题目内容
如图所示,某一真空区域内充满匀强电场和匀强磁场,此区域的宽度d =" 8" cm,电场强度为E,方向竖直向下,磁感应强度为B,方向垂直纸面向里,一电子以一定的
速度沿水平方向射入此区域.若电场与磁场共存,电子穿越此区域时恰好不发生偏转;若射入时撤去磁场,电子穿越电场区域时,沿电场方向偏移量y =" 3.2" cm;若射入时撤去电场,电子穿越磁场区域时也发生了偏转.不计重力作用,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201567005509.jpg)
(1)电子射入时的初速度的表达式;(注:表达式不必代入具体数值,只保留字母符号)
(2)电子比荷的表达式;
(3)画出电子穿越磁场区域时(撤去电场时)的轨迹并标出射出磁场时的偏转角
;
(4)电子穿越磁场区域后(撤去电场时)的偏转角
。
(
)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412015662272.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201567005509.jpg)
(1)电子射入时的初速度的表达式;(注:表达式不必代入具体数值,只保留字母符号)
(2)电子比荷的表达式;
(3)画出电子穿越磁场区域时(撤去电场时)的轨迹并标出射出磁场时的偏转角
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156715201.gif)
(4)电子穿越磁场区域后(撤去电场时)的偏转角
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156715201.gif)
(
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156778492.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156793493.gif)
(1)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156809289.gif)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156825579.gif)
(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201568406099.jpg)
(4)53°
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156809289.gif)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156825579.gif)
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201568406099.jpg)
(4)53°
(1)(4分)电子在复合场中不发生偏转,所受电场力和洛伦兹力平衡:
,得初速度的表达式:
。
(2)(6分)电子垂直进入匀强电场,向上偏转作类平抛运动:
, (1分)
, (1分)
,(2分)
得电子比荷:
。 (2分)
(3)(2分)正确作出轨迹和标出偏转角各给1分。(共2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201568406099.jpg)
(4)(6分)电子垂直进入匀强磁场作匀速圆周运动,洛仑兹力提供向心力:
(2分)
代入比荷的表达式得
(2分)
由图可知,![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412015699673.gif)
或
(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156856439.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156809289.gif)
(2)(6分)电子垂直进入匀强电场,向上偏转作类平抛运动:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156887362.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156903461.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156934453.gif)
得电子比荷:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156825579.gif)
(3)(2分)正确作出轨迹和标出偏转角各给1分。(共2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201568406099.jpg)
(4)(6分)电子垂直进入匀强磁场作匀速圆周运动,洛仑兹力提供向心力:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156965520.gif)
代入比荷的表达式得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120156981791.gif)
由图可知,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412015699673.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120157012595.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120157027519.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120157043395.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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