题目内容
如图所示,光滑导轨在竖直平面内,匀强磁场的方向垂直于导轨平面,磁感应强度B="0.5" T,电源的电动势为1.5 V,内阻不计。当电键K拨向a时,导体棒(电阻为R)PQ恰能静止。当K拨向b后,导体棒PQ在1 s内扫过的最大面积为多少?(导轨电阻不计)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241234519293995.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241234519293995.jpg)
设金属棒PQ长为L,电阻为R,电键接a时,电路中电流
I=
2分
导体棒PQ静止mg=BIL=
2分
电键K接b,导体棒PQ从静止下落,切割磁场线产生感应电流,同时PQ受安培力作用,导体棒向下做加速运动,
速度增大,而加速度减小,最后以vm做匀速运动。
此时mg=Fm=
有:
得vm=
3分
PQ在1 s内扫过的最大面积:Sm=vm·L·t=
="3" m2 3分
I=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123451944248.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412345196072.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123451975323.gif)
电键K接b,导体棒PQ从静止下落,切割磁场线产生感应电流,同时PQ受安培力作用,导体棒向下做加速运动,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412345199172.gif)
此时mg=Fm=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123452163474.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123452178640.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123452194275.gif)
PQ在1 s内扫过的最大面积:Sm=vm·L·t=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123452209545.gif)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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