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研究带电粒子在电磁场中的运动时,经常需要对带电粒子的运动轨迹进行讨论,在讨论的过程中,往往关注题目的条件而忽视轨迹的合理性,请看例题.例如图1所示,在 xOy 平面内的第一象限中有沿 y 方向的匀强电场,在第二、第三、第四象限中有匀强磁场,方向垂直于坐标平面向里.有一个质量为 m,电荷量为 e 的电子,从 y轴上的 P 点以初速度 v_0垂直于电场方向进入电场之后电子从 x 轴上 Q 点进入匀强磁场,最后恰从 P 点以垂直于 y 轴的方向射出磁场.若OP=h,OQ=3~(1/2)h,不计电子的重力.求:
When studying the motion of a charged particle in an electromagnetic field, it is often necessary to discuss the trajectory of the charged particle. In the process of discussion, we often pay attention to the condition of the subject and ignore the plausibility of the trajectory. See the example. For example, as shown in Figure 1, In the first quadrant of the xOy plane, there is a uniform electric field along the y direction. In the second, third and fourth quadrants, there is a uniform magnetic field, and the direction is perpendicular to the coordinate plane inwards. There is a mass m and the charge quantity is The electrons of e, from point P on the y-axis to the electric field at an initial velocity v_0 perpendicular to the direction of the electric field, enter the uniform magnetic field from point Q on the x-axis, and finally emit the magnetic field from the point P perpendicular to the direction of the y-axis. OP = h, OQ = 3 ~ (1/2) h, not counting the electronic gravity.