题目内容
如图导轨竖直放置,电源电动势
,内阻
,竖直导轨电阻可忽略,金属棒的质量
,电阻
,它与导轨间的摩擦因数
,有效长度为
,靠在导轨外面。为使金属棒静止,现施加一与竖直轨道夹角为
的斜向里的磁场,保证静止。问(1)磁场是斜向上还是斜向下?(2)求磁感应强度的范围是多少?认为其所受最大静摩擦力等于滑动摩擦力。(
)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643817270.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643833284.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643864307.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643880292.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643911269.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643927280.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643942274.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643958354.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146439731881.jpg)
(1)磁场斜向下。
(2)磁感应强度的范围是![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643989363.gif)
(2)磁感应强度的范围是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114643989363.gif)
本题的受力分析采用侧视图原理,可以选择左侧视图分析受力。如图c所示,电流在斜向上的磁场中受到的安培力与重力的合力必然会使物体产生加速度,而无法处于静止状态。所以磁场斜向下。
如图a所示的受力分析,若
,金属棒有沿导轨向下运动趋势,静摩擦力
沿导轨向上,,则有如下状态方程:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644036428.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644051237.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644098241.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644145238.gif)
当
(2、4式中的
为金属棒所受两根导轨总的弹力)
有磁感应强度最小:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644223721.gif)
如图如图b所示,若
,金属棒有沿导轨向上运动趋势,静摩擦力
沿导轨向下,,则有如下状态方程:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644410240.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644504242.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644519238.gif)
当
(式中的
为金属棒所受两根导轨施加给它的总弹力)
有磁感应强度最大:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644582731.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146445978802.jpg)
如图a所示的受力分析,若
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644020381.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644020217.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644036428.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644051237.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644067402.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644098241.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644114321.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644145238.gif)
当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644176342.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644192240.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644207239.gif)
有磁感应强度最小:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644223721.gif)
如图如图b所示,若
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644239382.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644020217.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644270429.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644410240.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644067402.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644504242.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644114321.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644519238.gif)
当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644176342.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644551242.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644207239.gif)
有磁感应强度最大:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114644582731.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146445978802.jpg)
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目