摘要：从O点返回磁场后的轨迹如图.圆心角为120°.故:T=t1+T+T??????????????????????? ⑥联立②④⑤⑥解得:E = ???????????????? ⑦(3)第二次离开磁场后到再进入电场.如图轨迹.则DF=OD=2R cos30°???????????????????? ⑧时间t2= =

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