis is distributed within the range of 0-180 °. Of the particles just leave P (3 ~ (1/2) a, a) at the magnetic field boundary at t = t_0