题目内容
正粒子(不计重力)从坐标原点O沿y轴正方向射入磁场,若要粒子垂直打在屏MN上.求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200001521807.gif)
①粒子从原点射入时的速度v;
②粒子从射入磁场到垂直打在屏MN上所需时间t.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200001521807.gif)
①粒子从原点射入时的速度v;
②粒子从射入磁场到垂直打在屏MN上所需时间t.
(1) (2)
(1)要使粒子垂直打在屏MN上,则有
S=2nR+R(n=0,1,2……) ① Bqv=m
②
由①②得v=
(n=0,1,2……) ③
(2)粒子在磁场中运动的时间为t1,则
t1=
T+
T(n=0,1,2……) ④ T=
⑤
由④、⑤式,得t1=
+
(n=0,1,2……)
粒子在电场中运动的时间为t2,则t2=2n
⑥ Eq=ma ⑦
由③⑥⑦三式,得 t2=
(n=0,1,2……)
∴粒子运动的总时间为:t=t1+t2=
+
(n=0,1,2……)
S=2nR+R(n=0,1,2……) ① Bqv=m
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120000168994.gif)
由①②得v=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200002301143.gif)
(2)粒子在磁场中运动的时间为t1,则
t1=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120000246965.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120000308962.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200003701049.gif)
由④、⑤式,得t1=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200003861046.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200004021046.gif)
粒子在电场中运动的时间为t2,则t2=2n
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120000620962.gif)
由③⑥⑦三式,得 t2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200006361146.gif)
∴粒子运动的总时间为:t=t1+t2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200007141157.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241200006361146.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目