题目内容
(18分)如图所示,水平固定的平行金属导轨(电阻不计),间距为l,置于磁感强度为B、方向垂直导轨所在平面的匀强磁场中,导轨左侧接有一阻值为R的电阻和电容为C的电容器。一根与导轨接触良好的金属导体棒垂直导轨放置,导体棒的质量为m,阻值为r。导体棒在平行于轨道平面且与导体棒垂直的恒力F的作用下由静止开始向右运动。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041436933814.jpg)
(1)若开关S与电阻相连接,当位移为x时,导体棒的速度为v。求此过程中电阻R上产生的热量以及F作用的时间?
(2)若开关S与电容器相连接,求经过时间t导体棒上产生的热量是多少?(电容器未被击穿)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041436933814.jpg)
(1)若开关S与电阻相连接,当位移为x时,导体棒的速度为v。求此过程中电阻R上产生的热量以及F作用的时间?
(2)若开关S与电容器相连接,求经过时间t导体棒上产生的热量是多少?(电容器未被击穿)
(1)
(2) ![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041437711309.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041437241412.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041437401183.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041437711309.png)
试题分析:(1)根据功能关系有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004143786860.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041438021417.png)
在F作用过程中根据牛顿第二定律有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004143833679.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004143849954.png)
根据纯电阻电路中:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004143864933.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041438801350.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041437401183.png)
(2)在F作用过程中根据牛顿第二定律有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004143833679.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041439421158.png)
可得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004143958754.png)
所以,导体棒的加速度为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004143989841.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004144005889.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250041437711309.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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