题目内容
两根完全相同的轻质弹簧将长度L=50cm,质量m=20g的金属杆悬挂起来,如图所示.金属杆处于水平状态,且处在垂直纸面向里的匀强磁场中,磁感应强度B=0.8T.(1)为了使弹簧处于原长,金属杆中应通以什么方向的电流?电流多大?(2)若金属杆中电流与(1)中求得数值相同,但方向相反,则两弹簧伸长多少? 已知每个弹簧的劲度系数均为k=0.1N/cm,g取10m/s2.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241955408701017.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241955408701017.png)
(1)0.5A(2)2cm
试题分析:1)电流方向从左向右(2分),
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195541354592.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195541947644.png)
(2)物体受到竖直向下的重力和安培力,两者的合力等于弹簧的拉力,故有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195542539926.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824195543163620.png)
点评:关键是对物体进行受力分析,根据共点力平衡条件分析
![](http://thumb2018.1010pic.com/images/loading.gif)
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