题目内容
一对平行金属板水平放置,板间距离为d,板间有磁感应强度为B的水平向里的匀强磁场,将金属板连入如图所示的电路,已知电源内阻为r,滑动变阻器的总电阻为R,现将开关S闭合,并调节滑动触头P至右端长度为总长度的
处,一质量为m、电荷量为q的带电质点从两板正中央左端以某一初速度水平飞入场区,恰好做匀速圆周运动.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241947392353255.jpg)
(1)求电源的电动势;
(2)若将滑动变阻器的滑动触头P调到R的正中央位置,可以使原带电质点以水平直线从两板间穿过,求该质点进入磁场的初速度v0;
(3)若将滑动变阻器的滑动触头P移到R的最左端,原带电质点恰好能从金属板缘飞出,求质点飞出时的动能.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194738533254.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241947392353255.jpg)
(1)求电源的电动势;
(2)若将滑动变阻器的滑动触头P调到R的正中央位置,可以使原带电质点以水平直线从两板间穿过,求该质点进入磁场的初速度v0;
(3)若将滑动变阻器的滑动触头P移到R的最左端,原带电质点恰好能从金属板缘飞出,求质点飞出时的动能.
(1)
(2)
(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241947411381249.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241947397971078.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194740577727.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241947411381249.png)
试题分析:(1)因带电质点做匀速圆周运动,故电场力与重力平衡,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194742183577.png)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194742854563.png)
两板间电场强度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194743525656.png)
两板间电压
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194743946615.png)
由闭合电路欧姆定律得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194744508614.png)
由①~⑤得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241947397971078.png)
(2)由题意知,电场力竖直向上,故质点带负电,由左手定则得洛伦兹力竖直向下,由平衡条件可得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194746099879.png)
因两极板间电压
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194746957769.png)
故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194747721592.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194748455794.png)
由⑥⑦解得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194740577727.png)
(3)因板间电压变为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194750264627.png)
故电场力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824194750795793.png)
由动能定理得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241947510751265.png)
由⑧⑨⑩解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241947411381249.png)
点评:本题主要考查了带电粒子在混合场中运动的问题,要求同学们能正确分析粒子的受力情况,难度适中
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目