题目内容
水平放置的金属框架abcd,宽度为0.5m,匀强磁场与框架平面成30°角,如图所示,磁感应强度为0.5T,框架电阻不计,金属杆MN置于框架上可以无摩擦地滑动,MN的质量0.05kg,电阻0.2Ω,试求当MN的水平速度为多大时,它对框架的压力恰为零,此时水平拉力应为多大?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241653469823770.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241653469823770.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165347403918.png)
试题分析:对金属棒进行受力分析,如下图
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241653477934855.png)
由图可知
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165347980838.png)
安培力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165348214587.png)
电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241653484481001.png)
联立①②③解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165348651571.png)
根据共点力平衡可得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241653488851101.png)
点评:本题要注意受到的各个力的方向,根据共点力平衡和法拉第电磁感应定律、安培力可以求得,在求感应电动势是一定要注意磁场和导体棒运动方向的关系。
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目