题目

让质子和氘核的混合物沿和电场垂直的方向进入匀强电场，要使它们离开电场时的偏转角相同，则这些粒子进入电场时必须具有相同的_________. 答案：动能解析：设粒子的质量为m，带电荷量为q，进入电场时的速度为v0，偏转电压为U,板长为L,两板间距为d，粒子的偏转角为θ，则tanθ=，对于质子和氘核来说，q、U、L、d都是相同的，若要它们离开电场时的偏转角相同，则质子和氘核进入电场时的动能必须相同. －How far apart do they live? －________ I know, they live in the same neighbourhood． [　　] A． As far as B． As long as C． As well as D． As often as