题目内容
(12分)如图12所示,两平行长直金属导轨置于竖直平面内,间距为L,导轨上端有阻值为R的电阻,质量为m的导体棒垂直跨放在导轨上,并搁在支架上,导轨和导体棒电阻不计,接触良好,且无摩擦.在导轨平面内有一矩形区域的匀强磁场,方向垂直于纸面向里,磁感应强度为B.开始时导体棒静止,当磁场以速度v匀速向上运动时,导体棒也随之开始运动,并很快达到恒定的速度,此时导体棒仍处在磁场区域内,试求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241414381274027.jpg)
(1)导体棒的恒定速度;
(2)导体棒以恒定速度运动时,电路中消耗的电功率.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241414381274027.jpg)
(1)导体棒的恒定速度;
(2)导体棒以恒定速度运动时,电路中消耗的电功率.
(1)v-
向上 (2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141438252756.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141438143693.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141438252756.png)
(1)设棒速为v′,有
E=BL(v-v′) ①
F安=BIL=
=
②
棒受力平衡有:mg=F安 ③
联立得:v′=v-
④
方向向上
(2)P=
⑤
联立①④⑤得:P=
.
E=BL(v-v′) ①
F安=BIL=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141438330553.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141438423787.png)
棒受力平衡有:mg=F安 ③
联立得:v′=v-
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141438143693.png)
方向向上
(2)P=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141438595496.png)
联立①④⑤得:P=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141438252756.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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