题质量为m、带电量为-q 且不计重力的微粒,从原点O处沿Oy轴方向以初速度v0射出, 如图1所示,欲加一垂直于纸面的匀强磁场,使这个带电粒子能在xOy平面内运动到点A(x0,y0),求这个磁场的磁感应强度的大小和方向．分析由左手定则可知,匀强磁场的方向应垂直纸面向里．带电微粒在磁场中做匀速圆周运动,在O点所受洛伦兹力与初速度v0垂 The particle with the mass m, charge quantity -q, and gravity is ejected at the initial velocity v0 along the direction of the Oy axis from the origin O. As shown in Fig. 1, a uniform magnetic field perpendicular to the paper surface is added to make this The charged particles can move to the point A (x0, y0) in the xOy plane to find the magnitude and direction of the magnetic induction of this magnetic field. From the left-hand rule, we can see that the direction of the uniform magnetic field should be perpendicular to the paper surface. The charged particles make a uniform circular motion in the magnetic field, and the Lorentz force and initial velocity v0 at the O point.