在磁场中运动的带电粒子若同时受到匀强电场和重力场的作用,往往给带电粒子配一对大小相等、方向相反的速度,这既不影响带电粒子的运动,又可使配给的一对速度中一个速度所对应的洛伦兹力与电场力或重力平衡,从而可使问题简化.下面举几个典型的例子加以比较说明. When a charged particle moving in a magnetic field is simultaneously subjected to a uniform electric field and a gravitational field, the charged particle is often assigned a pair of equal-sized and opposite-direction velocities, which does not affect the motion of the charged particle, but also makes it possible to pair the charged particles. The Lorentz force corresponding to a velocity in the velocity is balanced with the electric field force or gravity, so that the problem can be simplified. Here are a few typical examples to illustrate.