题目内容
把一个矩形线圈从有理想边界的匀强磁场中匀速拉出(如图),第一次速度为v1,第二次速度为v2且v2=2v1,则两种情况下拉力的功之比W1/W2= ,拉力的功率之比P1/P2= ,线圈中产生焦耳热之比Q1/Q2= .
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146004342614.jpg)
1∶2、 1∶4、 1∶2.
设线圈的ab边长为L,bc边长为L′,整个线圈的电阻为R,把ab边拉出磁场时,cd边以速度v匀速运动切割磁感线产生感应电动势
.
其电流方向从c指向d,线圈中形成的感应电流![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600637379.gif)
cd边所受的安培力![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600652422.gif)
为了维持线圈匀速运动,所需外力大小为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600668466.gif)
因此拉出线圈过程外力的功![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600761455.gif)
外力的功率![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600793418.gif)
线圈中产生的焦耳热![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600855731.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600621274.gif)
其电流方向从c指向d,线圈中形成的感应电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600637379.gif)
cd边所受的安培力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600652422.gif)
为了维持线圈匀速运动,所需外力大小为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600668466.gif)
因此拉出线圈过程外力的功
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600761455.gif)
外力的功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600793418.gif)
线圈中产生的焦耳热
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114600855731.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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