题目内容
(1)电子的质量是多少?
(2)穿过磁场的时间是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241154233632966.gif)
(1)2dBe/v(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115423379360.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115423379360.gif)
(1)电子在磁场中运动,只受洛伦兹力作用,故其轨迹是圆弧一部分,又因为f⊥v,故圆心在电子穿入和穿出磁场时受到洛伦兹力指向交点上,如图中的O点,由几何知识知,AB间圆心角θ=300,OB为半径.所以r=d/sin300=2d.
又由r=
得m=2dBe/v.
(2)又因为AB圆心角是300,所以穿过时间 t=
T=
×
=
.
又由r=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115423394381.gif)
(2)又因为AB圆心角是300,所以穿过时间 t=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115423410227.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115423410227.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115423441398.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115423379360.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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