[2005年高考理综题20]如图1,在一水平放置的平板MN的上方有匀强磁场,磁感应强度的大小为B,磁场方向垂直于纸面向里.许多质量为m、带电量为+q的粒子,以相同的速率v沿位于纸面内的各个方向,由小孔O射入磁场区域.不计重力,不计粒子间的相互影响.图1下列图中阴影部分表示带电粒子可 [2005 college entrance examination theory paper 20] As shown in Fig. 1, there is a uniform magnetic field above the horizontally placed flat panel MN, the magnetic induction intensity is B, and the direction of the magnetic field is perpendicular to the paper surface. Many masses are m and the charge is The particles of +q, at the same rate v along the various directions in the paper plane, enter the magnetic field from the small holes O. The gravity does not affect the mutual influence between the particles. Figure 1 The shaded parts of the following figures indicate that the charged particles can be